As many as 28,000 people with implanted heart pacemakers made by Guidant Corp. may need to have them replaced because of recently discovered defects, the company said yesterday. It was the second major safety alert from the medical device maker in the past month.

The announcement that thousands of people could face unexpected surgery to replace their pacemakers came on the same day that the Institute of Medicine issued a stinging report that criticized the Food and Drug Administration's monitoring of medical device safety as inadequate and in need of significant congressional reform.

The report found that the agency lacks the authority to demand that manufacturers do follow-up studies of widely used devices and has no way of determining whether promised safety studies are actually done or of informing consumers of the results.

"We were asked to take a look at the system . . . and we found that such a system needs to be built," said committee Chairman Hugh Tilson, a professor and senior adviser to the dean of the University of North Carolina School of Public Health. "We found numerous areas where substantial improvement could be made."

The Guidant alert for its pacemakers underscored the message of the study by the institute, a branch of the National Academies. The problems reported yesterday were in pacemakers implanted between 1997 and 2000 and followed by one month a safety warning involving another Guidant product -- about 109,000 implanted defibrillators. But unlike that recall, yesterday's announcement explicitly warned doctors that the pacemakers might need to be replaced.

The company said that it had reports of 69 failures in nine models of its pacemakers and that several patients lost consciousness or developed possible heart failure. One person, the Guidant statement said, might have died as a result, but the device was not returned for testing and the company could not confirm that the pacemaker was responsible.

Guidant said the problem resulted from gradual degrading of a seal in the pacemakers, which allowed a higher than normal amount of moisture to enter. The company said that about 28,000 of the 78,000 questionable implanted pacemakers are still in use and that about 18,000 are in the United States. Sales of the nine models were discontinued in 2000.

Since the arthritis painkiller Vioxx was abruptly removed from the market last fall because of evidence of potentially deadly cardiovascular side effects, the FDA has been sharply criticized for its safety monitoring and has faced pressure to upgrade its efforts. The agency has implemented a number of internal changes to try to improve its safety record, and last fall it asked the Institute of Medicine to do a full review of its drug safety policies.

The report released yesterday was requested by Congress in 2002, when medical device regulations were updated and device makers were required to pay user fees to finance a review and approval similar to the one implemented for new drug approvals a decade earlier. Congress initially asked for a report on the FDA's safety monitoring of medical devices for children, but the Institute of Medicine team found so little information on that subject that it decided to expand its review to the post-market surveillance of all medical devices.

"The most obvious deficits in FDA's performance are the agency's lack of effective procedures for monitoring the status of required post market studies and the lack of public information regarding such studies," the report said. It recommended that the agency establish a system for monitoring and publicly reporting all post-market studies -- those mandated by the FDA as well as voluntary ones negotiated by the FDA and manufacturers as part of the approval system.

The report also recommended that Congress give the agency authority to require far more post-market studies. Under current rules, many simpler devices (such as baby bottle nipples) are never evaluated by the FDA or are cleared for use with limited review. Only the most complicated devices, such as pacemakers, are subject to required full testing and approval. About 80,000 medical devices are in use in the United States.

When the agency does mandate a post-market study, the study cannot last more than three years. The institute report said that the FDA should be allowed to order post-market studies of simpler products as well as those put through a more rigorous review and that the three-year limitation should be eliminated -- especially in devices used by growing children.

The organization that represents most big device makers, the Advanced Medical Technology Association (AdvaMed), declined to comment on the report yesterday. When it testified in August before the IOM panel, it said that, "in general, AdvaMed believes FDA has strong and ample statutory and regulatory authority to obtain required medical device reporting of all adverse events." But the trade group also said the system for reporting problems involving medical devices remains incomplete.

Because doctors are not required to report harmful side effects from drugs or medical devices, authorities learn of only an estimated one-tenth of the actual problems and failures. The IOM report, for instance, said manufacturers reported 980 device-related deaths in 1998, while doctors and hospitals reported only 277.

The IOM panel said large computerized databases from health maintenance organizations, hospitals and other providers hold the promise of giving much broader and more immediate safety information on drugs and devices. But it said the system for computer coding of device records remains far behind the one for drugs.

The FDA is running a pilot program to more aggressively collect information about device failures and adverse events.

The Medical Product Surveillance Network (MedSun) collects information from 300 medical facilities, including 20 children's hospitals.