Left and Right Atria

Although there are exceptions, the position of the morphologic right and left atria is directly determined by the symmetry of the thoracic and abdominal contents. The right atrium lies on the side that contains the trilobed lung and the liver, whereas the left atrium connects to the thorax on the side of the bilobed lung and the spleen. These relationships are precise when there are no caval anomalies. The symmetric determination of the atrial position and morphology is ambiguous in bilateral right or left lungs and in asplenia or polysplenia.

Ventricular Looping

The next step is identification of the two ventricles as either D-loop or L-loop. These terms refer to the embryologic looping of the straight tube of the heart. A D-loop brings the cardiac apex initially to the right with the morphologic right ventricle anterior to the left ventricle; the normal heart has a D-loop. Final looping of the heart tube places the apex to the left with the left ventricle lying on the left-hand side of the interventricular septum as viewed through the tricuspid valve. A helpful but not infallible method of localizing the ventricles is the “loop rule”: the position of the aorta with respect to the pulmonary artery corresponds to a particular ventricular looping. Without regard to anteroposterior positions, when the aorta is located to the right of the pulmonary artery, a ventricular D-loop is probable. When the aorta is to the left of the pulmonary artery, a ventricular L-loop is probable.

The coronary arteries are also helpful for locating the position of the ventricles. The right coronary artery marks the atrioventricular sulcus of the right ventricle and the anterior descending artery marks the interventricular sulcus. When there is an L-loop heart, the right coronary artery is to the left of the anterior descending artery.

Dextrocardia

Dextrocardia signifies that the apex of the heart is directed toward the right. Primary dextrocardia exists because of an embryologic abnormality. This type of dextrocardia can exist with any type of situs position (Fig. 10-21). When dextrocardia exists with situs inversus, the atrial and ventricular relations are a mirror image of their positions in the usual situs solitus. When the dextrocardia exists in situs solitus, the term isolated dextrocardia is frequently applied. It is clear then that dextrocardia can occur in situs solitus, inversus, and ambiguus. Many associated cardiac anomalies exist in primary dextrocardia. Frequent conditions include ventricular septal defect, TGA, corrected TGA, double-outlet right ventricle, and juxtaposition of the atrial appendages.

FIGURE 10-21 Primary dextrocardia (dextroversion). The levophase of a pulmonary angiogram outlines a smooth-walled left ventricle (LV), which is the anterior ventricle because the heart is rotated to the right. An anomalous right inferior pulmonary vein (arrows) connects to the inferior vena cava (scimitar syndrome).

The goal of echocardiography, magnetic resonance imaging (MRI), and angiography is to define the position and location of each chamber of the heart and their connections and relations with one another and with the great arteries. In those malpositioned hearts in which the location of the interventricular septum is not known before angiography, posteroanterior and lateral projections serve as initial guidelines. Frequently, the projections can be reversed for a malposition; that is, those structures that are normally best seen in the left anterior oblique projection in the normal heart would be studied in the right anterior oblique projection in dextrocardia. As a rule, the dextrocardia itself does not cause clinical problems but rather the associated malformations mandate medical or surgical alleviation.

Levocardia

Strictly speaking, levocardia means that the cardiac apex is left sided. Isolated levocardias are those hearts that are left sided when situs inversus is present. This anomaly occurs in less than 1% of all patients with congenital cardiac malformation compared with a 2% incidence of dextrocardia in patients with CHD. With levocardia, the position of the thoracic and abdominal organs ranges from partial to complete situs inversus and also to heterotaxy (Fig. 10-22). Severe malformations are always associated with levocardia and frequently include ventricular septal defect, complete atrioventricular canal defects, and pulmonary stenosis or atresia. Isolated levocardia may be suspected on the chest film with a right-sided stomach bubble and left-sided liver shadow and a left cardiac apex. In contrast, in extrinsic levocardia the heart is intrinsically normal but the mediastinum is shifted from skeletal or pulmonary abnormalities (Fig. 10-23).

FIGURE 10-22 Levocardia with polysplenia. A, The catheter in the inferior vena cava has a high, left-sided loop indicating hemiazygos continuation before it enters the right superior vena cava. B, Posteroanterior view shows a single ventricle with a subaortic conus. The right aortic arch supplied a patent ductus arteriosus. The ventricle had pulmonary atresia and a complete atrioventricular canal.

FIGURE 10-23 Secondary levocardia. Because of a left pneumonectomy, the heart has moved with the mediastinum into the extreme left side of the thorax. The huge right lung now crosses the midline to fill much of the left hemithorax. The heart is invisible because of the oblique interface the right lung makes with the shifted mediastinum.

Mesocardia

Mesocardia is a variant of dextrocardia and levocardia. In this condition, the heart lies in the midline without a distinct apex pointing to either side. These patients may have situs solitus, inversus, or ambiguus of the atria and have similar associated defects.

Heterotaxy and the Syndromes of Asplenia and Polysplenia

Heterotaxy is the failure of the developing embryo to establish normal left-right asymmetry. Asplenia and polysplenia are part of this spectrum. In these patients the thoracic and abdominal contents have a degree of symmetry, unlike those in situs solitus or inversus in which right- and left-sided organs exist together. In the thorax, both lungs may be trilobed with bilateral epiarterial bronchi, or both lungs may be bilobed with bilateral hypoarterial bronchi. In the abdomen, the asymmetry is also frequently lost. The liver may be midline. The attachment of the mesentery, which usually runs from the left upper quadrant to the right lower quadrant, may have a midline attachment. The spleen may be absent (asplenia), bilobed with multiple accessory spleens, or multiple small spleens (Fig. 10-24) may be found throughout the mesentery (polysplenia). Situs ambiguus exists either when the right and left sides of the lungs, heart, and abdomen are similar or where a right-left relationship is difficult to identify. Boxes 10-5 and 10-6 summarize the characteristics of asplenia and polysplenia.)

FIGURE 10-24 Heterotaxia. A, The main stem bronchi are below the pulmonary arteries bilaterally. B, The abdominal situs is inverted with multiple small spleens occupying the right side of the abdomen. The liver is midline and occupies nearly equal space in the right and left sides of the abdomen.

Splenic anomalies with malpositions and malformations in multiple organ systems have been recognized since 1826 when Martin and later Ivemark described the absence of the spleen in cyanotic CHD. Complex cardiac malformations are typical when the type of thoracic and abdominal situs abnormality is uncertain or has features of both situs solitus and situs inversus (Table 10-1).

TABLE 10-1 Cardiovascular abnormalities in asplenia and polysplenia

* Of the ventricular septal defects in asplenia, 84% were of the atrioventricular canal type.

Modified from Rose V, Izukawa T, Moes CAF: Syndromes of asplenia and polysplenia; a review of cardiac and non-cardiac malformations in 60 cases with special reference to diagnosis and prognosis. Br Heart J 37:840-852, 1975.

Segmental analysis of the defects in hearts associated with asplenia begins with the atria and the atrial septum. On the chest film, the external contours of the heart frequently do not conform to the expected heart chambers (Fig. 10-25). Almost all these hearts show a common atrioventricular valve, frequently associated with separate, large atrial septal defects in the primum and secundum location. The size and location of these atrial defects are such that the malformation is called a common atrium. The ventricles also almost invariably have major malformations. About one fourth of the ventricles are inverted (as seen in corrected transposition), and half of the hearts have a univentricular chamber with a rudimentary outflow tract.

FIGURE 10-25 Heterotaxy syndrome with dextrocardia. A, The stomach bubble (St) is on the right and the liver (Li) is on the left; this is abdominal situs inversus. However, the appearance of the bronchi indicate thoracic situs solitus; this is thoracoabdominal situs discordance. The main pulmonary artery (PA) central pulmonary artery segments are dilated, indicating shunt. Notice the dilated left-sided azygos vein (arrow), reflecting interruption of the IVC with azygos connection. B, Angiography is performed from a left upper extremity venous approach with catheter passage from the left-sided superior vena cava to the right atrium. The angiogram shows that the right side of the heart is formed by the right ventricle, which connects to the pulmonary artery. The aorta fills simultaneously through a ventricular septal defect and forms the broad curve in the right anterior mediastinum (arrowheads).

Anomalies of the great vessels, including TGA and double-outlet right ventricle, have an incidence of 3% to 30%. Angiographically, the posteroanterior and lateral projections are best to allow identification of their right-left relationships. Anomalies in the ventricular septum and semilunar valve stenosis are common, so that filming is also done with the x-ray beam parallel to the interventricular septum with cranial angulation. Because two thirds of persons with asplenia have anomalous systemic venous or pulmonary venous connections, or both, these malformations frequently complicate catheterization.

The features of the heart in polysplenia are quite variable, and in fact, there is occasionally no cardiac malformation. With a femoral vein approach, you can recognize azygos continuation by the course of the catheter around the azygos arch (Figures 10-10A, 10-26). You should not make the diagnosis of tricuspid atresia if the catheter tip fails to pass leftward through the heart above the diaphragm but instead should continue advancing the catheter superiorly until it goes around the azygos arch.

FIGURE 10-26 Hemiazygos continuation in a patient with polysplenia and dextrocardia. An injection into the left femoral vein opacified the hemiazygos vein adjacent to the costovertebral sulcus before it emptied into a left superior vena cava.

Congenitally Corrected Transposition of the Great Vessels (Levotransposition of the Great Arteries)

In 1875 Rokitansky reported a form of transposition in which blood passed in normal serial fashion through the pulmonary and systemic circuits. The right atrium was connected to the left ventricle, which was connected to the pulmonary artery. On the oxygenated side of the lungs, the left atrium was connected to the right ventricle, which was connected to the aorta. The atrioventricular valves always correspond with their ventricles, even when there is atrioventricular discordance. That is, the mitral valve is a left ventricular structure, and the tricuspid valve is a right ventricular structure. In congenitally corrected transposition of the great vessels, the aorta lies to the left of and anterior to the pulmonary artery, whereas the pulmonary valve lies to the right and posterior. The aortic valve is usually somewhat anterior to the pulmonary valve, although the two great vessels may be exactly lateral to each other. The ascending aorta frequently has an unusual course, passing in a direction toward the left shoulder so that occasionally a distinctive contour in the left side of the mediastinum is visible on the chest film.

If there are no other defects, this malformation causes no hemodynamic problems and may go undetected during a normal life span. Unfortunately, associated malformations are the rule, and their site and severity determine the clinical course. Ventricular septal defects are frequent (Figures 10-27, 10-28) and may be large enough to cause pulmonary arterial hypertension. These defects are usually in the membranous septum adjacent to the pulmonary valve; muscular defects and supracristal defects are less common. Generally, the left-sided atrioventricular valve (i.e., the valve between the left atrium and the right ventricle) is displaced slightly into the ventricle in a manner resembling Ebstein anomaly. If the displacement is more than a few millimeters (because the tricuspid valve is usually displaced to the apex by that amount), the diagnosis of Ebstein anomaly is quite likely. Pulmonary stenosis is frequently associated with ventricular septal defect and may be caused by a malformed valve, a subpulmonary membrane, aneurysms of the membranous ventricular septum, or rarely, accessory tissue in the atrioventricular valve or a muscular bar in the subpulmonary region.

FIGURE 10-27 Congenitally corrected transposition of the great arteries with ventricular septal defect. The leftward course of the ascending aorta is not apparent on the chest film. The leftward cardiac apex represents the right ventricle, which is enlarged because of the ventricular septal defect. The main pulmonary artery is not part of the mediastinal interface with the lung because it is central; the hilar and peripheral pulmonary arteries are large from the left-to-right shunt.

FIGURE 10-28 Off-coronal spin echo acquisition from a 7-month-old boy with double inlet left ventricle and corrected transposition of the great arteries. Drainage from the right atrium (RA) into the dominant left ventricle (LV) is shown. LV blood passes directly to the medially placed main pulmonary artery (MP) and through a bulboventricular foramen (arrow) into a hypoplastic right ventricular outflow chamber (R), which supports a left-sided ascending aorta (Ao).

Imaging establishes the atrioventricular connections, the morphology of the ventricles, and the position of the aorta and pulmonary artery. The position of the venous and arterial catheters frequently give the first clue to a corrected transposition (Fig. 10-29). In situs solitus and levocardia, the venous catheter passes through the heart in the midline to reach the pulmonary arteries. The catheter in the pulmonary artery is posterior to its usual location, which is where the aorta should be in normal hearts. The retrograde arterial catheter has a distinctive curve in the ascending aorta as its course becomes convex medially and to the left before entering the heart (see Figure 10-18). On the lateral view, the aortic catheter is anterior and superior to the venous catheter. The venous and arterial catheters indicate the fundamental relationship between the aorta and the pulmonary artery in corrected transposition with situs solitus and levocardia; the pulmonary artery lies to the right and posterior, whereas the aorta is anterior and to the left.

FIGURE 10-29 Catheter positions in congenitally corrected transposition of the great arteries. A, The catheter in the inferior vena cava passes through the right atrium and left ventricle to end in the right pulmonary artery. B, The retrograde aortic catheter ends in the left-sided right ventricle. The ascending aorta lies to the left of the pulmonary valve.

In corrected transposition with situs solitus and levocardia, the ventricles lie nearly side by side with the interventricular septum, seen in the anterior-posterior orientation. The left ventricle lies slightly inferior to the right ventricle and has a triangular shape, with the mitral valve lying medially and to the right. The mitral valve of the left ventricle connects to the right atrium and lies in continuity with the pulmonary valve. The left ventricular outflow region is short and vertically oriented, with the anterior leaflet of the mitral valve on the medial side and the membranous portion of the interventricular septum forming the superior and lateral wall.

