Studies show improving pacemaker reliability, increased implantable defibrillator failure ratesBOSTON – Pacemakers and implantable cardioverter-defibrillators (ICDs) are among the most clinically important and technically complex medical devices in use today, but several recent high-profile device malfunctions have called into question their safety and reliability. Two reports in the April 26, 2006 issue of The Journal of the American Medical Association (JAMA) offer new insights into pacemaker and ICD performance by providing the most comprehensive analysis of malfunction data available to date.
"Despite millions of pacemaker and ICD implants worldwide and their increasingly frequent use, surprisingly little is known about device reliability," says the studies' lead author William H. Maisel, MD, MPH, director of the Pacemaker and Device Service at Beth Israel Deaconess Medical Center (BIDMC) and Assistant Professor of Medicine at Harvard Medical School. The devices work to stabilize abnormal heart rhythms, pacemakers by treating hearts that beat too slowly and ICDs by treating heart rhythms that have become dangerously fast.
In the first study, which Maisel performed with colleagues at the U.S. Food and Drug Administration (FDA), he found that, between the years of 1990 and 2002, there were 2.25 million pacemakers and almost 416,000 ICDS implanted in the U.S. During this same time period, 17,323 devices (8,834 pacemakers and 8,489 ICDs) were surgically removed from patients due to a confirmed device malfunction. (Battery, capacitor and electrical abnormalities accounted for approximately half of the device failures.) In addition, 61 patient deaths were attributed to pacemaker or ICD malfunction during this 13-year period.
"Overall, the annual ICD malfunction replacement rate of 20.7 per 1,000 implants was significantly higher than the pacemaker malfunction replacement rate of 4.6 per 1,000 implants," notes Maisel. "While pacemakers became increasingly reliable during the study period, a marked increase in the ICD malfunction replacement rate was observed between 1998 and 2002, suggesting that ICDs may have become less reliable during this time period."
In the second study (conducted by Maisel on non-FDA data), an analysis of international pacemaker and ICD registries involving hundreds of thousands of pacemakers and thousands of ICDs, the overall findings proved very similar to those reported in the analysis of the FDA data.
"Specifically, in this second report, pacemaker reliability improved markedly during the study period while the ICD malfunction rate trended down during the first half of the 1990s, reaching its lowest level in the mid-to-late 1990s. And, once again, the ICD malfunction rate increased substantially between the years of 1998 and 2002." But, he adds, this analysis showed a substantial improvement in ICD reliability in 2003 and 2004, years that were not included in the FDA analysis.
"Pacemakers and implantable defibrillators are amazing devices that have saved many lives," says Maisel. "But like any other complex device, they can and do malfunction. It appears that as ICDs became increasingly sophisticated [in the latter 1990s] there was an associated decrease in device reliability. Fortunately, the most recent defibrillator malfunction rates show a reassuring trend."
Maisel stresses that patients do not need to take any action as a result of these studies, and that routine pacemaker and defibrillator checks remain the best way to monitor device performance in individual patients.
"It's important to remember that during the time periods we analyzed, there were tens of thousands of lives saved as a result of these devices," he adds. "The chance of a person's life being saved by a pacemaker or ICD is about 1,000 times greater than the chance of the device failing when it's needed."
The analysis of FDA data (first study) was funded by the U.S. Food and Drug Administration, for which Maisel serves as a paid consultant and Chair of the FDA Circulatory System Medical Devices Advisory Panel. Study coauthors included Megan Moynahan, MS, Bram D. Zuckerman, MD, Thomas P. Gross, MD, MPH, Oscar H. Tovar, MD, Donna-Bea Tillman, PhD, MPA, and Daniel B. Schultz, MD, all of the FDA's Center for Devices and Radiologic Health, Rockville, MD.
The analysis of registry data (second study) was conducted independently by Dr. Maisel without FDA financial support.
Beth Israel Deaconess Medical Center is a patient care, research and teaching affiliate of Harvard Medical School and ranks fourth in National Institutes of Health funding among independent hospitals nationwide. BIDMC is clinically affiliated with the Joslin Diabetes Center and is a research partner of the Dana-Farber/Harvard Cancer Center. BIDMC is the official hospital of the Boston Red Sox. For more information, visit www.bidmc.harvard.edu.
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