Alterations in regional pulmonary blood flow in patients with congenital heart disease studied by radioisotope scanning.

External scintillation scanning of intravenously administered '31I-labeled macroaggregates of human serum albumin (1311-MAA) was employed to evaluate the distribution of pulmonary arterial blood flow in 61 normal subjects and in 100 patients with various congenital cardiovascular malformations. Intra-aortic administration of 131I-MAA demonstrated that blood flow through subelavian-pulmonary artery anastomoses is directed principally to the lung on the side of the anastomosis; the relative concentration of 1311-MAA in each lung after intravenous injection provided an index of the patency of the anastomosis or of the development of pulmonary atresia or pulmonary hypertension. In contrast to the findings in patients with a patent subclavian-pulmonary shunt, scans obtained from patients with a patent ductus arteriosus did not reveal a separation of the systemic arterial and systemic venous inflows to the lungs. The patency of superior vena caval-right pulmonary arterial anastomosis could be assessed after injection of 13I-MAA into an upper-extremity vein. Anomalies characterized by increased pulmonary blood flow or elevated pulmonary arterial pressures, or both, increased the ratio of pulmonary blood flow in the lung apices relative to that in the dependent lung zones. Anomalies characterized by elevated pulmonary venous pressure, such as cor triatriatum and mitral regurgitation, were readily detected by demonstrating both a decrease in blood flow to the lung bases as well as an increase to the apices. Thus, in patients with known pulmonary arterial hypertension (mean pressure, > 30 mm Hg) the ratio of upper to lower zone blood flow was always significantly higher if the arterial hypertension was accompanied by venous hypertension. For this reason, lung scans facilitated the screening of patients with pulmonary arterial hypertension for surgically correctable lesions such as cor triatriatum and mitral stenosis. The method described is technically simple, without risk, easily applicable to large numbers of patients, and provides clinically important information concerning many forms of congenital heart disease.