In the diagnosis of congenital cardiac defects, right to left shunts may be more difficult to detect and accurately localize than left to right shunts. A new procedure developed for detecting shunts consists of injecting a substance (131 -labeled sodium and methylglucamine diatrizoate) which serves as a rapidly excreted radioactive tracer. The injection is made into the various chambers of the heart by way of a catheter inserted through a vein, but injection by direct venipuncture also gives useful results. Three radiation counters are placed over the heart, over a peripheral lung field, and over a femoral artery, and the time of appearance of increased radioactivity at these three places is found to give information that cannot be obtained from electrocardiograms, pressure recordings, and angiocardiograms alone. The procedure demonstrated its usefulness in 42 patients suspected of having right to left shunts. A variety of other conditions can also be investigated by this means, and a marked delay (up to 20 seconds, as compared with a normal of 5 seconds) in the appearance of radioactivity in the femoral ortery and leg was among the featues noted in 17 patients with disease of the mitral valve. The apparatus needed in this procedure can be reduced to a compact, portable unit, and the method has obviated the need of puncturing the femoral artery in the detection of intracardiac and extracardiac shunts.
Greenspan RH, Lester RG, Marvin JF, Amplatz K. ISOTOPE CIRCULATION STUDIES IN CONGENITAL HEART DISEASE. JAMA. 1959;169(7):667–672. doi:10.1001/jama.1959.03000240005002
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