Electric shocks delivered by subcutaneous defibrillators are equally effective as shocks delivered by conventional transvenous defibrillators, according to a new study.

Researchers at Academic Medical Center (AMC; Amsterdam, The Netherlands), Emory University (Atlanta, GA, USA), Maastricht University Medical Center (MUMC; The Netherlands), and other institutions conducted a study of 849 patients in 39 centers, who were randomized to receive a subcutaneous implantable cardioverter-defibrillator (S-ICD) or a transvenous ICD (TV-ICD). ICD therapy was defined as therapy for ventricular arrhythmias, classified as discrete episodes and storm episodes.

The results showed that in the S-ICD group, 86 patients had a total of 256 episodes with appropriate ICD therapy, versus 78 patients in the TV-ICD group, with 348 episodes. There were no statistical differences in the number of patients with appropriate therapy between groups, although patients in the subcutaneous ICD group had a higher risk of shocks overall. A higher incidence of electrical storms was seen in the TV-ICD group. The study was published on November 14, 2021, in Circulation.

“For typical arrhythmias, S-ICDs are a reasonable alternative to transvenous defibrillators, which are not compatible with all patients,” said study co-author Alexandru Chicos, MD, of AMC. “They seem to be associated with a higher risk of appropriate and inappropriate shocks, but they avoid long-term intravascular hardware and potential complications associated with it. Technology under development may bring the capability of anti-tachycardia pacing to the subcutaneous defibrillator systems.”

An ICD resynchronizes the beating of the heart's lower chambers (ventricles), which often beat out of sync in heart failure patients, and provides back up treatment for sudden cardiac death (SCD). 

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