Shock efficacy of subcutaneous implantable cardioverter-defibrillator for prevention of sudden cardiac death: initial multicenter experience.

BACKGROUND Recently, subcutaneous implantable cardioverter-defibrillator (S-ICD) has become available. The aim of our study was to assess the efficacy of S-ICD in a clinical setting. METHODS AND RESULTS Between June 2010 and July 2011, 40 consecutive patients (42 ± 15 years; body mass index, 27 ± 6 kg/m(2); left ventricular ejection fraction, 47 ± 15%; 28 men) received an S-ICD for primary (n=17) or secondary prevention (n=23 [58%]) at 3 institutions in Germany. Intraoperative defibrillation efficacy testing failed in 1 patient with severely reduced left ventricular ejection fraction; testing was effective in all other patients. All episodes stored in the S-ICD were analyzed for appropriate and inappropriate detection, as well as effective shock delivery to convert ventricular tachyarrhythmia into sinus rhythm. During a median follow-up of 229 (interquartile range, 116-305) days, 4 patients experienced 21 episodes, with correct detection of ventricular tachyarrhythmia and subsequent shock therapy. A total of 28 shocks were delivered in these 4 patients. Mixed logistic regression modeling revealed a shock efficacy of 96.4% (95% CI, 12.8%-100%). The efficacy of first shocks, however, was only 57.9% (95% CI, 35.6%-77.4%). Four episodes were incorrectly classified as ventricular tachyarrhythmia, which led to inappropriate shock delivery in 2 patients. CONCLUSIONS Ineffective shock delivery may occur in patients with S-ICD, even after successful intraoperative testing. Multicenter trials are required with close monitoring of safety and efficacy end points to identify patients who may be at risk for shock failure.