Pulmonary atresia with and without ventricular septal defect: a different etiology and pathogenesis for the atresia in the 2 types?

In 15 of 20 hearts of neonates with pulmonary atresia and intact septum (PA-IVS) and in 4 with critical pulmonary stenosis, the pulmonary valve consisted of 3 fused cusps. One of the 11 patients with a ventricular septal defect (PA-VSD) had a well-developed pulmonary root; in 8 the pulmonary trunk arose from a dimple. Two had a bicuspid valve. In 10 of the 20 patients with PA-IVS and in those with critical stenosis, the diameter of the pulmonary trunk was normal or larger than normal. The authors believe that this is related to flow through an initially patent pulmonary valve and, perhaps more importantly, to poststenotic dilatation. In all hearts with PA-VSD, the pulmonary trunk was very small. In the patients with PA-IVS and a normal-sized pulmonary trunk and in 3 with critical pulmonary stenosis, the morphology of the ductus arteriosus was normal, suggesting that even in the former the valve was patent before birth, allowing forward flow. In all patients with small pulmonary trunk, the ductus was long, tortuous, and originated from the aortic arch in a proximal position, suggesting that reversal of flow had occurred early in development. The authors postulate that in patients with ventricular septal defect (VSD), the pulmonary ostium becomes atretic early in development, at or shortly after partitioning of the truncoconal part of the heart has taken place but before closure of the ventricular septum. In patients with intact ventricular septum, on the other hand, atresia very likely occurs sometime after cardiac septation has been completed. In these cases the pulmonary atresia may be due to a prenatal inflammatory process, rather than representing a true congenital malformation.