Definition

The classic transposition of the great arteries (TGA) consists of isolated ventriculoarterial discordance, with the aorta arising from the right ventricle and the main pulmonary artery arising from the left ventricle.^1,2,3 This results in separation of the systemic and pulmonary circulations, with limited mixing of oxygenated and deoxygenated blood. It usually refers to dextro-TGA (d-TGA; segmental anatomy {S,D,D}), in which the aortic valve is positioned anterior and to the right of the pulmonary valve. However, some refer to any segmental anatomy that results in this physiology as transposition. Occasionally, the conotruncus is further rotated so that the aorta is anterior and to the left of the pulmonary valve (segments {S,D,L}).

Prevalence and Epidemiology

The incidence of transposition of the great arteries is approximately 3 in 10,000 live births. It represents approximately 5% of all newborns with congenital heart disease.¹ It is rarely associated with syndromes or extracardiac malformations, but is more common in infants of diabetic mothers.

Etiology and Pathophysiology

D-TGA is in the spectrum of conotruncal alignment defects and is thought to result from abnormal positioning and rotation of the conotruncus during development. The exact cause or originating event during development is still unclear.

The basic defect is an abnormal rotation of the conotruncus so that the aorta sits over the right ventricle and the pulmonary artery sits over the left ventricle. Generally, the venous anatomy, atrial morphology, atrioventricular connections, and ventricular morphology are normal. The aorta is not in fibrous continuity with the mitral valve, but the pulmonary valve often is. The result is that oxygenated blood returning from the pulmonary veins to the left atrium and left ventricle is pumped back to the pulmonary arteries and lungs. The deoxygenated blood from the systemic veins returning to the right atrium and right ventricle is pumped to the aorta, resulting in profound cyanosis.

Systemic oxygen delivery is dependent on mixing between the two circulations. This can occur at three levels—atrial septal defect, ventricular septal defect (VSD), and patent ductus arteriosus.

In the absence of a VSD, the ductus generally shunts increasingly from the aorta to the pulmonary arteries as pulmonary vascular resistance decreases. In a steady state, the ductal shunt must be matched by a net left atrial to right atrial shunt, which provides for systemic oxygen delivery.

Aside from patent ductus arteriosus and atrial septal communication, the most common associations with d-TGA are VSDs. The VSD can be conoventricular, malalignment, or muscular. Malalignment ventricular septal defects are commonly posteriorly malaligned, and can result in significant left ventricular outflow tract (subpulmonary) obstruction. More rarely, there is anterior malalignment, which can, in turn, be associated with coarctation of the aorta, arch hypoplasia and, rarely, interruption of the aortic arch. Patients with an unrestrictive VSD generally have greater mixing and thus higher saturation.

Other less common associations with transposition of the great vessels include tricuspid atresia and straddling atrioventricular valves.

Manifestations of Disease

Imaging Techniques and Findings

Radiography

The classic radiographic findings of transposition of the great arteries include a narrow superior mediastinum (so-called egg on a string) caused by the anteroposterior orientation of the great vessels and inapparent thymus, increased pulmonary vascular markings, and cardiomegaly. However, these findings are rarely diagnostic and, in fact, were shown to be absent in the vast majority of newborns with d-TGA (Fig. 49-1).⁴

FIGURE 49-1 Chest radiograph from a patient with TGA shows mild cardiomegaly but lacks any of the classic findings, such as the narrow superior mediastinum or increased pulmonary vascular markings.

Ultrasound

Echocardiography can generally readily identify all the pertinent anatomic findings to manage patients with transposition of the great arteries. Subcostal imaging can readily identify the pulmonary artery arising from the left ventricle and the aorta arising from the right ventricle. The aorta can usually be identified by the coronaries and by its long length before branching (Fig. 49-2). The pulmonary artery branches early and the ductal arch should not be mistaken for the aorta (Fig. 49-3).

FIGURE 49-2 Subcostal imaging of unrepaired TGA demonstrating the parallel outflows, with the aorta arising from the right ventricle and the main pulmonary artery from the left ventricle.

FIGURE 49-3 The pulmonary artery arises from the left ventricle in TGA and is readily identified by the early branching from subcostal. The duct is also readily identified.

It is important to assess the atrial septum to determine whether it is restrictive (Fig. 49-4). In addition, the ventricular septum should be assessed to determine whether there are ventricular septal defects (Fig. 49-5). This is important for both preoperative management and surgical planning.

FIGURE 49-4 The patent foramen ovale in this TGA patient is small and mildly restrictive.

FIGURE 49-5 Small muscular VSD identified by color Doppler in a preoperative TGA patient.

Computed Tomography

CT scanning does not play a routine role in transposition of the great arteries. There is generally no indication in unrepaired TGA. It may have some use in postoperative patients when an MRI cannot be performed (e.g., because of a stent or coil artifact, or pacemaker) to evaluate the coronary arteries or branch pulmonary arteries after an arterial switch operation.

Magnetic Resonance Imaging

Cardiac MRI plays a limited role in the initial management of d-TGA, generally when there are residual questions after complete echocardiography. Cardiac MRI may be useful in some situations in which the coronary anatomy is unusual and needs to be better evaluated prior to arterial switch.

MRI plays an important role in the postoperative management of TGA. The standard for the treatment of TGA is the arterial switch (Jatene procedure), in which the aorta and main pulmonary artery are transected and sewn to the pulmonary and aortic root, respectively. The pulmonary arteries are generally brought anteriorly and draped over the aorta. The coronary arteries are transferred separately with buttons of tissue from the aorta to avoid ostial stenosis. Several problems can result, for which cardiac MRI is well suited to investigate. Supravalvular stenosis can occur at either anastomosis site (Fig. 49-6). Cine and velocity mapping can be used effectively to define regions of stenosis and quantify the degree of acceleration. Three-dimensional gadolinium sequences can also be useful to define stenoses and their relationships to other structures (Fig. 49-7). Unilateral or occasionally bilateral branch pulmonary artery stenosis may occur from stretching the branch pulmonary arteries after the Lecompte maneuver. Insufficiency of either valve can result from distortion during surgery. Through-plane velocity mapping can be used to quantify the degree of insufficiency of the valves precisely. Furthermore, short-axis cine volume sets can quantify the ventricular size, ejection, and wall motion abnormalities to screen for the effects of valve regurgitation or coronary abnormalities. Whole heart sequences can be used to evaluate for ostial stenosis of the transferred coronaries (Fig. 49-8). Perhaps more importantly, MRI can be used to evaluate for perfusion defects secondary to coronary stenosis. Gadolinium perfusion imaging is generally performed at rest and during adenosine administration. Adenosine administration causes coronary vasodilation and accentuates perfusion abnormalities by “stealing” flow from regions of marginal coronary perfusion.

FIGURE 49-6 Moderate supravalvular narrowing is seen at the suture line in this TGA patient who has undergone an arterial switch procedure.

FIGURE 49-7 Volume surface rendering of a three-dimensional gadolinium acquisition from a TGA patient who has undergone an arterial switch. Note that the pulmonary arteries are draped over the aorta and, in this case, the right pulmonary artery is mildly stretched and narrowed.

FIGURE 49-8 Patient with TGA status postarterial switch, with proximal narrowing of the left coronary artery as it runs underneath the RVOT conduit. Note that the coronary artery could be further compromised during stenting of the RVOT.

Older patients with transposition of the great vessels may have had an atrial switch (either a Mustard or Senning operation) in which the pulmonary venous return is baffled to the right ventricle and the systemic veins baffled to the left ventricle. This makes the right ventricle the systemic ventricle and it is subject to dilation and failure, usually starting in the third or fourth decade of life. MRI plays a key role in evaluating ventricular function, perfusion, and viability of the systemic right ventricle, as well as assessing the baffle for stenosis or leaks.

See later, “Single Ventricle,” for a more detailed description of the routine cardiac MRI examination.

Nuclear Medicine: Positron Emission Tomography

Perfusion imaging is useful in the postoperative management of patients undergoing an arterial switch procedure who have symptoms or clinical evidence of myocardial ischemia.

Angiography

Angiography is useful in evaluating for stenosis of the transplanted coronary arteries in patients who have undergone an arterial switch when there is suspicion clinically or from other imaging modalities. It also has a limited role preoperatively when the coronary anatomy is complex or cannot be delineated well noninvasively.

Definition

Tetralogy of Fallot is defined as the constellation of a large anterior malalignment ventricular septal defect, an aorta that overrides the defect, subvalvular or valvular pulmonary stenosis, and right ventricular hypertrophy.

