External validation of the unifying concept for the quantitative assessment of functional mitral regurgitation

Purpose: A novel conceptual framework was introduced to enhance the quantitative assessment of functional mitral regurgitation (FMR) and improve risk stratification. However, the data was derived from a single-center cohort and lack external validation. We aimed to validate the proposed algorithm using a different patient population. Methods: Patients with at least mild FMR and reduced left ventricular ejection fraction (< 50%) were retrospectively identified at a single-center. The cohort was stratified in low, intermediate and high-risk according to the proposed framework, on the basis of effective regurgitant orifice area (EROA) and regurgitant volume (RegVol). Patients within the intermediate-risk group were subsequently reclassified into either the low-risk category (Regurgitant Fraction, RegFrac < 50%) or the high-risk category (RegFrac ≥ 50%) based on their regurgitant fraction. The primary endpoint was all-cause mortality. Results: A total of 572 patients were included. During a median follow-up of 3.8 years there were 254 deaths (44%). On multivariable analysis, the proposed thresholds for FMR severity remained independently associated with all-cause mortality (adjusted hazard ratio: 1.488; 95% confidence interval [CI]: 1.110–2.013; p-value = 0.010). This algorithm demonstrated superior discriminative ability (C-statistic: 0.664) compared to contemporary guidelines (C-statistic: 0.522; p-value for comparison < 0.001). Additionally, it resulted in a significant improvement in the net reclassification index (0.162; p-value < 0.001). Conclusions: Within our cohort, the application of the proposed concept demonstrated a significant association with a higher risk of all-cause mortality. Moreover, this conceptual framework showcased the potential to improve the accuracy of risk prediction beyond current guidelines.