Safety and Efficacy of a Totally Subcutaneous Implantable-Cardioverter Defibrillator

Study Questions:

How safe and effective are totally subcutaneous implantable cardioverter-defibrillators (S-ICDs)?


This was a prospective, nonrandomized, multicenter trial that included adult patients with a standard indication for an ICD, who neither required pacing nor had documented pace terminable ventricular tachycardia (VT). The primary safety endpoint was the 180-day S-ICD System complication-free rate compared with a prespecified performance goal of 79%. The primary effectiveness endpoint was the induced ventricular fibrillation (VF) conversion rate compared with a prespecified performance goal of 88%, with success defined as two consecutive VF conversions of four attempts. Detection and conversion of spontaneous episodes were also evaluated.


Device implantation was attempted in 321 of 330 enrolled patients, and 314 patients underwent successful implantation. The cohort was followed for a mean duration of 11 months. The study population was 74% male with a mean age of 52 ± 16 years and mean left ventricular ejection fraction of 36 ± 16%. A previous transvenous ICD had been implanted in 13%. Both primary endpoints were met: The 180-day system complication-free rate was 99%, and sensitivity analysis of the acute VF conversion rate was >90% in the entire cohort. There were 38 discrete spontaneous episodes of VT/VF recorded in 21 patients (6.7%), all of which successfully converted. Forty-one patients (13.1%) received an inappropriate shock.


The authors concluded that the findings support the efficacy and safety of the S-ICD System for the treatment of life-threatening ventricular arrhythmias.


Totally subcutaneous ICD appears effective in terminating both induced and spontaneous VT/ VF. Advantages of S-ICD include making fluoroscopy unnecessary for implantation and avoidance of intravenous lead complications. This may be especially appealing to younger patients who have a higher likelihood of revisions with a conventional transvenous system, and in patients on hemodialysis who may have access issues. Lack of painless antitachycardia pacing therapy, however, is a major disadvantage of S-ICD. Long charge time of about 20 seconds in order to deliver an 80 Joule shock is less of an issue in the era of prolonged detection time to avoid unnecessary shocks.

Clinical Topics: Arrhythmias and Clinical EP, Noninvasive Imaging, Implantable Devices, SCD/Ventricular Arrhythmias, Atrial Fibrillation/Supraventricular Arrhythmias, Nuclear Imaging

Keywords: Prostheses and Implants, Renal Dialysis, Defibrillators, Fluoroscopy, Shock, Ventricular Fibrillation, Stroke Volume, Pacemaker, Artificial, Tachycardia

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