Prevalence and Epidemiology

The incidence of tetralogy of Fallot is approximately 4 in 10,000 live births, accounting for approximately 7% to 10% of cases of congenital heart disease.⁵ It occurs equally in males and females, and represents one of the most common lesions requiring intervention in the first year of life. It occurs commonly in association with genetic defects, including Down syndrome, DiGeorge syndrome (22q11 microdeletion), and Alagille syndrome (Jag1 mutation).^6,7

Etiology and Pathophysiology

While originally described by Fallot as a constellation of four findings,⁸ it is now understood that the pathogenesis appears to be related to a single abnormality. The anterior malalignment VSD with normally related great vessels is responsible for the associated aortic override and right ventricular outflow tract obstruction, which classically results in right ventricular hypertrophy.

Certain associated conditions may be important to the management of tetralogy of Fallot. A right aortic arch occurs in approximately 25% of patients. Coronary anomalies are common (approximately 9%), including the left anterior descending (LAD) artery from the right coronary and single coronary.⁹ Pulmonary atresia may occur, with or without the presence of major aortopulmonary collaterals. Patients may often have additional muscular VSDs, and it may occur in association with a complete common atrioventricular canal, especially in association with Down syndrome. Stenosis of the left pulmonary artery is common and, rarely, isolation of the pulmonary artery contralateral to the aortic arch may occur. A patent ductus arteriosus is common; when there is significant outflow tract obstruction, the duct may be tortuous.

Manifestations of Disease

Imaging Techniques and Findings

Radiography

The classic radiographic finding is a boot-shaped heart, with an upturned apex (Fig. 49-9). Other findings may range from a normal heart size and decreased pulmonary blood flow to an increased heart size and increased pulmonary blood flow, depending on the degree of obstruction. A right aortic arch can be noted on the radiograph.

FIGURE 49-9 PA chest radiograph from an infant with tetralogy of Fallot demonstrating mild cardiomegaly with an upturned apex.

Ultrasound

The mainstay of the preoperative evaluation of tetralogy of Fallot is echocardiography. In addition to making the diagnosis (Fig. 49-10), the echocardiogram should focus on the degree and location (subpulmonary, valvular or supravalvular) of right ventricular outflow obstruction (Fig. 49-11), the presence of additional ventricular septal defects, the size and origin of the branch pulmonary arteries, the presence of aortopulmonary collaterals, the coronary origins and courses (with particular attention to whether the LAD or other major branch crosses the right ventricular outflow tract [RVOT]), the arch sidedness and branching pattern, and the patency and course of the ductus arteriosus. With rare exception, these can be evaluated by routine transthoracic imaging.

FIGURE 49-10 A, Parasternal long-axis view demonstrating a large anterior malalignment ventricular septal defect with the overriding aorta. B, Subcostal RAO view demonstrating anterior malalignment of the conal septum, causing moderate subpulmonary obstruction (subps) as well as hypoplastic pulmonary valve (PV) annulus.

FIGURE 49-11 Subcostal RAO with color Doppler showing acceleration of flow starting below the PV and demonstrating significant subpulmonary obstruction (subPS).

Computed Tomography

The use of CT for the routine evaluation of tetralogy of Fallot should be limited. It is sometimes used in pulmonary atresia with major aortopulmonary collaterals to better define the collaterals in preparation for unifocalization, in which the collaterals are detached from the aorta and brought to a surgically created right ventricle (RV) to pulmonary artery (PA) conduit.

Magnetic Resonance Imaging

The preoperative use of cardiac MRI is limited to specific situations. In some cases, it may be useful to use respiratory and cardiac-gated, T2-prepared whole heart imaging to define the origins of the coronary arteries if they are not well seen by echocardiography. Gadolinium angiography is also useful to define aortopulmonary collaterals, and has been shown to be as effective as traditional angiography.¹⁰

MRI has become an important part of the postoperative management of tetralogy of Fallot. The repair for tetralogy of Fallot generally involves patch closure of the VSD and relief of the RVOT obstruction. Some patients may have an adequate pulmonary valve annulus and require only resection of an RV muscle bundle and/or pulmonary valvotomy. However, many will require a transannular patch. Patients in which a major coronary branch crosses the RVOT may require an RV to PA conduit, creating a double-barreled outflow. In patients who have had a transannular patch as part of the repair, pulmonary insufficiency may cause progressive RV dilation and decreased RV performance. In addition, left ventricular performance may decline, likely secondary to interactions with the left ventricle. Cardiac MRI can quantify the pulmonary regurgitation and right ventricular size, and is important in the monitoring of patients who have evidence of significant RV dilation by echocardiography or have poor echocardiographic windows (Figs. 49-12 and 49-13). MRI can also effectively evaluate residual RVOT obstruction or conduit stenosis, branch pulmonary artery stenosis, and pulmonary flow distribution to each lung (Fig. 49-14).

FIGURE 49-12 Four-chamber view of a patient with tetralogy of Fallot with pulmonary insufficiency at end-diastole. This view is used to aid in setting up the short-axis stack to define the basal and apical slices.

FIGURE 49-13 MRI short-axis views in diastole and systole demonstrating a severely dilated right ventricle secondary to severe pulmonary insufficiency. Comparison of the systolic and diastolic frames shows a flattened interventricular septum during diastole, good LV ejection, and moderately decreased RV ejection. A complete axial stack can accurately quantify ventricular volumes, mass, and ejection to aid in the timing of valve replacement.

FIGURE 49-14 Pulmonary insufficiency can be quantified by phase-encoded through-plane velocity mapping Forward flow is mapping in shades of white and reverse flow in shades of black. Manual or automated methods can be used to segment out only the pulmonary artery cross section. The flows in each pixel within the vessel are then summed to obtain the flow for that image. The total reverse and total forward flows can thereby be calculated, and the regurgitant fraction determined by dividing the reverse flow by the forward flow (35% in this example).

See later, “Single Ventricle,” for a more detailed description of the routine cardiac MRI examination.

Nuclear Medicine: Positron Emission Tomography

Nuclear scintigraphy perfusion imaging has been used postoperatively in patients with TOF in the setting of branch pulmonary artery stenosis to quantify pulmonary blood flow distribution.¹¹ However, this has largely been supplanted by cardiac MRI velocity mapping.^12,13 It still may be useful for patients in whom a stent or coil artifact precludes assessment by MRI.

Angiography

Angiography plays a limited role in the routine evaluation of tetralogy of Fallot. Selective aortic or coronary angiography may be useful for select patients with major aortopulmonary collaterals or unusual coronary patterns when the noninvasive images are inadequate.

Definition

This definition, which has been in use since 1942, is a heart that has a single arterial trunk arising from it that supplies the systemic, pulmonary, and coronary circulations. The first known description, however, dates back to 1798.

There are two major classification schemes in use—those of Collett and Edwards¹⁴ and Van Praagh.¹⁵ These are invariably based on the position of the main pulmonary artery segment and branch pulmonary arteries, with the Van Praagh classification using types A and B to delineate whether a VSD is present (almost all have VSDs). Of the different forms, 92% of all patients fall into type 1A or 2A. The following are the definitions used in the Van Praagh classification with its differences and similarities with the Collett and Edwards classification noted; the Van Praagh classification takes into account aortic arch anomalies.

The Collett and Edwards type IV is where the branch pulmonary arteries originate from the descending aorta.

Prevalence and Epidemiology

According to Hoffman and Kaplan,¹ the mean incidence of truncus arteriosus is 107 per million live births; it is thought to occur in 1% to 2% of patients with CHD at necropsy and represents approximately 0.7% of all congenital heart disease. The DiGeorge syndrome and patients with microdeletion of chromosome 22 have a high incidence of having truncus arteriosus. There is no race or gender predilection.

Etiology and Pathophysiology

Manifestations of Disease

Imaging Techniques and Findings

Radiography

In the native state, the findings on chest radiography usually demonstrate cardiomegaly, with increased pulmonary blood flow after the first day or two of life. The heart continues to grow as pulmonary overcirculation increases, with enlargement of the left atrium. A right aortic arch may be seen.

Ultrasound

Echocardiography is the primary imaging modality used from in utero diagnosis through the middle of childhood. Generally, enough information may be obtained to go directly to surgery with only the echocardiographic information. The initial diagnosis is made by determining that one great vessel arises from the base of the heart and gives rise to the aorta, coronary arteries, and pulmonary arteries. The initial diagnosis is made from the subcostal and parasternal short-axis views be visualizing the anatomy. The VSD can readily be seen from the subcostal left anterior oblique and sagittal views, along with parasternal views; the apical four-chamber view can be used to identify additional ventricular septal defects (sweeps in short axis can also do this) in addition to atrioventricular valve morphology. Truncal valve regurgitation or stenosis can readily be seen in the subcostal left anterior oblique and sagittal views, along with parasternal views and the apical view angled superiorly. Truncal valve morphology is best seen in the parasternal short-axis view. The sidedness of the aortic arch, as well as the presence or absence of aortic arch interruption, can be determined from the suprasternal notch view. Additional lesions such as a left superior vena cava should also be sought. Ventricular function should be documented.

