OBJECTIVES: The aim of this study was to determine the efficacy of implantable 
cardioverter-defibrillators (ICDs) in children and adolescents with hypertrophic 
cardiomyopathy (HCM).
BACKGROUND: HCM is the most common cause of sudden death in the young. The 
availability of ICDs over the past decade for HCM has demonstrated the potential 
for sudden death prevention, predominantly in adult patients.
METHODS: A multicenter international registry of ICDs implanted (1987 to 2011) 
in 224 unrelated children and adolescents with HCM judged at high risk for 
sudden death was assembled. Patients received ICDs for primary (n = 188) or 
secondary (n = 36) prevention after undergoing evaluation at 22 referral and 
nonreferral institutions in the United States, Canada, Europe, and Australia.
RESULTS: Defibrillators were activated appropriately to terminate ventricular 
tachycardia or ventricular fibrillation in 43 of 224 patients (19%) over a mean 
of 4.3 ± 3.3 years. ICD intervention rates were 4.5% per year overall, 14.0% per 
year for secondary prevention after cardiac arrest, and 3.1% per year for 
primary prevention on the basis of risk factors (5-year cumulative probability 
17%). The mean time from implantation to first appropriate discharge was 2.9 ± 
2.7 years (range to 8.6 years). The primary prevention discharge rate 
terminating ventricular tachycardia or ventricular fibrillation was the same in 
patients who underwent implantation for 1, 2, or ≥3 risk factors (12 of 88 
[14%], 10 of 71 [14%], and 4 of 29 [14%], respectively, p = 1.00). Extreme left 
ventricular hypertrophy was the most common risk factor present (alone or in 
combination with other markers) in patients experiencing primary prevention 
interventions (17 of 26 [65%]). ICD-related complications, particularly 
inappropriate shocks and lead malfunction, occurred in 91 patients (41%) at 17 ± 
5 years of age.
CONCLUSIONS: In a high-risk pediatric HCM cohort, ICD interventions terminating 
life-threatening ventricular tachyarrhythmias were frequent. Extreme left 
ventricular hypertrophy was most frequently associated with appropriate 
interventions. The rate of device complications adds a measure of complexity to 
ICD decisions in this age group.