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A ventricular septal defect (VSD) is an opening in the interventricular septum, causing a shunt between ventricles. Large defects result in a significant left-to-right shunt and cause dyspnea with feeding and poor growth during infancy. A loud, harsh, holosystolic murmur at the lower left sternal border is common. Recurrent respiratory infections and heart failure may develop. Diagnosis is by echocardiography. Defects may close spontaneously during infancy or require surgical repair.
VSD (see Fig. 3: Congenital Cardiovascular Anomalies: Ventricular septal defect. ) is the 2nd most common congenital heart anomaly after bicuspid aortic valve, accounting for 20% of all defects. It can occur alone or with other congenital anomalies (eg, tetralogy of Fallot, complete atrioventricular septal defects, transposition of the great arteries).
Classification
VSDs are classified by location:
Perimembranous defects (70 to 80%) are defects in the membranous septum adjacent to the tricuspid valve and they extend into a variable amount of surrounding muscular tissue; the most common type of this defect occurs immediately below the aortic valve.
Trabecular muscular defects (5 to 20%) are completely surrounded by muscular tissue and may occur anywhere in the septum.
Subpulmonary outlet defects (5 to 7% in the US; about 30% in Far Eastern countries) occur in the ventricular septum immediately under the pulmonary valve. These defects are often referred to as supracristal or doubly committed subarterial defects and are frequently associated with aortic leaflet prolapse into the defect, causing aortic regurgitation.
Inlet defects (5 to 8%) are bordered superiorly by the tricuspid annulus and are located posterior to the membranous septum. These defects are sometimes referred to as atrioventricular septal-type defects.
Pathophysiology
The magnitude of the shunt depends on defect size and downstream resistance (ie, pulmonary outflow tract obstruction and pulmonary vascular resistance); larger defects result in a large left-to-right shunt. Assuming there is no pulmonic stenosis, over time, a large shunt causes pulmonary artery hypertension, elevated pulmonary artery vascular resistance, right ventricular pressure overload, and right ventricular hypertrophy. Ultimately, the increased pulmonary vascular resistance causes shunt direction to reverse (from the right to the left ventricle), leading to Eisenmenger's syndrome (see Congenital Cardiovascular Anomalies: Eisenmenger's Syndrome).
Small defects cause a relatively small left-to-right shunt, and pulmonary artery pressure is normal. Heart failure (HF), pulmonary hypertension, and Eisenmenger's syndrome do not develop.
Symptoms and Signs
Symptoms depend on defect size and magnitude of the left-to-right shunt. Children with a small VSD are typically asymptomatic and grow and develop normally. In those with a larger defect, symptoms of HF (eg, respiratory distress, poor weight gain, fatigue after feeding) appear at age 4 to 6 wk when pulmonary vascular resistance falls. Frequent lower respiratory tract infections may occur. Eventually, untreated patients may develop symptoms of Eisenmenger's syndrome.
Auscultatory findings vary with the size of the defect. Small VSDs typically produce murmurs ranging from a grade 1 to 2/6 high-pitched, short systolic murmur (due to tiny defects that actually close during late systole) to a grade 3 to 4/6 holosystolic murmur (with or without thrill) at the lower left sternal border; this murmur is audible shortly after birth. The precordium is not hyperactive, and the 2nd heart sound (S2) is normally split and has normal intensity.
Moderate to large VSDs produce a loud holosystolic murmur that is present by age 2 to 3 wk; S2 is usually narrowly split with an accentuated pulmonary component. An apical diastolic rumble (due to increased flow through the mitral valve) and findings of HF (eg, tachypnea, dyspnea with feeding, failure to thrive, gallop, crackles, hepatomegaly) may be present. With large defects allowing equalization of left ventricular and right ventricular pressures, the systolic murmur is often attenuated.
Diagnosis
Diagnosis is suggested by clinical examination, supported by chest x-ray and ECG, and established by echocardiography.
If the VSD is large, chest x-ray shows cardiomegaly and increased pulmonary vascular markings. ECG shows right ventricular hypertrophy or combined ventricular hypertrophy and, occasionally, left atrial enlargement. ECG and chest x-ray are typically normal if the VSD is small.
Two-dimensional echocardiography with color flow and Doppler studies establishes the diagnosis and can provide important anatomic and hemodynamic information, including the defect's location and size and right ventricular pressure. Cardiac catheterization is rarely necessary.
Treatment
Small VSDs, particularly muscular septal defects, often close spontaneously during the first few years of life. A small defect that remains open does not require medical or surgical therapy.
Larger defects are less likely to close spontaneously. Diuretics, digoxin, and ACE inhibitors are indicated before surgery if HF develops. If infants do not respond to medical treatment or have poor growth, surgical repair may be done during the first few months of life. Even in asymptomatic children, a large shunt (pulmonary flow:systemic flow ratio ≥ 2:1) that persists after 2 to 4 yr requires surgical repair. Current surgical mortality rate is < 2%. Surgical complications may include residual ventricular shunt, right bundle branch block, and complete heart block.
Endocarditis prophylaxis is not needed preoperatively and is required only for the first 6 mo after repair or if there is a residual defect adjacent to a surgical patch.
Last full review/revision March 2010 by Lee B. Beerman, MD
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