Although prenatal detection of congenital heart defects (CHDs) is attempted during routine fetal ultrasonography, it is estimated that, at present, only 36% of CHDs are detected antenatally, with a wide variation among different localities and states.¹ Since the incidence of CHDs is approximately 8 per 1000 live births, and only a third are detected prior to birth, the proposition to perform echocardiography in all neonates for detecting CHDs² is a huge and costly undertaking in absence of appropriate infrastructure and adequate funding. However, the initial echocardiogram obtained in any neonate (for any indication) should be as complete as possible and interpreted by a pediatric cardiologist who is competent in the interpretation of echocardiograms, or alternately, if it is performed by a non-cardiologist physician, the physician should have enough training to at least suspect the presence of a CHD, which will then require referral to the pediatric cardiology service for further evaluation and management. Understanding fetal and transitional circulatory physiology, as it is affected by a CHD, is essential in anticipating the presentation of a CHD in the neonate. It is important to remember that CHDs that would have significantly affected fetal systemic or placental circulation would likely have led to a fetal demise. Therefore, almost all critical congenital cardiac defects (CCHDs) that present at the time of birth were compatible with a fetal circulation that had adjusted to provide normal or near normal fetal systemic and placental circulation in utero; in the few instances in which fetal circulation is compromised, it is not to such degree as to cause fetal demise prior to birth.

Review of Fetal and Transitional Physiology

In fetuses with a normal heart, the right and left ventricles work in parallel; thus, fetal cardiac output is nearly equal to the combined output of both ventricles and approximates 430 ml/kg/min.³ The right ventricle is dominant, accounting for approximately 56% of total cardiac output and pumps against a slightly greater resistance than the left ventricle (Figures 15-1 and 15-2). The fetal circulation in cases of aortic or pulmonary atresia are illustrated for comparison. In each case, the fetal systemic and placental circulations are preserved because of increases in the right or the left ventricular flow which will carry the function of combined ventricular outputs (Figure 15-3). Immediately following birth, ventilation of lungs, in association with increased arterial oxygen tension, leads to a sharp decrease in pulmonary vascular resistance and a marked increase in pulmonary blood flow. At the same time, separation of umbilico-placental circulation decreases inferior vena cava flow which in conjunction with increased pulmonary flow and venous return to the left atrium, results in the functional closure of the foramen ovale. Closure of ductus arteriosus during the first 48 hours of life,⁴ completes separation of the pulmonary and systemic circulations. Postnatally, the two ventricles work in series, so neonatal cardiac output represents the volume of blood pumped by either the right or left ventricle, not the combined output of the two ventricles (Figures 15-4 and 15-5). The presentation of a CCHD during the early neonatal period depends upon:

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  The status of the patent ductus arteriosus (PDA) that is widely patent initially, but develops signs of constriction and closure beyond 12 hours of life.

  
  
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  Patent foramen ovale (PFO) that usually remains patent, and, depending upon the pressure relationship between the right and left atria, either shunts right to left or left to right. Restriction of flow at the PFO often contributes to the clinical presentation of CHD.

  
  
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  Decreasing pulmonary vascular resistance. This will lead to increased pulmonary blood flow, further aggravating clinical symptomatology.

With few exceptions, neonates with CCHDs have minimal symptoms and appear deceptively healthy during the first 12 hours of life, which is mainly due to the presence of patent fetal channels (PFO, PDA) and the persistence of a relatively high pulmonary vascular resistance. The exceptions are heart failure that is already present prior to birth (such as in fetuses with tachyarrhythmia who generally have normal hearts), fetuses with cardiomyopathies, and fetuses with Ebstein’s malformation of the tricuspid valve. In the latter instance, when the Ebstein’s anomaly is severe enough, it can lead to fetal demise or severe heart failure at any gestational age. Other examples of neonates with symptomatic CCHDs include hypoplastic left heart syndrome (HLHS) and D-transposition of the great arteries (D-TGA) with a restrictive foramen ovale or intact atrial septum, or obstructed total anomalous pulmonary venous return (TAPVR). All of these forms of CCHDs can present immediately at birth, requiring vigorous resuscitation that is usually not effective, and they will likely require immediate transfer to the nearest pediatric cardiac center.

It is customary to divide CHDs in two broad categories: cyanotic and acyanotic heart defects. Typically, cyanotic defects present with hypoxemia as the presenting symptom, and acyanotic defects with no symptoms or congestive heart failure/respiratory distress. However, some forms of CCHDs can present with overlapping symptoms of both respiratory distress and varying degrees of cyanosis, and others can manifest both prominent cyanosis as well as cardiogenic shock as the presenting symptomatology. With expanded use of pulse oximetry and echocardiography in the newborn, a significant number of these infants are being diagnosed before developing life-threatening symptomatology.

The following sections discuss various forms of CHDs that may be encountered in the newborn period. The transitional circulation in neonates with CHDs will be briefly described as it pertains to each defect. The typical echocardiographic findings for each type of CHD will also be described briefly. These will be given as a guide to the examiner as how to suspect the presence of cardiac defects. A more detailed description of the clinical features, echocardiographic findings, clinical course, and treatments of these infants is well beyond the scope of this chapter and the present book. For more information, consult other, more comprehensive references.^5,6

Tetralogy of Fallot

The four classical findings in tetralogy of Fallot include pulmonary valvar and infundibular stenosis, often including a small pulmonary valve annulus; malaligned ventricular septal defect (VSD) that is subaortic and generally extends into membranous septum; overriding of the aorta over the VSD; right ventricular hypertrophy. Since neonates are born with right ventricular hypertrophy, the latter is not a distinguishing feature of this defect in the neonate (Figure 15-6). In tetralogy of Fallot, the VSD is large and unrestrictive; therefore, the symptomatology is mainly related to the degree and severity of infundibular and valvar pulmonary stenosis. Severe stenosis leads to a large right-to-left shunt, with increasing severity of cyanosis, unless compensated for by the presence of a PDA with left-to-right shunting that will augment pulmonary blood flow and improve the systemic oxygen saturation. Conversely, mild stenosis can result in a large left-to-right shunt, which can lead to pulmonary over circulation and congestive heart failure. This is aggravated further in the presence of a PDA, which increases the amount of left-to-right shunting into the pulmonary arteries. Therefore, the spectrum of clinical symptomatology in tetralogy of Fallot ranges from the non-cyanotic neonate with congestive heart failure to a ductal-dependent cyanotic lesion with critical cyanosis upon closure of the PDA.

