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Three-years' clinical experience with radioisotope powered cardiac pacemakers.

Radioisotope powered cardiac pacemakers have been in human clinical evaluation for over three years. The power supply of these units was developed in response to the need voiced by the medical community for pulse generators with longer lifetimes and more predictable performance characteristics than the conventional pulse generators which are powered by chemical cells. This thermoelectric power supply has Pu-238 as a source of thermal energy and a bismuth-telluride thermopile to generate electrical energy by the Seebeck effect. Over 650 of these radioisotopic power supplies have been built since 1968. By May 1, 1973, 260 of them had been incorporated into pulse generators and implanted in patients. All of the isotopic pulse generators and their power supplies are still functioning. Theoretical calculations predict that the radioisotopic power supply will reliably power a pulse generator for ten or more years, and clinical experience lends credence to these calculations. Progress is being made in modifying U.S. Atomic Energy Commission (USAEC) regulations which currently restrict the use of Pu-238 powered medical devices in the United States. The excellent clinical performance of the isotopic pulse generator and its acceptance by the medical profession in Europe indicate that this device has a promising future.