DEFINITION

In common usage, the term truncus arteriosus implies persistent truncus arteriosus at birth. Synonyms are common arterial trunk, truncus arteriosus communis, and common aorticopulmonary trunk. Truncus arteriosus is defined by the anatomy: the aorta and the pulmonary arteries arise from a common trunk above a single truncal valve.

CLASSIFICATIONS

Historically, two major classification schemes for anatomic variations of the truncus arteriosus were proposed by Collett and Edwards³ and by Van Praagh and Van Praagh.⁴ The Collett and Edwards classification is strictly defined by the anatomic origins of the pulmonary arteries. It divides truncus arteriosus into four types, I to IV (Fig. 45-1). In Collett and Edwards type I, a common arterial trunk divides into an aorta and a short pulmonary trunk, which divides into the left and right branch pulmonary arteries. This is the most common configuration (48% to 68% of cases). In Collett and Edwards type II (29% to 48% of cases), the left and right branch pulmonary arteries arise close together from the common arterial trunk without a distinct pulmonary trunk. Collett and Edwards type III (6% to 10% of cases) is similar to type II except that the origins of the pulmonary arteries are far apart. Collett and Edwards described a type IV configuration in which the pulmonary arteries arise from the descending aorta. These arteries are now known to be major aorticopulmonary collateral arteries associated with pulmonary atresia with ventricular septal defect (VSD) and not truncus arteriosus.

FIGURE 45-1 Collett and Edwards classification: type I, a pulmonary trunk connects the common arterial trunk to the branch pulmonary arteries; type II, branch pulmonary arteries arise closely from the common arterial trunk; type III, branch pulmonary arteries arise far apart from the common arterial trunk; type IV, branch pulmonary arteries arise from the descending aorta. LPA, left pulmonary artery; RPA, right pulmonary artery.

The Collett and Edwards classification developed in 1949 did not consider the roles of patent ductus arteriosus (PDA) and interrupted aortic arch, which are associated with truncus arteriosus and have prognostic and surgical implications. Subsequently, Van Praagh and Van Praagh⁴ proposed a different classification with four types, 1 to 4 (Fig. 45-2). Each number may have a prefix letter A if a VSD is present (common) or B if a VSD is absent (rare). Van Praagh and Van Praagh type 1 is identical to Collett and Edwards type I, describing a short pulmonary trunk arising from the common arterial trunk. Van Praagh and Van Praagh type 2 describes separate origins of the left and right branch pulmonary arteries arising from the common arterial trunk, regardless of the distance separating their origins (Fig. 45-3). It corresponds to Collett and Edwards type II and type III. Van Praagh and Van Praagh type 3 describes one branch pulmonary artery arising from the common arterial trunk and the other connected to a ductus arteriosus or an aorticopulmonary collateral artery (Fig. 45-4). Van Praagh and Van Praagh type 4 describes the coexistence of a common arterial trunk and an interrupted or a severely hypoplastic aortic arch. The descending aorta is supplied by a PDA. Van Praagh and Van Praagh type 3 and type 4 have no correspondence in the Collett and Edwards classification.

FIGURE 45-2 Van Praagh and Van Praagh classification: type 1, a pulmonary trunk connects the common arterial trunk to the branch pulmonary arteries; type 2, branch pulmonary arteries arise anywhere from the common arterial trunk; type 3, one branch pulmonary artery connects to a PDA or major aorticopulmonary collateral artery (MAPCA); type 4, interrupted aortic arch. LPA, left pulmonary artery; RPA, right pulmonary artery.

FIGURE 45-3 ECG gated CT scan of a Van Praagh and Van Praagh type 2 truncus arteriosus. Volume rendered image shows the left pulmonary artery (LPA) and the right pulmonary artery (RPA) arising separately from the common arterial trunk (TA). The LPA is typically positioned above the RPA. The topmost branch is the left carotid artery (LCA).

FIGURE 45-4 ECG gated CT scan of a Van Praagh and Van Praagh type 3 truncus arteriosus. Volume rendered image shows the right pulmonary artery (RPA) arising from the common arterial trunk (TA). The left pulmonary artery is connected by a major aorticopulmonary collateral artery (MAPCA) to the descending aorta (DA).

