Left Atrial Reservoir Strain Improves Sudden Cardiac Death Risk Stratification in Hypertrophic Cardiomyopathy.

BACKGROUND: Current risk scores for sudden cardiac death (SCD) in hypertrophic cardiomyopathy (HCM) have limited ability to identify high-risk subgroups. We aimed to investigate the prognostic value of left atrial reservoir strain (LARS) for SCD-related events and its utility for risk stratification. METHODS: This retrospective cohort study included 1,761 patients with HCM from two referral centers. The primary outcome was SCD-related events, including SCD, aborted SCD, and appropriate implantable cardioverter-defibrillator shocks. Explainable machine learning approaches were used to explore the importance of LARS and identify a clinically relevant threshold. The prognostic value of LARS was evaluated using Cox regression analyses, particularly among patients classified as low-to-intermediate risk (HCM Risk-SCD score<6%). RESULTS: During a median follow-up of 6.8 years (IQR: 3.0-10.7 years), 69 (3.9%) SCD-related events occurred. Decreased LARS was independently associated with a higher risk of SCD-related events (per 1% decrease, adjusted HR 1.11, 95% CI, 1.07-1.15, p<0.001). SHAP analysis identified LARS as the top-ranked predictor and a clinically relevant threshold of <21%. LARS <21% was significantly associated with a higher risk of SCD-related events (adjusted HR 5.01, 95% CI 2.77-9.03, p<0.001), even among patients without atrial fibrillation. Adding LARS to the HCM Risk-SCD score significantly improved risk discrimination in the low-to-intermediate risk population (5-year time-dependent AUC 0.73 vs. 0.63, p=0.005). Among low-to-intermediate risk patients, LARS <21% was associated with a significantly higher risk of SCD-related events (adjusted HR 6.13, 95% CI 3.13-12.03, p<0.001), whereas the original low- and intermediate-risk categories showed limited risk discrimination. CONCLUSIONS: LARS was an independent predictor of SCD-related events and effectively stratified risk among patients classified as low-to-intermediate risk by the HCM Risk-SCD score. Integrating LARS into the HCM Risk-SCD score may enhance risk stratification and guide preventive strategies.