Pacemaker Problems

When nature devised the delicate, low-voltage electrical system that keeps a human heart beating at about 70 times a minute, it did not anticipate interference from doctors' diathermy machines, radio transmitters or neon signs. Thanks to the amazing vitality of natural tissues, there was no possibility of metal fatigue, either, regardless of what else might go wrong. But in some of the artificial pacemakers that have been implanted in the bodies of thousands of heart-disease patients in the past few years, interference and fatigue are proving to be troublesome. Difficulties may show up when the patient is still on the operating table, while the pacemaker is being inserted in a pocket of chest or abdominal muscle, or they may develop years later.

New Zealand surgeons report in the British Medical Journal that they have had close calls with two patients. A man of 68 had been doing well in Dunedin Hospital after a week on an external pacemaker. The surgeons were installing an internal model that was designed to work indefinitely, but when they cut into the patient's heart sac to put an electrode in the heart muscle, the external pacemaker went wild, and the heart twitched ineffectively. The doctors traced the trouble to high-frequency interference from the diathermy machine that powered the electric scalpel they were using. This man and another who had a similar experience both recovered, but the surgeons were puzzled and worried, so they did a lot of experiments with animals.

They discovered that some types of internal pacemakers are so designed that a diathermy machine operated within three feet of them causes interference; the pacemaker pulses so fast that the heart cannot keep up, and so it will stop or just twitch. The same interference occurs within six inches of a neon sign, or close to the frequency-regulating coils of radio transmitters. One form of diathermy is commonly used in doctors' offices for simple surgery such as removal of warts. Human tissues afford some shielding for a patient with an implanted pacemaker, but interference may still be dangerous.

Fortunately, X rays apparently present no such hazard to a pacemaker; it is only from X rays that doctors can diagnose the trouble when the wires leading from the pacemaker to the heart break because of metal fatigue. The University of Kentucky's Dr. Harold D. Rosenbaum reports that this can easily happen, not only because of the incessant movement of the heart --which puts a strain on the wires--but also as a result of breathing and such everyday actions as tying shoelaces. If the breaks are detected in time, the patient can get along well again after an operation to replace the wires.

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