Color flow mapping is used to determine the physiology of truncal valve stenosis or insufficiency, along with Doppler examination, in regard to the exact systolic gradient and diastolic pressure half-time. Furthermore, color flow mapping sweeps in the short axis can determine the number of additional ventricular defects present. Atrioventricular valve insufficiency can also be determined using color flow techniques.

Postoperatively, narrowing of the reconstructed right ventricular outflow tract and pulmonary arteries needs to be assessed. Stenosis can be evaluated by color flow mapping and Doppler echocardiography can determine the gradient; this is best performed in the subcostal sagittal or parasternal short-axis views and, occasionally, in the apical view angled extremely anteriorly. Residual ventricular septal defects can be seen by short-axis sweeps. Assessment of the truncal valve, as in the preoperative assessment, must be made routinely (Figs 49-15 and 49-16).

FIGURE 49-15 Echocardiographic images of a truncus arteriosus type II A from the apical (left), high parasternal short-axis (middle), and parasternal long-axis (right) views. The truncus arising from the base of the heart, with branching into the aorta (Ao) and pulmonary artery (PA), is seen. Note the thickened truncal valve (TV). The right pulmonary artery (RPA) and left pulmonary artery (LPA) takeoffs are easily seen from the truncus (T). The ventricular septal defect (*) and truncal valve (TV) are seen.

FIGURE 49-16 Echocardiographic images of a truncus arteriosus type II A from the subcostal (left) and parasternal short-axis (right) views. The truncus arising from the base of the heart, with branching into the aorta (Ao) and pulmonary artery (PA), is seen. By Doppler color flow, truncal insufficiency is seen (arrows). Quadricuspid truncal valve (arrows). TV, truncal valve.

Computed Tomography

Because of radiation considerations, CT scanning plays a limited role in the care of the patient with congenital heart disease, and truncus arteriosus is no different. It is done chiefly when there is a contraindication to MRI and, when used, it is generally carried out postoperatively to visualize the right ventricular outflow tract and branch pulmonary arteries along with the aortic reconstruction if the aortic arch was interrupted. Because of its very limited temporal resolution, except if absolutely needed, ventricular function is best determined by MRI or echocardiography (Figs. 49-17 to 49-19).

FIGURE 49-17 CT scans of a patient with truncus arteriosus, type IIA. Left panel, Axial images demonstrate the right pulmonary artery (RPA) and left pulmonary artery (LPA) originating from the truncus (T). Middle panel, Transverse aortic arch (TAo). Right panel, A superior cut, demonstrating the ascending (AAo) and descending (DAo) aorta.

FIGURE 49-18 CT scan of a patient with truncus arteriosus, type IIA. Shown is a three-dimensional reconstruction of the truncus (T), right pulmonary artery (RPA), left pulmonary artery (LPA), and aorta (Ao) only from the off-axis anterior (A) and posterior (B) views.

FIGURE 49-19 CT scan of a patient with truncus arteriosus, type IIA. Shown is a three-dimensional reconstruction of the truncus, right pulmonary artery (RPA), left pulmonary artery (LPA), and aorta (Ao) with the ventricles and atria as well as from the posterior view.

Magnetic Resonance Imaging

In the native state, the goal of MRI is to define the type of truncus arteriosus (including origin of pulmonary trunk, branches, and collaterals), functional abnormalities of the truncal valve (regurgitation, stenosis, morphology of the valve, number of cusps), alignment of the truncal valve with respect to the ventricular septum, brachiocephalic vessels, pulmonary veins, and aorta, associated cardiac anomalies, and mediastinal structures (hypoplasia or absence of thymus). This can be performed with the protocol outlined later (see later, “Single Ventricles”). Specifically, static steady-state free precession (SSFP), cine imaging, and gadolinium imaging can visualize the truncus arteriosus and branching pattern of the pulmonary arteries from this vessel. Determining aortic arch interruption or hypoplasia along with the presence of the ductus arteriosus can easily be done. Truncal valve insufficiency and stenosis should be assessed with cine and phase-encoded velocity mapping, which can quantify the regurgitant fraction. The Qp/Qs ratio may be assessed by placing velocity maps on each pulmonary artery and in the aortic arch distal to the takeoff of the main or branch pulmonary arteries. Velocity mapping at the level of the truncal valve not only quantifies truncal insufficiency, but is also used as an internal check on the data—sum of the net flows in the branch pulmonary arteries and aorta distal to the takeoff of the main and branch pulmonary arteries must equal the net flow across the truncal valve—as well as visualizing the number of leaflets. Cine is used to quantify ventricular performance and assess for any additional ventricular septal defects. T2-prepared coronary imaging can be used to identify any coronary artery abnormalities.

Postoperatively, MRI is used more often than in the preoperative state, especially as the patient gets older and the echocardiographic windows become poorer. Similar to echocardiography, imaging of the reconstructed right ventricular outflow tract and pulmonary arteries for stenosis is an important component of the examination and can be done with steady SSFP cine, three-dimensional gadolinium-enhanced MRI, and dark blood imaging. Residual VSDs can be seen by cine imaging. Assessment of the truncal valve, now the neoaorta, as in the preoperative assessment, must be made routinely with cine and velocity mapping in the right ventricular outflow tract, branch pulmonary arteries, and neoaorta. Delayed enhancement imaging is used to determine myocardial scar tissue. Follow-up of ventricular function by quantification by cine is routine (Figs. 49-20 to 49-24).

FIGURE 49-20 Cardiac MR images of a truncus arteriosus, type IVA, from selected static SSFP axial images. Images progress from inferior to superior, going from left to right and top to bottom. A, The truncus (T) is seen in cross section. B, Moving superiorly, the truncus begins to divide into the aorta (Ao) and pulmonary artery (PA). C, Further superiorly, the division is complete and the left pulmonary artery (LPA) is seen. D, Even more superiorly, a patent ductus arteriosus (PDA) is visualized. DAo, descending aorta.

FIGURE 49-21 Cardiac MR images of a truncus arteriosus, type IVA, from selected SSFP images in the off-axis coronal and off-axis sagittal views. A, This clearly demonstrates the division into aorta (Ao) and pulmonary artery (PA). B-D, These are sagittal images that progress from left to right as the panels progress from left to right. The lower left image demonstrates the PA takeoff from the truncus (T) and left pulmonary artery (LPA); the middle panel highlights the patent ductus arteriosus (PDA); the right panel clearly delineates the candy cane view of the aorta (Ao). DAo, descending aorta.

FIGURE 49-22 A-C, Cardiac MR images of a truncus arteriosus, type IVA, from three-dimensional gadolinium-enhanced images and a phase contrast image of the truncal valve morphology (D) en face demonstrating a quadricuspid valve. The anterior (A) sagittal (B) view and the truncus viewed posteriorly (C). Note the small size of the right pulmonary artery (RPA). Ao, aorta; LPA, left pulmonary artery; PA, pulmonary artery; PDA, patent ductus arteriosus; RPA, right pulmonary artery; T, truncus.

FIGURE 49-23 Cardiac MR images of a truncus arteriosus, type IVA, from three-dimensional gadolinium-enhanced images highlighting an endoscopic fly-through (D). The multiplanar reconstruction image (A) in the coronal view visualizing the takeoff of the pulmonary artery from the truncus, the volume-rendered image (B) from the anterior view and the sagittal maximum intensity projection (C) all are used as orientation for the fly-through. Note how all the important structures such as the aorta (Ao), pulmonary artery (PA), right pulmonary artery (RPA), left pulmonary artery (LPA), and patent ductus arteriosus (PDA) can all be seen in one image—from inside the vessels.

FIGURE 49-24 Cardiac MR images of a truncus arteriosus after repair with RVOT hypoplasia. A-B, Volume-rendered images from a gadolinium injection highlighting the conduit (C); note the narrowing. C, SSFP cine of the conduit. LPA, left pulmonary artery; LV, left ventricle; RPA, right pulmonary artery; RV, right ventricle.

Nuclear Medicine: Positron Emission Tomography

This type of imaging is limited, as with CT, because of radiation concerns. It is generally used for relative flows to both lungs or for myocardial ischemia; however, this has been largely supplanted by cardiac MRI.

