Intracardiac Injection of Radioactive Krypton

Following injection of krypton85 in solution into the right side of the heart, approximately 95 per cent is cleared during 1 passage through the pulmonary circulation. Arterial blood activity is low when radioactive Kr85 is injected in the absence of, or distal to, the origin of a right-to-left shunt. However, when injected proximal to the origin of such a shunt, a fraction of the Kr85 bypasses the pulmonary capillary bed and appears in arterial blood. Thirty to 50 &mgr;c. Kr85 were injected into the right heart, and arterial blood was sampled during the next 15 seconds. In 19 patients without right-to-left shunts, the activity per milliliter of arterial blood was always less than 9.0 × 10−5 and averaged 2.5 ± 2.6 × 10−5 of the total radioactivity injected. In 9 patients with proved right-to-left shunts, the radioactivity per milliliter of arterial blood always exceeded 8.2 × 10−5 and averaged 30.1 ± 12.2 × 10−5 of the total activity injected. By appropriate rearrangement of the Stewart-Hamilton formula the data permit calculation of the magnitude of the right-to-left shunt. Following injection into the left heart, proximal to the origin of a left-to-right shunt, Kr85 promptly arrives in the pulmonary vascular bed and immediately appears in the expired gas, where it may be readily detected. In 22 such patients Kr85 appeared in the expired gas in an average of 4.0 ± 1.6 seconds. However, after injection distal to the origin of a left-to-right shunt in 18 patients, the appearance of Kr85 in the expired gas was delayed to a mean of 15.0 ± 5.0 seconds. The technics described are convenient, simple to apply during cardiac catheterization, and sufficiently sensitive to detect and localize even small cardiac shunts.