ICD's shock history may inform next steps after battery fades

For patients who received no shocks from an implantable cardioverter-defibrillator (ICD) before the end of its battery life, it may be worth considering a new risk-benefit analysis.

In a study published online in the December issue of the Journal of the American Heart Association, Faisal M. Merchant, MD, of the Emory University School of Medicine in Atlanta, and colleagues assessed incidence of defibrillator shocks before and following the first replacement of the device’s generator. Merchant and colleagues accessed data through the National Cardiovascular Data Registry on devices on the Latitude remote monitoring system (Boston Scientific).

Patients undergoing elective battery/generator replacement (24,203 patients) between 2000 and 2009 were included in this study. Cardiac resynchronization therapy-defibrillators (CRT-D) comprised 42.1 percent of devices. Dual-chamber ICDs made up 35.1 percent of devices, while single-chamber devices encompassed 22.8 percent of implants.

From this, they derived two groups: the first group (A) received no shocks over the first battery life (67 percent of patients), the second (B) received at least one shock from their implanted device over the same battery period (33 percent).

They found that among patients who had no shocks in the first round of ICD battery life, the incidence of being shocked in the second was far lower than those who had previously received ICD shocks. Over an average of almost two years, patients in group A received less than a third as many shocks as those in group B (9.9 percent vs. 27.7 percent). At five years after generator replacement, the rate of shocks in group A was half what it was in group B (25.7 percent vs. 51.1 percent).

Shocks for detection of rates below 200 bpm among group A comprised of 6 percent, 9.2 percent and 17.1 percent for periods of nearly two years, three years and five years, respectively. In group B, shocks for detection of rates above 200 bpm occurred at 18.6 percent, 24.3 percent and 33.3 percent for the same periods.

In group A, single-chamber, dual chamber and CRT-D devices had cumulative ICD shock rates of 11 percent, 10 percent and 10 percent at a mean follow-up of almost two years. Observing differences between highest and lowest risk of shock, single-chamber devices had a higher cumulative hazard rate than CRT-D devices, around 1.14. CRT-D had a higher cumulative rate at almost two years in group B (32 percent), with single chamber (31 percent) and dual chamber (28 percent) coming in thereafter. The data showed significant differences between cumulative shock hazard rates in patients with CRT-D (most shocks) over the least amount of group B shocks, dual chamber, around 1.18.

Merchant et al expressed concern for procedural risk to patients who had not received shocks over the first battery life against future benefits from elective replacement. They noted these patients are generally older and in poorer health than they were at the time of the initial implant.

Merchant et al wrote, “Given the shorter life expectancy, higher prevalence of comorbidities, and significant risk of peri-procedural complications among patients undergoing GE [generator exchange], it is conceivable that for many patients who reach the end of first battery life without having received ICD shocks, the risk–benefit analysis of proceeding with GE may no longer favor continued ICD therapy for primary prevention.”

They recommended careful consideration and informed discussion between patient and provider before performing elective generator replacement and suggested that the data from their study, as with others, may aid in that discussion.