Implanted Defibrillators: How Well Do They Work?

August 27, 2001

The implanted cardioverter defibrillator or I.C.D., a medical device that's become widely known due its use by Vice President Dick Cheney, saves lives most often in the sickest of patients, according to new research by the University of Rochester Medical Center. The results of the study, to be published in the Sept. 1, 2001, edition of the American Journal of Cardiology, represent a change in conventional thinking about how to treat severe heart disease, says Arthur J. Moss, M.D., lead author of the study and a professor of Medicine at the UR Medical Center. It had been believed that most patients who die of heart disease suffer from a progressive failure of the organ; the heart simply tires and stops pumping. In that type of case, an I.C.D. would not be a valuable treatment. However, more often patients die from an abrupt malfunction of the heart rhythm - a condition that can be treated by an implantable defibrillator, the study found. An I.C.D. monitors electrical signals in the body and detects abnormal heartbeats. It acts within seconds to shock the heart back into a normal rhythm, and if needed can deliver a more powerful jolt to take the place of an external defibrillator "The bottom line is that the sickest patients receive the most benefits from I.C.Ds.," Moss says. "The other side of that coin is that patients with chronic disease, who still have relatively good heart function, are not helped by defibrillators. This is important to note in that the number of new I.C.D. implants is increasing at a rate of more than 20 percent a year." The study evaluated 196 patients at medical centers across the country, who had previously suffered at least one heart attack. The researchers set out to investigate the life-saving features of the defibrillator in relation to the severity of the patients' heart problems. The patients were separated into high-risk and low-risk groups, and then monitored for an average of about two years. Moss became one of the country's leading experts in implantable defibrillators as a result of previous research he published in 1996 in the New England Journal of Medicine, which helped lay the foundation for cardiologists who were trying to decide if an I.C.D. would help high-risk patients. Although I.C.Ds have been used since the 1980s, the 1996 study was the first to formally prove its live-saving attributes. Cheney's physicians consulted Moss before they decided to implant the device in the Vice President. Use of the device - as well as general standards in cardiac care - have been in the public eye because of Cheney's condition. More than 150,000 patients worldwide are using implanted defibrillators; about 50,000 new devices were implanted in the past year, Moss estimates. "The implantable defibrillator saves lives," Moss says, "and its current use is the outgrowth of basic biomedical research and clinical investigation that has taken place during the past 20 years." Funding for the research came from CPI Guidant Corp., of St. Paul, Minn., and a maker of cardiovascular medical products, including implantable defibrillators.

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