Patent Ductus Arteriosus

Essentials of Diagnosis

• Adults with small or moderately large patent ductus are usually asymptomatic at least until middle age.
  
• Widened pulse pressure; loud S₂.
  
• Continuous murmur over pulmonary area; thrill common.
  
• Echo-Doppler is helpful, but the lesion is best visualized by aortography.

General Considerations

The embryonic ductus arteriosus fails to close normally and persists as a shunt connecting the left pulmonary artery and aorta, usually near the origin of the left subclavian artery. Prior to birth, the ductus is kept patent by the effect of circulating prostaglandins; in early infancy, a patent ductus can often be closed by administration of intravenous indomethacin (0.2 mg/kg intravenously).

If the defect is not closed, blood flows continuously from the aorta through the ductus into the pulmonary artery in both systole and diastole; the defect is a form of arteriovenous fistula, increasing the work of the left ventricle. If it remains open, obliterative changes in the pulmonary arterioles can cause pulmonary hypertension, with reversal of the direction of shunting. Then the shunt is bidirectional or right-to-left (Eisenmenger's syndrome). This complication does not correlate with shunt size.

Clinical Findings

A. Symptoms and Signs
There are no symptoms unless left ventricular failure or pulmonary hypertension develops. The heart is of normal size or slightly enlarged, with a hyperdynamic apical impulse. The pulse pressure is wide, and diastolic pressure is low. A continuous rough "machinery" murmur, accentuated in late systole at the time of S₂, is heard best in the left first and second interspaces at the left sternal border. Thrills are common.

B. Electrocardiography and Chest X-Ray
A normal tracing or left ventricular hypertrophy is found, depending upon the magnitude of shunting. On chest radiographs, the heart is normal in size and contour, or there may be left ventricular and left atrial enlargement. The pulmonary artery, aorta, and left atrium are prominent.

C. Diagnostic Studies
Echocardiography quantifies left ventricular and atrial size. MRI can demonstrate the abnormality, and the magnitude of the shunt can also be determined by radionuclide flow studies. Cardiac catheterization establishes the presence and severity of a left-to-right shunt and whether pulmonary hypertension is present; angiography can define its anatomy.

Prognosis & Treatment

Large shunts cause a high mortality rate from cardiac failure early in life. Smaller shunts are compatible with long survival, congestive heart failure being the most common complication. Infective endocarditis or endarteritis may also occur, and antibiotic prophylaxis is required. A small percentage of patients develop pulmonary hypertension and reversal of shunt (right- to-left shunting), such that the lower legs, especially the toes, appear cyanotic and clubbed in contrast to normally pink fingers. At this stage, the patient is inoperable.