TUESDAY, April 25 (HealthDay News) — The reliability of implanted cardiac pacemakers and defibrillators is getting better, but there’s still room for improvement, two new studies find.

Reliability is an important issue for the hundreds of thousands of Americans walking around with either a pacemaker — designed to keep the heart beating regularly — or a defibrillator — a device that delivers a shock to restart a malfunctioning heart.

One study examined data supplied by device manufacturers to the U.S. Food and Drug Administration from 1990 to 2002, a period when 2.25 million pacemakers and 415,780 defibrillators were implanted in Americans. During that time, 8,834 pacemakers and 8,489 defibrillators were removed because they malfunctioned. The higher percentage rate of defibrillator malfunction was predictable because they are more complex devices than pacemakers, said study author Dr. William H. Maisel, director of the pacemaker and device service at Beth Israel Deaconess Medical Center, in Boston.

The second study, which reviewed data from three registries from North America, Denmark and the United Kingdom, found similar malfunction rates. But the important information concerns the changes over time, and “the results are mixed,” said Maisel, who authored the second study as well.

“Data from both of these studies suggest that pacemaker reliability has improved considerably since the 1980s, and that it continued to improve in the 1990s,” Maisel said. “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.”

The companies results of both studies appear in the April 26 issue of the Journal of the American Medical Association.

The results, he said, “suggest that an ongoing monitoring of device performance is needed. 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.

However, one factor to consider when an implanted defibrillator acts up is the possibility of complications when replacement surgery is done, according to another report in the same issue of the journal.

Data on 533 patients who underwent replacement surgery found that 43 of them — 8.1 percent — had complications in the following three months. Two patients died of infections after surgery.

“Before this, there was very little information about the risk of having a replacement operation done,” said study leader Dr. Andrew D. Krahn, a professor of cardiology at the University of Western Ontario. “The high complication rate we reported indicates that when a decision is made on leaving things alone or intervening, the risk of intervening is higher than expected.”

The reliability of pacemakers and defibrillators became headline news last year, first when the Guidant Corp. issued an alert saying that about 28,000 pacemakers had defects that could make them malfunction, then when it was revealed that the company had decided not to issue alerts about life-threatening defects in some of its implanted defibrillators. The U.S. Food and Drug Administration then said it would strengthen its oversight of such heart devices.

Before that recent publicity about device malfunctions, “if you had asked physicians or patients what they thought the chance was of device malfunction, they would have been wrong by a factor of 100,” Maisel said. “They thought the devices were 100 times more reliable than they really are.”

His study found the annual replacement rate for pacemakers in the United States due to malfunction was 4.6 per 1,000 implants. For defi