Independent External Evaluation of Pediatric Hypertrophic Cardiomyopathy Risk Scores in Predicting Severe Ventricular Arrhythmias

BACKGROUND: Sudden cardiac death is the most common cause of death in childhood hypertrophic cardiomyopathy (HCM). Recently, 2 risk scores have been developed to estimate the 5-year risk of sudden cardiac death. We aimed to assess their respective performances in an independent cohort. METHODS: All patients with HCM aged <18 years from a single center were retrospectively included between 2003 and 2023. HCM Risk-Kids and PRIMaCY risk scores were calculated at diagnosis and during follow-up. The primary composite outcome included sustained ventricular arrhythmia, appropriate implantable cardioverter defibrillator (ICD) therapy, aborted cardiac arrest, or sudden cardiac death. RESULTS: A total of 100 primary prevention children were included (7.1±5.6 years, 59.0% males), with a mean follow-up of 8.6±5.5 years. Overall, 13 (13.0%) patients experienced the primary composite outcome. When only considering events during the 5 first years, Harrel C index was 0.52 (95% CI, 0.27–0.77) for HCM Risk-Kids (≥6%) and 0.70 (95% CI, 0.59–0.80) for PRIMaCY (>8.3%), with 1 patient potentially treated by ICD for every 25 ICDs implanted for HCM Risk-Kids and 1 for every 14 ICDs implanted for PRIMaCY. When risk scores were repeated and all primary outcomes during follow-up were considered, 12 of 13 (92.3%) events were correctly identified using both risk scores, with 1 patient potentially treated by ICD for every 5.6 ICDs implanted for HCM Risk-Kids and 1 for every 5.3 ICDs implanted for PRIMaCY. Among 44 (44.0%) patients implanted with an ICD, all primary prevention patients who had ≥1 appropriate ICD therapy during follow-up had an HCM Risk-Kids ≥6% and PRIMaCY >8.3% at implantation. CONCLUSIONS: In this independent evaluation, our findings suggest imperfect discrimination between low and high-risk patients using the HCM Risk-Kids and PRIMaCY risk scores, with predicted risks tending to be overestimated compared with the actual observed events. The performance or risk scores was substantially improved by periodic reassessment during follow-up.