Angiography

During catheterization prior to surgery, angiography is used to delineate the coronary artery anatomy further, assess for additional ventricular septal defects, evaluate the distal pulmonary arteries, evaluate the aortic arch, or define associated abnormalities. Postoperatively, right ventricular outflow tract, pulmonary arteries, and residual VSDs may be visualized by angiography for assessment. Generally, this has been supplanted by echocardiography and cardiac MRI. The patient may be taken to the catheterization laboratory to assess the pulmonary vascular resistance if there is a question regarding the pulmonary vascular obstructive disease. Generally, angiography at this point is usually carried out during interventional procedures, such as angioplasty of the aorta or pulmonary arteries or device placement.

Definition: Functional Single Ventricle

The simple definition of a functional single ventricle, sometimes called the univentricular heart, is a heart that has only one usable pumping chamber in the native state or with surgical correction. The detailed anatomy of functional single ventricles is highly variable; the ventricles can be of the RV or left ventricle (LV) morphologic type, can be D-looped or L-looped,¹⁷ or can be a true single ventricle. A true single ventricle is defined as an atrioventricular (AV) valve to ventricle connection in which two AV valves or a common AV valve (excluding atresia) enters into one ventricle only in the presence of only one ventricular sinus. A functional single ventricle can be any type of ventricular arrangement, including a true single ventricle (e.g., two ventricles with multiple large ventricular septal defects, straddling AV valve with hypoplasia of one ventricle), in which the ventricle acts like a single pumping chamber and needs to be treated as such. Examples of single ventricles are hypoplastic left heart syndrome (HLHS; functional single RV), double-inlet left ventricle, and tricuspid atresia (functional single LV).

Prevalence and Epidemiology

Because this section deals with a series of lesions grouped under the rubric of single ventricle, it is difficult to be precise regarding the epidemiology. According to Hoffman and Kaplan,¹ the mean incidence of hypoplastic left heart complexes, hypoplastic right heart complexes, single ventricle, and tricuspid atresia is 266, 222, 106, and 79 per million live births, respectively.

Hypoplastic left heart syndrome, one of the most common cyanotic CHD lesions, has been reported to occur in 0.016% to 0.036% of all live births and in 1.4% to 3.8% of pathologic series,¹⁸ with a male predominance (55% to 70%). Recurrence risk in siblings has been reported to be 0.5% and up to 13.5% for other forms of CHD. As a comparison, tricuspid atresia occurs in approximately 1 in 15,000 live births and has a prevalence in clinical series ranging from 0.3% to 3.7%, with no apparent gender predilection. In autopsy series, the rate is 2.9%.

Etiology and Pathophysiology

Manifestations of Disease

Imaging Techniques and Findings

Radiography

In the native state, the findings on chest radiography depend on the degree of pulmonary blood flow. With moderate restriction to blood flow, there may be near-normal pulmonary vascular markings and heart size. With severe pulmonary blood flow restriction, there is obvious decrease in pulmonary vascular markings with increased pulmonary blood flow, and the heart is enlarged with increased pulmonary vascular markings. In addition, for patients with heterotaxy syndromes, the tracheobronchial anatomy, stomach bubble, and sidedness of the liver may be assessed.

In the postoperative patient, the chest radiograph is used to assess heart size (e.g., pericardial effusion) and pulmonary vascular markings for assessment of pulmonary flow, pleural effusions, or ascites and to check for device placement (e.g. stent, coils) that may have been placed during cardiac catheterization (Fig. 49-25).

FIGURE 49-25 A, Chest radiograph from a patient with corrected transposition and tricuspid atresia with a right ventricular outlet chamber (after a Fontan procedure). The patient has dextrocardia. B, Neonate with hypoplastic left heart syndrome after stage I Norwood operation with obvious cardiomegaly. The patient had a small atrial septal defect and needed to have a stent placed in the atrial septal defect to remain open (arrow).

Ultrasound

Echocardiography is the primary imaging modality used from in utero diagnosis through the middle of childhood. The initial diagnosis is made by determining the relative sizes of the ventricles and the associated abnormalities of the atrioventricular and semilunar valves, along with the sizes of the great vessels.

Because functional single ventricles comprise a myriad of lesions, a systematic approach must be used. Systemic and pulmonary venous connections are defined; this is extremely important for this disease because the systemic venous connections will be manipulated during surgery. Is there an interrupted inferior vena cava with azygous continuation? Is there a left superior vena cava? Are there any anomalous veins noted? Atrial sidedness (for heterotaxy) and the status of the atrial septal defect (if present) are assessed; an intact atrial septum in the presence of HLHS is an emergency and requires an urgent procedure, surgery or catheterization. The atria to AV valve and AV valve to ventricle connections are visualized; the presence of an AV valve must be confirmed (e.g., tricuspid atresia) and how many (e.g., common AV valve). In conjunction with this is assessment of the sizes of the ventricles and determination of whether the child should undergo the single-ventricle procedure or a two-ventricle repair should be attempted. In addition, the echocardiographer must define whether the ventricles can be separated, even if both are of good size. Questions that must be answered include the following:

• How many ventricular septal defects are present and what are their sizes?

• Can all of them be closed?

• Are there overriding or straddling atrioventricular valves that will prevent a complete two-ventricle repair?

The ventricle to great artery connections must be assessed and the relative sizes of the great vessels must be determined. The size of the patent ductus arteriosus is also a question that the echocardiographer is often asked. Also, what is the sidedness of the aortic arch and the extent of aortic arch obstruction? Single-ventricle performance is an extremely important part of the examination and is assessed qualitatively.

Color flow mapping is used extensively to determine various parameters, such as detecting any anomalous veins and the direction and amount of flow across the atrial septal defect; it aids in determining systemic and pulmonary venous connections. In addition, color flow mapping is useful to assess semilunar and AV valve function (stenosis or insufficiency), as is determination of aortic arch obstruction. Flow patterns and direction across the patent ductus arteriosus are also important in determining the adequacy of systemic perfusion and can enter into the decision of whether to perform a one- or two-ventricle repair.

Postoperative assessment is also a key role of echocardiography in the patient’s care; however, at different stages of reconstruction, it is important to focus on different structures. There are parameters such as ventricular function that are significant at all stages and one must endeavor to evaluate these as well. See later, “Magnetic Resonance Imaging,” for important structures to image at each stage of surgical reconstruction (Figs. 49-26 to 49-28).

FIGURE 49-26 A,B, Echocardiographic images of a patient with hypoplastic left heart syndrome from the apical view with moderate tricuspid insufficiency (TR; B). Note how dilated is the right atrium (RA). D, Aortic to pulmonary (Ao to PA) anastomosis of the patient with hypoplastic left heart syndrome shown in the top panels. C, Patient with dextrocardia and double-inlet left ventricle from a subcostal view. LAVV, left atrioventricular valve; RAVV, right atrioventricular valve; RV, right ventricle.

FIGURE 49-27 Echocardiograph of a patient with a double-inlet left ventricle (apical view) after a bidirectional Glenn operation (A) and after Fontan operation (B). Note the Fontan baffle (B). C, Doppler color flow across a fenestration (F) in the baffle shunting from right to left. D, Doppler spectral recording of this flow. LAVV, left atrioventricular valve; LV, left ventricle; RAVV, right atrioventricular valve.

FIGURE 49-28 Echocardiographic images (suprasternal notch view). A, Frontal view of color flow in the superior vena cava (SVC) and right pulmonary artery (RPA) of a single ventricle patient after bidirectional Glenn; the aorta (Ao) is seen in cross section. B, Off-axis sagittal view of the candy cane view of the Ao and the RPA; note how the large size of the ascending aorta. C, Also a candy cane view but demonstrates the aortic to pulmonary (Ao to PA) anastomosis and a distal Ao arch obstruction. DAo, descending aorta; Inn V, innominate vein.

Computed Tomography

Because of radiation considerations, CT scanning plays a limited role in the care of the patient with CHD, and the single ventricle is no different. It is used chiefly when there is a contraindication to MRI. When used, it is usually done postoperatively to visualize the aortic reconstruction, pulmonary arteries, or systemic venous pathway. Because of the very limited temporal resolution, except if absolutely needed, ventricular function is best assessed by MRI or echocardiography.

Magnetic Resonance Imaging

At different stages of surgical reconstruction, certain structures and important points are different, but the overall goal remains the same—a complete assessment of anatomy, function, and physiology. At all stages, including the native state, the following is the minimum that should be included in an MRI examination:

• Aortic arch imaging

• Pulmonary artery imaging

• Pulmonary or systemic venous obstruction, including the status of the atrial septal defect

• Ventricular outflow tract obstruction

• Ventricular function

• Velocity mapping to assess for cardiac index, Qp/Qs ratio, relative flows to both lungs, and regurgitant fraction of the semilunar and, indirectly, AV valve.