In the sagittal view, the left ventricle appears to “stand on its apex” with a conical shape whose apex is in the diaphragmatic-sternal angle. The anterior wall of the left ventricle extends superiorly into a distinctive pouch that is characteristic of inverted ventricles, namely the anteriorly placed left ventricle (Fig. 10-30). This recess is separate from both the mitral and pulmonary valves and is the most anterior and superior structure of either ventricle. The outflow portion of the left ventricle in the lateral projection is posterior and connects to a pulmonary artery, which is beside or posterior to the aorta. The posterior wall of the left ventricle beneath the pulmonary valve is the membranous septum, and the anterior wall forms a neck above the blind recess and below the pulmonary valve.

FIGURE 10-30 Angiography of the left ventricle in congenitally corrected transposition of the great arteries. A, The septum runs obliquely, inferiorly on the right, and then superiorly on the left side. The distinctive recess (arrow) is typical of an inverted ventricle. B, The lateral view shows the pulmonary valve (arrow) posterior to the aortic valve.

In the frontal view, the right ventricle is to the left of and slightly superior to the left ventricle (Fig. 10-31). In this position, the right ventricle has an oval to triangular shape and the usual coarse trabeculations. The tricuspid annulus is in the posteroanterior plane separated from the aortic valve by the muscular infundibulum. This morphologic right ventricle connects with the left atrium. The crista supraventricularis in this projection is the medial wall of the infundibulum above the tricuspid valve. In the lateral projection, the crista is the posterior wall of the infundibulum and separates the tricuspid from the aortic valve.

FIGURE 10-31 Angiography of the right ventricle in congenitally corrected transposition of the great arteries. A, The subaortic conus of the right ventricle connects to the leftward ascending aorta, the border-forming structure of the left side of the mediastinum. B, The aortic valve is anterior to the heart and lies in a horizontal plane.

The aortic valve appears higher than the pulmonary valve and is the border-forming structure in the left side of the upper half of the mediastinum. Unlike in the normal heart, the main pulmonary artery does not form any interface with the lung on the frontal chest film.

Different ventricular patterns and shapes occur in situs inversus and in other rare malformations. Because the aortic arch may lie on either the left or right side, the distinctive mediastinal contour of the aorta (which is frequently not present in situs solitus with classic corrected transposition) may not be visible on the standard chest films.

About one third of patients with corrected transposition have tricuspid regurgitation (i.e., from the right ventricle connected to the left atrium). The apically displaced tricuspid leaflets of Ebstein anomaly are usually the cause of the regurgitation, but there are occasionally other leaflet abnormalities. When there is severe regurgitation in infants, the details of the leaflets and the origin of their insertion are frequently difficult to identify. If technical factors such as arrhythmia and catheter position can be excluded, it should be presumed that severe regurgitation into the left atrium is associated with a “left-sided” Ebstein anomaly (Fig. 10-32). The tricuspid annulus is adjacent to the right coronary artery, which may be opacified during the ventriculogram.

FIGURE 10-32 Ebstein anomaly in congenitally corrected transposition of the great arteries. Injection into the right ventricle has resulted in severe regurgitation into the left atrium. In contrast to isolated Ebstein anomaly, the tricuspid leaflets are poorly seen and have little apical displacement. A ventricular septal defect has allowed opacification of the pulmonary arteries.

Complete Dextrotransposition of the Great Arteries

In 1797 Baillie described the heart of an infant in which the aorta connected to the right ventricle and the pulmonary artery to the left ventricle. The term transposition of the aorta and pulmonary artery is ascribed to Farre in 1814. Since that time, there has been controversy about whether it should be defined by the abnormal anteroposterior position of the great arteries or by the abnormal connections to the ventricles. TGA is a ventriculoarterial abnormality in which the aorta originates above the right ventricle and the pulmonary artery originates over the left ventricle.

After tetralogy of Fallot, complete TGA is the second most common cause of cyanosis from heart disease in infancy. In this malformation, the systemic and pulmonary circulations connect in parallel, in contrast to the serial connection in the normal infant. The blood flow through the lungs returns to the left atrium and to the left ventricle only to pass again through the lungs; in a similar fashion, the systemic venous and arterial circulations form a closed loop. For life to be sustained, mixing must occur between these two circuits. Therefore, one of the objectives of imaging is to determine the location and amount of these intracardiac or extracardiac shunts. The foramen ovale is almost always patent but is too small for adequate mixing. Occasionally, a secundum atrial septal defect will allow a large shunt to provide adequate mixing of oxygenated blood at this level.

Ventricular septal defects occur in about one third of babies with transposition (see Figure 10-7A), and when present, may result in congestive heart failure from the large blood flow. Extracardiac shunts may occur, as in patent ductus arteriosus or with bronchopulmonary connections to the pulmonary vascular bed. The ductus arteriosus remains patent in one fourth to one half of infants who do not receive prostaglandin E1 and allows blood to flow from the pulmonary artery to the aorta if the pulmonary vascular resistance is high and from the aorta to the pulmonary artery when the high fetal pulmonary artery pressures fall below the systemic blood pressure.

Besides the ventricular septal defect, the other major associated malformation is obstruction to blood entering the pulmonary arteries. About one fourth of those with TGA have some form of pulmonary stenosis (Fig. 10-35). The site of obstruction is usually in the subpulmonary region and it has a variety of causes:

FIGURE 10-35 Gradient echo acquisition from a 24-year-old woman with shortness of breath. A, Cranially angulated coronal early systolic acquisition. The pulmonary valve leaflets (arrows) are thickened and dome into the dilated main pulmonary artery. The right ventricular (RV) myocardium is trabeculated and thickened. B, Image obtained 200 msec later. RV myocardial thickening has increased and the signal void jet of pulmonic stenosis (arrows) is evident in the main pulmonary artery.

Valvular pulmonary stenosis also occurs from a unicuspid or bicuspid valve. Dynamic pulmonary stenosis is common in those patients with an intact ventricular septum and is caused by systolic anterior motion of the mitral valves, like that in idiopathic hypertrophic subaortic stenosis.

The typical chest radiograph in the first few days of life of a child with TGA shows mild cardiomegaly, a narrow superior mediastinum, and increased size of the pulmonary vessels that is consistent with a left-to-right shunt. All these signs are variable, and in fact, the chest radiograph may appear normal. The size of the pulmonary vessels depends on the amount of blood carried by them: If the degree of mixing between the pulmonary and systemic circuits is small or if there is some type of pulmonary stenosis, the pulmonary vessels will be small; if there are large intracardiac or extracardiac shunts, the pulmonary vessels are large (Fig. 10-36).

FIGURE 10-36 Chest film abnormalities in transposition of the great arteries. A, The common presentation is a slightly enlarged heart and large pulmonary arteries, which suggests increased pulmonary blood flow. The mediastinum is narrow with an unusual appearance because of the absence of the thymic shadow and the posterior position of the main pulmonary artery. B, A less typical radiograph shows cardiomegaly and huge, indistinct pulmonary vessels indicating severe intracardiac shunting from the ventricular septal defect. Again, the narrow mediastinum reflects the non–heart-border-forming main pulmonary artery. C, The rare occurrence of pulmonary atresia with transposition of the great arteries is reflected in the tiny hilar vessels. In these three patients (A, B, and C), the circulation to the lungs was reliably indicated by the size of the hilar pulmonary vessels.

D-Transposition of the Great Arteries

In D-transposition of the great arteries (D-TGA), the aorta arises from the right ventricle and the pulmonary artery arises from the left ventricle. The blood circulates through two parallel circuits, and mixing of blood is necessary to get oxygenated blood to the systemic circulation. Up to 45% of patients can have a ventricular septal defect for mixing. When the ventricular septum is intact, mixing must occur through a patent foramen ovale or a PDA, and if these communications are inadequate, an emergent balloon atrial septostomy is performed. There are four different approaches to the repair of D-TGA which either correct the circulation physiologically (Mustard and Senning operations) or anatomically (Jatene and Rastelli operations; Table 10-2).

TABLE 10-2 Surgical repair of D-transposition of the great arteries

Beginning in the 1960s, the Mustard and Senning operations were the first definitive approaches for repair of TGA. Both operations correct the abnormal blood flow of the transposed vessels by switching the blood at the inflow (atrial) level. An intraatrial baffle composed of atrial tissue (Senning; Fig. 10-42) or pericardium or synthetic tissue (Mustard) directs the pulmonary venous return into the right ventricle and the systemic venous return into the left ventricle. Although this does correct the physiologic abnormality of TGA with deoxygenated blood now flowing to the pulmonary circulation and oxygenated blood flowing to the systemic circulation, the left ventricle remains as the pulmonary ventricle and the right ventricle as the systemic ventricle. The Senning and Mustard operations were initially well tolerated with relatively few complications. Late follow-up has shown increased incidence of complications requiring reoperation, exercise intolerance, arrhythmias, and sudden death. There continues to be great concern about the ability of the anatomic right ventricle to sustain the systemic circulation in the long term, and many patients have moderate to severe right ventricular dysfunction 25 years after repair.

FIGURE 10-42 A 24-year-old man with Senning atrial switch operation. Axial acquisition image from a contrast-enhanced computed tomography examination shows contrast-enhanced blood (arrow 1) from the upper extremity injection site mixing with unopacified blood from the inferior vena cava (arrow 2) medial to the curving filling defect (arrowheads) of the intraatrial baffle. Pulmonary venous blood (including that from the right lower lobe pulmonary vein (arrow 3) passes lateral to the baffle, to the anterior “neo right atrium.”

Cardiac magnetic resonance (MR) imaging is now used as the primary imaging for follow-up of patients after the atrial switch operation (Fig. 10-43). In addition to assessing right ventricular volumes and function, detection of baffle leaks and quantification of tricuspid regurgitation is performed. These are important volume-loading lesions that contribute to impaired right ventricular function and can be treated with transcatheter or surgical intervention. Cardiac MR can detect obstruction to either the systemic or pulmonary venous pathways with better accuracy as compared with echocardiography.

FIGURE 10-43 A 23-year-old man 23 years post Mustard atrial switch operation for D-transposition of the great arteries. A, Anterior most off-coronal double inversion recovery acquisition demonstrates connection between the morphologic right atrium (notice the broad-based and triangular right atrial appendage, arrow 1) and the trabeculated, anterior morphologic right ventricle (RV). The aortic root (arrow 2) is separated from the fat (arrowhead) of the anterior atrioventricular ring and tricuspid valve. B, Off-coronal double inversion recovery image obtained through the morphologic left ventricle (LV), a few centimeters posterior to A. Systemic venous blood from the inferior vena cava (IV) and hepatic vein (HV) enters the inferior aspect of the neo right atrium (NR) and flows to the morphologic left ventricle. The inferior aspect of the Mustard baffle (arrowheads) segregates oxygenated blood passing from the lungs to the anterior morphologic right ventricle, from desaturated lower extremity blood.

When patients with D-TGA have a ventricular septal defect and left ventricular outflow tract obstruction (usually from a sub pulmonary conus), the Rastelli operation is performed. An intracardiac baffle is created to divert blood flow from the left ventricle via the ventricular septal defect to the aorta (Fig. 10-44). The pulmonary valve is over sewn, and a right-ventricle-topulmonary-artery conduit is placed. Although it is advantageous to have the left ventricle as the systemic ventricle, patients will usually require future operations for replacement of the right-ventricle-to-pulmonary-artery conduit.

FIGURE 10-44 An 8-year-old girl with pulmonary atresia and ventricular septal defect with a Rastelli repair. A, The signal void (**) of the extra cardiac right-ventricle-to-pulmonary-artery conduit lies immediately posterior to the chest wall. The right (RA) and left (LA) atria and left ventricle (LV) are labeled. B, Oblique sagittal double inversion recovery image through the muscular interventricular septum. The conduit (**) passes immediately posterior to the chest wall before anastomosis with the main pulmonary artery (MP). The septum is flat. The right (RV) and left (LV) ventricles are labeled. C, In this nearly straight sagittal double inversion recovery section, the typical curving course of the ventricular septal defect patch (arrowheads) extending from the muscular interventricular septum to the anterior aspect of the anteriorly displaced aortic root (Ao) is seen. The patch obstructs right ventricular (RV) outflow, necessitating the conduit. The left atrium (LA) is labeled.

Following the Rastelli operation for D-TGA, there are long-term complications similar to those occurring after the atrial switch operations, including left and right ventricular dysfunction, arrhythmias, and sudden death (Table 10-3). In addition to assessing ventricular function, the cardiac MRI examination should include evaluation for intracardiac baffle obstruction or leak, and right-ventricle-to-pulmonary-artery conduit obstruction and regurgitation.

TABLE 10-3 Complications after repair of D-transposition of the great arteries

In 1975, Jatene described the first successful arterial switch operation (ASO) for D-TGA, which has now replaced the atrial switch procedures. The operation includes transection of the aorta and pulmonary artery above the level of the valve sinuses and transfer of the coronary arteries to the neoaortic root. The main pulmonary artery is then moved anterior to the aorta (the Lecompte maneuver) and the great arteries are sutured in place. The postoperative appearance of the great arteries is characteristic, with the main pulmonary artery located anteriorly and the pulmonary arteries “draped” to either side of the ascending aorta (Fig. 10-45). One of the most important aspects of the preoperative evaluation before the ASO is identification of the coronary artery anatomy by echocardiography. Although the overall perioperative mortality is low, there are certain coronary artery patterns that are associated with early mortality and need for early repair.

FIGURE 10-45 A 13-year-old girl with Jatene arterial switch repair of D-transposition of the great arteries. A, Axial double inversion recovery image demonstrates the typical appearance of the main pulmonary artery (arrow 1) lying anterior to the ascending aorta (Ao), and the right (arrow 2) and left (arrow 3) pulmonary arteries draped around the Ao. Notice the focal left pulmonary artery stenosis (arrow 4). B, Oblique coronal gradient echo image through the mid ascending aorta (Ao). The left pulmonary artery (arrow 1) is viewed in cross section, and again, appears narrow, with respect to the right pulmonary artery (arrow 2).

