Determinants of implantable defibrillator discharges in high-risk patients with hypertrophic cardiomyopathy

Objectives: To identify the determinants of appropriate and inappropriate implantable cardioverterdefibrillator ( 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.