A lifesaving shock from an implanted heart defibrillator provides relief that a crisis was avoided, but new research suggests it can also be a sign that more trouble is ahead.
A study found that heart failure patients were far more likely to die within four years after their defibrillator zapped the heart into beating normally than those who got no shock.
Experts said patients should promptly tell their doctors if their defibrillator triggers. And doctors should check to see if their patients' condition has worsened and whether tests or medication changes are needed.
"We need to think about everything else we possibly could do to make them as healthy as they can be," said the study's lead author, Dr. Jeanne Poole of the University of Washington.
The findings are in Thursday's New England Journal of Medicine, along with another study that concluded that having an implanted defibrillator doesn't appear to diminish one's quality of life.
About 234,800 North Americans have defibrillators, which cost between $25,000 and $35,000. The devices, about the size of a stopwatch, are designed to correct dangerously high or erratic heartbeats in the lower, pumping chambers of the heart.
Previous research found that the devices cut the risk of death by 23 percent. The new reports come from that same study of 2,500 heart failure patients - their weakened hearts didn't pump efficiently - who hadn't yet had a life-threatening irregular heartbeat.
The new government-funded reports show that a defibrillator prolongs "survival in patients with heart failure, with relatively little compromise in the quality of life," wrote Drs. Jeff Healey and Stuart Connolly of McMaster University in Hamilton, Ontario, in a journal editorial. But they added: "It is somewhat disturbing to realize that actually receiving a shock is such an important predictor of death."
In the study, about a third of the 811 patients with defibrillators were shocked during nearly four years of follow-up. Data recorded by the devices shows whether the shock corrected a life-threatening irregularity or was inappropriately fired by another problem, such as an abnormal rhythm in the heart's upper chambers.
The researchers found that those who needed a shock were more than five times more likely to die over the next four years than those who didn't require one. Even people who didn't seem to need a shock but got one had double the risk of dying.
Dr. N.A. Mark Estes, president of the Heart Rhythm Society, noted that the defibrillators used in the study are a generation-old, and that newer devices can often correct a high heartbeat through painless pacing techniques, before a shock would be needed.
"The frequency of shocks would be considerably less with contemporary devices," said Estes, of Tufts Medical Center in Boston. He had no role in the studies but has been involved in others.
For the quality of life study, participants were questioned four times over 2 1/2 years about their activities and well-being to see how the defibrillator was affecting their lives. There was no difference between the groups treated with defibrillators, medication or dummy pills, the researchers said.
"We found no evidence that the patients who got the defibrillator were feeling any worse for having received that therapy," said Dr. Daniel Mark, lead author of the study from Duke University Medical Center.
A patient at Duke, John McKinnon, said he was initially reluctant to get a defibrillator about two years but has had no concerns since. Months ago, the 65-year-old pastor got a shock, which he described as a strong kick. Since then he's had a procedure to treat an abnormal heartbeat.
"I'm getting my energy back, doing some walking, getting some exercise," said McKinnon.
Medtronic Inc. provided the defibrillators used in the research and Wyeth provided the medicine. Many of the researchers and the editorial writers have received lecture fees or grants from makers of defibrillators.
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