Residency · Residency · Pediatrics

Congenital Heart Disease: Acyanotic Lesions

Overview

Congenital heart disease (CHD) affects approximately 1% of all live births (8-12 per 1000). Acyanotic lesions involve either left-to-right shunts or obstructive lesions without initial right-to-left shunting. Left-to-right shunts cause volume overload and may lead to pulmonary overcirculation and heart failure. Obstructive lesions cause pressure overload and ventricular hypertrophy. The most common CHD overall is bicuspid aortic valve (affecting 1-2% of the population), while the most common symptomatic defect is the ventricular septal defect.

Left-to-Right Shunt Lesions

Ventricular Septal Defect (VSD)

The VSD is the most common congenital heart defect, accounting for 25-30% of all CHD. VSDs are classified by location: perimembranous defects (70-80%) are the most common, located adjacent to the membranous septum and tricuspid valve, and may close spontaneously. Muscular VSDs (5-20%) are within the muscular septum and have the highest rate of spontaneous closure, reaching up to 80%. Inlet VSDs (5-8%) are associated with AV canal defects and are common in Down syndrome. Outlet (supracristal/doubly committed subarterial) VSDs (5-7%) are subpulmonic, more common in Asian populations, rarely close spontaneously, and carry a risk of aortic valve prolapse.

The pathophysiology involves left-to-right shunting through the defect, producing volume overload of the left atrium and left ventricle with resultant pulmonary overcirculation. The clinical presentation depends on defect size. A small VSD paradoxically produces a loud holosystolic murmur (because the small, restrictive defect generates high-velocity flow) while the patient remains asymptomatic with normal growth. A large VSD produces a softer murmur but causes symptoms of heart failure at 4-8 weeks of age as pulmonary vascular resistance drops: tachypnea, diaphoresis with feeds, poor weight gain, and hepatomegaly. An apical diastolic rumble (mitral flow murmur) indicates a significant shunt with Qp:Qs greater than 2:1.

Diagnosis is by echocardiography. Chest radiography in large VSDs shows cardiomegaly with increased pulmonary vascular markings. Management depends on size: small restrictive VSDs require only observation, as most perimembranous and muscular defects close spontaneously by age 2. Large VSDs causing heart failure are managed medically with diuretics, ACE inhibitors, and caloric supplementation, followed by surgical closure typically by 3-6 months of age. Indications for closure include failure to thrive despite medical therapy, Qp:Qs greater than 2:1, pulmonary hypertension, and aortic valve prolapse in outlet VSDs. Transcatheter device closure is increasingly available for muscular VSDs.

Atrial Septal Defect (ASD)

ASDs are classified by type: secundum defects (70%) involve the central fossa ovalis and are most amenable to device closure. Primum defects (20%) are in the inferior septum near the AV valves, associated with cleft mitral valve, and form part of the AV canal spectrum. Sinus venosus defects (10%) are located superiorly or inferiorly and are associated with partial anomalous pulmonary venous return. Coronary sinus defects are rare.

The pathophysiology involves left-to-right shunting at the atrial level causing right heart volume overload and RV dilation. The clinical presentation is often asymptomatic in childhood. The hallmark physical finding is a wide, fixed split S2 that does not vary with respiration. A soft systolic ejection murmur is heard at the left upper sternal border from increased flow across the pulmonic valve (not from the ASD itself). Untreated large ASDs may lead to right heart failure, atrial arrhythmias, paradoxical embolism, and pulmonary hypertension in adulthood.

Small ASDs (less than 5-8 mm) may be observed as many close spontaneously in the first 1-2 years. Moderate-to-large ASDs with RV dilation are closed at age 3-5 years. Secundum ASDs with favorable anatomy undergo transcatheter device closure (Amplatzer). Primum and sinus venosus ASDs require surgical repair.

Atrioventricular Septal Defect (AVSD / AV Canal)

AVSD represents a spectrum from partial (primum ASD with cleft mitral valve) to complete (primum ASD, inlet VSD, and common AV valve). There is a strong association with Down syndrome: 40-50% of children with trisomy 21 have CHD, and AVSD is the most common lesion. Complete AVSD produces significant left-to-right shunting at both atrial and ventricular levels with early heart failure and pulmonary hypertension risk. Surgical repair is typically performed at 3-6 months, earlier in Down syndrome due to accelerated pulmonary vascular disease. AV valve regurgitation is common postoperatively and may require re-intervention.

Patent Ductus Arteriosus (PDA)

In term infants, a PDA that fails to close by 72 hours is pathologic. A small PDA produces a continuous "machinery" murmur at the left upper sternal border and is usually asymptomatic. A large PDA causes wide pulse pressure, bounding pulses, and heart failure symptoms. Closure is performed via transcatheter device or coil (preferred) or surgical ligation. Whether even small asymptomatic PDAs should be closed to eliminate endocarditis risk remains controversial.

<image>Anatomical diagrams of major acyanotic congenital heart lesions showing ventricular septal defect (perimembranous location), secundum atrial septal defect, complete atrioventricular septal defect with common AV valve, and patent ductus arteriosus with arrows indicating direction of left-to-right shunt flow</image>

Obstructive Lesions

Coarctation of the Aorta

Coarctation is a discrete narrowing of the aorta, typically at the aortic isthmus just distal to the left subclavian artery origin, near the ductus or ligamentum arteriosum. Important associations include bicuspid aortic valve (50-80% of cases), Turner syndrome (35% of whom have coarctation), and intracranial berry aneurysms.

Neonatal presentation of severe or critical coarctation occurs as a ductal-dependent systemic circulation. Symptoms emerge as the PDA closes at days 5-14, with shock, metabolic acidosis, poor perfusion, and differential cyanosis (lower extremity cyanosis). The cardinal sign is absent or diminished femoral pulses. Treatment is prostaglandin E1 to reopen the ductus followed by surgical repair.