Long-term follow-up of the ASO has shown that the majority of patients have good ventricular function and low incidence of arrhythmias and sudden death. The most common complication is supravalvular or branch pulmonary artery stenosis, which is well assessed by cardiac MR or multidetector computed tomography (MDCT) to guide further catheter-based or surgical intervention when needed. Although less frequent, significant coronary artery lesions have been detected by both cardiac MR and MDCT, and both modalities are being used more frequently for follow-up.

Double-Outlet Right Ventricle

Double-outlet right ventricle is a congenital cardiac defect in which both great arteries originate exclusively from the morphologic right ventricle. The only outlet for the left ventricle is through the ventricular septal defect, which is usually large but may be restrictive. The malformation occurs in two varieties, depending on the location of the ventricular septal defect in relation to the aorta and pulmonary artery. In the more common type, the ventricular septal defect is adjacent to the aorta with the pulmonary outflow situated on the far side of the right ventricle. In the less common type, the Taussig-Bing heart (Fig. 10-46), the ventricular septal defect is adjacent to the pulmonary outflow, whereas the aorta arises on the far side of the right ventricle. The aorta is usually to the right of the pulmonary artery, either slightly to the front or directly to the side, but it may arise in front of the pulmonary artery. Although there are rare exceptions, bilateral conus is a major criterion for distinguishing double-outlet right ventricle from tetralogy of Fallot or complete transposition of the great arteries. Bilateral conus is recognizable by muscle between each atrioventricular valve and the semilunar valves. These features place the aortic and pulmonary valves on approximately the same level in the transverse plane.

FIGURE 10-46 Taussig-Bing malformation. In this double-outlet right ventricle (RV), a small bilateral conus is present with moderate subaortic stenosis. The pulmonary artery (P) originates above the ventricular septal defect. An aortic coarctation is associated with mild hypoplasia of the arch. The large ventricular septal defect is the only outlet of the left ventricle (LV).

In addition to the ventriculoarterial malformation and the requisite ventricular septal defect, there are usually a large number of associated anomalies. Subpulmonary stenosis is frequent, occasionally in conjunction with a bicuspid or absent pulmonary valve. Partial or complete atrioventricular canal defects form a spectrum of abnormally formed leaflets. Subaortic stenosis is recognizable by hypoplasia or hyperkinesis of the aortic conus. Extracardiac anomalies abound and include anomalous pulmonary venous connection, bilateral superior vena cava, PDA, coarctation and interruption of the aortic arch, and the heterotaxy syndrome.

The angiographic evaluation of double-outlet right ventricle necessitates biplane right and left ventriculograms. Simultaneous opacification of both great arteries after a ventriculogram is a typical feature of this malformation, but one artery may fill before the other when premature ventricular contractions occur or when there is subpulmonary or subaortic stenosis.

There are many angiographic features characteristic of double-outlet right ventricle in situs solitus (Fig. 10-47). In the frontal view, the heavily trabeculated right ventricle partially overlies the posterior left ventricle. Both semilunar valves have the same height and are separated from the rest of the heart by a bilateral conus. The central lucency between the aortic and pulmonary outflow tracts is the crista supraventricularis. On the lateral view, there is discontinuity between the atrioventricular and semilunar valves. Behind the great arteries and the mitral valve there is a notch that represents the ventriculoinfundibular recess. The conus under both great arteries generally overlaps completely so that, unless one artery fills before the other, the relation of the conus to the ventricle may be difficult to recognize.

FIGURE 10-47 Angiographic features of double-outlet right ventricle. A, In the frontal projection, the aorta originates adjacent to the ventricular septal defect. Severe subaortic stenosis narrows the outflow tract to a few millimeters. The crista supraventricularis (C) is common to both the subaortic and subpulmonary conus. B, In the lateral view, the left ventricle (LV) is opacified through a large ventricular septal defect. The aorta is not visualized because it lies beside and is obscured by the large pulmonary artery. A loose pulmonary band (arrowheads) is present. A, aorta; P, pulmonary artery; RV, right ventricle.

Pulmonary stenosis (Fig. 10-48), both the subvalvular (Fig. 10-49) and valvular varieties (see Figure 10-35), exists in about half of patients with double-outlet right ventricle. Conversely, subaortic stenosis occurs in about 20% of patients with this defect. Because the semilunar valves tend to lie on a transaxial plane, nonangled films in the frontal plane project the annulus of both the aortic and pulmonary valves in tangent. An injection in the outflow tract or directly beneath the crista supraventricularis may aid in making these outflow obstructions visible. (Table 10-4 illustrates the differential diagnosis of double-outlet right ventricle.)

FIGURE 10-48 Subpulmonary stenosis associated with double-outlet right ventricle. A right ventricular injection opacifies both the aorta (AO) and the pulmonary artery (PA). On other views, the aorta was adjacent to the ventricular septal defect. There is severe bulboventricular malalignment resulting in subpulmonary narrowing, with the pulmonary valve sharply angled toward the ventricle.

FIGURE 10-49 Valvular pulmonary stenosis associated with subvalvular stenosis. Off-coronal late systolic gradient echo acquisition through the pulmonary valve. The leaflets (white arrowheads) are thickened and leave a narrow valve orifice. In addition, a signal void jet of accelerating blood (black arrowheads) is seen extending from within the right ventricular cavity toward the outflow tract.

TABLE 10-4 Differential diagnosis of double-outlet right ventricle

Double-Outlet Left Ventricle

Double-outlet left ventricle is a rare type of partial transposition. In its complete form, both the aorta and pulmonary artery connect above the left ventricle. This malformation has one great artery and half of the other great artery arising above the left ventricle. Because this classification involves only the ventriculoarterial relations, it is not surprising that double-outlet left ventricle comprises a heterogeneous group of malformations that are associated with multiple anomalies and malpositions of the atrioventricular segments. Anomalies associated with double-outlet left ventricle are:

Most hearts with this malformation have a bilaterally absent conus, although there may be a subpulmonary or subaortic conus.

The purpose of imaging in double-outlet left ventricle is to identify the associated anomalies and to locate the position of the great arteries. Because the only outlet for the right ventricle is through the ventricular septal defect, a right ventricular injection alone may allow misinterpretation of this defect as another form of transposition or even as tetralogy of Fallot. To recognize double-outlet left ventricle you must be able to visualize both great arteries over the left ventricle or one artery over the ventricular septal defect and the other over the left ventricle (Fig. 10-50). With this definition there is usually, but not always, continuity between the mitral valve and either the aortic or pulmonary valves. For example, in complete TGA with a ventricular septal defect, the pulmonary and mitral valves are adjacent and the aorta may override the ventricular septal defect; if the aorta is malpositioned so that more than 50% of its annulus corresponds to the left ventricle, then there is double-outlet left ventricle rather than complete transposition.

FIGURE 10-50 Double-outlet left ventricle. The aortic valve projects equally over both ventricles above a large ventricular septal defect (arrows). There is hypoplasia of the pulmonary valve, subpulmonic infundibulum, and main pulmonary artery. Ao, aorta; LPA, left pulmonary artery; LV, left ventricle; PA, main pulmonary artery; RPA, right pulmonary artery; RV, right ventricle.

Truncus Arteriosus

Truncus arteriosus is a congenital malformation in which only one great artery arises from the base of the heart and gives origin to the systemic, pulmonary, and coronary arteries proximal to the aortic arch (Fig. 10-51). Buchanan first described this in 1864 from an autopsy specimen. In 1949 Collett and Edwards described five types of truncus arteriosus based on the connections of the pulmonary artery and the aorta (Fig. 10-52):

FIGURE 10-51 Contrast-enhanced four-detector computed tomography examination in a 43-year-old man with Type 1 truncus arteriosus. A, A main pulmonary artery (MP) arises from the posterolateral aspect of the main truncal artery (T), and provides the right pulmonary artery (RP). Note the right lower lobe infiltrate (arrow). B, Acquisition image just below the truncal valve. The hypertrophied right ventricle (RV) communicates with the larger left ventricle (LV) through a large subaortic ventricular septal defect (arrow). SV, superior vena cava.

FIGURE 10-52 Classification of truncus arteriosus. Top row, Collett-Edwards types 1 to 4. Bottom row, Van Praagh types A1 to A4. Ao, aorta; LC, left carotid artery; LSA, left subclavian artery; PA, pulmonary artery.

This classification assumes that all hearts with this defect have a ventricular septal defect and only one semilunar valve. Truncus arteriosus can be differentiated from aortic or pulmonary valve atresia because a nubbin of the atretic valve is usually found in the latter.

A later classification by Van Praagh and colleagues in 1965 relies on the absence of either the primitive fourth or sixth aortic arches. They classify four types of truncus:

Types A1, A2, and A3 then represent agenesis of the sixth embryonic aortic arch, which normally becomes the proximal main pulmonary artery, and type A4 results from agenesis of the fourth embryonic aortic arch. This latter classification has the advantage of recognizing the high incidence of aortic arch interruptions with truncus arteriosus.

The prior classification systems have been further modified and simplified by the Society of Thoracic Surgeons to reflect the anatomy and features that affect the surgical approach to repair. The three types are:

The truncus usually is centered over a ventricular septal defect but may originate predominately from either ventricle. The mitral valve is in fibrous continuity with the truncal valve. The tricuspid valve may be adjacent to the truncal valve or a septal band may intervene. There is no subtruncal conus. The truncal (semilunar) leaflets are tricuspid in about 70% of patients but may have from two to five cusps. The truncal valve can be either stenotic or regurgitant with prolapse of one or more cusps. The pulmonary arteries, originating either as a main artery or separately supplying each lung, may also be stenotic at their origins.

Aortic arch anomalies with truncus arteriosus are common, with a right arch present in 20% to 40% of cases and an interrupted arch in 20%. The arch interruptions, Van Praagh type A4, are associated with a large PDA, which may be mistaken for the aortic arch; the PDA supplies most of the thorax and inferior part of the body and usually the left subclavian artery. Because the ductus arteriosus contains contractile tissue, patients with type A4 truncus arteriosus may physiologically have no blood supply to most of the thorax and abdomen when the ductus contracts and closes.

The coronary circulation is quite variable in its origin. There is frequently an ectopic high origin of one or both coronary arteries. There is a single coronary artery in 13%, usually arising from the posterior cusp. The left coronary artery tends to arise from a more posterior level than in normal hearts.

Truncus Arteriosus

The surgical repair of truncus arteriosus with confluent or near confluent pulmonary arteries consists of separating the pulmonary arteries from the arterial trunk and connecting them to the right ventricle via a conduit or homograft and closure of the ventricular septal defect (see Figure 10-44). When the aortic arch is interrupted or has a significant coarctation, the repair also consists of reconstruction of the aortic arch with the arterial trunk.

The cardiac MR protocol for evaluating patients following repair of truncus arteriosus is essentially the same as the protocol for tetralogy of Fallot because the complications are similar with respect to conduit stenosis and regurgitation and branch pulmonary artery stenosis and their inherent effects on right ventricular volumes and function (Table 10-5). In addition, there is a significant incidence of progressive truncal root dilatation and valvular regurgitation postoperatively that can be quantified and followed serially by cardiac MR for possible root or valve replacement.

TABLE 10-5 Complications after repair of tetralogy of Fallot

Hemitruncus Arteriosus

In hemitruncus one of the pulmonary arteries originates from the aorta and the other from the right ventricle. There are separate aortic and pulmonary valves that distinguish hemitruncus from truncus type A3. The lung connected to the aorta is subject to the systemic pressure and has aneurysmal hilar branches and serpentine peripheral vessels. The lung supplied by the right ventricle has normal vasculature. The aortic arch tends to be large and may displace the trachea away from the side of the arch. It is right sided in 20% to 30% of cases. When the thymus does not obscure the mediastinum, the right boundary is the edge of the large ascending aorta.

Large PDA, tetralogy of Fallot with pulmonary atresia, and aortopulmonary septation are the other major cardiac anomalies to be differentiated from truncus arteriosus. If two semilunar valves are identified, the diagnosis is not truncus. A blind infundibular chamber in the right ventricle is typical of tetralogy of Fallot with pulmonary atresia. In the lateral projection, this chamber is seen as an outpouching anterior to the aorta; this chamber is not present in truncus arteriosus.

Aortopulmonary Septation

Separate aortic and pulmonary valves and a defect between the ascending aorta and the main or right pulmonary artery are characteristic of aortopulmonary septation (Fig. 10-57). This rare malformation is also called aortopulmonary septal defect and aortic pulmonary window. The defect is usually in the left lateral wall of the ascending aorta and connects with the right lateral wall of the pulmonary trunk. The defect can extend from the annulus of the two semilunar valves to involve the ascending aorta to varying degrees. About half have aortic arch interruption or a preductile coarctation.

FIGURE 10-57 Aortopulmonary septation. Injection into the ascending aorta simultaneously opacifies both the aortic and pulmonary valves. The descending aorta is opacified before the aortic arch, indicating a patent ductus arteriosus.

Anatomically Corrected Malposition of the Great Arteries

In this malformation, the left ventricle ejects into the aorta and the right ventricle into the pulmonary artery. However, the great arteries are abnormally related to one another. In situs solitus, the aorta is to the left of the pulmonary artery. The ventriculoarterial connections are normal but their relations are malpositioned (Fig. 10-58). The levotransposed aorta is characteristic of corrected transposition of the great arteries, and if the loop rule applies, indicates ventricular inversion and L-looping of the ventricles. Levotransposed aorta rarely occurs in other types of malformations, including those that defy the loop rule and have noninverted ventricles.

