Development of the ductus arteriosus in right ventricular outflow tract obstruction.

We studied the morphology of the ductus arteriosus in 14 infants, ages 2--90 days. Eight (group 1) had pulmonary atresia (structural and functional) with an intact interventricular septum; six (group 2) had pulmonary atresia with a ventricular septal defect. The inferior angle of the ductus arteriosus at the aortic junction was measured in each patient. In group 1, this angle was obtuse in all but one patient. In group 2, the angle was acute in all. Further study of intracardiac anatomy suggested that in group 1, the obtuse inferior angle of the ductus arteriosus was the result of a late and progressive obstructive phenomenon that allowed normal right-to-left flow through the ductus arteriosus during much of fetal life. In group 2, the direction of ductus arteriosus flow (normally from the pulmonary trunk to the aorta) was reversed, and flowed from the aorta to the pulmonary trunk. This reversal of flow was probably of early onset in the fetus, the aorta receiving the total combined ventricular output, and produced a small ductus arteriosus with an acute inferior angle. It is extremely important not to rule out pulmonary atresia with an intact interventricular septum when aortography in the newborn shows a normal-sized ductus arteriosus with an obtuse inferior angle. Despite existing pulmonary atresia, these patients have neither a hypoplastic right ventricle nor discontinuity of the right ventricle with the pulmonary artery.