In older children with moderate coarctation, presentation includes upper extremity hypertension, headaches, and leg fatigue with exercise. The blood pressure differential (20 mmHg or more higher in upper versus lower extremities) is diagnostic. A systolic murmur is heard in the left interscapular area. Chest X-ray may show rib notching from collateral intercostal arteries (typically after age 5) and the "3 sign."

Diagnosis is by echocardiography, with CT or MR angiography for detailed anatomy. Treatment in neonates and infants is surgical repair (resection with end-to-end anastomosis); balloon angioplasty with or without stent placement is used for older children and recurrent coarctation. Long-term complications include re-coarctation (5-10%) and persistent hypertension even after successful repair (up to 30%), necessitating lifelong cardiology follow-up.

Aortic Stenosis

Valvar aortic stenosis (the most common form, 70%) results from a bicuspid valve with commissural fusion. It produces a systolic ejection murmur at the right upper sternal border radiating to the carotids with an ejection click (fixed, not varying with respiration). Mild disease is asymptomatic; moderate-to-severe disease causes exertional chest pain, syncope, and exercise intolerance. Critical AS in neonates presents with duct-dependent systemic circulation and shock. Treatment is balloon valvuloplasty for critical or severe disease, with the Ross procedure or mechanical valve replacement for failed valvuloplasty.

Subvalvar (subaortic) stenosis involves a membrane or fibromuscular ridge below the aortic valve. It is progressive and causes aortic regurgitation over time. The absence of an ejection click distinguishes it from valvar disease. Surgical resection is indicated even at moderate gradients due to its progressive nature.

Supravalvar aortic stenosis (narrowing above the aortic valve) is associated with Williams syndrome (elfin facies, intellectual disability, hypercalcemia, "cocktail party" personality). It may involve the branch pulmonary arteries and coronary ostia.

Pulmonary Stenosis

Valvar pulmonary stenosis (the most common form) produces a dome-shaped valve with restricted opening. It causes a systolic ejection murmur at the left upper sternal border with an ejection click that characteristically decreases with inspiration (unique to the pulmonic valve). Mild-to-moderate disease is well-tolerated; severe disease causes RV hypertrophy and heart failure. Treatment is balloon valvuloplasty for peak gradients greater than 40-50 mmHg. Noonan syndrome is associated with a dysplastic pulmonary valve (thick and myxomatous), which is less responsive to balloon valvuloplasty.

<image>Clinical and diagnostic findings comparison for coarctation of the aorta showing absent femoral pulses, upper-lower extremity blood pressure gradient, chest X-ray with rib notching and "3 sign," and echocardiographic/MRI appearance of the narrowed aortic isthmus</image>

Eisenmenger Syndrome

Eisenmenger syndrome develops when a long-standing left-to-right shunt causes irreversible pulmonary vascular remodeling. Pulmonary vascular resistance eventually exceeds systemic vascular resistance, and the shunt reverses to right-to-left with resultant cyanosis. Once established, surgical repair of the original defect is contraindicated because the right ventricle cannot handle the sudden afterload. Prevention requires timely repair of significant shunts before irreversible pulmonary vascular disease develops. Management includes pulmonary vasodilators (sildenafil, bosentan), avoidance of dehydration and hypotension, and heart-lung transplantation as a last resort.

Endocarditis Prophylaxis

Prophylaxis is not recommended for isolated ASD, VSD, or PDA. It is recommended for unrepaired cyanotic CHD, repaired CHD with residual defects adjacent to prosthetic material, prosthetic valves, and cardiac transplant recipients with valvulopathy. The regimen is amoxicillin 50 mg/kg PO (maximum 2g) given 1 hour before dental procedures.

Clinical Pearls

Femoral pulses must be checked on every newborn examination because absent pulses in a well-appearing infant represent coarctation until proven otherwise. A loud murmur does not always indicate a large defect; small VSDs are louder than large ones due to higher-velocity jets across the restrictive opening. Wide, fixed splitting of S2 is pathognomonic for ASD, with the key word being "fixed" (not varying with respiration). Complete AVSD in a child with Down syndrome requires repair by 3-6 months to prevent irreversible pulmonary vascular disease. Neonatal critical lesions (critical coarctation, critical AS) may present as shock when the ductus closes, and CHD should always be in the differential for neonatal shock. Patients with repaired coarctation need lifelong blood pressure monitoring because hypertension persists in 30%.

Key Controversy: Timing of ASD Closure

Many small-to-moderate secundum ASDs close spontaneously in the first 1-2 years. The traditional approach closes ASDs with RV dilation at age 3-5 years. Debate persists over whether very small ASDs without RV dilation (less than 5 mm) ever require closure. Some advocate closing even small ASDs to eliminate the lifetime risk of paradoxical embolism for stroke prevention.

References

• Allen HD, et al. Moss and Adams' Heart Disease in Infants, Children, and Adolescents. 10th Edition. Wolters Kluwer. 2022.
• Penny DJ, Vick GW. Ventricular Septal Defect. Lancet. 2011;377(9771):1103-1112.
• Webb G, Gatzoulis MA. Atrial Septal Defects in Adults. Lancet. 2006;367:1964-1976.
• Brown JW, et al. Coarctation of the Aorta: Surgical Management. Ann Thorac Surg. 2017.
• Fulton DR, Freed MD. The Pathology, Pathophysiology, Recognition, and Treatment of CHD. In: Keane JF, et al., eds. Nadas' Pediatric Cardiology. 2006.
• Wilson W, et al. Prevention of Infective Endocarditis (AHA Guidelines). Circulation. 2007;116(15):1736-1754.

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