FIGURE 10-58 Anatomically corrected levomalposition of the great arteries. A, Frame from a selective left ventricular cineangiocardiogram in the anteroposterior projection. The venous catheter is in the left-sided, morphologic left ventricle (LV). Contrast material opacifies the large morphologic left ventricle, and a hypoplastic right ventricular outlet chamber (RV). The right pulmonary artery (RPA) is seen. The left pulmonary artery is probably absent. The aorta (AO) originates above the morphologic left ventricle and is to the left of the pulmonary artery. Bilateral conal myocardium (c) is evident. B and C, Selected lateral cineframes from the left ventricular injection. The semilunar valves are at the same level and appear side by side in this projection. The pulmonary artery (PA) originates above the right ventricular outlet chamber and is slightly anterior. The aortic valve is clearly separated from the mitral valve by subaortic conal myocardium (c), which is quite dynamic. The right ventricular infundibulum (INF) is narrow and becomes even narrower with systole (C). Bilateral conal myocardium is thus present.

(From Freedom RM, Harrington DP: Anatomically corrected malposition of the great arteries. Report of 2 cases, one with congenital asplenia: frequent association with juxtaposition of atrial appendages, Br Heart J 36:207-215, 1974.)

Total Anomalous Pulmonary Venous Connection

All pulmonary veins may connect anomalously in three ways:

The most common anomaly is connection of all pulmonary veins to a systemic vein in the thorax (Fig. 10-59). The one or two veins draining each lung merge to form a common confluence behind the left atrium but without connecting to it. The outflow of this common vein may go into the left innominate vein, the right superior vena cava, or to the azygos or hemiazygos system of veins. When the connection is to a vein on the left side of the mediastinum, this vascular structure may be either a left superior vena cava or an anomalous vertical vein. Most vertical veins in the supracardiac type of total anomalous pulmonary venous drainage do not connect to the coronary sinus, hemiazygos, or left atrium as a left superior vena cava would. Therefore, it is actually an anomalous vein between the common pulmonary vein and the left innominate vein. This anomalous vertical vein may pass posterior to the pulmonary artery or may pass between the left main stem bronchus and the left pulmonary artery. In the latter instance, an obstruction to flow may occur by compression of these adjacent structures on to the anomalous vein.

FIGURE 10-59 A, Coronal maximum intensity projection image from a magnetic resonance angiogram showing the left and right (R) pulmonary veins joining to a vertical vein (VV) connecting to the innominate vein (arrow 1) to superior vena cava (SV). B, Off-axial maximum intensity projection from the same examination, showing the confluence of the pulmonary veins to the posterior-lying vertical vein (VV).

In the intracardiac type of total anomalous pulmonary venous connection (TAPVC), the common pulmonary vein connects directly to the right atrium or coronary sinus (Fig. 10-60), either as one vessel or with separate connections of two or more of the pulmonary veins. The intracardiac type of anomaly is frequently accompanied by polysplenia or asplenia with the associated bilateral superior vena cava and azygos continuation. The pulmonary veins may also attach to the coronary sinus, in which case this structure is considerably enlarged.

FIGURE 10-60 Coronal maximum intensity image from an magnetic resonance angiogram shows the confluence of the left (LPV) and right (RPV) pulmonary veins with a dilated coronary sinus (CS) draining to the right atrium (RA).

The infracardiac type of anomalous pulmonary connection always demonstrates pulmonary vascular obstruction. In this type, a venous channel from the common pulmonary vein passes inferiorly through the diaphragm at the esophageal hiatus to connect with the portal vein or its tributaries or the ductus venosus. In the extreme form, which represents atresia of the common pulmonary vein, all egress from the common pulmonary vein is absent except into minute venous channels adjacent to the esophagus.

The physiology of this malformation then is determined by the amount of mixing of oxygenated blood, the amount of blood that reaches the left ventricle and systemic circulation, and the degree of pulmonary vascular obstruction. Most of these patients have either an atrial septal defect or patent foramen ovale, which serves as the conduit to the systemic circulation. The blood flow is bidirectional at the right atrium, passing either into the left atrium or into the right ventricle and pulmonary artery. Increased pulmonary blood flow occurs in the supracardiac and cardiac level anomalies. Decreased pulmonary blood flow can, of course, occur from an Eisenmenger reaction with an increase in the precapillary vascular resistance. In the infracardiac type, the pulmonary venous return is obstructed mainly by the portal circulation. The physiologic consequences are signs of pulmonary venous hypertension and pulmonary edema.

Partial Anomalous Pulmonary Venous Connection

Partial anomalous pulmonary venous connection (PAPVC) is present when one or more, but not all, of the pulmonary veins connect to a systemic vein (Fig. 10-66). The veins of the right lung have 2 to 10 times as many anomalous connections as those of the left lung. When an anomalous vein exists, it usually connects to the nearest adjacent systemic vein or to the right atrium (Fig. 10-67). For example, the right superior pulmonary vein usually connects to the right superior vena cava (Fig. 10-68) or azygos vein. The right inferior vein may connect with the inferior or superior vena cava, a hepatic vein, or occasionally the azygos vein. The left lung veins connect to an anomalous vertical vein draining into the left innominate vein, the coronary sinus, or the hemiazygos vein (Fig. 10-69). Although these examples are typical, there are many variations in number, size, and connections of the pulmonary veins. The atrial septum is usually intact. Conversely, if an atrial septal defect is present, about 10% of these patients will have a pulmonary venous anomaly.

FIGURE 10-66 Anomalous pulmonary vein draining the left upper lobe. A, The oval density adjacent to the aorta (arrow) is an anomalous vein that connects to the left innominate vein. B, Lung windows show the tortuous peripheral course to the left side of the mediastinum.

FIGURE 10-67 Partial anomalous pulmonary venous connection to the right atrium. A long-axis image perpendicular to the interventricular septum shows a right pulmonary vein (arrow) entering the right atrium. The interatrial septum is intact.

(From Miller SW, Brady TJ, Dinsmore RE, et al.: Cardiac magnetic resonance imaging: the Massachusetts General Hospital experience. Radiol Clin North Am 23:745-764, 1985.)

FIGURE 10-68 Axial gradient echo image from a 24-year-old man with a sinus venosus atrial septal defect and an anomalous right upper pulmonary vein draining to the superior vena cava. The anomalous vein (long arrow) passes anterior to the right pulmonary artery (RP) to enter the superior vena cava (SV). Notice the mildly dilated right atrial appendage (short arrow).

FIGURE 10-69 Partial anomalous pulmonary venous connections. The venous phase of a pulmonary angiogram shows the left superior pulmonary vein connecting to the left innominate vein (large arrow). The right inferior pulmonary vein (small arrows) joins the right atrium at the inferior vena caval junction.

The chest radiograph is usually normal because the pulmonary-to-systemic flow ratio is generally less than 2:1. When an entire lung is drained by an anomalous connection, the main pulmonary arteries and peripheral branches are enlarged similarly to the situation with a left-to-right shunt. In this case, the right ventricle is enlarged, whereas the other cardiac chambers and the vena cava are equivocally dilated. The isolated lower lobe veins that connect to the inferior vena cava present the most striking radiographic abnormalities. The anomalous vein is almost always seen on the right side but may occasionally be a left-sided structure. Curving medially and inferiorly through the lung, the vein has been likened to a scimitar because, unlike a normal pulmonary artery, it increases in diameter as it goes toward the base of the lung (Fig. 10-70).

FIGURE 10-70 Two patients with scimitar syndrome. A, Young child with a murmur. The venous phase of a pulmonary arteriogram shows all the right pulmonary veins (arrow) connecting to the inferior vena cava. As it courses inferiorly, the size of the vein becomes larger in contradistinction to the pulmonary arteries, which become smaller as they pass toward the lung base. B, Scimitar syndrome. Axial gradient echo acquisition from a 45-year-old man with an unusual chest film through the left atrium (LA) shows a dilated right atrium (RA) and right ventricle (RV) and cardiac dextroposition. Notice that no right-sided pulmonary veins drain to the LA. The crista terminalis (arrow) appears as a filling defect along the lateral wall of the RA. C, Off-coronal gradient echo acquisition through the left ventricle (LV) and right atrium, Two large pulmonary veins (arrowheads) drain to the RA.

Felson named it the venolobar syndrome. Fraser preferred the hypogenetic lung syndrome. The syndrome is a rare congenital anomaly that consists of an anomalous pulmonary venous connection of the right lung to the inferior vena cava; it is associated with hypoplasia of the right lung and its bronchus and pulmonary artery. The heart is secondarily rotated toward the right hemithorax because of the small right lung. The right lung may have abnormal lobation, frequently having two rather than three lobes. This condition is also called the pulmonary venolobar syndrome.

Pulmonary angiography is a common examination for locating all the pulmonary veins. If the right atrium is visible during the levophase, an anomalous pulmonary vein, an atrial septal defect, or both must be present (Fig. 10-71). When a PAPVC to the superior vena cava or right atrium exists, an atrial septal defect occurs in 90% of patients, whereas when the anomalous vein connects to the inferior vena cava, only 15% have an atrial septal defect. A technique of localizing the anomalous pulmonary vein with respect to the atrial septal defect involves placing a catheter into the right pulmonary vein from an inferior vena caval approach. Using cranial angulation with the hepatoclavicular or “four-chamber” view, the atrial septum is projected in profile so that the connection of the vein to the atrium is seen during a 10-ml injection.

FIGURE 10-71 Atrial septal defect and anomalous pulmonary vein. A, After selective right pulmonary artery injection, the confluence (C) of the right pulmonary veins projects behind the junction of the superior vena cava and the right atrium. The right atrium is opacified before the left atrium. B, The venous phase of a selective left pulmonary angiogram reveals normal drainage of the left pulmonary veins into the left atrium. The filling defect in the left atrium (arrows) is caused by unopacified blood crossing a sinus venosus atrial septal defect in a right-to-left direction.

Patent Foramen Ovale

A patent foramen ovale is a normal structure that has a flap of tissue permitting passage of blood in utero from the right atrium to the left atrium. After birth, when left atrial pressure exceeds that in the right atrium, this flap is held closed and, in most people, gradually fuses with the rest of the atrial septum after the first year of life. However, in about one fourth of adults, the foramen ovale remains patent, placing these patients at risk for paradoxical emboli.

Ostium Secundum and Primum Defects

An ostium secundum atrial septal defect is an absence or deficiency of tissue in the region of the fossa ovalis (Fig. 10-72). An ostium primum atrial septal defect is medial and adjacent to both atrioventricular valves. This abnormality is associated with developmental defects in the endocardial cushions that contribute to the inferior atrial septum (Fig. 10-73). If all endocardial cushions are deficient, associated defects occur in the superior ventricular septum and in the leaflets and chordal attachments of both the mitral and tricuspid valves.

FIGURE 10-72 An asymptomatic 58-year-old woman with a murmur. A, Axial spin echo acquisition. The heart is enlarged. Notice that the right atrium (RA) and right ventricle (RV) are dilated (the heart is rotated into the left chest) but the left atrium (LA) and left ventricle (LV) are not. The left lower lobe pulmonary vein is dilated. There is a break in the interatrial septum (double-headed arrow) indicating the secundum interatrial septal defect. B, Diastolic short-axis gradient echo acquisition. The dilated right pulmonary artery (RP) lies above the normal LA. A signal void jet (arrows) extends from the interatrial septum into the dilated right atrium (RA).

FIGURE 10-73 Axial spin echo acquisition from a 16-year-old girl with partial atrioventricular septal defect and pulmonary hypertension. Notice how severely hypertrophied the right ventricular (RV) myocardium is. The medial aspect of the interatrial septum (arrow 1) is absent as is the posterior, basal portion of the interventricular septum (arrow 2). Although no clearly defined atrioventricular valves are identified, there is redundant valve tissue (arrow 3) across the orifices of the RV and left ventricle (LV). LA, left atrium; RA, right atrium.

Sinus Venosus Defects

A sinus venosus atrial septal defect occurs in the superior and lateral portion of the atrial septum adjacent to the connection with the right pulmonary veins (Fig. 10-74). Because of this location, anomalies of pulmonary venous connection are commonly found in the triangle defined by the superior vena cava, the interatrial septum, and the right superior pulmonary vein.

FIGURE 10-74 Gradient echo acquisition from a 24-year-old man with a sinus venosus atrial septal defect. Axial diastolic gradient echo acquisition through the aortic root (Ao). Notice that the dilated right ventricular outflow (RVO) is displaced toward the patient’s left. The right atrial appendage (RAA) is dilated. There is a break (arrow) in the posterior wall of the superior vena cava (SV), allowing communication between the left atrium (LA) and right heart.

Less Common Defects

Less common atrial defects are those between the fossa ovalis and the inferior vena cava and in the region of the coronary sinus (Fig. 10-75). An absent coronary sinus, connection of the left superior vena cava to the left atrium, and a large atrial septal defect make up this unusual developmental complex.

FIGURE 10-75 Oblique coronal gradient echo image obtained from a 26-year-old woman with an unroofed coronary sinus type interatrial communication. The inferior aspect of the left atrium (LA) is continuous with the coronary sinus (CS). Note the dilated pulmonary artery (arrow).

Chest Film Features

The classic chest film features of an atrial septal defect (Fig. 10-76) are enlargement of the right atrium, the right ventricle, and all segments of the pulmonary arteries (“shunt vascularity”). Because the chest film does not accurately reflect the size of the right atrium and ventricle, the heart size may appear normal. These signs of enlargement are apparent when the flow through the pulmonary artery is at least twice that through the aorta. The large size of the main pulmonary artery is usually striking when compared with the normal size of the aortic arch.

FIGURE 10-76 Atrial septal defect. Notice that the bulk of the cardiac silhouette is displaced toward the left, and the superior mediastinum at the level of the (left sided) aortic arch is narrow. The left heart border appears to run parallel to the shadow of the left bronchus. The displacement is caused by leftward cardiac rotation in right heart enlargement. The narrow mediastinum results from leftward rotation of the superior vena cava over the spine. When the heart rotates toward the left, the right ventricular outflow becomes the mid portion of the more convex left heart border. The pulmonary artery pressure is normal, illustrating that dilated central pulmonary arteries can reflect either increased blood flow or pressure.

