ESSENTIALS OF DIAGNOSIS
Rare in adults.
Adults with a small or moderate size patent ductus arteriosus are usually asymptomatic, at least until middle age.
Widened pulse pressure; loud S2.
Continuous murmur over left pulmonary area; thrill common.
The lesion is best visualized by MRI, CT, or contrast angiography.
The embryonic ductus arteriosus allows shunting of blood from the PA to the aorta in utero (thus bypassing the lungs). The ductus arteriosus normally closes immediately after birth so that all right heart blood flows to the pulmonary arteries. Failure to close results in a persistent left-to-right shunt connecting the left PA 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 the neonate, a patent ductus can often be closed by administration of a prostaglandin inhibitor, such as indomethacin. The effect of the persistent left-to-right shunt on the pulmonary circuit is dependent on the size of the ductus. If large enough, pulmonary hypertension (Eisenmenger physiology) may occur. A small ductus may be well tolerated until adulthood.
There are no symptoms unless LV 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 (AUDIO 10–14). Thrills are common. If pulmonary hypertension is present (Eisenmenger physiology), the shunt may reverse and the lower body receives desaturated blood, while the upper body receives saturated blood. Thus, the hands appear normal while the toes are cyanotic and clubbed (differential cyanosis).
Audio 10-14. Patent ductus arteriosus (PDA).
Continuous murmur. S2 is obliterated by the waxing and waning of the murmur.(Reproduced, with permission, from T. Anthony Michael, MD, Mastering Auscultation [CD-ROM], McGraw-Hill, 2000.)
B. ECG and Chest Radiography
A normal ECG tracing or LVH is found, depending on the magnitude of shunting (eFigure 10–27). On chest radiographs, the heart is normal in size and contour, or there may be LV and LA enlargement. The PA, aorta, and LA are prominent because they all are in the shunt pathway.
Left ventricular hypertrophy. The mean frontal plane QRS axis is –15 degrees. The R wave exceeds 15 mm in aVL, and the sum of the S wave in V1 and the R wave in V5 exceeds 35 mm. ST-segment depression is present in leads I and aVL, and T wave inversion is present in I, aVL, and V5-6...