Ventricular tachycardia/fibrillation early after defibrillator implantation in patients with hypertrophic cardiomyopathy is explained by a high-risk subgroup of patients

Background Implantable cardioverter-defibrillator (ICD) studies in patients with coronary artery disease report higher risk of ventricular tachycardia/fibrillation (VT/VF) early post-implant, potentially related to local proarrhythmic effects of ICD leads. Objective To characterize early and long-term risk of ICD discharge for VT/VF in a large hypertrophic cardiomyopathy (HCM) cohort. Methods By using HCM multicenter registry data, we compared long-term risk of VT/VF subsequent to an early post-implant period (a priori defined as within 3 months of implant) between patients with or without VT/VF within 3 months after ICD implantation. Results Over a median follow-up of 4.3 years, 109 of 506 (22%) patients with HCM who received ICDs received at least 1 ICD discharge for VT/VF. Risk of first ICD discharge for VT/VF was highest in the first year post-implant (10.8% per person-year; 95% confidence interval 7.9–13.8) and particularly in the first 3 months (17.0% per person-year; 95% confidence interval 9.8–24.3). Patients with early VT/VF (≤3 months post-implant) were older, and more commonly had secondary prevention ICDs following cardiac arrest or systolic dysfunction (end-stage HCM with ejection fraction<50%). Only 2 of 247 (0.7%) patients with primary prevention ICDs and preserved systolic function had early VT/VF. Patients with VT/VF early post-implant (≤3 months) had more than 5-fold higher risk for future VT/VF during long-term follow-up compared with patients without early VT/VF (adjusted hazard ratio 5.4; 95% confidence interval 2.3–12.6). Conclusions High-risk patients with HCM and VT/VF early after ICD implantation are particularly prone to subsequent VT/VF throughout follow-up. Early ICD interventions for VT/VF are largely confined to patients with prior cardiac arrest or systolic dysfunction and therefore more likely driven by higher arrhythmic risk rather than lead-related proarrhythmia.