Abstract / Summary
Background: Contemporary series report declining sudden cardiac death (SCD) in hypertrophic cardiomyopathy (HCM), but whether this reflects fewer arrhythmic events or a greater proportion of deaths successfully prevented is unclear. We examined the proportion of arrhythmic events that were prevented rather than fatal over two decades, and its determinants. Methods: We conducted a systematic review of observational HCM cohorts published in 2000–2024 reporting SCD, resuscitated cardiac arrest (RCA) and appropriate ICD discharge (ICD-d). The primary outcome, the prevented fraction, was (RCA + ICD-d)/(SCD + RCA + ICD-d). Proportions were pooled using random-effects models (Freeman–Tukey transformation), compared between periods (2000–2013 vs. 2014–2024) and examined by meta-regression. Results: Fourteen cohorts (14,069 patients; 712 arrhythmic events) were included. The prevented fraction was 53.2% (95% CI 36.0–70.1) overall, and higher in 2014–2024 than in 2000–2013, (60.8% vs. 27.7%; p = 0.08), although this comparison relied on only three cohorts in the first period. This variation was strongly associated with cohort ICD penetration (β = 0.022, p < 0.0001), which explained 72% of the between-study heterogeneity, whereas calendar year was not independently associated (p = 0.45 when adjusted for ICD penetration). SCD fell from 72.3% to 39.2% of events while appropriate discharges rose from 9.8% to 40.5%; the share prevented by resuscitation did not increase. SCD incidence fell from 0.69 to 0.27 per 100 patient-years, while appropriate discharges rose from 0.10 to 0.27; the yield per implanted device did not improve (16.7% vs. 12.9%) and devices per prevented event rose from 5.8 to 8.1. Conclusions: Arrhythmic events in HCM have shifted from predominantly fatal to predominantly prevented, driven by ICD therapy rather than by the passage of time or by improved out-of-hospital resuscitation, but at the cost of broader implantation.