Background: Identifying hypertrophic cardiomyopathy (HCM) patients who warrant a primary prevention implantable cardioverter defibrillator (ICD) is one the greatest challenges in HCM. Although ICD is effective it is overused due to lack of optimally defined risk factors and carries risk of complications.
Objective: To assess the incidence and predictors of appropriate ICD therapies, inappropriate shocks and device-related complications in HCM patients with primary prevention ICDs in an HCM center of excellence.
Methods: All HCM patients who underwent primary-prevention ICD implantation at Toronto General Hospital between 9/2000-12/2017 were identified. ICD therapies for ventricular tachycardia >180bpm were considered appropriate
Results: During 1,818 patient-years of follow up (mean 6.1 years), 36 of 299 consecutive patients (12.0%) received at least 1 appropriate ICD therapy (2.2%/year). The 5-year cumulative probability of appropriate ICD therapy was 10.1%. On multivariable analysis none of the conventional risk factors (unexplained syncope, severe hypertrophy, family history of sudden death, non-sustained ventricular tachycardia on Holter monitor, abnormal blood pressure response to exercise), nor the ESC score were significantly associated with appropriate ICD therapy. Apical aneurysm, age <40 at implant and atrial fibrillation were independent predictors of appropriate ICD therapy. A sub-group analysis of 184 patients who had cardiac magnetic resonance prior to ICD implantation identified severe late gadolinium enhancement (>15% of the total left ventricular mass) and age<40 at implant as predictors of appropriate ICD therapies. ICD-related complications and/or inappropriate shock occurred in 29.7% of patients. 11.0% of patients suffered inappropriate shock (2.1%/year). The 5-year cumulative probability of inappropriate ICD shock was 10.7%. On multivariable analysis age<40 at implant and atrial fibrillation were predictors of inappropriate shocks.
Conclusion: The incidence of appropriate ICD therapies is lower than previously reported. A substantial proportion of patients experience ICD related complications or inappropriate shocks. Larger multi-center studies are needed to improve risk stratification in HCM.