AIMS: Sudden cardiac death (SCD) may complicate hypertrophic cardiomyopathy (HCM) natural course. Patient selection for implantable cardioverter defibrillator (ICD) therapy in the primary prevention setting is still a challenge.METHODS: Thirty-seven HCM patients with a primary prevention ICD were included. All patients underwent preimplantation SCD risk assessment and semi-annual device interrogation during follow-up. Primary end point was the time to first appropriate ICD intervention including antitachycardia pacing or shock. Inappropriately delivered ICD therapies served as secondary end point.RESULTS: During a median follow-up of 3.1 years, 10 (27%) patients received one or more appropriate ICD therapies. First appropriate ICD intervention rate was 7.2%/year (95% CI: 3.4-13.2) with a 5-year cumulative probability of 29.2 ± 7.4%. No SCD risk marker was significantly associated with the primary end point, whereas event rates were comparable among patients with one, two or three or more SCD risk markers (log-rank P = 0.58). Patients with a history of SCD in first-degree relatives with HCM were at 3.8 times higher risk of experiencing an ICD intervention compared with those with no family history of SCD (HR: 3.8; 95% CI: 1.0-14.1, P = 0.05). Seven (18.9%) patients experienced one or more inappropriate ICD therapies; beta-blocker therapy was associated with 75% fewer inappropriate ICD interventions (HR: 0.15; 95% CI: 0.03-0.89).CONCLUSION: Current criteria identify a subgroup of patients with HCM at increased risk of major arrhythmic events as indicated by high ICD intervention rates. However, no individual risk marker demonstrated superior predictive ability over the others, whereas simple arithmetic summing of risk markers was not associated with increased ICD intervention rates.