Clinical Experience with Nuclear-Powered Pacemakers (Plutonium-238)

Abstract

Laurens-Alcatel Model Medtronic 9000 (1). From that time to July, 1974, 886 pacemakers have been implanted over the world of which 36 were implanted in Dusseldorf and Essen. TECHNOLOGY AND RADIATION The Medtronic nuclear pacemaker design has been described elsewhere (31) and now will merely be supplemented. The fuel capsule (Fig. 1) contains 151-168 mg of pure plutonium-238 which is suitable for use as an alpha emitter because of its half-life of 87.8 years, its specific activity of 17.55 Curie/gm, its constant rate of splitting yielding a uniform temperature, and its relatively easy shielding (39). The decay of 155 milligrams of plutonium-238 produces uranium-234 and 0.11 ml of helium each year. The daughter products of plutonium-236 which exists as an impurity in plutonium-238 emit gamma rays. While plutonium -236 contributes only about 1 % of the total radiation during the first year of decay, its share increases to approximately 40 % during the tenth year of function of a cardiac pacemaker. The helium accumulates inside an hermetically sealed fuel capsule which has a double layer, the inner made of tantalum and the outer of platinum iridium. After 10 years of helium accumulation the calculated pressure on the inner capsule is 30 kg/cm 2 (2,9), a pressure level which the capsule has withstood without damage during extensive testing. It has survived temperatures of 1000 0 C for 6 hours, 1300 0 C for 1 1/2 hours, a 485 M. Schaldach et al. (eds.), Engineering in Medicine © Springer-Verlag Berlin-Heidelberg 1975