Intracardiac Injection of Radioactive Krypton

IN RECENT years the efforts of many groups have been directed to the development of more refined methods for the precise characterization of cardiac shunts. The application of inhaled foreign gases and the various extensions and improvements in the dye dilution method have already proved of considerable value in the study of patients with congenital heart disease.1 In the course of clinical studies in which the radioactive gas krypton (Kr85) was inhaled2 it was found that the isotope was slightly soluble in saline solution. When such solutions were injected into a systemic vein, the right side of the heart, or pulmonary artery, the isotope could be immediately detected in expired air and little passed through the lung into arterial blood.2 3 When injections were made proximal to an experimental right-to-left shunt, a significant fraction bypassed the lung and high levels were found in systemic arterial blood.4 In other experiments injections of the dissolved gas were made into the chambers of the left heart and aorta. Under such circumstances, the appearance of the isotope in the pulmonary circulation and expired air was delayed by its passage through the systemic bed. When an injection was made into the left heart proximal to the origin of a left-toright shunt, however, the Kr85 was detected almost immediately and in high concentration in expired air.5 Following these experimental studies, these methods were applied in the study of patients undergoing diagnostic evaluation at the National Heart Institute.6 7 The present report presents the experiences with these technics in 48 patients.