There is no enlargement of the left heart in a simple atrial septal defect unless there are other complications. For example, when the right ventricle is enlarged as a result of increased volume, there is a distortion of the geometry of the left ventricle so that mitral prolapse and occasionally mitral regurgitation ensue. Similarly, in an atrioventricular canal defect, the left atrium and ventricle are enlarged when either a ventricular septal defect or mitral regurgitation causes volume overload in these chambers.

When cyanosis results from pulmonary arterial hypertension (Eisenmenger syndrome), the pulmonary arteries become quite large. However, evaluating the size of the hilar pulmonary vessels is not a reliable way of differentiating pulmonary arterial hypertension with a small left-to-right shunt from normal pulmonary artery pressures with a torrential shunt. When an Eisenmenger syndrome causes blood to flow in a reverse direction (from the right to the left atrium), the heart becomes smaller. Radiographic signs of pulmonary arterial hypertension at this stage include calcification of the pulmonary arteries (Fig. 10-77), aneurysmal dilatation of the hilar branches, and a serpentine course of the lower lobe pulmonary arteries.

FIGURE 10-77 Eisenmenger syndrome resulting from an atrial septal defect. The heart size is small. The hilar pulmonary arteries are aneurysmal and calcified. The peripheral pulmonary arteries are vasoconstricted and nearly invisible. The dramatic difference in caliber between central and peripheral arterial segments reflects pulmonary hypertension.

Imaging Techniques and Features

Atrial septal defects are routinely imaged by echocardiography. In the four-chamber view (Fig. 10-78), the entire atrial septum can be seen: superiorly from the entrance of the right upper pulmonary vein and inferiorly to the tricuspid valve. With a catheter in the right upper pulmonary vein, contrast material streams along the left atrial side of the septum and then through the defect to opacify the right atrium. In these projections, if the interatrial septum is divided into thirds, a sinus venosus defect will occur in the upper outer third, a secundum defect will occur in the middle third, and a primum defect will occur in the central third.

FIGURE 10-78 Angiography of atrial septal defect. In the left anterior oblique cranial view, a catheter was passed from the inferior vena cava through the secundum atrial septal defect into the right upper pulmonary vein. Contrast passes across the defect from the left atrium (LA) to the right atrium (RA). In this view, the secundum atrial septal defect is in the central part of the atrial septum. A sinus venosus defect would be present in the upper one third of the septum, whereas an atrioventricular canal defect would be in the lower one third of the septum.

In the same manner, MRI shows these three types of atrial septal defects in the plane aligned perpendicular to the septum. From an axial multislice series of images, a first set of oblique images is obtained oriented to the interventricular septum—these are images parallel to the septum. A second set of oblique images is then acquired from the first set along the axis of the mitral valve to the left ventricular apex—these images are the four-chamber view, or perpendicular to the septum. As with echocardiography, the four-chamber view in MRIs has venosus, secundum, and primum defects in the upper, middle, and lower third of the interatrial septum, respectively. A pitfall in MRI of secundum defects is that an intact septum may have signal dropout in the fossa ovale because the septum is less than a pixel thick and has too few protons to generate a signal. If a secundum defect is suspected, a flow-sensitive sequence should also be obtained to confirm blood passing through the signal void.

Complete Atrioventricular Canal Defects

In the complete form of atrioventricular septal defect, the mitral and tricuspid valves may be formed into a single large common valve, or they may have separate annuli. The mitral valve has a deficiency or cleft in the anterior leaflet, while the tricuspid valve has a cleft in its septal leaflet. This division results in five leaflets, two of which bridge from the left to the right ventricle. A posterior leaflet extends from the posterior papillary muscle of the left ventricle to the right posterior papillary muscle of the right ventricle. The anterior leaflet extends from the medial papillary muscle of the right ventricle to the anterolateral papillary muscle of the left ventricle. The anterior leaflet may be divided with chordae tendineae going to the septum and to the papillary muscles, or it may be undivided with no attachments to the septum. The combination of defects makes the size of the mitral orifice appear two or three times as large as that of the aortic valve.

The complete form includes unequal inlet and outlet lengths of the ventricular septum, a malorientation of the aortic valve relative to the atrioventricular valves, atrial and ventricular septal defects, and a deficiency and malattachment of part of the right and left atrioventricular valves. The complete form of an atrioventricular canal defect, which constitutes about 20% of all types of canal defects, has an atrial septal defect that communicates with a ventricular septal defect. The atrioventricular valve may be common or may be partitioned by the tricuspid and mitral annuli. Among patients with a complete atrioventricular canal defect, 50% to 80% have Down syndrome. Of patients with Down syndrome, 40% have an atrioventricular septal defect (Fig. 10-79).

FIGURE 10-79 Chest film in atrioventricular canal defect. The hilar vessels at 3 years of age are large and indistinct because of pulmonary edema surrounding them. The heart is globally enlarged, reflecting intracardiac shunting and heart failure.

Partial or Incomplete Atrioventricular Canal Defects

A partial or incomplete atrioventricular canal defect has separate mitral and tricuspid orifices, and may have atrial or ventricular septal defects, or both, and clefts in the mitral and tricuspid valve leaflets (see Figure 10-73). About two thirds of all patients with an atrioventricular canal defect have the partial form. The most common partial form is an ostium primum atrial septal defect and a cleft in the anterior (septal) leaflet of the mitral valve.

Segmental Analysis

The atrial septal defect is of the ostium primum variety, involving the central portion of the atria adjacent to the atrioventricular valves. This type of atrial defect, inferior to that of the ostium secundum type, is found below the fossa ovalis. The central part of the defect extends to the annuli of the atrioventricular valves so that no intervening tissue is present between the hinge point of the valve leaflets and the atrial septal defect. At times the defect may also include the fossa ovalis and other more superior portions of the atrial septum. A common atrium exists when the entire atrial septum is absent. This entity is associated with a cleft in the anterior leaflet of the mitral valve and frequently with a persistent left superior vena cava.

The ventricular septal defect extends from the annuli of the atrioventricular valves inferiorly to involve not only the posteromedial portion of the septum but also the inferior free wall, and posterolaterally to the lateral portion of the mitral annulus. The membranous part of the septum may be either normal or deficient and is anterior and superior to the canal type of ventricular septal defect.

The mitral valve is displaced toward the apex of the left ventricle, as compared with the aortic valve. The papillary muscles are in front of one another rather than in the anterolateral and posteromedial locations. In the normal heart, the distance from the aortic valve to the apex is the same as that from the mitral valve to the apex. The ratio of the length of the left ventricular inflow tract to the outflow tract may vary from 0.5 to almost 1.0 (in the normal heart, this ratio is 1.0). In the complete form of atrioventricular septal defect, the ratio tends to be between 0.5 and 0.7, and in the partial form is between 0.7 and 0.9 (Fig. 10-80). The mitral leaflets are quite redundant and scalloped. Rarely, this extra valve tissue can appear as a tumor mass and obstruct the outflow tract. Because of the cleft, the mitral regurgitation may go directly into the right atrium through the atrial septal defect rather than into the left atrium.

FIGURE 10-80 In this diastolic frame from right anterior oblique left ventriculogram, the aortic valve is closed and the mitral valve is opened. The elongated subaortic region is the gooseneck deformity. The malformed atrioventricular valve is reflected by the long curved filling defect (arrowheads). The length from the mitral valve to the apex (M-A) is nearly half that from the aortic valve to the apex (A-A), indicating the distinctive displacement of the mitral valve toward the apex in atrioventricular canal defect. In the normal heart, these lengths are equal.

The outflow tract of the left ventricle is usually deviated anteriorly and to the right side. Compared with the normal heart, in which the direction of blood through the aortic valve is toward the right shoulder, the direction in a canal defect is more horizontal and toward the right pectoral region.

Chest Film Abnormalities

The appearance of the heart and lungs on the chest film reflects the abnormal blood flow (see Figure 10-79). Because there is a left-to-right shunt across an atrial or ventricular septal defect, or across both, all segments of the pulmonary arteries are enlarged. All four chambers of the heart are large, reflecting not only the flow through the septal defect but also mitral and tricuspid regurgitation. When a combination of high cardiac output and mitral regurgitation coexist, interstitial and alveolar pulmonary edema may be visible, particularly in the hilar regions, even though the left atrial pressure is normal.

On chest film it is often impossible to distinguish a secundum atrial septal defect or an isolated membranous ventricular septal defect from either the complete or partial form of atrioventricular canal defect. There are, however, several clues on the chest film that may suggest the latter (Table 10-6). First, the age of the patient is helpful in that it is unusual in a person less than a few months old for a secundum atrial septal defect to produce visible large pulmonary vessels and signs of congestive heart failure, whereas canal defects may be associated with signs of heart failure within the first few weeks of life. Second, the left atrium is not visibly enlarged in a secundum atrial septal defect; this feature, however, is typical of an atrioventricular septal defect with mitral regurgitation. Third, an enlarged right atrium is not a feature of a simple ventricular septal defect but is present in an atrioventricular septal defect when there is either an atrial septal defect or a left ventricular-right atrial defect. These findings, coupled with left axis deviation of the QRS complex on the electrocardiogram (ECG), are likely to represent some type of atrioventricular septal defect.

TABLE 10-6 Distinguishing features of acyanotic lesion

From Van Praagh R, Weinberg PM, Smith SD, et al.: Malpositions of the heart. In: Emmanoulides GC, Riemenschneider TA, Allen HD, et al., eds.: Moss and Adams heart disease in infants, children and adolescents including the fetus and young adults, ed 5, Baltimore, 1995, Williams & Wilkins.

Angiographic Features

The angiographic features of atrioventricular canal defects were first recognized in a classic paper by Baron and colleagues in 1964. They described the diagnostic pattern in the left ventriculogram as a “gooseneck” deformity and explained how this resulted from a deficiency in the inferior interventricular septum. The characteristic deformity in the left ventricle is visible in the right anterior oblique projection and is accentuated in diastole. The left ventricular inflow is concave and not straight as it is in the normal heart. This concave edge represents in part the apically displaced mitral valve; it has a serrated edge, which is the redundant leaflet of tissue pulled by the chordae tendineae. A radiolucent horizontal line in the mitral valve represents the cleft of the anterior leaflet. These features are present with or without a ventricular septal defect and also persist after surgical closure of the atrial and ventricular septal defects (Fig. 10-81).

FIGURE 10-81 Partial atrioventricular canal defect. Diastolic (A and C) and systolic (B and D) frames in the right anterior oblique projection (A and B) and the four-chamber left oblique projection (C and D) show the septal, inferior, and posterior deficiency of the left ventricle that constitutes the gooseneck deformity. An ostium primum atrial septal defect and a cleft anterior leaflet of the mitral valve are present with mild mitral regurgitation. The diameter of the mitral valve is about three times the aortic valve diameter. Note the redundant scalloped mitral valve (arrows).

The right anterior oblique left ventriculogram, performed with the venous catheter passing across the atrial septal defect, demonstrates the relation between the atrioventricular valve and the left ventricular inflow and outflow tracts. The anterior leaflet of the mitral valve is denoted by the cleft and its septal attachments. In contrast, the posterior part of the mitral valve lies beside the left circumflex artery. Both of these leaflets appear concave and contribute to the gooseneck deformity. Therefore, the characteristic shape of the base of the left ventricle results from a deficiency of the diaphragmatic and posterior wall and from the defect of the septum.

When separate mitral and tricuspid valves exist, the septal leaflet forms the right border of the left ventricular outflow tract. When there is a common atrioventricular valve, contrast material passes from the left ventricle into the right ventricle beneath the leaflets of the common valve (Fig. 10-82). The leaflets may be attached to the septum or may form a continuous bridge from the superior rim of the common valve. The chordal attachments of the common leaflet may extend to their adjacent ventricular papillary muscles or the lip of the ventricular septal defect or may cross into the opposite ventricle. The partial form of this malformation, in which the chordae attach on opposite sides of the septum, is the straddling atrioventricular valve.

FIGURE 10-82 Complete atrioventricular canal. Left ventricular angiography was performed by passing the catheter across the atrial septal defect into the left ventricle. Diastolic frames in the frontal (A) and left anterior oblique (B) projections show the gooseneck deformity of the outflow region (long white arrow). In systole there was simultaneous opacification of the pulmonary arteries and aorta. The open common atrioventricular valve (arrowheads) straddles the ventricular septum.

Magnetic Resonance Imaging Features

In the four-chamber view perpendicular to the interventricular septum, spin echo sequences will show defects at the junction of the interatrial and interventricular septum (Fig. 10-83). White blood sequences, which are sensitive to movement, are needed to assess valve regurgitation and shunt flow.

FIGURE 10-83 Magnetic resonance imaging of atrial septal defect. A cardiac-gated image in a plane perpendicular to the long axis of the septum shows a primum defect (arrow) adjacent to the mitral and tricuspid valves. The mitral valve is closed, indicating a diastolic frame.

(From Miller SW, Brady TJ, Dinsmore RE, et al.: Cardiac magnetic resonance imaging: the Massachusetts General Hospital experience, Radiol Clin North Am 23:745-764, 1985.)

Classifications

Several surgical and pathologic classifications have divided these defects into supracristal and infracristal varieties. However, the crista supraventricularis is not always identified in its entirety by imaging. In addition, the ventricular septum is curvilinear so that other landmarks, such as the mitral and aortic valves, are more readily recognizable. To overcome these problems, Soto devised a classification in 1980 that divides the left ventricle into the inlet part near the mitral valve, the muscular portion, and the outflow tract portion below the aortic valve. Using this way of dividing the ventricle, defects in the posterior ventricular septum are those associated with atrioventricular septal defects. Muscular defects have slight overlap with defects in the other categories but are mainly holes of varying sizes between the trabeculations of the two ventricles. Ventricular septal defects in the left ventricular outflow region mainly occur in the membranous part of the septum. In complex defects, such as tetralogy of Fallot, the defect extends into the crista and occasionally into the muscular septum. Isolated membranous defects, viewed from the right ventricular side, are infracristal in location. The least common defect is in the supracristal location below the pulmonary valve. Also called conoventricular defects, these malformations are frequently associated with malalignment between the ventricular septum and the conal septum that separates the aortic from the pulmonary valves.

