AIMS: The totally subcutaneous implantable-defibrillator (S-ICD) is a new alternative to the conventional transvenous ICD system to minimize intravascular lead complications. There are limited data describing the long-term performance of the S-ICD. This paper presents the first large international patient population collected as part of the EFFORTLESS S-ICD Registry. METHODS AND RESULTS: The EFFORTLESS S-ICD Registry is a non-randomized, standard of care, multicentre Registry designed to collect long-term, system-related, clinical, and patient reported outcome data from S-ICD implanted patients since June 2009. Follow-up data are systematically collected over 60-month post-implant including Quality of Life. The study population of 472 patients of which 241 (51%) were enrolled prospectively has a mean follow-up duration of 558 days (range 13-1342 days, median 498 days), 72% male, mean age of 49 ± 18 years (range 9-88 years), 42% mean left ventricular ejection fraction. Complication-free rates were 97 and 94%, at 30 and 360 days, respectively. Three hundred and seventeen spontaneous episodes were recorded in 85 patients during the follow-up period. Of these episodes, 169 (53%) received therapy, 93 being for Ventricular Tachycardia/Fibrillation (VT/VF). One patient died of recurrent VF and severe bradycardia. Regarding discrete VT/VF episodes, first shock conversion efficacy was 88% with 100% overall successful clinical conversion after a maximum of five shocks. The 360-day inappropriate shock rate was 7% with the vast majority occurring for oversensing (62/73 episodes), primarily of cardiac signals (94% of oversensed episodes). CONCLUSION: The first large cohort of real-world data from an International patient S-ICD population demonstrates appropriate system performance with clinical event rates and inappropriate shock rates comparable with those reported for conventional ICDs. Clinical trial registration URL: http://www.clinicaltrials.gov. Unique identifier NCT01085435.

Auckland City Hospital Auckland New Zealand

Boston Scientific Corporation St Paul MN USA

Cardiology Department Russells Hall Hospital Dudley UK

Cardiology Department The Heart Hospital Institute of Cardiovascular Science University College London 16 18 Westmoreland Street W1G 8PH London UK

Center of Research on Psychology in Somatic Diseases Department of Medical and Clinical Psychology Tilburg University Tilburg The Netherlands Department of Cardiology Thoraxcenter Erasmus Medical Center Rotterdam The Netherlands

Department of Cardiology and Electrophysiology Academic Medical Center Amsterdam The Netherlands

Department of Cardiology Electrophysiology Section Odense University Hospital Odense Denmark

Department of Cardiology Homnolka Hospital Prague Czech Republic

Department of Clinical Electrophysiology Erasmus Medical Center Rotterdam The Netherlands

Division of Electrophysiology Campus Grosshadern University of Munich Munich Germany

King's College Hospital London UK

St Antonius Ziekenhuis Nieuwegein The Netherlands

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