Pathophysiology

The ductus arteriosus is part of the normal fetal circulatory system. This vessel connects the aorta and the pulmonary artery. Prior to birth the ductus arteriosus allows for antegrade flow from the right ventricle to the aorta. Following birth the ductus arteriosus normally closes. If the ductus remains open, blood will shunt from the aorta into the pulmonary artery due to the decrease in pulmonary vascular resistance. The amount of left-to-right shunting depends upon the size of the PDA and the relative resistances of the systemic and pulmonary circulations. Left-to-right shunting of blood caused by patency of the ductus arteriosus results in increased pulmonary artery blood flow as well as left atrial and left ventricular overload. Extensive aortic runoff, with low aortic diastolic pressure secondary to a large patent ductus arteriosus can result in systemic organ hypoperfusion. Pulmonary vascular obstructive disease may occur, sometimes as early as one year of life.

In very rare instances, usually in the presence of other complex cardiovascular anomalies, there is a bilateral DA. In the typical left aortic arch, the aortic end of the DA arises distal to the left subclavian artery and the pulmonary end inserts at the junction of the main and left pulmonary arteries.