Although the Van Praagh and Van Praagh classification provides a more refined description of truncus arteriosus, it does not completely serve the needs of surgeons. In 2000, the Society of Thoracic Surgeons proposed a uniform reporting system with modifiers that better describe anatomic features useful for surgical outcome studies.⁵ In this system, cryptic numerical labels are replaced by descriptive phrases. Three major types are described: truncus arteriosus with confluent or near-confluent pulmonary arteries (corresponding to Van Praagh and Van Praagh type 1 and type 2), truncus arteriosus with absence of one pulmonary artery (corresponding to Van Praagh and Van Praagh type 3), and truncus arteriosus with interrupted aortic arch or coarctation (corresponding to Van Praagh and Van Praagh type 4). Additional modifiers describe the presence or absence of VSD, the number of truncal leaflets, the presence of truncal insufficiency or stenosis or both, coexisting coronary anomalies, any ventricular hypoplasia, the truncal valve position relative to the ventricles, and the presence or absence of thymus.

EPIDEMIOLOGY AND GENETICS

Truncus arteriosus occurs in 1% to 2% of infants born with congenital heart defects, or about 10 cases per 100,000 live births.⁶ Among conotruncal anomalies, truncus arteriosus has a similar rate of occurrence as congenitally corrected transposition of the great arteries and double outlet right ventricle, but it is three times less common than complete transposition of the great arteries and four times less common than tetralogy of Fallot. There is no predilection by sex. Of patients with truncus arteriosus, 34% to 41% harbor a chromosome 22q11 deletion.⁷ This deletion is also seen in a large proportion of patients with conotruncal developmental anomalies as found in DiGeorge syndrome, velocardiofacial syndrome, and interrupted aortic arch, suggesting the importance of this gene in the regulation of the embryologic development of the conotruncus. Today, this chromosomal deletion is readily detected with the fluorescence in situ hybridization technique.

Genetic screening is important because 22q11 deletion is inherited in an autosomal dominant fashion from one parent in 6% to 28% of cases.⁸ This is important information for genetic family counseling. Knowledge of this deletion also heightens clinical suspicions for associated anomalies, including athymia, hypocalcemia, and nasopalatal malformation. Truncus arteriosus is also associated with trisomy 8 and chromosomal 10p deletion.⁹

ETIOLOGY AND PATHOPHYSIOLOGY

Associated Cardiac Anomalies

Because the conus cordis is not partitioned properly below the truncal valve, a VSD usually exists at the infundibular septum beneath the truncal valve (Fig. 45-5). This VSD is often large and nonrestrictive. The right ventricle, subjected to the systemic pressure generated by the left ventricle, becomes hypertrophic. In most instances (68% to 83%), the common arterial trunk and the truncal valve straddle the ventricular septum in a manner resembling the overriding aorta in tetralogy of Fallot or pulmonary atresia with VSD. Uncommonly (11% to 29%), the truncal valve aligns exclusively with the right ventricle. Rarely (4% to 6%), it aligns with the left ventricle. In the two latter situations, the VSD may be small or absent.

FIGURE 45-5 ECG gated CT scan. Long-axis reformatted image shows a large subtruncal VSD (arrow). The truncal valve (TV) straddles the ventricular septum between the right ventricle (RV) and the left ventricle (LV).

The truncal valve may have one to five leaflets. Tricuspid truncal valve (Fig. 45-6A) is the most common (69%), followed by quadricuspid valve (22%) (see Fig. 45-6B) and bicuspid valve (9%). The truncal valve has fibrous continuity with the mitral valve, similar to the normal relationship between the aortic valve and mitral valve. A muscle bridge usually separates the truncal valve from the tricuspid valve. Competency of the truncal valve has important implications to survival and surgical outcome. In most autopsy cases, the truncal valve leaflets are dysplastic and thickened with myxomatous degeneration. Truncal regurgitation is common, occurring in half of the cases. In 20% of cases, the truncal valve may be stenotic.¹¹ Severe regurgitation or stenosis heralds a poor prognosis.

FIGURE 45-6 ECG gated CT scan. A and B, Short-axis reformatted image shows a tricuspid truncal valve (A) and a quadricuspid truncal valve (B).