• Anomalous venous structures

At each stage, the following are important to image.

Native State

A detailed assessment of the anatomy must be performed because much less is known about the patient’s anatomy than at other stages. The presence of anomalous venous structures such as a left superior vena cava or visceral situs, and the presence or absence of an inferior vena cava, are all important. Assessment of ventricular function and valve insufficiency is also extremely important because some patients may have been compromised at birth.

After Stage I

Assessment of the aortic arch for obstruction as well as the aortic to pulmonary anastomosis and the aortic to pulmonary shunt (generally with dark blood imaging or possibly gadolinium) must be visualized. Turbulence in the shunt causing signal loss precludes cine imaging. An RV to pulmonary artery shunt should be evaluated in the same fashion. Qp/Qs is obtained by velocity mapping. The status of the atrial septal defect should be assessed and since this is a volume-loaded stage, ventricular function is also a key imaging goal.

After the Bidirectional Superior Cavopulmonary Connection

The major extra focus in this examination is the superior vena cava to pulmonary artery anastomosis—either the bidirectional Glenn or hemi-Fontan. This can be done with cine or gadolinium (rarely dark blood) sequences. The Qp/Qs ratio can be calculated by flow in the superior vena cava or in both branch pulmonary arteries. However, recent data suggest that pulmonary vein mapping is much more appropriate because it also captures aortic collateral flow to the lungs,²² much different from catheterization-derived data. If a hemi-Fontan procedure was performed, leaks into the atrium from the superior vena cava to pulmonary artery anastomosis should be assessed.

After the Fontan Procedure

The most important structure to image is the systemic venous pathway for thrombus, obstruction, and fenestration flow. Fontan patients generally have ventricular dysfunction, so evaluating ventricular performance such as end-diastolic volume, ejection fraction, and cardiac output is essential. Gadolinium-enhanced imaging can help determine the presence of collaterals and assess the aortic arch.

The MRI examination is typically performed in less than 1 hour, generally using the following step-wise procedure:

1 SSFP contiguous axial images. These survey the cardiovascular anatomy and are used as localizers for other imaging modalities in the study. An advantage to starting with this is that if the scan is terminated early because of technical problems or patient instability, a full anatomic volume data set has been obtained and can be reformatted to determine the important parts of the anatomy.

2 Reformatting of axial images. Multiplanar reconstruction of the axial images to localize subsequent imaging is carried out next.

3 Half-Fourier acquisition single-shot turbo spin-echo (HASTE) contiguous axial images. These are acquired while the imager performs reformatting of the images from step 1. They are also used to view structures that may contain diastolic turbulence.

4 Double-inversion dark blood imaging. This is used sparingly to image the systemic to pulmonary artery shunt, evaluate for clot or masses in the systemic venous pathway, or as an alternative to bright blood–cine CMR imaging of various important structures (e.g., pulmonary arteries and aortic arch).

5 Cine CMR. Generally, assessment of ventricular performance and answering other anatomic questions are evaluated by cine (e.g., the pulmonary arteries [long axis, cavopulmonary anastomosis], candy cane view of the aorta, systemic and pulmonary venous pathways).

6 Three-dimensional gadolinium imaging. This is used for three-dimensional viewing of the salient points of the anatomy. It provides the foundation for subsequent viability imaging 5 to 10 minutes later.

7 Velocity mapping. This is performed after gadolinium to add increased signal to the images. It is typically done across the branch pulmonary arteries, semilunar valves (if two are present), vena cavae, AV valves, and pulmonary veins. After stage I, flow in the systemic to pulmonary artery or RV to pulmonary artery shunt can be determined using high encoding velocity (VENC) MRI and echo time (TE).

8 Viability. This is determined in the ventricular short-axis and two-chamber long-axis views.

9 Special imaging. This is specific to the patient (e.g., selected coronary imaging if there is a question regarding the coronary arteries, assessment of regional wall motion abnormalities using myocardial tagging).

See Figures 49-29 to 49-32.

FIGURE 49-29 The cardiac MR image of a patient with double-inlet left ventricle from the apical view after Fontan operation (A). Note the Fontan baffle (B) and fenestration (arrow). B, Same patient as in short-axis view of the ventricle; note the right ventricular outflow chamber (RVOC). C, Left anterior oblique view of left ventricular tract through the ventricular septal defect of the RVOC to the aorta (Ao). B, baffle; LAVV, left atrioventricular valve; RAVV, right atrioventricular valve;

FIGURE 49-30 The cardiac MR image of a patient with hypoplastic left heart syndrome after a Fontan procedure. A, Off-axis coronal image of the Fontan baffle (B), the systemic venous pathway. B, Off-axis transverse image of the superior vena cava (SVC) to right pulmonary artery (RPA) anastomosis. C, “Candy cane” view of the aorta demonstrating the aortic to pulmonary anastomosis. Ao, aorta; DAo, descending aorta; LPA, left pulmonary artery; PA, pulmonary artery.

FIGURE 49-31 This cardiac MR image is a three-dimensional volume rendered reconstruction of a patient with a double-inlet left ventricle after a Fontan operation. A, View of the heart from anterior. B, View of the heart from posterior. Note how well the Fontan baffle (B) can be visualized along with the superior vena cava (SVC) to pulmonary artery anastomosis. Ao, aorta; DAo, descending aorta; LPA, left pulmonary artery; LV, left ventricle.

FIGURE 49-32 This cardiac MR image is a three-dimensional time-resolved gadolinium injection peripherally reconstructed as a maximum intensity projection in the coronal and sagittal views. The patient has a double-inlet left ventricle (after a Fontan operation). Temporally, the injection proceeds from left to right. Note how the gadolinium can be tracked from the systemic venous phase (A) through the lungs (B) to the systemic arterial phase (C), and then back to the systemic venous phase (D). E, Systemic venous-pulmonary arterial phase. F, Systemic arterial phase. Ao, aorta; B, baffle; DAo, descending aorta; LPA, left pulmonary artery; LV, left ventricle; RPA, right pulmonary artery; SVC, superior vena cava.

Nuclear Medicine: Positron Emission Tomography

This type of imaging is limited, as with CT, because of radiation concerns. It is generally used for relative flows to both lungs or for myocardial ischemia, but this has been largely supplanted by cardiac MRI.

Angiography

During catheterization, angiography is used to assess all the structures listed earlier in the cardiac MRI subsection. Generally, in most cases, noninvasive means have been able to assess almost all important structures so angiography at this point is usually used during interventional procedures (e.g., angioplasty of the aorta or pulmonary arteries, device placement; Fig. 49-33).

FIGURE 49-33 The patient has corrected transposition and tricuspid atresia with a right ventricular outlet chamber (RVOC) after a Fontan operation. A, The angiographic injection is into the Fontan baffle (B) in an anteroposterior view, revealing the right pulmonary artery (RPA) and left pulmonary artery (LPA). B, The catheter (C) is in the single left ventricle (LV) and is seen to course retrograde from the aorta (Ao) into the RVOC through one of two ventricular septal defects (arrows) into the LV.

Definition

Levo-transposition of the great arteries (L-TGA) refers to a wide spectrum of structural heart disease, encompassing two-ventricle and single-ventricle hearts and dextro-, meso-, and levocardia. For the purposes of this section, L-TGA will consist of situs solitus and two good-sized ventricles in the setting of mesocardia or levocardia. The resultant setup gives rise to both AV and ventriculoarterial (VA) discordance (double discordance). The resultant anatomy results in physiologically corrected (atrioarterial concordance) flow so that systemic venous flow is directed to the lungs and pulmonary venous flow is directed to the body. Some have referred to this disorder as congenitally corrected TGA. Segmentation for this anatomy is classically {S,L,L} and includes situs solitus {S} to position the right atrium (RA) to the right, L-looping of the ventricles {L} to position the RV to the left, and L malposition of the great arteries to position the aorta (Ao) anterior and leftward to the PA. By definition, the PA arises from the LV and the Ao arises from the RV.²⁴

Incidence and Epidemiology

The incidence of all forms of L-TGA is approximately 0.3 per 10,000 live births and represents approximately 0.5% to 1% of congenital heart disease. The vast majority of patients with L-TGA have levocardia or mesocardia. In the setting of all ventricular inversions, 99% of patients will have L-TGA. In the setting of L-TGA, 99% of patients will have additional cardiac defects. There is a noted absence with right aortic arches and microdeletion of chromosome 22 in patients with this disorder.

