The ductus arteriosus connects the descending aorta (just distal to the left subclavian artery) to the left pulmonary artery. In the fetus, it permits pulmonary arterial blood to bypass the unexpanded lungs and enter the descending aorta for oxygenation in the placenta. It normally closes soon after birth, but in some infants it does not close spontaneously, and there is continuous flow from the aorta to the pulmonary artery (i.e., left-to-right shunting).Patent ductus arteriosus accounts for about 10 percent of cases of congenital heart disease. Its incidence is higher than average in pregnancies complicated by persistent perinatal hypoxemia or maternal rubella infection and among infants born at high altitude or prematurely.
A patient with patent ductus arteriosus and a moderate or large shunt has bounding peripheral arterial pulses, a widened pulse pressure, and a hyperdynamic left ventricular impulse. The first heart sound is normal. A continuous “machinery” murmur, audible in the second left anterior intercostal space, begins shortly after the first heart sound, peaks in intensity at or immediately after the second heart sound (thereby obscuring it), and declines in intensity during diastole. With a large shunt, mid-diastolic and systolic murmurs (from increased flow through the mitral and aortic valves, respectively) may be noted. If pulmonary vascular obstruction and hypertension develop, the continuous murmur decreases in duration and intensity and eventually disappears and a pulmonary ejection click and a diastolic decrescendo murmur of pulmonary regurgitation may appear.
With a small patent ductus arteriosus, the electrocardiogram and chest x-ray film are normal. With a large patent ductus arteriosus and substantial left-toright shunting, left atrial and ventricular hypertrophy are evident, and the chest film shows pulmonary plethora, proximal pulmonary arterial dilatation, and a prominent ascending aorta. The ductus arteriosus may be visualized as an opacity at the confluence of the descending aorta and the aortic knob. If pulmonary hypertension develops, right ventricular hypertrophy is noted. With two-dimensional echocardiography, the ductus arteriosus can usually be visualized, and Doppler studies demonstrate continuous flow in the pulmonary trunk. Catheterization and angiography make it possible to quantify the magnitude of shunting and the pulmonary vascular rsistance as well as visualize the ductus arteriosus.
A patent ductus arteriosus rarely closes spontaneously after infancy. A small patent ductus arteriosus causes no symptoms, and a person with a defect of this size can have a normal life expectancy. However, the presence of a small patent ductus arteriosus entails an elevated risk of infective endocarditis, which involves the pulmonary side of the ductus arteriosus or the pulmonary artery opposite the duct orifice, from which septic pulmonary emboli may arise. A patent ductus arteriosus of moderate size may cause no symptoms during infancy; during childhood or adulthood, fatigue, dyspnea, or palpitations may appear. In addition, the ductus arteriosus may become aneurysmal and calcified, which may lead to its rupture (37-40). With larger shunts, flow is markedly increased, which may precipitate left ventricular failure. Eventually, pulmonary vascular obstruction may develop; when the pulmonary vascular resistance equals or exceeds the systemic vascular resistance, the direction of shunting reverses. One third of patients with a patent ductus arteriosus that is not surgically repaired die of heart failure, pulmonary hypertension, or endarteritis by the age of 40 years, and two thirds die by the age of 60 years.
Surgical ligation of patent ductus arteriosus, generally accomplished without cardiopulmonary bypass, has an associated mortality of less than 0.5 percent. However, in patients with ductal aneurysmal dilatation or calcification, resection with cardiopulmonary bypass may be required. Because of the risk of endarteritis associated with unrepaired patent ductus arteriosus (estimated at 0.45 percent annually after the second decade of life) and the low risk associated with ligation, we recommend that even a small patent ductus arteriosus be ligated surgically or occluded with a percutaneously placed closure device. Once severe pulmonary vascular obstructive disease develops, surgical ligation or percutaneous closure is
contraindicated.