Echocardiography

Parasternal long axis reveals a large VSD, with the aorta overriding the VSD, and a large aortic valve annulus. Right-to-left, left-to-right, or bidirectional shunting can be noted across the VSD (Figure and Video 15-7). Parasternal short axis at the base of the heart or parasternal long axis of the right ventricular outflow tract and pulmonary artery demonstrate infundibular and valvar pulmonary stenosis, with a small pulmonary annulus, and turbulent flow through pulmonary valve (Figure and Video 15-8). With the use of two-dimensional (2D) imaging and color flow Doppler, parasternal short axis at the base and suprasternal ductal cut can visualize the presence and the size of a PDA. Associated defects can be investigated through other appropriate views.⁷

Tetralogy of Fallot with Pulmonary Atresia

This condition, also known as pulmonary atresia with VSD, represents an extreme form of tetralogy of Fallot in which the pulmonary outflow tract is completely atretic, and there is obligatory pure right-to-left shunting through the VSD. Pulmonary blood flow will be entirely dependent upon the size of left to right shunting through a PDA (Figure 15-9) or aortopulmonary collateral flow (see Chapter 14). If pulmonary blood flow is dependent solely upon a PDA, any constriction or closure of the ductus will lead to profound cyanosis.

Echocardiography

The echocardiographic findings are the same as in tetralogy of Fallot with pulmonary stenosis, except that there is no flow through the atretic pulmonary outflow tract. The branch pulmonary arteries (and main pulmonary artery, if present) are filled in retrograde fashion through a PDA. Parasternal long- and short-axis and suprasternal aortic arch and ductal cut imaging will delineate the typical findings (Figures and Videos 15-10 and 15-12). The presence of aortopulmonary collaterals can be suspected or surmised by visualization of one or more collateral vessels arising from the descending aorta and/or aortic arch, and displaying a continuous arterial spectral Doppler waveform. In the most extreme cases of multiple aortopulmonary collateral arteries (also known as MAPCAs), confluent central branch pulmonary arteries might not be visible.

Pulmonary Atresia with Intact Ventricular Septum

Most infants with this condition have a hypoplastic right ventricle and diminutive tricuspid valve in association with pulmonary atresia (Figure 15-13). However, a few can have a normal or massively enlarged right ventricular cavity, and present with severe tricuspid regurgitation leading to both fetal and neonatal heart failure. In any case, all neonates with pulmonary atresia and intact ventricular septum have a ductal-dependent pulmonary circulation, and cyanosis increases markedly with ductal constriction or closure.

Echocardiography

Apical four-chamber view demonstrates the size of the right ventricle and tricuspid valve in comparison to the left ventricle and mitral valve (Figure and Video 15-14). The right ventricle is heavily trabeculated and small indentations in the ventricular septum or free wall of right ventricle might be indicative of the ventriculo-coronary artery fistulae that can be encountered in this condition. Parasternal long-axis right ventricular outflow or parasternal short-axis at base demonstrate pulmonary valve atresia and retrograde filling of the main pulmonary artery via a PDA (Figure and Video 15-15). The presence and size of the PDA is best viewed from the suprasternal aortic arch and ductal cut (Figure and Video 15-16). The PDA is often tortuous and has an abnormal takeoff opposite the left common carotid artery (and a vertical orientation) from the transverse aortic arch. The atrial septal communication is best viewed from subcostal coronal posterior or sagittal bicaval view. The large right to left atrial shunt constitutes total cardiac output, and unobstructed shunting is only possible through a widely stretched PFO or good sized atrial septal defect.

Tricuspid Atresia

In this condition, there is congenital absence or agenesis of the tricuspid valve. The inflow portion of the right ventricle is absent and the right ventricular cavity is decreased in size, whereas the left ventricle is enlarged and hypertrophic. During fetal life, the left ventricle carries the majority of total fetal cardiac output; postnatally, it carries most of the pulmonary and systemic circulation. There is an obligatory right to left shunt that equals systemic flow through a stretched PFO or an atrial septal defect. An associated muscular VSD of variable size is commonly present (Figure 15-17). The great arteries are usually normally related, but less commonly they can be transposed. With normally related great arteries, the degree of cyanosis and ductal dependency is related to the degree of obstruction to blood flow through the VSD as well as the degree of pulmonic or subpulmonic stenosis. When there is severe flow restriction through the VSD and/or pulmonary artery, the PDA becomes the major conduit of flow to the lungs, and its constriction or closure will lead to progressively severe cyanosis. In contrast, in neonates with no flow restriction through the VSD or pulmonary valve, there can be increased flow to the lungs and congestive heart failure may be the consequence.

Echocardiography

The apical four-chamber view is usually diagnostic for tricuspid atresia. The VSD and atrial communication can also be seen in this view (Figure and Video 15-18). However, the size of the VSD, atrial shunt, and the relationship of the great arteries can best be evaluated by other views described in their appropriate sections. A detailed discussion of the variation in anatomy and associated defects with tricuspid atresia is beyond the scope of this review.