CHICAGO, July 24 (Reuters) - Researchers toting up the pluses and minuses of implanting defibrillators in the chests of people with a potentially fatal heart defect said on Tuesday the devices can save lives, but can also deliver unnecessary jolts and expose patients to deadly risks.

An estimated 500,000 Americans were born with a genetic heart defect that causes a condition called hypertrophic cardiomyopathy, or HCM.

HCM can cause the heart to beat abnormally and damage the heart muscle which, in up to 5 percent of cases, can lead to a sudden, fatal heart attack, the researchers said. It is one of the most common causes of death in young people, including trained athletes.

In a global study of 506 patients described as "high risk" who had been implanted with defibrillators, one in five received shocks that likely saved their lives, according to author Dr. Barry Maron and colleagues at the Minneapolis Heart Institute Foundation.

Another 27 percent of the patients received unnecessary shocks from their devices, while a number developed dangerous side effects: nearly 4 percent suffered infections, 2 percent developed hemorrhaging or blood clots and 7 percent had mechanical problems with the device.

One patient was killed by a faulty device.

"The device may not activate for up to 10 years, but when it does, it does," Maron wrote in the Journal of the American Medical Association.

Maron was a key whistle-blower in identifying defective defibrillators, and testified last year to a U.S. congressional committee on the subject.

DILEMMA

Doctors and patients with HCM have struggled over how to weigh risk factors when deciding whether to implant a defibrillator.

There are wide variations in the severity of the condition, and a majority of people are unaware they have it, researchers said. It can be detected with an electrocardiogram test but even that can be controversial when a star athlete is suspected of having HCM.

Young people with HCM who get a defibrillator face a lifetime of follow-up operations to replace devices that wear out. Electric leads from the device are threaded through blood vessels to the heart, and those can cause damage by fracturing or forming scar tissue, said Dr. Robert Schweikert of the Cleveland Clinic.

Schweikert did not participate in the study, which was partly funded by defibrillator manufacturer Medtronic Inc., but he commented on the findings in a telephone interview.

Among the risk factors to consider before implanting a defibrillator are whether a close relative died from HCM before age 50, bouts of rapid heartbeat, enlargement of the heart, thickening of the heart's walls and fainting spells.

Schweikert said further examination of the risk factors and how they interact is essential in understanding HCM and deciding the best treatment.

Maron noted in the study that erring on the side of caution by implanting a defibrillator protectively could provide "reassurance" which is a "psychological benefit," while potentially limiting job prospects and quality of life.

REUTERS