Complex Congenital Heart Disease

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CHAPTER 49 Complex Congenital Heart Disease

Complex congenital heart disease is obviously one of the most challenging issues faced by the health care provider who takes care of the pediatric patient with cardiac lesions. Taken as a group, this set of lesions represents only a small portion of congenital heart disease (CHD) and is rare in the population; nevertheless, these diseases take up a considerable amount of the physician’s time. Hoffman and Kaplan1 have reported the results of a meta-analysis of the literature and found the incidence of moderate to severe forms of congenital heart disease to be 6/1,000 live births, rising to 19/1,000 live births if potentially serious bicuspid aortic valves are included. Putting this in perspective, all forms of CHD represent 75/1,000 live births, including such lesions as tiny muscular ventricular septal defects. In addition, the New England Infant Cardiac Program2 has reported that 3/1,000 live births need cardiac catheterization or surgery, or will die with CHD in early infancy (excluding premature infants with patent ductus arteriosus). This number rises to 5/1,000 live births who will need some type of specialized care during their lifetime. All these issues are a measure of the severity of the lesion. With improvements in diagnosis and treatment of CHD, along with a greater understanding of the anatomy and physiology, patients are living longer3 and represent a growing patient base seen by adult cardiologists and internists. In 1980, there were an estimated 300,000 adults with CHD, whereas this rose to approximately 1 million in 2000. In 2020, the number is anticipated to be 1.4 million.

Complex CHD is an ill-defined entity because the word complex is ill defined. Is it complex in the anatomic relationships of the various portions of the cardiovascular system, physiologic or blood flow phenomenon, or care and management of these patients? For example, double-outlet right ventricle (DORV) with a subaortic ventricular septal defect and no outflow tract obstruction is clearly anatomically complex but, in the absence of associated lesions (e.g., mitral hypoplasia), the physiology is of a simple ventricular septal defect. There are obviously simple lesions such as atrial septal defects and complex ones such as truncus arteriosus and single ventricles; however, there is a grey zone in between. These lesions can be acyanotic, such as in DORV, or cyanotic, such as tetralogy of Fallot (TOF).

This chapter cannot be exhaustive in the treatment of complex CHD. Instead, it will focus in detail on imaging of four different lesions in this group—transposition of the great arteries, tetralogy of Fallot, single ventricle, and truncus arteriosus.

TRANSPOSITION OF THE GREAT ARTERIES

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}).

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

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.

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.

TETRALOGY OF FALLOT

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.

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.

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).

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.

TRUNCUS ARTERIOSUS

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

Pathophysiology

The pathophysiology is dominated by the consequences of the pulmonary circulation and systemic circulation in direct communication with each other. The pulmonary arteries are rarely obstructed, so the pulmonary vascular bed is directly exposed to systemic arterial level pressures similar to those of a large isolated ventricular septal defect with left to right shunting. However, unlike the ventricular septal defect, the pulmonary bed is exposed to systemic diastolic pressures as well, increasing the left to right shunt and acting as a runoff lesion similar to that of a patent ductus arteriosus. Relative flow to either circulation is determined by the relative resistances. Systemic oxygen saturations are only mildly decreased to approximately 90%.

The truncal valve is commonly dysplastic and nodular, which may result in insufficiency (reported in approximately 50% of cases) or, less commonly, stenosis (reported in approximately one third of patients). The valve may have a variable number of leaflets, although the most common is trileaflet; quadricuspid valves have been reported in 9% to 24% and bicuspid valves have been reported in 6% to 23%. Because of the possibility of truncal valve insufficiency as well as the runoff physiology from the pulmonary arteries directly connected to the systemic circulation, coronary blood flow may be compromised. A widened pulse pressure may be seen.

As the patient ages and pulmonary vascular resistance drops, the patient may develop congestive heart failure from overcirculation of the pulmonary vascular bed.

There are associated cardiovascular malformations, such as abnormalities of the coronary arteries, a right aortic arch, persistent left superior vena cava, aberrant origin of the left subclavian, patent foramen ovale, partial and complete atrioventricular canal defects, mitral and tricuspid malformations, double-inlet or hypoplastic left ventricle, left pulmonary artery sling, and anomalous pulmonary venous connections.16

Manifestations of Disease

Imaging Techniques and Findings

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).