In the most common situation, the truncal valve is tricuspid with a posterior cusp, a right anterior cusp, and a left anterior cusp. The right coronary artery usually arises from the right anterior cusp, and the left main coronary artery arises from the posterior cusp (Fig. 45-7A).¹² Variation from this pattern is extremely common, however, because the development of the proximal coronary arteries is closely coordinated with the development of the conotruncus. In a quadricuspid valve, the right and left coronary arteries most commonly originate from the opposing right and left cusps (see Fig. 45-7B). In pathology series, a single coronary artery was seen in 10% to 20% of cases,¹³ and stenosis at the coronary ostium was found in 7% of cases.¹⁴

FIGURE 45-7 ECG gated CT scan. A, Short-axis reformatted image shows the typical origins of the right coronary artery (RCA) from the right anterior cusp (RA) and the left main coronary artery (LMCA) from the posterior cusp (P). This patient had undergone surgical repair, and the VSD patch is calcified (arrow). B, The coronary arteries are shown originating from the opposite cusps of a quadricuspid valve.

Compared with a normal ascending aorta, the common arterial trunk usually appears large, but some can expand into an aneurysm. Histologic studies have shown tissue pathology similar to that of Marfan syndrome. The pathophysiology is unknown, but pulmonary hypertension may play a role. Truncus rupture and dissection have been reported.¹⁵ The aortic arch is right-sided in one third of truncus arteriosus cases, usually with a mirror-image branching pattern of the cervical arteries. Aortic arch interruption is seen in 11% to 38% of cases. The most common interruption (84%) occurs between the left common carotid artery and the left subclavian artery (type B interrupted aortic arch).¹⁶ In this configuration, the left and right carotid arteries are fed by the common arterial trunk, and the descending aorta and left subclavian artery are fed by the PDA. The right subclavian artery may be fed by either of these arteries depending on whether it has a normal or an aberrant origin. Less commonly (16%), the interruption occurs distal to the left subclavian artery (type A interrupted aortic arch). Interruption between the left and right carotid arteries (type C interrupted aortic arch) is rare.

The pulmonary arteries usually arise from the left posterior aspect of the common arterial trunk. When the branch pulmonary arteries arise from the common arterial trunk separately, the left branch pulmonary artery is often superiorly related to the right branch pulmonary artery (see Fig. 45-3). If a PDA is present, its size is inversely related to the aortic arch and the aortic isthmus. In the extreme case of aortic arch interruption, blood flow to the descending aorta is carried entirely by a large ductus arteriosus. Other cardiac anomalies associated with truncus arteriosus are secundum atrial septal defect, aberrant subclavian artery, persistent left superior vena cava, and tricuspid stenosis.

MANIFESTATIONS OF DISEASE

Clinical Presentation

Although truncus arteriosus is classified as a cyanotic congenital heart disease with admixture of pulmonary and systemic venous blood, cyanosis is not a prominent feature, unless there is coexisting pulmonary artery stenosis. Instead, patients present with symptoms of heart failure a few days after birth and symptoms of pulmonary hypertension in the first year of life. These clinical presentations can be explained by the underlying hemodynamic derangements. In truncus arteriosus, because the pulmonary arteries and the aorta share a common origin, the pressures driving the pulmonary flow and the systemic flow are the same. Blood flow is equal to the arteriovenous pressure divided by vascular resistance. The shunt ratio, defined as pulmonary flow divided by systemic flow, is equal to systemic vascular resistance divided by pulmonary vascular resistance.

During the first week of life, the pulmonary vascular resistance decreases rapidly below the systemic vascular resistance. The shunt ratio can reach 5 : 1 or greater, which implies a pulmonary flow five times the systemic flow. This torrential pulmonary flow returns through the pulmonary veins into the left ventricle. Assuming that there is no shunting at the atrial level, the left ventricle must handle this amount of flow by stroking five times the volume of the right ventricle. The left ventricle is severely volume overloaded, leading to congestive heart failure. Chest radiography may show evidence for shunt vascularity and pulmonary edema (Fig. 45-8). If the truncal valve is incompetent, the regurgitant flow adds to the volume load, exacerbating the heart failure.

FIGURE 45-8 Chest radiograph. Frontal view shows prominent peripheral pulmonary arteries from large pulmonary flow and diffuse ground-glass opacity from pulmonary edema.

