Seven percent of patients implanted with subcutaneous implantable cardioverter-defibrillators (S-ICDs) experienced inappropriate shocks, according to an analysis of registry data presented May 9 at the Heart Rhythm Society (HRS) scientific sessions in Denver.

S-ICDs were approved by the FDA in October 2012 for the treatment of life-threatening ventricular tachyarrhythmias. The system uses leads implanted subcutaneously rather than connected into the heart, which potentially extends lead longevity and reduces lead-related complications. It is intended to provide defibrillation therapy in patients who do not have symptomatic bradycardia, incessant ventricular tachycardia, or spontaneous, frequently recurring ventricular tachycardia that is reliably terminated with antitachycardia pacing.

Louise R.A. Olde Nordkamp, MD, of the Academic Medical Center in Amsterdam, the Netherlands, and colleagues reported in 2012 that S-ICDs effectively terminated ventricular arrhythmias but 13 percent of the 118 Dutch patients in their study received inappropriate shocks. At HRS.13, they offered results from an analysis of the EFFORTLESS S-ICD Registry, which contains data from hospitals in Europe and New Zealand on implantation and 60-month follow-up.

They focused on inappropriate shock-related incidence, predictors and therapy. Of the 369 S-ICD patients in the analysis, 7 percent experienced a total of 37 inappropriate shocks during a 15-month follow-up. Cardiac signal oversensing accounted for 62 percent of the inappropriate shocks. Eight shocks were on supraventricular tachycardias in the shock-only rate zone; none were in the discrimination zone.

Men and patients with nonischemic disease were more likely to experience inappropriate shocks, according to the analysis. In most cases, a change in programming, often by changing the sensing vector, resolved the inappropriate shock issue.

The study was presented as an abstract.