Chest Film Findings

In all types of ventricular septal defect, the appearance of the heart and lungs on the chest radiograph depends on the flow and pressure in the pulmonary artery. In small shunts that represent less than a 2:1 shunt-to-pulmonary-artery ratio, the chest film is usually normal. In larger shunts, cardiac size increases roughly in proportion to the amount of the shunt. The left ventricular apex projects to the left and inferiorly and posteriorly. The left atrium is enlarged and can be seen as a double density behind the right atrium. The main pulmonary artery and all pulmonary vessels increase in size depending on the degree of the blood flow (Fig. 10-84). If pulmonary vascular obstruction increases so that blood flow reverses and becomes a right-to-left shunt (Eisenmenger physiology), the heart size becomes smaller. At this point, the central pulmonary arteries appear as aneurysms, and rarely, may be calcified. The basilar pulmonary arteries tend to elongate when pulmonary artery hypertension occurs, resulting in a serpentine course. The right ventricle, seen mainly on the lateral chest film, also enlarges as the size of the shunt increases. Both ventricles have a corresponding increase in diastolic volume and a similar ejection fraction.

FIGURE 10-84 Central pulmonary arteries in pulmonary hypertension and Eisenmenger syndrome. A, The main and right pulmonary arteries are more than twice as large as the ascending aorta and clearly exceed the 3-cm upper limits of normal. B, The hilar pulmonary arteries (arrows) are two to four times as large as their corresponding bronchus.

Imaging Features

The imaging evaluation shows the size and location of these ventricular defects. The optimal projection to show the septum is a stack of four-chamber views that demonstrates the anterior and posterior portions of the septum.

Muscular ventricular septal defects typically appear on MR cine angiography as thin, small jets of contrast material that pass directly into the right ventricle. These defects are usually located in the apical half of the ventricular septum but may exist adjacent to the membranous septum at its trabeculated edge (Fig. 10-85). Although these defects usually range from a few millimeters to a centimeter in size, most of the muscular septum may be absent, making a common ventricle. Small muscular defects, which are seen as thin streams into the right ventricle, are visible throughout most of systole. If the defects are tiny, the contracting trabeculations may close these holes so that they are visible on ventriculography only during the early part of systole.

FIGURE 10-85 Multiple ventricular septal defects. The lower three arrows point to defects in the muscular septum, whereas the upper arrow outlines a membranous defect.

Defects in the membranous septum are seen in the outflow tract inferior to the aortic valve and medial to the mitral valve (Figures 10-86, 10-87). From the right ventricular side, the septum is deficient below the crista and behind and adjacent to the sepal leaflet of the tricuspid valve. During a left ventriculogram the path of contrast material is seen going through the septum, then apically down the right ventricular side of the septum (Fig. 10-88). This “waterfall” motion is typical of a membranous defect and opacifies the entire right ventricle when the size of the defect is moderate. When the pulmonary artery pressures are normal, left-to-right shunting is visible during the left ventriculogram in both systole and diastole, although the major portion of contrast media crosses the ventricular septal defect in systole. If the peak right ventricular pressure is within 30 mm Hg of that in the left ventricle, transient right-to-left shunting occurs during isovolumetric relaxation. When pulmonary vascular obstruction ensues with systemic pulmonary artery pressures and cyanosis (Eisenmenger syndrome), most of the blood flow is from the right ventricle into the left ventricle; the degree of opacification depends less on the size of the defect than on the pressure gradient between the ventricles.

FIGURE 10-86 Two patients with subaortic (membranous) ventricular septal defect. A, Oblique axial double inversion recovery acquisition through the posterior right aortic sinus of Valsalva (pr) in a 25-year-old man with a large ventricular septal defect (arrow) and heart failure. The right ventricular (RV) myocardium is thickened, and the cavity is dilated, as evidenced from the clockwise rotation of the heart into the left chest. The left ventricle (LV) and left atrium (LA) are dilated, as is the right pulmonary artery (RP). Right heart failure is revealed by dilatation of the right atrial appendage (RAA) and superior vena cava (SV). AoD, descending aorta. B, Right anterior oblique sagittal spin echo acquisition through the muscular interventricular septum from a 16-year-old boy with mild shortness of breath. The left-sided aortic arch (Ao) displaces the trachea (T) to the right. Immediately beneath the aortic valve annulus (double-headed arrow) and superior to the muscular interventricular septum (mu) is the signal void (arrow) of the membranous ventricular septal defect. The main (MP) and visualized right (RP) pulmonary arteries are dilated. RA, right atrium.

FIGURE 10-87 Two patients with ventricular septal defect. A, Axial systolic gradient echo acquisition from a 7-year-old boy. The right (RV) and left (LV) ventricles are dilated; the heart is rotated into the left chest. The fan-shaped signal void of the subaortic (membranous) ventricular septal defect (arrows) extends from just beneath the anterior aortic sinus of Valsalva (a) into the RV and spreads in width as it strikes the right ventricular free wall. B, Four-chamber view systolic gradient echo acquisition from an asymptomatic 50-year-old man with a tiny membranous ventricular septal defect. The fan-shaped signal void jet (black arrows) extends from just beneath the aortic valve and ascending aorta (AoA) into the normal-sized right ventricle. The LV and transverse right pulmonary artery (RP) are normal in size. The long white arrow identifies the right atrial appendage.

FIGURE 10-88 Angiographic approaches to membranous ventricular septal defect. A, The catheter is passed retrogradely through the hypoplastic aortic arch into the left ventricle (LV). The injection opacifies the right ventricle (RV) and the large pulmonary arteries. B, Left ventriculography was performed by passing the catheter from the inferior vena cava through a patent foramen ovale. By filming in the left anterior oblique projection with steep cranial angulation, the ventricular septum is elongated and shows the subaortic membranous defect (arrow).

Supracristal or subpulmonary ventricular septal defects have a high incidence of associated anomalies. These include aortic regurgitation, aneurysm of the aortic sinus of Valsalva, prolapse of the right aortic cusp, and the Taussig-Bing anomaly, which is a double-outlet right ventricle with the pulmonary artery adjacent to the ventricular septal defect. In contrast to the other types of ventricular septal defects, the right oblique view best shows the supracristal defect below the pulmonary valve. The ventricular septum is malaligned with the plane of the crista, which causes the semilunar valves to obscure one another during angiography in the long-axis oblique projection. The orthogonal right oblique projection is necessary to show the relation of the ventricular septal defect to the semilunar valves.

Aneurysms of the membranous septum look like a windsock (Fig. 10-89) and project into the ventricle adjacent to the septal leaflet of the tricuspid valve. These aneurysms, which appear to represent closing membranous defects, are frequently round and smooth-walled but may have a scalloped and irregular margin. The aneurysm may connect to the right ventricle through its center, or it may be completely closed allowing no communication between the ventricles. Rarely, the aneurysms extend into the right atrium. Common lesions associated with a membranous septal aneurysm are aortic insufficiency with prolapse of a cusp into a portion of this aneurysm, bacterial endocarditis, and (rarely) right ventricular outflow obstruction and tricuspid regurgitation. In views other than the left anterior oblique projection, the aneurysms may appear as masses adjacent to either the aortic or mitral valve. Masses in the right atrium and right ventricle represent the other side of the sac.

FIGURE 10-89 Ventricular septal defect. Aneurysm of the membranous septum resulting from a closed ventricular septal defect. The left anterior oblique view shows a subaortic saccular aneurysm (arrow) projecting into the right ventricle.

Left ventricular–right atrial shunting is an unusual type that is the result of tricuspid valve abnormalities, including clefts or perforations in the septal leaflet adjacent to a perimembranous ventricular septal defect and aneurysms in the membranous septum. Left ventricular–right atrial shunting associated with a perimembranous ventricular septal defect is different from that with atrioventricular canal defects. Only in the latter does left ventriculography show a cleft in the anterior leaflet of the mitral valve and a deficiency in the basilar part of the interventricular septum.

Characteristics

The altered hemodynamics that arise from a persistent ductus arteriosus depend on the size of the ductus and the ratio of the pulmonary-to-systemic vascular resistance. In fetal life, the shunt created by the ductus is from right to left because of the high pulmonary vascular resistance. Shortly after birth, the complex changes that happen in the first few minutes in the lungs result in a lowered pulmonary arterial pressure of one fourth to one sixth of the aortic pressure. A left-to-right shunt is thereby created through the patent ductus. This results in varying degrees of overcirculation to the lungs, left atrium, left ventricle, and the ascending and arch portions of the aorta. If the ductus does not close and an Eisenmenger reaction to the increased pulmonary flow results, the pulmonary vascular resistance again exceeds the systemic resistance and causes a right-to-left shunt across the ductus arteriosus.

The diameter and length of the ductus arteriosus varies considerably depending on whether partial closure has occurred (Fig. 10-90). In the newborn infant, the ductus is nearly the size of the descending aorta and may be mistaken for the aortic arch because of the size similarity. The length of the ductus is also quite variable and ranges from several centimeters to an aortic-pulmonary fistula without any intervening neck.

FIGURE 10-90 Two patients with patent ductus arteriosus. A, Coronal spin echo acquisition from a 24-year-old woman with a patent ductus arteriosus. The underside of the aortic arch (Ao) and the superior aspect of the proximal left pulmonary artery (PA) are joined by the tubular signal void (arrow) of the patent ductus. B, Left anterior oblique sagittal spin echo acquisition from a 7-week-old child with coarctation of the aorta. The left atrium (LA) is separated from the left ventricle (LV) by the anterior mitral leaflet. In this section, the origins of the left common carotid (arrow 1) and left subclavian (arrow 2) arteries are visualized. The aortic arch distal to the left subclavian artery is narrow and indents to more severe narrowing (the “coarctation” itself; arrow 3) just opposite the ductus arteriosus (arrow 4) originating from the main pulmonary artery (MP).

Complications

The major complication related to an isolated patent ductus arteriosus is the development of pulmonary arterial hypertension with resultant right-to-left flow reversal with cyanosis. Rare complications include aneurysm with thrombosis or rupture of the ductus, bacterial aortitis, and aortic dissection beginning at the ductus. Distal thromboembolism can originate from an aneurysm of the ductus arteriosus, and left phrenic nerve compression may be caused by an adjacent aneurysm.

Infant Chest Film Abnormalities

The radiographic signs of a persistent patent ductus have a rough correlation with the degree of pulmonary circulation. In the infant and young child, the hilar and segmental pulmonary arteries are enlarged, when not obscured by the thymus (Fig. 10-91). When the shunt is greater than 2:1, perihilar pulmonary edema may begin to develop from the high cardiac output in the infant and may progress to generalized alveolar edema. Concomitant cardiac changes include an enlarged cardiac silhouette with cardiothoracic ratios greater than 0.55. In the infant, the differentiation of individual enlarged chambers is frequently difficult; however, on the lateral view, left atrial enlargement can be detected by the posterior displacement of the left mainstem bronchus. Other noninvasive tests, such as the echocardiogram, show more accurately that the left atrium is enlarged and has an anteroposterior diameter exceeding that of the aorta. In the normal newborn infant, the anteroposterior left atrial dimension is less than that of the adjacent ascending aorta.

FIGURE 10-91 Patent ductus arteriosus in children. The typical chest film shows a large heart with the apex to the left and inferior. The enlarged pulmonary vessels are hazy, reflecting a mild degree of pulmonary edema. The aortic contour is obscured by the thymus.

Adult Chest Film Abnormalities

Because the mediastinum is not obscured by the thymus in the adult, other radiologic signs may point to the existence of a PDA. The “ductus bump” is a localized dilatation adjacent to the descending aorta next to its arch at the entrance of the ductus. Embryologically, this dilatation is thought to be distinct from the involuted end of the right aortic arch. The large ascending aorta and arch may elongate so that the ascending aorta and innominate artery are visible on the right side of the mediastinum, whereas the left subclavian artery projects into the left lung apex. Assuming an isolated left-to-right shunt is present, the large aortic arch indicates that the shunt is extracardiac; for example, a PDA is present rather than an atrial or ventricular septal defect. An aortopulmonary septal defect (a connection between the ascending aorta and the main pulmonary artery) produces similar findings, but the amount of the shunt usually is larger. Rarely, a linear or circular calcification exists in the region of a ductus arteriosus (Fig. 10-92). The significance of this deposition of calcium usually is unclear; it may be a result of either an episode of aortitis or atherosclerosis at the aortic end of the duct. A calcified ligamentum arteriosus implies a closed ductus.

FIGURE 10-92 Calcified patent ductus arteriosus (arrow). Posteroanterior (A) and lateral (B) chest films. Moderate pulmonary hypertension has enlarged the hilar arteries and the right ventricle. The large aortic arch indicates the site of the shunt is extracardiac.

Angiographic Examination

In the cardiac catheterization laboratory, a PDA can be evaluated by cineangiography in several ways. A catheter advanced up the inferior vena cava can usually be manipulated out of the pulmonary artery, through the duct, and into the descending aorta. In the frontal projection, the shape of the catheter looks like a musical treble clef (Fig. 10-93).

FIGURE 10-93 Catheter position in patent ductus arteriosus. The catheter enters from the inferior vena cava, passes from right to left across the tricuspid valve, and into the main pulmonary artery. It then passes cephalad across the duct to the descending aorta. Note that the catheter does not pass through the aortic arch.

When the flow through the ductus arteriosus is left to right, if the duct is not seen with ultrasound, aortography provides the best visualization of the ductus (Fig. 10-94) and of associated juxtaductal abnormalities, such as aortic coarctation. Similarly, when the flow is reversed, a pulmonary artery injection defines the ductal anatomy, but the proximal aortic arch is usually not visualized. The flow through the ductus recorded by angiography depends on the force of the injection and the natural direction of shunting. In addition, most shunts have some degree of bidirectional flow so that contrast material occasionally seems to oscillate from aorta to pulmonary artery and back.

