Atom-Powered Heartbeats

Pacemakers implanted in the chest to reinforce the beat of a damaged heart have been in widespread use since 1960. But the thousands of patients who live with the devices suffer a major inconvenience: they must return to the hospital every two years or so and undergo minor surgery so that the pacemaker's mercury batteries can be replaced. That drawback has spurred researchers to develop a tiny nuclear power source, to replace batteries, that could theoretically last a lifetime and still pose no radiation danger to the patient.

Last week a Frenchwoman was up and doing well with just such a radioactive source in her chest. In an operation at Hopital Broussais in Paris, Drs. Paul Laurens and Armand Piwnica had successfully performed the first human implant of an atomic pacemaker in Suzanne Peragin, 58. If all goes well, the device should sustain her without further operations for the rest of her life, giving her heart a boost to 65 beats per minute whenever it begins to falter.

Soft Particles. For a while last week, medical circles were abuzz with a rumor that a U.S.-designed atom-powered pacemaker had also been implanted--in an American patient. That word proved to be premature; scientists at the National Heart and Lung Institute are still testing their prototypes in dogs.

Both American and French designers settled on plutonium-238 as the best radioactive source. The artificially produced element emits "soft" alpha particles, which have so little energy that they will not penetrate a sheet of heavy notepaper; thus they will not harm a patient. The French put 150 mg. (about one two-hundredth of an ounce) of Pu-238 into a capsule of platinum and tantalum. The Americans put 500 mg. (one-sixtieth of an ounce) in their capsule. In both devices, the patient is sufficiently shielded from the heat of the radioactive source by its plastic container. That heat is directed to a thermocouple that generates 200 milliwatts of electricity. This powers a tiny generator that sends an impulse to the heart through internally implanted wires. Both of the complex pacemakers are small. The French device is cylindrical and about the size of a 35-mm. film cassette; the American is rectangular, half the size of a cigarette pack. The half life of Pu-238 (the time in which it loses half of its radioactivity) is almost 90 years. But for safety's sake the surgeons expect to replace the plutonium power source after about ten years.

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