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.