Complex Congenital Heart Disease

Published on 26/02/2015 by admin

Last modified 26/02/2015

Print this page

This article have been viewed 3557 times

CHAPTER 49 Complex Congenital Heart Disease

Kevin K. Whitehead, Stanford Ewing, Mark A. Fogel

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 Kaplan ¹ 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}).

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

Clinical Presentation

The clinical presentation of transposition of the great vessels largely depends on the associated lesions. Patients with an intact ventricular septum will generally present with profound cyanosis in the first few hours to days of life as the ductus arteriosus closes and mixing is limited to the patent foramen, which is often restrictive. These patients require the immediate initiation of prostaglandins. If the foramen ovale is restrictive, these patients may require a balloon septostomy to improve left to right shunting.

Patients who have an unrestrictive VSD may not present with profound cyanosis, but with an arterial saturation from 70% to 90%. If undiagnosed, these patients may present later with overt heart failure caused by pulmonary overcirculation. Patients with significant subpulmonary obstruction may have physiology more similar to that of tetralogy of Fallot and present with varying degrees of cyanosis. Finally, patients with coarctation or arch obstruction may present with acidosis, shock, and reverse differential cyanosis.

Imaging Indications and Algorithm

The mainstay of imaging for unrepaired transposition of the great arteries is cardiac echocardiography; all infants suspected of transposition should undergo complete echocardiography when they are stabilized. This often includes the initiation of prostaglandins and a balloon atrial septostomy. For unstable patients, limited echocardiography should be carried out to confirm the diagnosis of transposition and evaluate the atrial septum to determine whether a restrictive atrial septum is present.

Beyond these initial requirements, a complete echocardiogram should focus on delineating the conotruncal anatomy, defining the coronary origins and proximal course, the patency, size and shunting of the ductus arteriosus, the presence and type of a ventricular septal defect, the presence of subarterial (usually subpulmonary) obstruction, and the aortic arch. In addition to defining the coronary anatomy, the exact relationship between the aorta and pulmonary artery should be delineated, as a more side by side relationship of the great vessels may make a Lecompte maneuver less desirable. Any questions left unanswered after complete echocardiography can be obtained by cardiac magnetic resonance imaging.

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.

TETRALOGY OF FALLOT

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

Clinical Presentation

The presentation of these patients largely depends on the degree of outflow tract obstruction. Patients with severe obstruction present in the newborn period with profound cyanosis. Moderate obstruction may result in a relatively balanced circulation and, if not diagnosed prenatally, may be noticed during routine evaluation for a murmur. Patients with only mild outflow obstruction will present with a large left to right shunt, pulmonary overcirculation, and heart failure. Patients with moderate obstruction may be at risk for hypercyanotic spells (“tet spells”), which are caused by dynamic increases in the degree of right ventricular outflow tract obstruction, changes in the ratio of pulmonary to systemic vascular resistance, or a combination of the two.

Imaging Indications and Algorithm

Cyanotic newborns suspected of having tetralogy of Fallot should have prostaglandins initiated. A brief confirmatory echocardiogram may be obtained while this is being done, if available. As soon as the patient is stable, a complete echocardiogram should provide the information needed for initial management and surgical planning.

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.

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 Edwards ¹⁴ 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.

• Type 1A—proximal single arterial trunk with a distal main pulmonary artery segment, which is similar to Collett and Edwards type I.

• Type 2A—left and right branch pulmonary arteries originate from the trunk separately, with no main pulmonary segment present. This takes into account the Collett and Edwards type II (pulmonary arteries from the posterior part of the trunk) and type III (pulmonary arteries from the lateral walls of the trunk).

• Type 3A—the origin of one pulmonary branch artery is truncal and the contralateral artery is ductal or aortic in origin, or that lung is supplied entirely by collaterals.

• Type 4A—large ductus arteriosus supplying the descending aorta, with a coexisting hypoplastic or interrupted aortic arch (usually type B) supplying the innominate arteries.

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.