Patent Ductus Arteriosus

During the fetal period the ductus arteriosus connecting the descending aorta with the pulmonary artery serves as an essential pathway supplying blood partly oxygenated by the placenta to the arteries of the lower part of the fetal body. Normally the duct closes immediately after birth, but owing to a developmental error it may remain open, or patent, in some infants. The altered pressure conditions during postnatal life (higher in the systemic circulation than in the pulmonary circulation) allows blood to flow through the duct in the opposite direction, that is, from the aorta to the pulmonary artery. This left-to-right shunt on the arterial level is analogous to the atrial and ventricular septal defects. As in the other two conditions, fully oxygenated blood returns to the lungs; gas exchange proceeds normally, but the excess blood may overfill the pulmonary circulation. Since that excess has to be pumped into the aorta by the left ventricle, the latter may be affected by the increased workload if the shunt volume is large.

The size of persistent ducts varies widely. A small duct has no significant effect on circulatory dynamics but is at risk of developing infective endarteritis (an infection analogous to endocarditis,

striking the arteries rather than the heart). The turbulent flow through the duct produces an audible murmur in the patient's chest different from murmurs caused by lesions inside the heart. A large duct, by overloading the left ventricle and the pulmonary circulation, may produce pulmonary hypertension in adulthood. Rarely, a very large duct shunts so much blood away from the aorta of an infant that a surgical emergency is created.

Surgical correction of patent ductus arteriosus consists of tying off the duct in an operation that does not require use of the pump-oxygenator. The duct can also sometimes be closed through a non-surgical technique involving cardiac catheterization. The simplicity and low risk of duct closure justifies its performance even in cases where the condition has no effect on the circulation, to guard against infection. Spontaneous closure of the duct occurs in infancy or childhood in an estimated 5 percent of cases.