Objectives: To identify the determinants of appropriate and inappropriate implantable cardioverter-defibrillator (ICD) discharges in patients with hypertrophic cardiomyopathy (HCM).

Design: Retrospective cohort study.

Setting: ICD clinic at an academic hospital.

Patients: 61 patients with HCM who received ICDs for the primary or secondary prevention of sudden cardiac death (SCD).

Outcome measures: (a) Analysis of appropriate and inappropriate ICD discharges; (b) predictors of ICD discharges.

Results: Mean (SD) age at ICD insertion was 46 (18) years (range 10–79). Follow-up time was 40 (27) months (range 7–151). Eight patients experienced an appropriate discharge, occurring 24.5 (13.6) months after ICD insertion. Appropriate ICD intervention was more common in the secondary (36%) than the primary (8%) prevention group (p = 0.02). Inappropriate ICD discharges occurred in 20 (33%) patients. Multivariate Cox regression analysis identified two significant predictors of inappropriate ICD discharges: (a) age <30 years at the time of ICD insertion (hazard ratio (HR) = 3.0 (95% CI 1.1 to 8.0; p = 0.03) and (b) history of atrial fibrillation (HR = 3.1 (95% CI 1.2 to 8.1; p = 0.02).

Conclusions: ICDs are effective in the prevention of SCD in HCM. However, there is a high incidence of inappropriate ICD discharges.