Intracardiac Injection of Radioactive Krypton

Abstract

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 µc. 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 x 10^–5 and averaged 2.5 ± 2.6 x 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 x 10^–5 and averaged 30.1 ± 12.2 x 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.