Acyanotic Congenital Heart Disease

Etiology And Epidemiology

Table 1.0 Classification of Congenital Cardiac Defects  Shunting  Stenotic Right→Left Left→Right MixingAortic stenosis Tetralogy Patent ductus arteriosus TruncusPulmonic stenosis Transposition Ventricular septal defect TAPVRCoarctation of the aorta Tricuspid atresia Atrial septal defect HLH

HLH, hypoplastic left heart syndrome; TAPVR, total anomalous pulmonary venous return.

Congenital heart disease occurs in 8 per 1000 births. The spectrum of lesions ranges from asymptomatic to fatal. Although most cases of congenital heart disease are multifactorial, some lesions are associated with chromosomal disorders, single gene defects, teratogens, or maternal metabolic disease. Congenital heart defects can be divided into three broad pathophysiologic groups: (1) left-to-right shunts, (2) right-to-left shunts, and (3) obstructive stenotic lesions (Table 1.0). Acyanotic congenital heart disease includes left-to-right shunts resulting in an increase in pulmonary blood flow and obstructive lesions, which usually have normal pulmonary blood flow. The most common left-to-right shunts are VSD, ASD, and PDA. All three lesions have normal systemic oxygen saturations in the presence of excessive pulmonary blood flow. 1

Ventricular Septal Defect

Etiology and Epidemiology

The ventricular septum is a complex structure that can be divided into four components. The largest component is the muscular septum. The inlet or posterior septum comprises endocardial cushion tissue. The subarterial or supracristal septum comprises conotruncal tissue. The membranous septum is below the aortic valve and is relatively small. VSDs occur when any of these components fails to develop normally ( Fig. 1 .0). VSDs are the most common congenital heart defect, accounting for 25% of all congenital heart disease. Perimembranous VSDs are the most common of all VSDs (67%). 2

Although the location of the VSD is important prognostically and in approach to repair, physiologically, the amount of flow crossing a VSD depends on the size of the defect and the

pulmonary vascular resistance. Even large VSDs are not symptomatic at birth because the pulmonary vascular resistance is normally elevated at this time. As the pulmonary vascular resistance normally decreases over the first 6 to 8 weeks of life, however, the amount of shunt increases, and symptoms may develop. 2

Clinical Manifestations

The size of the VSD affects the clinical presentation. Small VSDs, with little shunt, are often asymptomatic, other than a loud murmur. Moderate to large VSDs result in pulmonary overcirculation and CHF, presenting as fatigue, diaphoresis with feedings, and poor growth. The typical physical finding with a VSD is a pansystolic murmur usually heard best at the lower left sternal border. There may be a thrill in the same region. Larger shunts result in increased flow across the mitral valve causing a mid-diastolic murmur at the apex. The splitting of S2 and intensity of P2 depend on the pulmonary artery pressure. 2

Figure 1.0 Ventricular septal defect. AO, aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.

Imaging Studies

ECG and chest x-ray findings depend on the size of the VSD. Small VSDs may have normal studies. Larger VSDs cause volume overload to the left side of the heart resulting in ECG findings of left atrial and ventricular enlargement and hypertrophy. A chest radiograph may reveal cardiomegaly, enlargement of the left ventricle, and an increase in the pulmonary artery silhouette and increased pulmonary blood flow. Pulmonary hypertension due to either increased flow or increased pulmonary vascular resistance may lead to right ventricular enlargement and

hypertrophy. 2

Treatment

Approximately 35% of all VSDs close spontaneously. Small VSDs usually close spontaneously; if they do not close, surgical closure may not be required, but prophylactic antibiotics are needed to prevent subacute bacterial endocarditis. Initial treatment for moderate to large VSDs includes diuretics and digoxin. Continued poor growth or pulmonary hypertension despite therapy requires closure of the defect. Most VSDs are closed in surgery, but some VSDs, especially muscular defects, can be closed with devices placed at cardiac catheterization. 2

Atrial Septal Defect

Etiology and Epidemiology

During the embryologic development of the heart, a septum grows toward the endocardial cushions to divide the atria. Failure of septal growth or excessive reabsorption of tissue leads to ASDs (Fig. 1.1). ASDs represent approximately 10% of all congenital heart defects. A secundum defect, with the hole being in the region of the foramen ovale, is the most common ASD. A primum ASD, located near the endocardial cushions, may be part of a complete atrioventricular canal defect, but can be present with an intact ventricular septum. The least common ASD is the sinus venosus defect, which may be associated with anomalous pulmonary venous return.3

Figure 1.1 Atrial septal defect. AO, aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.

