Different grades of medial hypertrophy and intimal changes in small pulmonary arteries among various types of congenital heart disease with pulmonary hypertension.

Morphometric analysis of small pulmonary arterial changes was performed in three patients with different congenital heart disease with pulmonary hypertension: congenital mitral stenosis (MS), ventricular septal defect (VSD) and transposition of the great arteries (TGA). The material was biopsy or autopsy lung specimens, all having the same degree of elevated pulmonary arterial pressure. Medial thickness was determined by the method of Suwa and Takahashi, and the degree of intimal changes was quantified using the index of pulmonary vascular disease (IPVD) by Yamaki and Tezuka. It was demonstrated that the medial thickening of the small pulmonary arteries was the strongest in the patient with congenital MS, moderate in VSD, and the weakest in TGA, with statistically significant differences between each pair of these three conditions. Interestingly, the order of severity for intimal changes was reversed: it was the severest in TGA and the mildest in congenital MS. We surmise that in patients with TGA, medial hypertrophy is suppressed by sustained vasodilation resulting from the high oxygen saturation of pulmonary arterial blood, while in congenital MS, the media undergoes the severest hypertrophy because of the low oxygen saturation. We also conclude that in TGA intimal changes readily develop in the presence of attenuated media, while in congenital MS, the thickened media seems to prevent intimal changes. From a clinical viewpoint, these results urge us to recommend early surgical intervention in TGA and VSD where severe intimal changes can develop in the absence of extreme medial thickening. It may not be appropriate to extend operation on patients with congenital MS, since strongly thickened media can trigger vasospasms and medial necrosis.