Long-term incidence of implantable cardioverter-defibrillator therapy in patients with hypertrophic cardiomyopathy: analysis of appropriate and inappropriate interventions.

Background: Treatment with implantable cardioverter-defibrillators (ICDs) effectively prevents sudden cardiac death (SCD) in patients with hypertrophic cardiomyopathy (HCM). Identifying patients most likely to benefit from a primary prevention ICD remains challenging. We aimed to investigate the long-term incidence of ICD therapy in patients with HCM according to SCD-risk at baseline.

Methods: The study retrospectively included all patients with HCM treated with an ICD for primary or secondary prevention between 1995 and 2022 in Eastern Denmark. Medical records for each patient were evaluated. Patients were stratified into risk groups according to the European Society of Cardiology HCM Risk-SCD score.

Results: We included 208 patients (66% male) with HCM and an ICD for primary (78%) or secondary prevention (22%). During a median 10-year follow-up, 66 patients (32%) received appropriate ICD therapy (antitachycardia pacing and/or shock), while 20 (10%) received inappropriate therapy. Patients with an ICD implanted for secondary prevention were almost twice as likely to receive appropriate therapy compared with patients with an ICD implanted for primary prevention (47% vs 28%, p=0.02). The 5-year cumulative incidences of appropriate shock therapy were 17% in patients with a high HCM Risk-SCD score, 16% in patients with an intermediate-risk score and 6% in patients with a low-risk score. A high-risk score was associated with higher cumulative incidence of appropriate shock therapy (p=0.012).

Conclusion: One-third of patients with HCM treated with an ICD experienced appropriate ICD therapy. The HCM-Risk SCD score adequately distinguished between low-risk and high-risk patients among those who underwent ICD implantation. Further improvements of risk-tools are needed to identify a larger proportion of the two-thirds of patients who did not benefit from ICD implantation after 10 years of observation.