Study tracks malfunctions of heart devices

Defibrillator diagram
A diagram showing how a defibrillator works.
Image courtesy of Guidant Corp.

Pacemakers and defibrillators are credited with saving countless lives among the millions of people who have them throughout the world. But occasionally they fail.

Device manufacturers are required to report those failures to the FDA each year. But despite that reporting, the agency knew very little about actual device reliability. Dr. William Maisel from Harvard Medical School was hired to analyze the FDA data.

Maisel examined FDA records from 1990 to 2002, a period when more than two million pacemakers and more than 400,000 defibrillators were implanted in patients in the U.S. Malfunctions occurred in more than 17,000 cases. Sixty-one patients died as a result of device failure.

How a pacemaker works
This diagram shows how a dual-chamber pacemaker is inserted into a patient's chest.
Image courtesy of Ohio State University Medical Center

Mathematically speaking, Maisel says that's not a huge failure rate. But he says it's still troubling because the number of defibrillator malfunctions grew markedly in the later years of the study.

"The peak year of malfunctions, 2001, the rates were between two and 3-percent for the failure rates for defibrillators. That's a three-fold increase in the failure rate just over a four-year period," he says.

That means out of every 1000 defibrillators, an average of 36.4 failed in 2001, compared to only 7.9 failures in 1996.

"It is significant," Maisel says. "When a device like this fails, because the device is designed to be life-saving, the only solution typically is to replace the device which requires a minor surgical procedure, but surgery non-the-less."

Manufacturers reported various issues with their devices ranging from software problems to manufacturing errors. But Maisel says most malfunctions were attributed to hardware problems. "Battery, capacitor and electrical abnormalities accounted for about half of the observed malfunctions," he says.

A cardiac defibrillator manufactured by Medtronic.
Photo courtesy of Medtronic

Maisel says it's not clear why there were more electrical problems toward the end of the study, but he suspects it has to do with some of the changes made to defibrillators in those years.

"It's speculation, but during that same time period these defibrillators became increasingly complex," he says. "The amount of memory increased. The circuitry became increasingly complex. The devices decreased significantly in size. And it would appear that increased complexity was transiently associated with a decrease in device reliability."

In contrast to the defibrillators, the number of pacemaker malfunctions decreased steadily over the course of the study period. Maisel suspects that's because pacemakers are a more mature technology. They've been around 20 years longer than defibrillators and pacemakers are less complex.

The findings are published in the latest edition of the "Journal of the American Medical Association."

In a companion editorial in JAMA, Cleveland Clinic cardiologist Dr. Bruce Wilkoff says Maisel's data is important and should be taken into consideration by doctors and patients. But he worries some might over-react and conclude that the defibrillators are too risky. Wilkoff says that would be a mistake.

A cardiac defibrillator manufactured by Guidant Corp.
Photo courtesy of Guidant Corp.

"It's not perfect. It still works. And, it's still the right thing to do. But, there's a cost," he says.

Wilkoff has done consulting work for the country's three largest defibrillator and pacemaker manufacturers, including Minnesota-based Medtronic and St. Jude Medical and Boston Scientific's recent acquisition, Guidant, whose cardiac rhythm management operation is based in Arden Hills.

Wilkoff predicts defibrillator reliability will improve significantly in time. But he says patients need to be more realistic about what's possible.

"There will always be some malfunction. There will always be a substantial enough rate, that you're going to have to talk about it and consider it," he says.

In the past year, some Guidant defibrillators were involved in major product recalls that resulted in hundreds of patient lawsuits against the company.

But the trade group that represents device makers, AdvaMed, says the industry as a whole has made great improvements in its reliability rates since the study period. Its own analysis of recent FDA malfunction data shows that overall defibrillator malfunction rates fell to just 1-percent last year.

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