FIGURE 10-94 Two patients with patent ductus arteriosus. A, In this newborn boy, a catheter was passed from the inferior vena cava, and threaded through the pulmonary artery (P) into a small short ductus (arrow). B, In this newborn girl, left ventricular injection opacifies a long, redundant ductus (arrow) lying just below the aortic arch.

A PDA may exist with other more complex cardiac defects. When a ventricular septal defect exists, a left ventriculogram is inadequate for identifying a PDA. In this case, the mixing through the ventricular septal defect will opacify the arch of the aorta and the main right and left pulmonary arteries nearly simultaneously, thereby obscuring the ductus. In this situation and in other connections between the aorta and pulmonary artery, such as truncus arteriosus, aortic-pulmonary window, or other aortic-pulmonary fistulas, an injection must be made in the descending aorta at the mouth of the suspected ductus. In a similar fashion, the rare anomaly of a bilateral ductus arteriosus, which forms a vascular ring around the trachea and esophagus, necessitates an injection in the proximal descending aorta with 30 to 40 degrees of cranial angulation to project both ductus from their respective aortic arches in the right and left anterior oblique projection.

Definition

It is not surprising that the definition of single ventricle or a univentricular heart is controversial given its extreme complexity. Van Praagh and colleagues believe that each cardiac chamber can be recognized by its gross morphologic characteristics; the ventricles are named by their trabecular pattern and not by their vessels or valves of entry or exit. Shinebourne and colleagues (1980) and Soto and colleagues (1979) argue that univentricular hearts possess only one ventricular chamber, which is connected to the atrial chambers. The latter group considers a normal ventricle to have an inlet segment, a trabecular portion, and an outlet segment. By their definition, a chamber is a ventricle if it contains an inlet segment and a trabecular portion, and the inlet arbitrarily must have at least half of an atrioventricular valve entering this segment. Depending on the ventricular morphology, this malformation is also called double-inlet left ventricle and double-inlet right ventricle or, when such a distinction cannot be made, a primitive ventricle.

A single ventricle is a heart with two atria but only one ventricular chamber. Either mitral and tricuspid valves or a common atrioventricular valve connect the atria with the ventricle. Excluded from this definition of single ventricle are mitral atresia and tricuspid atresia. In the univentricular heart, the ventricle may be of a left ventricular, right ventricular, or indeterminate type, depending on its trabecular type.

A rudimentary chamber may be adjacent to the ventricle but not connected to the atrioventricular valves. If this chamber is attached to the aorta or pulmonary artery, it is called an outlet chamber. If it is connected to neither the atrioventricular valves nor the semilunar valves, the chamber is called a trabecular pouch.

Because of the primitive nature of single ventricular hearts, it is not always possible to identify the morphologic features of the ventricle by imaging. Generally, the right ventricular type has more trabeculations but, because the other ventricle is absent, there is no comparison within the same heart to be certain which ventricle remains.

The univentricular heart of the left ventricular type is the most frequent and occurs in both noninverted and inverted forms. In noninverted ventricles, the right ventricular infundibulum, although quite variable in size, is adjacent to the tricuspid valve in a posterolateral position. An inverted ventricle has a blind pouch in the ventricle that projects anteriorly and is distinctly separate from the atrioventricular valve, similar to the inverted ventricles in congenitally corrected transposition of the great arteries.

In univentricular hearts of the right ventricular type, the rudimentary chamber is posterior and either to the right or left of the main chamber. This trabecular pouch tends to be quite small and can easily be missed by confusing its vestigial septum with a papillary muscle.

A common ventricle is not a single ventricle because the atrioventricular valves enter separately on each side of the rudimentary interventricular septum. The interventricular septum has either single or multiple large defects with the remaining ventricular muscle having recognizable elements of right ventricular morphology on one side and of left ventricular morphology on the other.

Associated anomalies are quite common in single ventricle. About two thirds have either valvular or subvalvular pulmonary stenosis, whereas a small number have pulmonary atresia. In univentricular hearts of the left ventricular type, there is usually aortic obstruction when the aorta arises from an outlet chamber. Anomalous pulmonary venous connections, PDA, and levomalposition of the aorta are frequent enough that additional selective injections are worthwhile to make the identifications.

Chest Film Features

The signs of single ventricle on the frontal chest film are indirect, reflecting the amount of intracardiac shunting and the degree of pulmonary stenosis or pulmonary arterial hypertension from vascular obstruction. In situs solitus and noninversion of the ventricles, there is an enlarged cardiomediastinal silhouette. The ventricular apex may point inferiorly in a “left ventricular pattern,” or it may point to the left and superiorly with a notch between the lateral heart and diaphragm in a typical “right ventricular pattern.” The left atrium is usually enlarged with signs of a double density on the right side of the cardiac silhouette and posterior displacement of the left main stem bronchus. If TGA is also present, the superior mediastinum is frequently quite narrow; in infancy this pattern has been ascribed to a relative diminution in the amount of thymus. When the aorta is levotransposed, the left side of the mediastinum still retains its distinctive convex shape.

An inverted ventricle is the only distinctive sign of single ventricle that separates it from all other types of CHD on a chest film with a large heart and shunt vascularity. The trabecular pouch or rudimentary outflow chamber is anterior, superior, and to the left. In this position, the outflow chamber has a convexity separate from the other cardiac chambers, projecting where the left atrial appendage would normally be (Fig. 10-95). This bulge extends along the lateral border of the cardiac silhouette as far as and frequently further than does the usual enlarged left atrial appendage. The pulmonary vasculature has a shunt pattern unless there is severe pulmonary stenosis. The hilar arteries are quite large, particularly those on the right side, which are not hidden behind other mediastinal structures.

FIGURE 10-95 Single ventricle. A 7-year-old child with a rudimentary outflow chamber (long arrow) connected to an anterior and leftward transposed aorta (short arrow). The large pulmonary arteries reflect the intracardiac shunting and the moderate pulmonary hypertension.

Imaging Examination

The cineangiographic evaluation starts with a biplane ventriculogram in the frontal and lateral projections (Fig. 10-96). However, the cranially angled views in the left anterior oblique projection better delineate the straddling atrioventricular valves and the trabecular pouch (Fig. 10-97). Selective injections in the subaortic and subpulmonary regions or in the trabeculated pouch help to determine whether the great arteries originate from an outlet chamber.

FIGURE 10-96 Single right ventricle and heterotaxy syndrome. A, Angiography in cranialized right anterior oblique projection. The catheter was passed retrograde through a left-sided inferior vena cava. The trabeculated ventricle has a subaortic conus with discontinuity between the common atrioventricular valve and the semilunar valve. B, In lateral view, the long course of the catheter from left-sided inferior vena cava (arrow 1) to hemiazygos continuation (arrow 2) to coronary sinus (arrow 3) to the right atrium and anterior right ventricle (RV) is demonstrated. C, Retrograde catheterization through the right aortic arch revealed that both pulmonary arteries arose from a patent ductus arteriosus (arrows).

FIGURE 10-97 Single ventricle with outlet chamber. The levotransposed aorta originates from a small outlet chamber (arrow). The diameter of the atrioventricular valve is more than twice that of the semilunar valves, indicating a single common inlet valve. Infundibular (arrowhead) and valvular pulmonary stenosis is present.

The atrioventricular valves are best identified by seeing the leaflets open and close. Secondary signs of the location of an atrioventricular valve are the appearance of nonopacified blood entering the ventricle, particularly if the catheter passed through the valve for the ventricular injection. Because both atrioventricular valves enter a common chamber, the two valves are identified by having the catheter pass through one of them and seeing the pulmonary venous return with its washout of contrast material pass through the other. A common atrioventricular valve is suspected if only one large annulus is identified and if both systemic and pulmonary venous blood passes through this common orifice. Atrial injections are useful in excluding mitral or tricuspid atresia if they are not identified on echocardiography.

Characteristics

Tricuspid atresia is characterized by congenital absence of the morphologic tricuspid valve. This anomaly, which results in cyanosis, is always associated with a group of other malformations. There is an interatrial communication and enlargement of the left ventricle and mitral valve. The right ventricle is always hypoplastic (Fig. 10-98). Variable features include a ventricular septal defect, malposition of the great arteries, abnormalities in the ventriculoarterial connections, and obstruction to pulmonary blood flow.

FIGURE 10-98 A 4-year-old boy with tricuspid atresia. A, Axial spin echo acquisition through the fat-infiltrated anterior atrioventricular ring (arrow 1). A large interatrial communication (arrow 2) between the dilated right atrium (RA) and left atrium (LA) is demonstrated. B, Sagittal spin echo acquisition shows the slit-like hypoplastic right ventricle (arrows) within the interventricular septum. LV, left ventricle.

Anatomy

The anatomy of specific defects in tricuspid atresia varies depending on the presence of other associated anomalies. The right atrium is separated from the right ventricle by a membrane or area of fibrosis. Occasionally, a dimple exists on the right atrial side with a slight invagination in the region where the tricuspid valve should be. A patent foramen ovale is the interatrial communication in two thirds of those with tricuspid atresia, whereas the remainder has secundum or primum atrial septal defects. These atrial defects are frequently restrictive, and because systemic blood must pass through this defect to reach the lungs, the atrial defect serves as one source of obstruction to pulmonary blood flow.

Both the left ventricle and the mitral valve are relatively large compared with the remainder of the heart. The left ventricle is both dilated and hypertrophied and occupies the diaphragmatic and anterolateral positions in the mediastinum that are usually taken by the right ventricle. In addition, the remainder of the left ventricle lies in its usual lateral and posterior location. The right ventricle is always hypoplastic, ranging from a moderate-sized chamber in some hearts to a thin sinus only a few millimeters long in the most extreme cases. A ventricular septal defect may be present, and when it exists, frequently serves as another location to obstruct pulmonary blood flow. In the absence of a ventricular septal defect, the lungs are supplied by a patent ductus arteriosus and other bronchial collaterals.

TGA occurs in 20% to 30% of cases of tricuspid atresia. In dextrotransposition, the aorta connects to the right ventricular side of the ventricular septal defect and is anterior to the main pulmonary artery.

Common malformations that occur with tricuspid atresia are:

In summary, tricuspid atresia without transposition is a complex of anomalies in which the blood entering the right atrium passes across an interatrial defect into the left atrium, the left ventricle, and then into the lungs either through a ventricular septal defect into the right ventricle or through the aorta and into a PDA. With TGA, the returning blood in the venae cavae goes from the right atrium through the atrial septal defect to the left atrium, to the left ventricle, and into the pulmonary artery.

Chest Film Abnormalities

The chest film in tricuspid atresia illustrates that phrases such as “left (or right) ventricular enlargement,” which are appropriate for acquired diseases, are inappropriate in discussing certain types of CHD. The position, size, and relation of the chambers in tricuspid atresia are not those of a normal adult heart. Yet the cardiac silhouette sometimes has an apex that points inferiorly and to the left, which in acquired heart disease resembles left ventricular enlargement. Other cases of tricuspid atresia have a cardiac silhouette that resembles the coeur en sabot appearance of right ventricular enlargement in tetralogy of Fallot. Obviously, because the right ventricle is never enlarged in tricuspid atresia, this latter interpretation is fallacious. Similarly, when the ventricles are inverted or TGA is present, the usual position of the heart and mediastinal structures is altered so that their position in the cardiomediastinal silhouette may be unknown. In these instances, reference to a particular chamber of the heart on the chest film may be incorrect.

The size of the heart on the frontal radiograph is typically normal to slightly enlarged in tricuspid atresia (Fig. 10-99). The right atrial segment has slight rounding at the superior vena caval border, indicating atrial enlargement. The inferior half of the right atrial segment has a straight or sometimes concave appearance, the latter suggesting juxtaposition of the atrial appendages. When there is decreased pulmonary flow, the pulmonary artery segment is flat or concave. In this situation, the heart size tends to be normal, and the cardiac silhouette may appear to have an uplifted apex. This coeur en sabot shape is identical to that seen in tetralogy of Fallot. When pulmonary artery flow is increased, indicating no obstruction to pulmonary flow, the overall heart size may become quite large, and transposition of the great arteries is quite likely.

FIGURE 10-99 Tricuspid atresia with and without pulmonary stenosis. A, The size and shape of the heart and pulmonary vessels appear normal on the posteroanterior chest film. In fact, the main pulmonary artery segment appears flat. Moderate pulmonary stenosis was identified by angiography. B, The large heart and central pulmonary arteries indicate unrestricted pulmonary blood flow from the intracardiac shunt. Tricuspid atresia with transposition of the great arteries has the same appearance.

The pulmonary vascular markings in tricuspid atresia reflect the amount of pulmonary blood flow. In 60% to 70% of all cases of tricuspid atresia, there is diminished pulmonary vasculature. This sign indicates that there is obstruction to pulmonary blood flow at the interatrial or interventricular septal defects or at the level of the patent ductus arteriosus and other bronchial collaterals. Increase in size of the peripheral pulmonary vessels in comparison with those in the hila, along with accessory signs such as rib notching, suggest collateral flow.

Angiographic Findings

The angiographic evaluation in tricuspid atresia involves a right atrial injection to establish the diagnosis. It requires a left ventricular injection to identify the size and location of a ventricular septal defect, the relation of the great arteries, and pulmonary stenosis or atresia. Typically, a catheter from the femoral vein is passed into the right atrium, but the right ventricle cannot be entered. Care should be taken that the catheter is in the right atrium and not in an azygos continuation of the inferior vena cava. Advancing the catheter allows it to pass through the interatrial communication and into the left ventricle. An aortogram is used to demonstrate a PDA or bronchial collateral vessels.