Etiology and Pathophysiology

The cause of L-TGA is still under debate. There are ventricular inversion and conotruncal components. One theory has proposed L-looping of the ventricles along with inversion of the infundibulum (subaortic) and normal aortopulmonary septation (involving the cardiac neural crest), but absence of aortopulmonary rotation. Another theory has proposed that L-TGA involves not only L-looping with ventricular inversion but also suggests that the LV structures appear upside-down—there are posterolateral and anteromedial LV papillary muscles. This would help account for the inverted position of the dominant anterior AV node and the course of the AV bundle superior to a VSD. In contrast, normal looping of the ventricles gives rise to a posterior AV node and the course of the AV bundle is inferior to a VSD.²⁵

As a result of physiologically corrected circulation, there is no cyanosis. The pathophysiology is related to the additional heart defects. These include tricuspid valve (TV) anomalies (e.g., dysplasia or Ebstein anomaly) in 90%, VSDs in 80%, and subpulmonary stenosis in 50% of patients. In general, significant TV dysplasia or Ebstein anomaly causes significant TV insufficiency, VSDs cause left-to-right shunt physiology, and subpulmonary stenosis causes RV hypertrophy.

Manifestations of Disease

Imaging Techniques and Findings

Radiography

Typically, the AP chest radiograph shows situs solitus, levocardia or mesocardia with a prominent leftward and anterior aortic knob, a left aortic arch, a normal-sized cardiac silhouette and normal to increased pulmonary vascular markings, depending on the size of the VSD (Fig. 49-34).

FIGURE 49-34 Newborn chest radiograph of a patient with L-TGA. Situs solitus is noted, with mesocardia. The left heart border has a distinctly RV shape, with mild upturning of the apex. The left hilum is full and represents the anterior and left aorta. Pulmonary vascular markings are mildly increased. A good-sized thymus appears to be present. As seen by echo, a double aortic arch was present, which was confirmed at cardiac catheterization.

Ultrasound

Transthoracic echocardiography is a standard imaging procedure for L-TGA. All associated defects can be delineated with great accuracy, and echocardiography is superior for the evaluation of AV straddle. A careful search for common associated lesions should be undertaken, including delineation of TV anomalies, VSDs, and subpulmonary stenosis (Figs. 49-35 to 49-38).

FIGURE 49-35 Apical four-chamber view in a patient with LTGA. Right, Finely trabeculated LV. Left, Coarsely trabeculated RV. The normal TV offset toward the RV is reversed with the L-looped RV. In addition, distance measurements of the septal TV leaflet downward displacement are consistent with mild Ebstein anomaly.

FIGURE 49-36 Modified apical four-chamber view showing the right-sided LV giving rise to the main pulmonary artery (MPA). The two branch PAs are seen coming off the MPA to form “pant legs.” The outflow tract from the LV is unobstructed and the ventricular septum is intact.

FIGURE 49-37 Parasternal short-axis view of a patient with L-TGA. The anterior papillary muscle (ant medial) is medial to the septum and the posterior papillary muscle (post lateral) is lateral to the septum. In this regard, the LV does appear to be upside down in its rightward placement.

FIGURE 49-38 Parasternal short-axis view of the great artery relationship in LTGA. The aorta (Ao) is anterior and left with the pulmonary artery (PA) posterior and right. The left pulmonary artery courses posterior to the aortic arch in contrast to normally related great arteries and the right pulmonary artery courses posterior to the aortic arch.

Computed Tomography

CT has little place in congenital heart disease because of radiation exposure, even though it can demonstrate systemic and pulmonary venous connections, aortic arch and pulmonary artery anomalies, and aortopulmonary collateral arteries. However, most of this can be determined by cardiac MRI without the significant radiation exposure, relegating the role of CT largely to situations in which MRI cannot be performed.

Magnetic Resonance Imaging

Cardiac MRI plays a particularly important role in the preoperative and postoperative management of patients with corrected TGA. In particular, for patients without repair or those who have had a repair in which the RV is still the systemic ventricle, cine MRI can help quantify ventricular size and performance. Deteriorating performance is often an indication to consider a double switch procedure (see later surgical section). Furthermore, by combining cine imaging with phase contrast velocity measurements of the RV outflow volume, the tricuspid regurgitant fraction can be accurately assessed. In addition, cardiac MRI plays a role in surgical planning for these patients with regard to anatomy and function.

It also plays an important role in the management of the late double switch, during which a pulmonary artery band is placed to retrain the left ventricle. Several centers have advocated monitoring the LV mass by serial cardiac MRI to ensure that the LV is properly trained before performing the double switch (Figs. 49-39 and 49-40).²⁶

FIGURE 49-39 MRI plays an important role in assessing the patient after a double switch. The complex pathways of the pulmonary venous pathway (A) and systemic venous pathway (B) can be assessed for obstruction or baffle leak by cine, although it can be challenging to image the entire pathway in a single cine. C, A time-resolved three-dimensional gadolinium sequence effectively isolates the pulmonary venous pathway, demonstrating that it is widely patent. This can be an important adjunct to cine imaging.

FIGURE 49-40 Patient with LTGA who has undergone a double switch. A, The pulmonary venous pathway is markedly narrowed, causing turbulence artifact on this SSFP cine. B, Through-plane velocity mapping demonstrates significant acceleration. The peak measured velocity was 2 m/sec, confirming significant venous obstruction.

Additionally, respiratory-gated whole heart sequences are effective in defining the origins and proximal course of the coronary arteries preoperatively in preparation for a double switch when echocardiography cannot definitively delineate them. Viability can be used to assess for myocardial scarring.

Nuclear Medicine: Positron Emission Tomography

This imaging modality can be useful for evaluating cardiac perfusion defects in patients who have had an arterial switch procedure along with coronary button transfer. It is often combined with preexercise and postexercise imaging.

Cardiac Catheterization and Angiography

Angiography remains the gold standard for hemodynamic and pulmonary arterial and vascular resistance studies, but its role in the routine care of patients is limited. It often plays an important role in measuring LV pressures after a pulmonary artery band procedure to ensure, along with MRI LV mass measurements, that the LV has been properly retrained to withstand a double switch.

Definition

DORV refers to a wide spectrum of structural heart disease, encompassing both two-ventricle and single-ventricle hearts and dextrocardia and levocardia. Included in this complex spectrum is heterotaxy, in which DORV is a predominant diagnosis. For the purposes of this section, DORV will consist of situs solitus and two good-sized ventricles in the setting of levocardia. The resultant setup gives rise to AV concordance, with both great arteries committed to the RV (bilateral subarterial conus). Essentially all DORVs have a VSD, 80% of which are malalignment in type. The remainder of VSDs are conoventricular but additional muscular VSDs are present in a small percentage of cases. The resultant anatomy gives rise to varying degrees of VSD physiology, with the VSD being the only outlet for the LV. VSDs have been classically divided into four categories according to their location to the great arteries: subaortic (nearly 50%), subpulmonary (8%), doubly committed, and noncommitted. The subpulmonary VSD in DORV is commonly referred to as the Taussig-Bing variant. A significant portion of DORVs will have subpulmonary stenosis (70%), with variable degrees of obstruction.

Typically, the spatial relation of the great arteries has also been important in the classification of DORV. This relation is usually divided into four types, according to the position of the aorta to the pulmonary artery: right and posterior, right and side by side, right and anterior, and left and anterior. Segmentation for DORV anatomy is classically {S,D,D} and includes situs solitus {S} to position the right atrium (RA) to the right, D-looping of the ventricles to position the right ventricle (RV) to the right, and D position of the great arteries to position the aorta (Ao) rightward to the pulmonary artery (PA). By definition, both great arteries arise from the RV and there is absence of aortic to mitral continuity.

Incidence and Epidemiology

The incidence of all forms of DORV is approximately 0.9 per 10,000 live births and represents approximately 1% to 1.5% of congenital heart disease. The vast majority of patients with DORV have levocardia although DORV is seen frequently in patients with heterotaxy and dextrocardia. In the setting of all forms of DORV, more than 99% will have a VSD. There is a noted paucity of right aortic arches and microdeletion of chromosome 22 (<5%) in patients with DORV and levocardia.

Etiology and Pathophysiology

The cause of DORV is still under debate but overall is thought to be an abnormality of the conotruncus and mesenchymal tissue migration. In the developing embryo, the single arterial trunk sits over the bulbous cordis, which subsequently forms the RV. There is normal aortopulmonary septation (involving the cardiac neural crest) and the presence of aortopulmonary rotation; however, both great arteries remain over the RV. The amount of aortopulmonary rotation varies, resulting in varying positions of the aorta in relation to the pulmonary artery.