The lack of cyanosis after the first few days of life can be explained by the fact that the oxygenated pulmonary venous flow is much greater than the desaturated systemic venous flow. Despite admixture at the VSD and the common arterial trunk, the systemic oxygen saturation remains elevated. Left untreated, the large amount of pulmonary flow and the high pulmonary pressure induce remodeling in the pulmonary microvasculature, termed pulmonary arteriopathy. This condition irreversibly constricts flow, increasing pulmonary vascular resistance, leading to pulmonary hypertension and Eisenmenger syndrome in patients 6 to 8 months old.

The prognosis of truncus arteriosus without surgical repair is poor. The median age of survival ranges from 2 weeks to 3 months; mortality at 1 year of life is greater than 80%. Adult survivors have been reported, but are extremely rare.¹⁷ As expected, early deaths are mostly due to heart failure and later mortality caused by pulmonary hypertension. Other factors that worsen prognosis are coexisting interrupted aortic arch, coarctation, truncal valve regurgitation, and truncal valve stenosis. Late survivors may have benefited from incidental pulmonary artery stenoses that protect the pulmonary vasculature from high flow and high pressure.

TREATMENT OPTIONS

Because of the poor prognosis of truncus arteriosus and the early onset of pulmonary vascular disease, current treatment favors primary surgical repair within the first month of life.^18,19 Before the current era, pulmonary banding was performed to reduce pulmonary flow and the left ventricular volume load. Pulmonary banding was a palliative approach that did not require cardiopulmonary bypass, but its long-term outcome was generally unsatisfactory. The first complete repair was performed by McGoon and colleagues²⁰ in 1967 using an aortic homograft for the pulmonary connection.

The basic surgical approach for complete repair is the same today. After establishing cardiopulmonary bypass, the pulmonary arteries from the common arterial trunk or the aorta are identified and excised. Through a right ventriculotomy, the subtruncal VSD is visualized. A patch is sutured along the margin of the VSD and right ventricular side of the truncal annulus, connecting the common arterial trunk and the truncal valve to the left ventricle exclusively (Fig. 45-9). A valved pulmonary conduit is placed at the right ventriculotomy site and connected to the excised pulmonary arteries, establishing the pulmonary flow (Fig. 45-10). After surgery, the truncal valve effectively becomes the aortic valve, and the common arterial trunk becomes the ascending aorta. If the native truncal valve is dysfunctional and cannot be repaired, it is replaced with a prostatic valve. In cases with associated interrupted aortic arch or coarctation (Van Praagh and Van Praagh type 4), the arch is reconstructed to maintain continuity among the common arterial trunk, the cervical arteries, and the descending aorta.

FIGURE 45-9 ECG gated CT scan after surgical repair. Long-axis reformatted image shows a calcified VSD patch connecting the ventricular margin of the VSD (arrow) to the right ventricular margin of the truncal valve (arrowhead). The left ventricle (LV) is connected to the common arterial trunk (TA) exclusively.

FIGURE 45-10 ECG gated CT scan after surgical repair. Volume rendered image shows a valved pulmonary conduit (PC) connecting the right ventricle (RV) to the branch pulmonary arteries.

Long-term prognosis after successful surgical repair is very good, with 80% survival rate at 20 years.²¹ Major factors associated with postoperative complications and mortality are truncal valve abnormalities, interrupted aortic arch, nonconfluence or small pulmonary arteries, and coronary anomalies.²² Of these, interrupted aortic arch seems to be of the greatest concern, with some series reporting early modality near 50%.^16,23 Reoperation, even after successful initial repair, is common. Most reoperations are done for the replacement of a malfunctioning pulmonary conduit. Other reasons for reoperation include the repair or replacement of an incompetent truncal valve, arterioplasty of branch pulmonary artery stenoses, and closure of residual VSD.²¹

