Washington, DC - Although still extremely rare, the rate of implantable cardioverter-defibrillator (ICD) malfunctions has risen in recent years. In contrast, pacemaker malfunctions have been decreasing. The experts can't fully explain the finding. The data were presented at the Policy Conference on Pacemaker and ICD Performance, jointly sponsored by the Food and Drug Administration (FDA) and the Heart Rhythm Society [1].

The study was conducted by officials at the FDA and by Dr William Maisel (Beth Israel Deaconess Medical Center, Boston, MA). While working on the report, Maisel served as a special government employee. The study, which was initiated in 2003, was not performed in response to the recent round of ICD recalls, the FDA said.

According to the study, between 1990 and 2002 approximately 2.25 million pacemakers and 416 000 ICDs were implanted in the US. The replacement rate for malfunctioning ICDs was substantially higher than that for pacemakers. Nearly 80% of the malfunctions for both pacemakers and ICDs were caused by a hardware malfunction, and most of these resulted from an electrical malfunction or a battery/capacitor malfunction.

Over the course of the study, the rate of malfunction for pacemakers declined. In contrast, the rate for ICDs, after starting to decline during the early 1990s, increased significantly during the second half of the study. More than half the ICD malfunctions occurred in the final three years of the study, according to an FDA press release. Maisel said the pattern in the FDA data was similar to the pattern found in a meta-analysis of non-FDA published registries.

In his concluding remarks, Maisel noted that despite the malfunctions, his study found that "pacemakers and ICDs have saved countless lives and remain an important therapy for patients with or at risk for life-threatening arrhythmias."

The explanation for the discrepancy between pacemakers and ICDs is not known. In a prepared statement, the FDA speculated about the reasons: "The increase may be partially attributable to the fact that ICDs are a rapidly changing technology. Over the past 10 years, ICDs have shrunk in size, maintained their high-energy output, provided more therapeutic features (such as the addition of dual chamber pacing), and increased their memory. The decrease in size, in particular, has necessitated modifications to battery, capacitor, and circuitry design that may account for some of the observed malfunctions."

In a prepared statement, the FDA said it was considering a number of steps to improve regulation of these devices, including better coordination of pre- and postmarket regulation of the devices, requiring more comprehensive data from manufacturers, and improving its communication with physicians and patients when devices malfunction.