Clinical Manifestations

Regardless of the site of the ASD, the pathophysiology and amount of shunting depend on the size of the defect and the relative compliance of the right and left ventricles. Even with large ASDs and significant shunts, infants and children are rarely symptomatic. A prominent left precordium with a right ventricular impulse at the left lower sternal border often can be palpated. A soft (grade I or II) systolic ejection murmur in the region of the right ventricular outflow tract and a fixed split S2 (owing to overload of the right ventricle with prolonged ejection into the pulmonary circuit) are often audible. A larger shunt may result in a mid-diastolic murmur at the left lower sternal border as a result of the increased volume passing across the tricuspid valve.3

Imaging Studies

ECG and chest x-ray findings reflect the increased blood flow through the right atrium, right ventricle, pulmonary arteries, and lungs. The ECG may show right axis deviation and right ventricular hypertrophy. A chest radiograph may show cardiomegaly, right atrial enlargement, and a prominent pulmonary artery.3

Treatment

Medical management is rarely indicated; prophylaxis for subacute bacterial endocarditis is warranted for nonsecundum ASDs. If a significant shunt is still present at around 3 years of age, closure is usually recommended. Many secundum ASDs can be closed with an ASD closure device in the catheterization laboratory. Primum and sinus venosus defects require surgical closure.3

Patent Ductus Arteriosus

Etiology and Epidemiology

The ductus arteriosus allows blood to flow from the pulmonary artery to the aorta during fetal life. Failure of the normal closure of this vessel results in a PDA (Fig. 1.2). With a falling pulmonary vascular resistance after birth, left-to-right shunting of blood and increased pulmonary blood flow occur. Excluding premature infants, PDAs represent approximately 5% to 10% of congenital heart disease. 4

Figure 1.2 Patent ductus arteriosus. AO, aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.

Clinical Manifestations

Symptoms depend on the amount of extra blood flow to the lungs. The magnitude of the shunt, which can be similar to a VSD, depends on the size of the PDA (including diameter, length, and tortuosity) and the pulmonary vascular resistance. Patients with small PDAs are asymptomatic. Moderate to larger shunts produce the symptoms of CHF as the pulmonary vascular resistance decreases over the first 6 to 8 weeks of life. 4

The physical examination depends on the size of the shunt. A widened pulse pressure is often present due to the runoff of blood into the pulmonary circulation during diastole. A continuous machine-like murmur can be heard at the left infraclavicular area, and a thrill may be palpable. The murmur radiates along the pulmonary arteries and is often well heard over the left back. Larger shunts with increased flow across the mitral valve may result in a mid-diastolic murmur at the apex and a hyperdynamic precordium. Splitting of S2 and the intensity of the P2 depend on the pulmonary artery pressure. Higher pulmonary pressures result in greater intensity of P2

and may result in an earlier closing of the pulmonary valve. 4

Imaging Studies

ECG and chest x-ray findings are normal with small PDAs. Moderate to large shunts may result in a full pulmonary artery silhouette and increased pulmonary vascularity. ECG findings vary from normal to evidence of left ventricular hypertrophy. If pulmonary hypertension is present, there is also right ventricular hypertrophy. 4

Treatment

Spontaneous closure of a PDA after a few weeks of age is uncommon in full-term infants. Moderate and large PDAs may be managed initially with diuretics and digoxin, but eventually require closure. Closure of small PDAs also is recommended because of the risk of subacute bacterial endocarditis. Most PDAs can be closed in the catheterization laboratory by either coil embolization or a PDA closure device.4

Aortic Stenosis

Etiology and Epidemiology

Valvular, subvalvular, or supravalvular aortic stenosis represents approximately 5% of all congenital heart disease. The valve forms early in gestation, and lesions result from failure of development of the three leaflets or failure of resorption of tissue around the valve.5

Clinical Manifestations

Symptoms depend on the degree of stenosis. Mild to moderate obstructions cause no symptoms. More severe stenosis results in symptoms of easy fatigability, exertional chest pain, and syncope. Infants with critical aortic stenosis may present with symptoms of CHF. 5

A systolic ejection murmur is heard at the right second intercostal space along the sternum and radiating into the neck. The murmur increases in length and becomes higher in frequency as the degree of stenosis increases. With valvular stenosis, a systolic ejection click often is heard, and a thrill may be present at the right upper sternal border or in the suprasternal notch. The aortic component of S2 may be decreased in intensity. 5

Imaging Studies

ECG and chest x-ray findings are normal with mild degrees of stenosis. Left ventricular hypertrophy develops with moderate to severe stenosis and is detected on the ECG and chest x-ray. Poststenotic dilation of the ascending aorta or aortic knob may be seen on chest radiographs. Echocardiography shows the site of stenosis, valve morphology, and presence of left ventricular hypertrophy and allows estimate of the pressure gradient.5

Treatment

The degree of stenosis frequently progresses with growth. Aortic insufficiency often develops or progresses. Serial follow-up with echocardiography is indicated because of the likelihood of progressive obstruction. Balloon valvuloplasty is usually the first interventional procedure for significant stenosis. It is not as successful as pulmonary balloon valvuloplasty and has a higher risk of significant valvular insufficiency. Surgical management is necessary when balloon

valvuloplasty is unsuccessful, or significant valve insufficiency develops. Subacute bacterial endocarditis prophylaxis is indicated throughout the child's life. 5