The role of pulmonary hypertension and thromboembolism in the production of pulmonary arteriosclerosis.

Thromboembolism and pulmonary hypertension have been assessed as factors in the production of pulmonary arteriosclerosis. A study was made of autopsy records and tissue sections from 59 cases of congenital heart disease with anomalies permitting shunting of blood from the systemic to the pulmonary circulation and 31 cases of pulmonary stenosis with septal defect. Pulmonary arteriosclerosis was found to be common and of equal frequency in the two groups of cases, indicating that hypertension is not a necessary factor. There was a close correlation between the presence of pulmonary arterial thrombi and pulmonary arteriosclerosis. E XTENSIVE STUDIES of pulmonary arteriosclerosis have disclosed a number of etiologic factors of possible importance. Hypertension and thromboembolism are the two factors that have been recently considered most important. Another factor which must be considered in certain cases is increased rate of flow. Thrombo-embolism: The work of Duguid' has stimulated a series of experiments demonstrating that fibrous intimal plaques can be produced in the pulmonary arteries of rabbits by intravenous injection of emboli composed of blood clot.2-6 It has been established by Rich7 that pulmonary arterial thrombi frequently occur in patients with congenital pulmonary stenosis. He attributed this frequency to sluggish pulmonary blood flow and polycythemia, both of which increase the likelihood of intra-vascular thrombosis. In the study being presented here, a search for thrombi in the pulmonary arteries has also been made on a series of cases of the hemodynamically opposite conditions , the congenital anomalies with shunting of blood from the systemic circulation to the pulmonary circulation (hereinafter referred to as left-to-right shunt). These patients with left-to-right shunt usually have normal or reduced numbers of circulating erythrocytes.s They also have increased rate of pulmonary blood flow or pulmonary hypertension, or both. Several reports have described thrombosis of small pulmonary arteries in such cases, but these cases have commonly been classified as "'pulmonary arteritis".9' 10 Hypertension: The fibrous intimal thickening often described in cases with left-to-right shunt has been considered the result of pulmonary hypertension.' Barnard6 considered the concentric fibrous intimal lesions found in the pulmonary arteries of rabbits injected intravenously with blood clot to be due to concomitant hypertension. In this study we are evaluating the effect of pulmonary hypertension on the pulmonary arteries in cases of congenital heart disease with left-to-right shunt. Comparison will be made with cases having pulmonary valvular or in-fundibular stenosis and a septal defect (herein-after referred to as …