IMAGING INDICATIONS AND REPORTING

The goals of imaging are to secure the early diagnosis of truncus arteriosus, to delineate vascular anatomy for surgical planning, to identify factors that adversely affect surgical outcome, and to evaluate complications that require reoperation. Fetal ultrasonography can diagnose truncus arteriosus, and this information may be useful for parental counseling during pregnancy.²⁴ In the neonatal period, echocardiography is the modality of choice for the diagnosis and characterization of truncus arteriosus.²⁵ In some centers, an echocardiographic diagnosis of uncomplicated truncus arteriosus is deemed sufficient for surgery without additional angiographic imaging. Color and gray-scale imaging at multiple imaging planes should be performed by an experienced operator, with special attention in differentiating truncus arteriosus, pulmonary atresia with VSD, and tetralogy of Fallot. Presurgical echocardiography should report (1) the alignment of the common arterial trunk with respect to the ventricles, (2) the size and location of the VSD, (3) the ventricular functions, (4) the morphology and function of the truncal valve, (5) the origins of the coronary arteries, (6) the origins of the pulmonary arteries, and (7) any anomaly of the aortic arch.

If echocardiography is unable to define the central pulmonary arteries, or if it detects aortic arch anomalies, these patients should undergo formal angiographic evaluation. This can be done with noninvasive MR angiography (which has the advantage of offering functional and anatomic information without the use of ionizing radiation) or CT angiography. The goals are to evaluate and report (1) any interrupted aortic arch or coarctation, (2) origins and patency of the cervical arteries, (3) existence and size of any PDA and aorticopulmonary collateral arteries, (4) location of the descending aorta, (5) origins and course of pulmonary arteries, and (6) any pulmonary artery stenosis.

For unoperated patients after 6 months of age, catheterization is necessary to measure pulmonary hemodynamics for signs of irreversible pulmonary vascular disease. In older children or adults, echocardiography may not adequately visualize all relevant cardiovascular structures. Echocardiography may be supplemented by MR angiography to evaluate the truncal anatomy, cine MRI to assess ventricular sizes and functions, and MRI phase contrast technique to quantify truncal regurgitation or stenosis.

Patients who have undergone complete surgical repair for truncus arteriosus are now surviving to adulthood in increasing numbers. Imaging goals for these patients are to detect postoperative complications and to help determine the optimal timing for reoperation. The two most important postoperative structures are the valved pulmonary conduit and the truncal valve. Regurgitation or stenosis of either or both valves has deleterious effects on the right and left ventricles. For these reasons, postoperative patients usually undergo routine surveillance with echocardiography. The problem with the valved pulmonary conduit after truncus arteriosus repair is analogous to the problem after tetralogy of Fallot repair. Surgical replacement of a failing pulmonary conduit is best timed just before the irreversible loss of right ventricular function because the new conduit would also deteriorate over time.²⁶ MRI, by quantifying right ventricular size and function, may be helpful in decision making.²⁷ These results may be applicable to truncus arteriosus. In addition, cardiac MRI can evaluate the truncal valve and the left ventricular function in the same study. The clinical role of MRI in the postoperative management of truncus arteriosus is of ongoing research interest.

Less commonly, new vascular lesions develop after surgery in the forms of pseudoaneurysm from a ruptured pulmonary conduit (Fig. 45-11); coarctation restenosis; branch pulmonary artery stenosis; and compression of the pulmonary arteries, veins, or airways by an aneurysmal common arterial trunk (Fig. 45-12).²⁸ These lesions are readily evaluated noninvasively by CT angiography or MR angiography.

FIGURE 45-11 ECG gated CT scan after surgical repair. Axial image shows a large, saccular pseudoaneurysm (A) arising from the proximal anastomosis of the pulmonary conduit (PC).

FIGURE 45-12 Contrast-enhanced MR angiography after surgical repair. Axial reformatted image shows that the common arterial trunk (TA) is more posteriorly located than usual, compressing the right branch pulmonary artery (arrow) against the descending aorta (DA).

KEY POINTS

Truncus arteriosus is an uncommon congenital heart disease that is lethal within the first year of life.

Neonatal patients with incomplete characterization of the pulmonary arteries or any aortic arch anomaly should undergo CT angiography or MR angiography.

Childhood deaths are mainly caused by heart failure or early pulmonary hypertension.

Adult survivors of truncus arteriosus have undergone surgical repair.

Reoperation is commonly performed to replace the malfunctioning pulmonary conduit or truncal valve.

MRI can be helpful in determining the optimal timing for pulmonary conduit replacement.