Pulmonary arterial development in infants with large perimembranous ventricular septal defects associated with overriding of the aortic valve.

Intracardiac anatomy and pulmonary vascular structure were studied in 13 cases having large perimembranous ventricular septal defects associated with overriding of the aortic valve, 12 of whom died aged 2 days-9 months. In all cases the ventricular septal defect and aorta were of the same size, but the diameter of the pulmonary orifice was usually greater. Quantitative morphometric techniques were used to study the lungs. Structural adaptation to extra-uterine life was shown to have occurred normally in the 4 patients who died as neonates. In the cases aged 2 months-4 years, there was an increase in arterial medial thickness and extension of muscle, while the intra-acinar arteries were larger than normal in size and normal in number. Intimal proliferation was seen in 1 case at 4.5 months, but such proliferation caused significant obstruction only in one child aged 4 years. These findings emphasize the rapidity with which structural adaptation to extra-uterine life can occur in the patient with a large unrestrictive ventricular septal defect. A rapid increase in muscularity can be seen by 2 months of age. Should banding of the pulmonary artery be required in patients with more complicated intracardiac abnormalities in whom it is desirable to achieve a normal pulmonary vascular bed, our findings encourage its early performance, particularly in those destined for a Fontan repair.