Cardiac Shocks

Space-age help for the heart

Each year 300,000 people in the U.S. die from cardiac arrest, usually caused by uncontrolled contraction of muscle fibers in the heart's pumping chambers. Known as ventricular fibrillation, these attacks cut off circulation and halt the flow of blood to the brain. Only powerful electrical shocks administered directly to the chest or heart with bulky machines called defibrillators seem to stop such life-threatening episodes. But all too often, victims are stricken at home or in the streets and help does not arrive in time.

Last week a team of doctors and scientists at Sinai Hospital of Baltimore and Johns Hopkins University announced the successful use in patients of a space-age machine that may eventually avert many such deaths. Their device: a mini-defibrillator, only about as big as a cigarette pack, that can be implanted in the patient's body, where it continually monitors the heart and, if attacks occur, automatically orders up charges of electricity to jolt the heart back into a normal rhythm.

Twelve years in development at a cost of $4 million, AID (for Automatic Implantable Defibrillator) is largely a triumph for Cardiologist Michel Mirowski, 55, who migrated from Israel with the aim of perfecting it against almost unanimous medical opposition. Experts doubted that such miniaturized equipment could work inside the body. The implant's electronic heart and soul is its microcircuitry. Designed by Dr. M.S. Heilman and Engineer Alois Langer at Medrad/Intec Systems, a small medical technology firm in Pittsburgh, the little package (total weight: 250 grams, or 9 oz.) is placed just under the skin of the abdomen. In a 1 1/2-hour operation, two electrodes are led to the heart--one through veins to the right atrium, the other to the tip of the heart's ventricles. Unlike pacemakers, which give a steady stream of tiny electric prods to a sluggish heart, the defibrillator is programmed not to interfere with the heart's normal pattern. Rather, it responds only to severe aberrations in beat, and within 15 to 20 seconds administers a corrective shock (700 volts) that a conscious patient feels as a sharp tingle. If the heart does not resume normal beating, the defibrillator commands up to three more jolts. During the three-year life of its lithium batteries, it would be able to provide as many as 100 shocks.

Mirowski and his colleagues have implanted the device in six people, all of whom had already been stricken at least twice by episodes of cardiac arrest. Since their surgery, the patients have experienced a total of eleven cardiac incidents; during all but two of them, the machine restored normal heartbeat. One patient died even though the defibrillator worked faultlessly. The doctors shut down the device in a 16-year-old Pennsylvania boy because his heartbeat was so rapid that it triggered frequent shocks. The device is now being reprogrammed to accept the boy's quick pulse. The longest user is a 57-year-old California woman who, after six months with a defibrillator, is leading a normal life.

In an editorial that accompanies the Baltimore team's report in the New England Journal of Medicine, Cardiologist James Willerson of the University of Texas in Dallas notes that the device (expected unit cost: $5,000) is still very experimental. Willerson is also worried that there may be damaging scarring of heart tissue from repeated shocks. But despite these cautionary words, he calls the mini-defibrillator "a potentially important therapeutic contribution" for the care of ailing hearts.

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