BOSTON (Reuters) - A jolt from an implanted defibrillator is a very bad sign -- heart failure patients are about six times more likely to die after they receive their first life-saving shock, researchers reported on Wednesday.

And 30 percent of those deaths come within a day of the jolt, the researchers found. They said their study, published in the New England Journal of Medicine, suggests that implantable defibrillators often merely delay the inevitable.

Dr. Jeanne Poole of the University of Washington in Seattle said, “The most important thing to remember is that the defibrillators save lives,” and the findings mean a defibrillator shock may be a danger signal that patients and doctors should heed.

“The important message is that the first occurrence of shocks is not a random event in an otherwise stable clinical course but a sign of clinical deterioration in the underlying disease process,” Drs. Jeff Healey and Stuart Connolly of McMaster University in Hamilton, Ontario, wrote in a commentary.

Dr. Mark Estes of Tufts University in Boston and the Heart Rhythm Society said defibrillators are less likely to deliver a jolt today than earlier models because newer devices try to use pacing impulses to restore an abnormal heart rhythm before resorting to shocks.

A shock “is a sign that the patient’s clinical status has changed,” Estes said in a telephone interview.

“They may be developing more heart failure. There may be blockages in heart arteries causing the heart muscle not to function effectively.

DELAYING DEATHS

Implantable cardioverter-defibrillators or ICDs, are known to reduce the risk of death. In the study that served as the basis of the new findings, Medtronic ICDs reduced the death rate by 23 percent over nearly four years.

Using data from the Sudden Cardiac Death in Heart Failure Trial, Poole and her colleagues followed the cases of 811 people with defibrillators.

Any shock increased the risk of death, they found.

Another study from the same trial, also published in the Journal, found that ICDs seem to provide short-term comfort for patients during the first year, although the psychological benefit disappeared at the 30-month mark.

The exception, not surprisingly, came among patients who had received a shock in the previous month or two.

That study, led by Dr. Daniel Mark of Duke University Medical Center in Durham, North Carolina, used quality-of-life tests to assess the psychological well-being of 833 volunteers who received standard medical care, 830 who got additional drug treatment with amiodarone, also known by the Wyeth-Ayerst Pharmaceuticals brand name Cordarone, and 816 who received Medtronic ICDs.

“One concern is that the use of ICD therapy could trade a quick, relatively painless (albeit premature) death for a more unpleasant death from progressive deterioration of the underlying heart disease or a coexisting illness,” the researchers wrote.

But Healey and Connolly said that should not be surprising. “In severe chronic conditions, most worthwhile interventions only modestly delay death,” they wrote.