Objective Implantable cardioverter defibrillators (ICDs) are routinely used to prevent sudden cardiac death (SCD) in selected hypertrophic cardiomyopathy (HCM) patients, but the determinants of device-related complications, therapies and long-term cardiovascular mortality in ICD recipients are not known.

Design Retrospective observational cohort study.

Setting Single-centre tertiary referral cardiomyopathy clinic.

Patients 334 consecutively evaluated HCM patients (median age 40 years, 62% male, 92% primary prevention) at risk of SCD treated with ICD. Thirty-six patients (11%) received concurrent cardiac resynchronisation therapy for heart failure symptoms.

Results During the 1286 patient-years of follow-up, cardiovascular mortality (including transplantation) occurred in 22 (7%) patients (1.7%/year) and was associated with New York Heart Association (NYHA) class III/IV (adjusted HR=9.38, 95% CI 3.31 to 26.55, p≤0.001), percentage fractional shortening (HR=0.92, 95% CI 0.87 to 0.96, p=0.001) and implantation for secondary prevention (HR=0.07, 95% CI 0.01 to 0.86, p=0.04). There were no SCD. Twenty-eight (8%) patients received appropriate shocks (2.3%/year), which were predicted by baseline fractional shortening (HR=0.96, 95% CI 0.92 to 0.99, p=0.04). Fifty-five (16%) patients received inappropriate shocks (4.6%/year). Sixty (18%) patients experienced implant-related complications (5.1%/year), including two deaths. Adverse ICD-related events (inappropriate shocks and/or implant complications) were seen in 101 (30%) patients (8.6%/year). Patients with cardiac resynchronisation therapy were more likely to develop implant complications than those with single-chamber ICDs (HR=4.39, 95% CI 1.44 to 13.35, p=0.009) and had a higher 5-year cardiovascular mortality than did the rest of the cohort (21% vs 6%, p<0.001).

Conclusions HCM patients with an ICD have a significant cardiovascular mortality and are exposed to frequent inappropriate shocks and implant complications. These data suggest that new strategies are required to improve patient selection for ICDs and to prevent disease progression in those that receive a device.