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Implanted Defibrillators Are Getting Better

Failure rates are falling, but one expert also sees flaws in a new study

FRIDAY, May 11, 2007 (HealthDay News) -- Implanted defibrillators, which deliver occasional jolts to the heart to keep it beating regularly, are becoming much more reliable, experts report.

"What really sticks out is the continuous improvement and the fact that we see a very low level of electronic failure," said Dr. Robert J. Hauser, a senior cardiac consultant at the Minneapolis Heart Institute, who led a study of the devices made by three American manufacturers.

His team was expected to present its findings Thursday at the annual meeting of the Heart Rhythm Society, in Denver.

"We've been collecting data for eight years, only failure data, and the devices removed from service in 2004-2006 were fewer than for those removed in 2000-2003," Hauser said. "That was true of all three manufacturers. They are failing less often, and fewer patients are experiencing adverse events due to ICD [implantable cardioverter defibrillator] failure."

In 2000-2003, 48 of 708 single-chamber defibrillators implanted were replaced for electronic and housing defects; in 2004-2006 there were just 3 such replacements of 244 devices for those defects. In 2000-2003, 27 of 179 dual-chamber devices failed versus 3 of 265 such devices in 2004-2006.

"What we are seeing is continuous improvement in the life of these devices," Hauser said. "There is improvement in the technology and also in the quality insurance process."

An ICD registry has been developed that requires listing of all hospitals in the United States, noted Dr. Stephen Hammill, professor of medicine at the Mayo Clinic and past president of the Heart Rhythm Society. Some 120,000 patients have already been registered, and 10,000 more register each month, he said.

"Two numbers stand out for me," Hammill said. "The first is improved longevity, by 36 percent. That is dramatic, because it means the device is in longer, [meaning] more cost-effective use. The second is the number of failures, down from 35 to 9, so it confirms the devices are improving. We saw the same thing with pacemakers. Defibrillators are more complex devices, which have to deliver a shock without disrupting the device. This is a report showing that these devices are improving over time."

One expert was a little more skeptical.

Dr. William H. Maisel, director of the pacemaker and defibrillator service at Beth Israel Deaconess Hospital, Boston, said that, "You can't really talk about the longevity of the devices implanted in 2004-2006," because not enough time has passed to judge them.

The report also does not include devices that are removed because of advisories issued by the manufacturers, Maisel noted. About 17 percent of the devices are removed early because of advisories, he said.

"So, one in six needs replacement early," Maisel said. "For single-chamber devices, there is the select group that is lucky enough not to have advisories. The manufacturers say they last five to seven years."

There has been progress but not as much as could be desired, Maisel concluded. "There is a mixed message," he said. "Certainly, the more modern devices implanted in the late 1990s and early 2000s appear better than the earlier generation. But we still don't know how well the modern devices implanted this year or last will do."

More information

The basics of ICDs are explained by the American Heart Association.

SOURCES: Robert J. Hauser, M.D., senior cardiac consultant, Minneapolis Heart Institute; Stephen Hammill, M.D., professor, medicine, Mayo Clinic, Rochester, Minn; William H. Maisel, M.D., director, pacemaker and defibrillator service, Beth Israel Deaconess Hospital, Boston; May 10, 2007, Heart Rhythm Society scientific sessions, Denver
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