Inspite of the reliability of implanted cardiac pacemakers and defibrillators having improved studies have shown that these devices still tended to malfunction at times.

For the thousands of Americans who depend on the pacemaker or the defibrillator reliability of these devices is an important issue. The pacemaker’s job is to keep the heart beating regularly whereas the defibrillator delivers a shock to restart a malfunctioning heart.

Dr. William H. Maisel, director of the pacemaker and device service at Beth Israel Deaconess Medical Center, in Boston authored two studies in this regard. The results of the studies have been published in the April 26 issue of the Journal of the American Medical Association.

One study examined data supplied by device manufacturers to the U.S. Food and Drug Administration from 1990 to 2002 during which 2.25 million pacemakers and 415,780 defibrillators were implanted in Americans. Data has revealed that 8,834 pacemakers and 8,489 defibrillators were removed because they malfunctioned.

The second study, reviewed data from three registries from North America, Denmark and the United Kingdom and found similar malfunction rates.

The studies have indicated that pacemaker reliability has improved considerably since the 1980s, and that it continued to improve in the 1990s. On the other hand defibrillator reliability decreased from 1998 to 2002, when there was an increase in the number and rate of malfunctions, but then declined again down to the lowest levels in the past decade.

Of course the possibility of complications during a replacement surgery is an important factor to be considered during malfunctioning of an implanted defibrillator acts up. Data on 533 patients who underwent replacement surgery found that 43 of them had complications in the following three months. Two patients died of infections after surgery.

The somewhat unpredictability of pacemakers and defibrillators first became headline news when the Guidant Corp. issued an alert saying that about 28,000 pacemakers had defects that could make them malfunction. In addition it was revealed that the company had decided not to issue alerts about life-threatening defects in some of its implanted defibrillators. Since then the U.S. Food and Drug Administration has increased its watch of such heart devices.

Maisel’s study found the annual replacement rate for pacemakers in the United States due to malfunction was 4.6 per 1,000 implants. For defibrillators, the rate was 20.7 per 1,000 implants. The annual replacement rate for pacemakers decreased steadily over the years, while the defibrillator replacement rate decreased from 1993 to 1996, and then rose sharply. More than half the defibrillator malfunctions occurred in the last three years of the study.

There were 30 deaths attributed to device failure from 1990 to 2002 among pacemaker patients and 31 among the much smaller number of defibrillator patients.

According to Maisel the study only calls for an ongoing monitoring of device performance. Industry needs to be reporting device performance in a more timely fashion, informing physicians and patients of malfunction.

At the same time, people who have the devices implanted need to have "a more realistic expectation of device performance," Maisel said.