The implantable defibrillator, an enhanced pacemaker that can stop cardiac arrest by shocking the heart into beating again, can prevent deaths in a much broader group of patients than it has been used in so far, concludes a new study.
The study divided participants into two groups, all of whom were implanted with a defibrillator. Two-thirds of the defibrillators were turned on, and the rest were left off.
Those with active defibrillators had a 31 percent lower death rate in a 20-month period than participants whose defibrillators were not turned on, said Arthur J. Moss, M.D., of the University of Rochester, N.Y., lead researcher in the study.
Dr. Moss presented results of the study, which enrolled about 1,200 participants at 76 medical centers, at the annual meeting here of the American College of Cardiology, the nation’s largest group of heart doctors. The research also is being published in the March 21, 2002, issue of the New England Journal of Medicine.
Implantable defibrillators first got widespread public attention in summer 2001, when Vice President Richard Cheney was implanted with a defibrillator made by Medtronic Inc.
The current study was funded by Guidant Corp., which manufactured the defibrillators used in the study. St. Jude Medical Inc. also makes implantable defibrillators.
Researchers have wondered whether implantable defibrillators could benefit patients who were not quite as sick as those for whom the devices originally were intended.
In the current study, all participants had had a previous heart attack, and their hearts’ pumping ability was measured as less than half that of a normal heart. About 3 million to 4 million people in the United States would meet these criteria, according to the study results.
But these patients, unlike those in previous studies that led to approval of implantable defibrillators by the U.S. Food and Drug Administration, were not tested to see if they had specific types of irregular heart rhythm that might put them at risk of sudden death.
Nevertheless, researchers had good reason to think patients who had survived a heart attack and had reduced heart-pumping ability (a measurement called ejection fraction) might be at risk for sudden death from a heart-rhythm abnormality, or arrhythmia. According to the American College of Cardiology, about one-tenth of heart attack patients who are left with poor heart function will die from a heart-rhythm abnormality within two years.
Cardiac arrest, a stoppage of the heart, typically occurs as the result of a sudden, severe malfunction in the heart’s rhythm. About 95 percent of people who collapse from cardiac arrest die before they reach the hospital. Cardiac arrest in older adults — the group most at risk — often is caused by blockages in the coronary arteries or scarring from an earlier heart attack, according to Dr. Moss.
Of the 1,232 participants in the study, 742 — about two-thirds — received the active defibrillator and 490 were given an inactive device, Dr. Moss reported at the conference. The patients’ average age was about 53, and 85 percent were men.
All patients received other treatments, the most common of which were the drugs known as ACE inhibitors and beta-blockers. “We worked hard to optimize treatment,” Dr. Moss said.
After an average follow-up of 20 months, 14.2 percent of the patients who received the active defibrillator had died, compared with 19.8 percent in the group with inactive devices, he said.
About half of the deaths among the inactive-defibrillator group were caused by an irregular heart rhythm, Dr. Moss said. Only about 27 percent of the deaths were from arrhythmia in the group that had the active defibrillators.
One concern raised by the study was that although patients with the active defibrillators had lower death rates, they had a higher rate of hospitalization for heart failure than the patients with the inactive devices.
Asked to explain this difference, Dr. Moss said, “We believe that it relates to the improved survival of the [active defibrillator] patients.” In other words, the patients with active defibrillators were more likely to be admitted to the hospital than the other group, in part because more of them lived longer.
Besides this concern about hospitalization, the cost of implanting defibrillators also could limit their usefulness, says J. Thomas Bigger, M.D., in an editorial that accompanies the study in the New England Journal of Medicine. Continued follow-up of the patients should give a better idea of how long the defibrillator extends their lives, Dr. Bigger writes.