Myocardial fibrosis predicts sudden cardiac death in patients with hypertrophic cardiomyopathy after cardiac electronic device implantation: a retrospective study

Background Hypertrophic cardiomyopathy (HCM) patients faces increased risk of sudden cardiac death (SCD). Growing evidence supports the association between myocardial fibrosis and ventricular arrhythmias. Purpose We aimed to determine whether the location, pattern, and percentage of myocardial fibrosis predicts SCD in HCM patients after cardiac implantable electronic device (CIED) implantation. Method This study included HCM patients who completed cardiac magnetic resonance and received CIED between June 2017 and January 2023, and followed up until January 2025. The primary outcome was SCD or SCD-equivalent events, defined as the composite of SCD, resuscitated cardiac arrest, sustained ventricular tachycardia or ventricular fibrillation, or appropriate ICD therapy (shock or anti-tachycardia pacing). Results Eighty-eight patients were included (age 52.3 ± 15.3 years; 67.0% male). Over a median follow-up period of 38.1 months, 27 (30.6%) SCD events were recorded. Myocardial fibrosis in inferior wall (HR = 3.75, 95% CI 1.48-9.51, P = 0.005), or with a transmural pattern (HR=9.29, 95% CI 3.47-24.87, P<0.001) were associated with SCD. Total fibrosis quantified using the 2-SD method (TF2SD; HR=1.05, 95% CI 1.03–1.08, P<0.001), the 3-SD method (TF3SD; HR=1.06, 95% CI 1.03–1.10, P<0.001, the 5-SD method (TF5SD; HR=1.05, 95% CI 1.02–1.09, P=0.005), and the full-width at half-maximum (TFFWHM; HR=1.07, 95% CI 1.04–1.11, P<0.001) were independently associated with SCD. Gray zone fibrosis quantified using the 3-SD method (GZF3SD; HR=1.10, 95% CI 1.00–1.21, P=0.042), and the 5-SD method (GZF5SD; HR=1.07, 95% CI 1.02–1.12, P=0.003) were also independently associated with SCD. After adjusting HCM SCD risk factors, fibrosis in inferior wall, transmural pattern, TF2SD, TF3SD, TFFWHM, GZF3SD, and GZF5SD, remained as independent predictors of SCD. Compared to 2024 AHA risk score, which assesses myocardial fibrosis using TF5SD, the updated score incorporating 1) transmural pattern, 2) elevated TF2SD and/or elevated GZF5SD showed significant improvement (old AUC: 0.77, 95% CI 0.66-0.89 vs. updated AUC: 0.82, 95% CI 0.72-0.93; NRI: 0.83, P<0.001; IDI: 0.09, P<0.001) Conclusion Myocardial fibrosis with transmural pattern, elevated TF2SD, and elevated GZF5SD are potential predictors of SCD in HCM patients after CIED implantation and provide additional value to existing risk scoring systems.