Figure 143-2 Atrial septal defect. AO, Aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.
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. 143-2). ASDs represent approximately 10% of all congenital heart defects. A secundum defect, with the hole 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 or may 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.
The pathophysiology and amount of shunting depend on thesize of the defect and the relative compliance of the both ventricles. Even with large ASDs and significant shunts, infants andchildren are rarely symptomatic. A prominent right ventricular impulse at the left lower sternal border (LLSB) often can bepalpated. A soft (grade I or II) systolic ejection murmur in the region of the right ventricular outflow tract and a fixed split S2 (due to overload of the right ventricle with prolonged ejectioninto the pulmonary circuit) are often audible. A larger shuntmay result in a mid-diastolic murmur at the LLSB as a result ofthe increased volume passing across the tricuspid valve.
ECG and chest x-ray findings reflect the increased blood flow through the right atrium, right ventricle, pulmonary arteries,
Figure 143-3 Patent ductus arteriosus. AO, Aorta; LA, left atrium; LV, left ventricle; PA, pulmonary artery; RA, right atrium; RV, right ventricle.
and lungs. The ECG may show right axis deviation and right ventricular enlargement. A chest radiograph may show cardiomegaly, right atrial enlargement, and a prominent pulmonary artery.
Medical management is rarely indicated. 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.
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. 143-3). 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.
Symptoms depend on the amount of pulmonary blood flow. The magnitude of the shunt depends on the size of the PDA (diameter, length, and tortuosity) and the pulmonary vascular resistance. Small PDAs are asymptomatic; moderate to large shunts can produce the symptoms of heart failure as the pulmonary vascular resistance decreases.
The physical examination findings depend on the size of the shunt. A widened pulse pressure is often present as a result of the runoff of blood into the pulmonary circulation during diastole. A continuous, machinelike murmur can be heard at the left infraclavicular area, radiating along the pulmonary arteries and often well heard over the left side of the 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 intensity of P2 depend on the pulmonary artery pressure. A thrill may be palpable.