International external validation study of the 2014 European society of cardiology guidelines on sudden cardiac death prevention in hypertrophic cardiomyopathy (EVIDENCE-HCM)

Implantable cardioverter defibrillators (ICD) are recommended in patients with HCM deemed to be at high risk of sudden cardiac death (SCD) but identification of such individuals remains challenging. In 2014 the European Society of Cardiology (ESC) proposed a new risk stratification method based on a risk prediction model (HCM Risk-SCD) which estimates the 5-year risk of SCD.The validation cohort consisted of 3703 patients. During a follow-up period of 28,186 patient years (median 5.9 years) 159 patients (4%) reached the SCD end-point with an annual rate of 0.6% (95% CI 0.5, 0.7). Seventy three (2%) patients reached the SCD end-point within 5 years of follow-up, with a 5-year incidence of 2.4% (95% CI 1.9, 3.0). Validation revealed a calibration slope of 1.02 (95% CI 0.93 to 1.12); C-index was 0.70 (95% CI 0.68 to 0.72) and D-statistic was 1.17 (95% CI 1.05 to 1.29). In a complete case analysis (n= 2147; 44 SCD end-points at 5 years) patients with a predicted 5-year risk of <4% (n=1524; 71%) had an observed 5-year SCD incidence of 1.4% (95% CI 0.8, 2.2); patients with a predicted risk of ≥6% (n=297; 14%) had an observed SCD incidence of 8.9% (95% CI 5.96, 13.1) at 5 years. There were 23 SCD end-points in patients with ≥6% SCD risk suggesting that for every 13 (297/23) ICD implantations in this group, 1 patient can potentially be saved from SCD at 5 years. HCM Risk–SCD provides accurate prognostic information and by preferentially targeting the highest risk group may help reduce unnecessary ICD implantation.