Right atrial angiography in the frontal projection delineates most of the features of tricuspid atresia (Fig. 10-100). The flow of contrast material is from right atrium to left atrium to left ventricle; the right ventricle opacifies later than the left ventricle. A triangular lucency representing the right ventricle exists inferiorly between the medial border of the right atrium and the opacified left ventricle. This defect is typical of tricuspid atresia but may rarely be seen in congenital tricuspid stenosis (Fig. 10-101).

FIGURE 10-100 Right atrial angiography in tricuspid atresia. A, Frontal view superimposes the right atrium on the left atrium. No flow enters the right ventricle. The coronary sinus is seen faintly (arrow). B, Lateral view projects the right atrium (RA) in front of the left atrium (LA). C and D, Later simultaneous frames show left ventricular and aortic opacification. Note the notch (arrow) between the right atrium and left ventricle (LV).

FIGURE 10-101 Congenital tricuspid stenosis. Hypoplasia of the tricuspid valve may also create a notch (arrow) between the right atrium and right ventricle.

In tricuspid atresia, the left ventriculogram shows a large chamber and mitral valve. The ventricular septal defect, if present, is usually between the membranous septum and the lower muscular septum (Fig. 10-102). In the lateral view, origin of the aorta anterior to the pulmonary artery indicates transposition. The pulmonary valve and subpulmonary region may be clearer on a cranially angled left anterior oblique projection.

FIGURE 10-102 Left ventriculography in tricuspid atresia. Simultaneous frames (A and B) show the aortic and pulmonic connections. The ventricular septal defect is low in the muscular septum. The right ventricle is hypoplastic. Severe infundibular (i) and annular pulmonary stenosis and small pulmonary arteries are present. Note the distinctive interventricular notch (arrow).

Blood flow from right atrium to left atrium may be seen in conditions other than tricuspid atresia. The morphology of the tricuspid region and not the flow pattern should determine the diagnosis. When mean right ventricular pressure is higher than that in the right atrium, a right atrial injection will not flow directly into the right ventricle, even though the tricuspid valve is fully patent. Such conditions exist when the pulmonary arterial or right ventricular pressure is quite high, as in pulmonary atresia, Ebstein anomaly, pulmonary arterial hypertension (Eisenmenger syndrome), and right ventricular infarct.

The Fontan Operation

The Fontan procedure was originally performed in patients with tricuspid atresia and the indications for the operation have been extended to palliate many forms of CHD that have a functionally single ventricle (such as hypoplastic left heart syndrome) or cannot undergo a biventricular repair (Table 10-7). A surgically created pathway reroutes the systemic venous return from the inferior vena cava and superior vena cava directly to the pulmonary arteries (Fig. 10-103). The Fontan procedure effectively separates the pulmonary and systemic circulations and creates one circuit of blood flow with the dominant ventricle functioning as the single pumping chamber for the systemic circulation.

TABLE 10-7 Types of congenital heart disease requiring Fontan

FIGURE 10-103 Coronal gradient echo acquisition from a 13-year-old boy with double-inlet left ventricle and Fontan repair. In this section, the superior-vena-cava-to-right-pulmonary-artery (arrow) and the lateral tunnel Fontan conduit (arrowheads) to right pulmonary artery anastomoses are well visualized. Notice that the liver (Li) is transverse, and the stomach (St) is on the right, and the inferior vena cava (IV) is on the left (patient is situs ambiguus).

In the early versions of the Fontan operation, the right atrial appendage was directly anastomosed to the main or right pulmonary artery. Over time, progressive right atrial dilatation occurred (Fig. 10-104) within the pathway because of relative stasis of slow flowing blood, leading to complications of right atrial thrombus, pulmonary vein compression, and arrhythmia (Fig. 10-105). The operation has been changed over the years and now the lateral tunnel or extracardiac conduit approaches are used to direct deoxygenated blood from the inferior vena cava and superior vena cava to the pulmonary arteries. Usually the Fontan operation is preceded by the bidirectional Glenn shunt that directs blood from the superior vena cava to the pulmonary arteries (Figures 10-103, 10-106). In some centers, at the time of Fontan completion, a fenestration is created between the inferior vena cava pathway or lateral tunnel and the right atrium to reduce early complications from pulmonary overcirculation and increased pulmonary pressures. The fenestration is later closed with an occlusion device that is placed percutaneously.

FIGURE 10-104 Coronal double inversion recovery acquisition from a 24-year-old woman with tricuspid atresia and a right-atrium-to-pulmonary-artery Fontan anastomosis 16 years ago. The right atrium (RA) is markedly dilated, and contains mixed signal, indicating turbulence and slow blood flow.

FIGURE 10-105 A 31-year-old woman with double-inlet right ventricle and Fontan repair 22 years ago, now complaining of shortness of breath. A, Axial double inversion recovery image obtained through the diaphragmatic aspect of the heart. Note the increased signal within the right atrium (RA) and dilated inferior vena cava (IV) and coronary sinus (CS). In addition, there are mixed high and low signal in the posterior mediastinum (arrows 1 and 2) surrounding the descending aorta (arrow 3). B, Coronal double inversion recovery acquisition through the posterior mediastinum. Mixed low and high signal masses running along both left and right paraspinal gutters are serpiginous systemic venous collaterals enlarged by years of elevated systemic venous pressure.

FIGURE 10-106 A 3-year-old boy with tricuspid atresia palliated with a bidirectional Glenn shunt. Anastomosis between the superior vena cava (arrow 1) and the top of the transverse right pulmonary artery (arrow 2), as the artery passes over the roof of the left atrium (LA). The right atrium (RA) is enlarged; the interatrial septum is absent (large secundum atrial septal defect).

After completion of the Fontan palliation, the pulmonary blood flow is supplied directly from systemic venous return (without an intervening pumping chamber) and relies on the difference between systemic and pulmonary venous pressure to adequately perfuse the lungs. Therefore, any obstruction along the course of this pathway, including ventricular outflow tract obstruction (such as recurrent coarctation), narrowing of the cavopulmonary connections or lateral tunnel, and pulmonary artery or pulmonary vein stenosis will not be well tolerated. Imaging evaluation is therefore directed to establish the overall patency of the Fontan pathway.

Cardiac MR is now used to assess for all of these possible levels of obstruction as well as quantification of ventricular function, valvular regurgitation, and differential pulmonary blood flow. Both cardiac MR and MDCT are helpful to evaluate for systemic to pulmonary vein collaterals and pulmonary arteriovenous malformations, which can contribute to significant cyanosis and can be treated by coil occlusion. Patients who have older versions of the Fontan surgery and have developed complications are now often referred to cardiac MR for morphologic and functional evaluation in preparation for surgical revision to either the lateral tunnel or extracardiac conduit Fontan pathways (Table 10-8).

TABLE 10-8 Complications after the Fontan procedure

In general, patients with CHD are at increased risk for developing thromboembolic complications as a result of sluggish flow through dilated chambers, presence of prosthetic devices, conduits and baffles, and use of central venous catheters and cardiac catheterization. Patients who are status post Fontan are at particularly high risk for development of pulmonary embolism that may be clinically silent, and chronic pulmonary embolus can result in an increase in pulmonary vascular resistance that can lead to failure of the Fontan circulation. These patients require routine surveillance for thrombus throughout the Fontan pathway and pulmonary arteries with either cardiac MR or MDCT angiography.

Many patients with CHD can develop conduction abnormalities or arrhythmias related to the surgical repair (especially following the Mustard or Senning or Fontan operations) or related to abnormal intracardiac connections, such as in congenitally corrected TGA. An indwelling pacemaker and retained pacing wires or leads are contraindications for MR imaging, and MDCT can be used as an alternative method for both morphologic and functional imaging in these patients.

Classification

A useful division is to classify into one group those patients who have a small right ventricle and into another group those who have a large right ventricle. The tricuspid valve associated with a tiny right ventricle is small in proportion to the right ventricular chamber and is usually competent. In contrast, when the right ventricle is large, so are the components of the tricuspid apparatus. In this latter case, tricuspid regurgitation is invariably present. Because the pressure in a right ventricle with pulmonary atresia and intact septum is usually suprasystemic, estimating the amount of tricuspid regurgitation from an injection into a hypertensive ventricle may be fraught with inaccuracy.

Another way of classifying this malformation is to divide the right ventricle into an inlet portion, a trabecular part, and a conus. In pulmonary atresia with an intact ventricular septum, the trabecular portion or conus, or both, can be absent. The pulmonary valve is always absent. The remaining part—the tricuspid apparatus—is always present and can be sized. The diameter of the tricuspid annulus often correlates well with the size of the right ventricle and with the presence or absence of the trabecular and conal portions of the right ventricle.

Anatomic Features

The right atrium is always large. When the right ventricular cavity is small and the tricuspid valve competent, the right atrium tends to be only mildly enlarged, whereas tricuspid regurgitation with a large right ventricle tends to produce extreme enlargement of the right atrium. The attachment of the tricuspid valve may resemble an Ebstein anomaly with the posterior leaflet attaching apically at a distance from the tricuspid annulus. Usually the interatrial communication is a patent foramen ovale, although true atrial septal defects are occasionally present. The left side of the heart and the ascending aorta and arch are larger than normal, reflecting the increased cardiac output to both the systemic and pulmonary circulations. As a general rule, when either aortic or pulmonary hypoplasia or atresia is present, the uninvolved great artery is always compensatorily large, and in fact, serves as a marker for hypoplasia of the other vessel.

The ascending aorta, which is normally slightly smaller than the main pulmonary artery, may be up to six times the diameter of the main pulmonary artery. Hypoplasia of the main pulmonary artery frequently extends into the right and left pulmonary arteries. The size of the arteries within the lung parenchyma reflects the blood flow through them. However, in general, patients with pulmonary atresia with an intact ventricular septum tend to have a pulmonary trunk of normal diameter, in contrast to those patients with pulmonary atresia with a ventricular septal defect who have a small pulmonary trunk.

Chest Film Abnormalities

The typical features of pulmonary atresia on the chest film are a large cardiac silhouette, a concave pulmonary artery segment, and diminished pulmonary vasculature (Fig. 10-107). The severity of each of these abnormalities depends on the degree of obstruction in the pulmonary circuit and the competence of the tricuspid valve. The pulmonary vessels at birth are visibly small, and in extreme cases, the pulmonary vessels beyond the hila are invisible. The pulmonary artery segment in older children appears concave, reflecting the hypoplasia of the main and left pulmonary arteries. In newborns, the thymus may obscure the entire superior mediastinum so that the true pulmonary artery segment and the hila are not visible. When atresia of the pulmonary valve is associated with a normal-sized main pulmonary artery, the pulmonary artery segment is straight.

FIGURE 10-107 Pulmonary atresia with intact ventricular septum. The large heart differentiates this lesion from isolated pulmonary stenosis. The pulmonary vessels, partially obscured by the heart, are small.

The left ventricular apex in pulmonary atresia is projected inferiorly and to the left, reflecting mild to severe left ventricular enlargement. The right ventricle, whether small or of normal size, is not part of the cardiac silhouette on the frontal film. The right atrial segment has an exaggerated convexity and reflects the degree of right atrial enlargement. In those 80% who have a small right ventricle, the right atrium is only mildly to moderately enlarged. In the remaining 20% with an enlarged right ventricular cavity, the right atrium may be so large as to touch the lateral thoracic wall. This latter pattern of a giant cardiac silhouette with striking enlargement of the right atrium and decreased pulmonary vascularity is pathognomonic of tricuspid regurgitation from right ventricular outflow obstruction. The only malformations in which this occurs to this degree are pulmonary atresia with intact ventricular septum, tricuspid atresia, severe forms of Ebstein anomaly, congenital dysplasia of the right ventricular wall (Uhl’s anomaly), and intrapericardial teratoma.

Imaging Evaluation

The primary diagnosis is usually established by echocardiography. The size of the pulmonary arteries may require MRI or angiography before surgery. Depending on the size of the cavity, a hand injection or pressure injection with reduced volume generally shows an irregular and highly trabeculated chamber and documents the pulmonary atresia and intact septum (Fig. 10-108). The amount of contrast material opacifying the right atrium reflects the degree of tricuspid regurgitation. A severely dilated right atrium and reflux into the superior or inferior vena cava are signs of severe tricuspid insufficiency.

FIGURE 10-108 Right ventriculogram in pulmonary atresia with intact ventricular septum. The right ventricle is heavily trabeculated. Mild tricuspid regurgitation across a small tricuspid annulus (arrowheads) outlines a dilated right atrium. Several characteristic sinusoids (black arrows) are opacified traversing the myocardium. The white arrow points to the atretic pulmonary valve.

A striking appearance on the right ventriculogram is sinusoids leading to the coronary arteries (see Figure 10-108). These connections between the right ventricle and the coronary arteries alter the coronary flow and produce ischemia. Left coronary artery flow in the normal heart is mainly diastolic. In pulmonary atresia, the coronary flow from the hypertensive right ventricular sinusoids partially reverses the normal antegrade direction in the coronary arteries, leading to inadequate oxygenation of the myocardium and myocardial infarction.

The central pulmonary arteries have a characteristic seagull shape when the pulmonary valve is atretic. The right and left pulmonary arteries are the wings of the bird, the main pulmonary artery is the head, and the atretic valve is the beak (Fig. 10-109). If the pulmonary arteries are confluent, a conduit between the right ventricle and the confluence might be constructed, whereas if the arteries are not confluent, a systemic-pulmonary artery anastomosis might be attempted.

FIGURE 10-109 Pulmonary valve atresia. A, In posteroanterior projection, a catheter from the aorta has been passed across a patent ductus arteriosus into the main pulmonary artery. No washout of contrast media through the pulmonary valve (arrow) is visible during systole. The pulmonary arteries have midline continuity. B, Aortogram obtained in anterior view demonstrates aortic dilatation, a hallmark of this malformation. The small pulmonary arteries (arrows) fill from bronchial collaterals.