Evaluation of subcutaneous ICD early performance in hypertrophic cardiomyopathy from the pooled EFFORTLESS and IDE cohorts

Background The subcutaneous implantable cardioverter-defibrillator (S-ICD) is a potential alternative to transvenous systems in hypertrophic cardiomyopathy (HCM) where lead complications are a significant issue. Objectives To compare the S-ICD efficacy of defibrillation threshold (DFT) testing, arrhythmia therapy, and complications in HCM versus non-HCM patients. Methods Outcomes of patients with HCM implanted with S-ICD were compared to non-HCM S-ICD recipients using pooled data from a total of 872 subjects enrolled in the EFFORTLESS Registry and US IDE study. Results The cohort included 99 HCM (75% male) and 773 non-HCM (72% male) patients with a median follow-up of 637 days. The HCM cohort was younger and more likely to receive a primary-prevention S-ICD (88.5% vs 67.5%, P < .0001). During implant testing, successful defibrillation at ≤80 J was achieved in 98.9% of HCM and 98.5% of non-HCM patients. One year postoperative complication-free rates were similar: 92.7% in HCM (with no lead complications) versus 89.5% in non-HCM. There were 3 appropriate shocks for ventricular tachycardia in 3 HCM patients that were all converted by the first shock. Overall final shock conversion efficacy was 100% in HCM versus 98% in non-HCM ( P = ns). Inappropriate shocks occurred in 12.5% of HCM patients and 10.3% of non-HCM patients ( P = ns), being reduced by 47% using dual-zone programming. Conclusion These initial data indicate the S-ICD is safe and effective in patients with HCM who are at high risk of ventricular arrhythmias and pass preimplantation electrocardiogram screening. Inappropriate shocks were mainly due to T-wave oversensing, but there were no lead complications requiring reintervention.