The pathophysiology of DORV is related primarily to the dominant cardiac defects and position of the VSD. A subaortic or noncommittal VSD manifests primarily left to right shunt physiology. In contrast, a subpulmonary VSD (Taussig-Bing DORV) results in pulmonary venous blood streaming across the VSD into the PA and manifests transposition physiology with cyanosis. A doubly committed VSD results in elements of shunt and transposition physiologies.

The conal septum plays an important role in DORV physiology. This septum is hypoplastic in doubly committed VSDs, resulting in unobstructed flow to either great artery. In contrast, malalignment VSDs often result in deviation of the conal septum toward a great artery. Deviation toward the PA results in tetralogy of Fallot physiology, whereas deviation toward the aorta results in coarctation physiology.

Manifestations of Disease

Imaging Techniques and Findings

Radiography

Typically, the AP chest radiograph shows situs solitus, levocardia with a prominent heart size, a left aortic arch, and normal to increased pulmonary vascular markings, depending on the position of the VSD and conal septum deviation (Fig. 49-41).

FIGURE 49-41 Chest radiograph in a patient with DORV. Situs solitus is noted, with levocardia and a normal heart size. The left heart border has a typical LV apex shape. The left upper heart border shows a prominent pulmonary artery segment. The trachea angles slightly to the right, consistent with a left aortic arch. There are high-normal pulmonary vascular markings. Minimal thymus tissue appears to be present.

Ultrasound

Transthoracic echocardiography remains one of the standard imaging techniques for DORV. Associated defects can be delineated and echocardiography is superior for the evaluation of AV straddle. A careful search for common associated lesions should be undertaken, including delineation of inlet and outlet anomalies, VSD location, subpulmonary or subaortic stenosis, and great artery caliber and narrowing. One important echo measurement for consideration of surgical management is the distance from the medial portion of the TV to the pulmonary valve annulus. Depending on the relation of the aorta to the PA, this distance can be accurately measured from subcostal views in varying planes. It represents the potential baffle pathway diameter to the aorta in a two-ventricle repair (Figs. 49-42 to 49-46).

FIGURE 49-42 Subcostal frontal view in a patient with DORV and a large malalignment VSD. The area of subpulmonary conus is identified. The VSD appears to be subpulmonary in this patient, consistent with the Taussig-Bing variant.

FIGURE 49-43 Subcostal LAO view in the same patient with DORV as shown in Figure 49-42. The aorta is significantly smaller than the PA, despite the fact that the conal septum appears slightly deviated toward the PA.

FIGURE 49-44 Apical four-chamber in the same patient with DORV as shown in Figure 49-42. The VSD is large and nonrestrictive.

FIGURE 49-45 Parasternal long-axis view in the same patient with DORV as shown in Figure 49-42. There is a modest subpulmonary conus present, forming mitral to pulmonary discontinuity. The VSD appears subpulmonary in this view also.

FIGURE 49-46 Suprasternal sagittal view in the same patient with DORV as shown in Figure 49-42. There is significant aortic arch hypoplasia, leading to a large patent ductus arteriosus (PDA). The arch will require augmentation at the time of surgery.

Computed Tomography

CT has little place in congenital heart disease because of radiation exposure, even though it can demonstrate systemic and pulmonary venous connections, aortic arch and pulmonary artery anomalies, and aortopulmonary collateral arteries. However, most of this can be obtained by cardiac MRI without the significant radiation exposure, relegating the role of CT largely to situations in which MRI cannot be performed

Magnetic Resonance Imaging

MRI is complementary for imaging complex anomalies of the systemic and pulmonary venous connections, aortic arch and pulmonary artery anomalies, and calculation of cardiac output, regurgitant valve fractions, and systolic and diastolic volumes of the RV and LV (Fig. 49-47). Because DORV can take on many different types of physiology and anatomic variants, see the discussions of individual lesions for the use of MRI. It can also be useful for surgical planning.

FIGURE 49-47 Patient with repaired DORV with subaortic VSD (tetralogy type) can be readily distinguished from tetralogy of Fallot by the elongated LVOT with a subaortic conus. In this patient, there is mild subaortic acceleration at the level of the conus, seen on the systolic images of orthogonal LVOT cines. This acceleration can be readily quantified by in-plane or through-plane (shown here) velocity mapping and the gradient can be estimated using the modified Bernoulli equation.

Nuclear Medicine: Positron Emission Tomography

This imaging modality can be useful for evaluating cardiac perfusion defects in patients who have had an arterial switch procedure along with coronary button transfer. It is often combined with pre-exercise and postexercise imaging.

Angiography

Angiography remains the gold standard for pressure studies and pulmonary arterial and vascular resistance studies. It should be completed when definitive shunt or ventricular performance data, or full evaluation of the pulmonary artery tree, is required.

From Clinical Presentation

The clinical presentation and physical examination will allow differentiation among most forms of complex heart disease. The first differential is usually based on the presence or absence of cyanosis. Whereas cyanosis in the newborn can be seen with single-ventricle physiology and tetralogy of Fallot, profound cyanosis is highly suggestive of TGA or anomalous pulmonary venous connections with obstruction. Pulmonary stenosis with cyanosis can be differentiated by the presence of a loud outflow murmur, and often a thrill is palpated. Cyanosis in the absence of an outflow murmur is suggestive of transposition physiology or pulmonary atresia.

Another common presentation of complex congenital heart disease is pulmonary overcirculation. Patients with a large VSD and no significant outflow obstruction, such as in truncus arteriosus or tetralogy with only mild pulmonary obstruction, will present with increasing overcirculation over days to weeks as the pulmonary vascular resistance falls. This generally causes progressive tachypnea, tiring with feeding, and failure to thrive.

A third common presentation of complex heart disease is shock, manifested by poor peripheral pulses and perfusion, metabolic acidosis, and lethargy. It often manifests on the second or third day of life, and should be one of the first problems considered in an infant presenting with shock. It suggests a lesion with duct-dependent systemic circulation and can include hypoplastic left heart syndrome, critical aortic stenosis, coarctation of the aorta, interrupted aortic arch, and Taussig-Bing–type DORV. Suspicion of these conditions should elicit the immediate initiation of prostaglandins. Coarctation, interrupted arch (unless one or both subclavian arteries arise distal to the interruption), and HLHS with aortic stenosis will result in differential cyanosis, whereas HLHS with aortic atresia or critical aortic stenosis may not.

From Imaging Findings

TGA must be distinguished from other forms of cyanotic heart disease. In general, it can readily be identified by echocardiography or MRI by identifying the aorta arising from the right ventricle. The aorta is identified by its longer distance before branching and giving rise to the coronary arteries. It is also important to demonstrate that the pulmonary artery arises from the left ventricle to distinguish it from DORV and RV-aorta with pulmonary atresia.

Tetralogy of Fallot is identified by the features discussed—namely the normal segmental anatomy with an anterior malalignment VSD and some degree of RVOT obstruction. It should be distinguished from DORV by the absence of subaortic conus (i.e., muscle between the aortic valve and the mitral valve).

The major differential diagnosis of truncus arteriosus is with tetralogy of Fallot with pulmonary atresia. In general, tetralogy of Fallot with pulmonary atresia does not have the pulmonary arteries originating from the ascending aorta, as in the Van Praagh classifications 1 to 3. In the case of the pulmonary arteries arising from the descending aorta (Edwards and Collett type 4), the Van Praagh classification would be considered tetralogy of Fallot with pulmonary atresia. Clues that may hint at the diagnosis of truncus arteriosus is the anatomy and morphology of the single semilunar valve (e.g., quadricuspid, dysmorphic) and the coronary artery anatomy, which is commonly abnormal. Hemitruncus is not a form of truncus arteriosus; it has two semilunar valves arising from the heart, with one branch pulmonary artery arising from the ascending aorta.

Medical Treatment

In conditions in which there is a suspicion of duct-dependent pulmonary blood flow (e.g., severe pulmonary stenosis, pulmonary atresia without major aortopulmonary collaterals), prostaglandins should be initiated immediately. Suspicion of TGA with cyanosis should also prompt initiation of prostaglandins, although the patient must be watched carefully; this physiologic setup may increase pulmonary blood flow and close the flap valve of the foramen ovale, which actually decreases mixing. Other conditions with duct-dependent systemic circulation (e.g., HLHS, critical aortic stenosis, coarctation, interrupted aortic arch) should also prompt initiation of prostaglandins, ideally immediately after birth if a prenatal diagnosis is obtained. See individual sections.

