Millions of people with abnormal heart rhythms have received pacemakers and implantable cardioverter-defibrillators (ICDs) . These devices are inserted under the skin and attached to the heart to stabilize heart rhythms. Both pacemakers and ICDS are proven to reduce the risk of death in people with life-threatening heart rhythm abnormalities, but there is little evidence about their reliability.

Two studies in the April 26, 2006 issue of the Journal of the American Medical Association found that while pacemakers have become increasingly reliable in recent years, ICDs may have become less reliable.

About the Study

In the first study, researchers analyzed annual reports submitted to the Food and Drug Administration (FDA) by pacemaker and ICD manufacturers. These reports include the number of device implants and any reported malfunctions between 1990 and 2002. During this time, 2.5 million pacemakers and 416,000 ICDs were implanted in the US.

During the study period, 8,834 pacemakers and 8,489 ICDs were surgically removed due to confirmed malfunction. The annual pacemaker malfunction rate decreased during the study, from a high of 9.0 malfunctions per 1,000 implants in 1993 to a low of 1.4 per 1,000 implants in 2002. The ICD malfunction rate, however, increased in the second half of the study, from 7.9 malfunctions per 1,000 implants in 1996 to 26.4 per 1,000 implants in 2001.

The second study evaluated three large registries that monitored the performance of 475,618 pacemakers and 20,633 ICDs implanted from 1983-2004. During this time, 2,981 pacemakers and 384 ICDs malfunctioned. While pacemaker malfunction rate improved markedly during the study, ICD malfunction rate increased more than four-fold from 1998-2002 before decreasing substantially in 2003-2004.

In both studies, the most common reason for device failure was battery malfunction.

The results of these studies were limited because it is likely that not all device malfunctions were reported, or that there were inconsistencies in the reporting of malfunctions.

How Does This Affect You?

Do these studies question the wisdom of routinely using pacemakers and ICDs in people with life-threatening heart rhythm abnormalities? Absolutely not. While the studies did show that device malfunctioning is not uncommon and that the reliability of ICDs may have decreased in recent years, these risks are far outweighed by the benefits of pacemakers and ICDs. These devices can dramatically prolong the lives of the people who receive them.

The most likely reason that ICDs have become less reliable in recent years is that the technology advanced dramatically during the 1990s (e.g., memory increased, device size decreased). These improvements may have caused the devices to become more vulnerable to malfunction. But it is promising that the malfunction rate decreased more recently. Further improvements in technology along with advanced ways to monitor device performance (e.g., wireless monitoring, monitoring via the Internet) are needed to improve reliability. In the meantime, if you have a pacemaker or ICD, the best way to monitor its performance is to schedule regular checks with your doctor.