Cardiac index: A superior parameter of cardiac function than left ventricular ejection fraction in risk stratification of hypertrophic cardiomyopathy

BACKGROUND An appropriate indicator of cardiac function in the risk stratification of hypertrophic cardiomyopathy (HCM) patients is urgently needed. Cardiac index that reflects cardiac pumping func-tion may be suitable.OBJECTIVE The purpose of this study was to investigate the clinical significance of reduced cardiac index in HCM patients.METHODS A total of 927 HCM patients were enrolled. The primary endpoint was cardiovascular death. The secondary endpoints were sudden cardiac death (SCD) and all-cause death. Combination models were constructed by adding reduced cardiac index and reduced left ventricular ejection fraction (LVEF) to the HCM risk- SCD model. Predictive accuracy was determined by C-statistics.RESULTS Reduced cardiac index was defined as cardiac index <2.42 L/min/m2. During median follow-up of 4.3 years, 51 patients reached the endpoint. Reduced cardiac index independently increased the risk of cardiovascular death (adjusted hazard ratio [aHR] 2.976; P = .007), SCD (aHR 6.385; P = .001), and all-cause death (aHR 2.428; P = .010). By adding reduced cardiac index to the HCM risk-SCD model, the model C-statistic increased from 0.691 to 0.762, with an integrated discrimination improve- ment of 0.021 (P = .018) and a net reclassification improvement of 0.560 (P = .007). The addition of reduced LVEF failed to improve the original model. Better predictive accuracy for all endpoints was also indicated in reduced cardiac index than in reduced LVEF.CONCLUSION Reduced cardiac index is an independent predictor of poor prognoses in HCM patients. Combining reduced cardiac in- dex rather than reduced LVEF improved the HCM risk-SCD stratifica- tion strategy. The reduced cardiac index showed better predictive accuracy than reduced LVEF for all endpoints.