Conversely, there are conditions with pulmonary overcirculation, which include tetralogy without significant RVOT obstruction (so-called “pink tet”), truncus arteriosus, and some forms of DORV without sufficient pulmonary stenosis. These can often be managed for several months with anticongestive medications such as furosemide and digoxin. Hypercaloric formulas and nasogastric supplements are sometimes required for adequate weight gain. It should be noted that truncus arteriosus and aortopulmonary window are very difficult to manage clinically and are at high risk for the development of early pulmonary vascular disease. Therefore, these conditions are generally repaired in the neonatal period at most centers.

Surgical and Interventional Treatment

The approach to surgical correction of truncus arteriosus type A1 and A2 is the separation of the right and left branch pulmonary arteries from the arterial trunk and association of those branch pulmonary arteries with the right ventricle by construction of an RVOT with a conduit. Reoperation because of conduit stenoses and regurgitation in the homograft is usually done as the child grows. The size of the conduit is, as would be expected, related to how quickly the conduit needs to be replaced, with earlier failure of smaller conduits. Aneurysms may develop at the location of surgical incisures. The openings created by the relocation of the branch pulmonary arteries are closed primarily or with a patch. The truncal valve regurgitation or stenosis is also addressed with valvuloplasty; however, future valve replacement may be needed. Patients should have their truncal valve monitored for progressive valve dysfunction. The VSD must also be closed, usually by a patch.

With aortic arch hypoplasia or interruption, as in type A4 truncus arteriosus, the aortic arch is reconstructed with direct anastomosis between the aortic arch and descending aorta or with conduit. A Lecompte maneuver may be performed as needed. There is, of course, a small risk of recurrent or residual obstruction or aneurysm formation.

The surgical options for single-ventricle, tetralogy of Fallot, and LTGA patients are discussed in their respective sections.

If the patient has L-TGA with an intact ventricular septum, no significant subpulmonary stenosis, and good TV and RV function, most centers advocate diligent observation. Surveillance intervals vary with age but generally would be twice yearly. Medium- and long-term RV function will determine eventual therapy. Natural history studies have shown that most patients begin to show symptoms of significant heart failure by the fourth or fifth decade of life, with worsening systemic right ventricular failure and tricuspid regurgitation.²⁷ This has prompted some centers to adopt a more aggressive approach, primarily performing a so-called double switch, consisting of an atrial switch and arterial switch operation with the goal of preventing right ventricular failure. Patients who are diagnosed at a later age, generally those without associated lesions, must first undergo pulmonary artery banding to retrain the left ventricle and prepare it for the increased workload of supporting the systemic circulation. This is often done in two stages, with a loose band first applied and then tightened at a later date once the left ventricle has acclimated. The pulmonary artery band itself can often improve symptoms by shifting the ventricular septum and reducing RV-LV interactions and tricuspid regurgitation, leading some to propose this as a palliative procedure. However, most advocate proceeding to a double switch as a long-term strategy, assuming the that LV tolerates the banding.²⁶

For patients with L-TGA, large VSD, no evidence of subpulmonary stenosis, and good TV, surgery would be recommended, usually consisting of VSD patch closure along with an atrial switch and an arterial switch (a double switch). Postoperative surveillance intervals vary with age but generally would be twice yearly. For patients with L-TGA, large VSD, and significant subpulmonary stenosis, surgery would be recommended, usually consisting of a Rastelli operation (VSD baffle closure to the aorta) along with an atrial switch and an RV-PA valved homograft conduit.²⁸ Postoperative surveillance intervals vary with age but generally would be twice yearly. The RV-PA conduit will require future replacement. For patients with L-TGA and hemodynamically significant left-sided TV insufficiency, surgical intervention would be recommended. In general, direct surgical evaluation of the TV must be performed to determine if valvuloplasty or replacement benefits the patient the most. For some L-TGA patients, failed supraventricular tachycardia medical therapy will lead to an invasive electrophysiology study along with radiofrequency ablation of the accessory left-sided pathway. For L-TGA patients with symptomatic complete AV block, insertion of a dual-chamber pacemaker will be required.

Almost all patients with DORV require palliative or corrective surgery for optimal long-term survival. Exceptions to this would include concomitant lethal anomalies. For patients with DORV, subaortic VSD, and no significant pulmonary stenosis, surgery is usually performed in the neonatal period, usually consisting of VSD baffle closure to the aorta. Postoperative surveillance intervals vary with age but generally would be twice yearly. For patients with DORV, subaortic VSD, and significant pulmonary stenosis, surgery is usually performed in the infant period, usually consisting of VSD baffle closure to the aorta and relief of the subpulmonary stenosis. Postoperative surveillance intervals vary with age but generally would be twice yearly. For patients with DORV and subpulmonary VSD, surgery would be recommended early, usually consisting of VSD patch closure to align the PA with the LV, along with an arterial switch procedure. Aortic arch problems require attention at the same procedure. Postoperative surveillance intervals vary with age but generally would be twice yearly. For patients with DORV and a doubly committed VSD, surgery would be recommended early, usually consisting of VSD baffle closure to the aorta. Postoperative surveillance intervals vary with age but generally would be twice yearly. For patients with DORV and noncommitted VSD, the surgical pathway may involve complex palliation while waiting for possible corrective repair. For patients with complex DORV, including inlet abnormalities, AV valve straddle, unbalanced ventricles, and/or complex outlet anatomy, the surgical pathway often involves offering staged Fontan palliation or transplantion.²⁹

KEY POINTS

Dextrotransposition of the great arteries (DTGA) is defined as isolated ventriculoarterial discordance, with the aorta arising from the right ventricle and the main pulmonary artery arising from the left ventricle.

The mainstay of preoperative imaging for DTGA is echocardiography. Care must be taken to evaluate the adequacy of the ASD and patent ductus arteriosus (PDA) for mixing, presence and type of VSD, coronary origins and proximal course in preparation for an arterial switch, precise relationship of the proximal great vessels and semilunar valves, presence of subarterial obstruction, and aortic arch.

MRI plays an increasingly important role in postoperative imaging of complex congenital heart disease. In certain situations, preoperative imaging allows for precise quantification of ventricular volumes, mass and ejection, cardiac index, valvular regurgitation, valvular stenosis, main and branch pulmonary artery stenosis, residual arch obstruction, baffle leaks and residual septal defect (Qp/Qs ratio). It is also becoming the standard for identifying coronary perfusion defects (adenosine perfusion imaging) and screening for evidence of myocardial scar or fibrosis (delayed enhancement imaging).

Preoperative imaging of tetralogy of Fallot is also routinely performed by echocardiography, defining the conotruncal anatomy, degree and location of RVOT obstruction, presence and location of additional VSDs, presence and location of any aortopulmonary collaterals, arch sidedness and branching pattern, and delineation of the proximal coronary arteries with particular attention to whether any major coronary branches cross the RVOT.

Truncus arteriosus is defined as a heart with a single arterial trunk arising from it that supplies the systemic, pulmonary, and coronary circulations.

The Edwards and Collett and Van Praagh classifications are the most widely used systems to classify truncus arteriosus.

Almost all truncal lesions have associated ventricular septal defects. There is also truncal valve pathology, more commonly with regurgitation and less commonly with stenosis and abnormalities associated with the coronary arteries.

The differential diagnosis of truncus arteriosus is with tetralogy of Fallot with pulmonary atresia. Hemitruncus is not a form of truncus arteriosus.

Functional single ventricles are those hearts that have either one usable pumping chamber or two pumping chambers, which cannot be separated surgically.

Two or three surgeries are needed to separate the systemic and pulmonary circulations. The first is a modified Blalock-Taussig shunt, Norwood stage I procedure, PA banding, or nothing (depending on the anatomy). The second is a bidirectional Glenn or hemi-Fontan procedure, and the final surgery is the Fontan operation.

In the Fontan physiology, blood flows passively from the systemic veins into the lungs.

Echocardiography and cardiac MRI are mainstays of imaging for these patients. Assessment of the various surgical manipulations at the different stages of surgery is key to successful repair.

For L-TGA or corrected transposition, monitoring RV function is key. Some advocate a double switch, which consists of a Senning and arterial switch operation. A Rastelli-type operation may be needed for patients with pulmonic stenosis. Echocardiography and cardiac MRI are the mainstays of imaging.

DORV is actually composed of many diseases. Patients may have ventricular septal defect, tetralogy of Fallot, TGA, or single-ventricle physiology. Different types of repairs are needed. Echocardiography and cardiac MRI are the mainstays of imaging.