Isotope Technics in Clinical Cardiology.

THIS REVIEW is an attempt to answer two questions. First, are there any isotope technics available at the present time that are really useful in the care of patients? And second, what will be the role of isotope technics in clinical cardiology a few years from now? Historical Review The use of isotopes in clinical cardiology was introduced by Blumgart, Yens, and Weiss, who used radium C and a cloud chamber to estimate the linear velocity of blood flow in an extensive series of studies starting in 1927.1, 2 Undoubtedly the major stimulus to the adoption of tracer technics came from the introduction of man-made radioisotopes after World War II. During the immediate postwar period several new methods were described. Quimby and Smith3 and Kety4 introduced the use of isotope clearance as a method of measuring the rate of blood flow to tissues. Prinzmetal and his collaborators used a Geiger counter placed over the pre-cordium to follow the circulation of a bolus of radioactive blood through the right and left sides of the heart. They dubbed this procedure "radiocardiography."3 In 1953, WVaser and Hunzinger made the first attempts to measure coronary blood flow by labeling the coronary blood with an isotope.6 Although the first of these technics was introduced almost 40 years ago, the practical application of isotope technology to clinical problems has been slow. There have been a number of reasons for the lag. The crude nature of the counters and radioactive tracers that have been available until recently is probably the most important factor. The requirement of a special federal license to use isotopes has undoubtedly been a deterrent. Recently steps have been initiated to make isotopes available to all physicians without special approval. This is an important step in the right direction. Radiocardiography Several of the successfully developed methods have not been used by clinicians in the care of patients. For instance, from the radio-cardiogram it is possible to determine cardiac output,7-9 the amount of blood in the lungs, 10, 11 and the relative amounts of blood in the right and left sides of the heart.12 A single injection of 1131 albumin and the use of inexpensive counting equipment are all that is needed. Serial measurements of cardiac output or pulmonary and intracardiac blood volumes might be helpful in some clinical situations, but to date cardiologists have relied on a history of the patient's illness and a …