RACI: A Novel Prognostic Marker in Functional Tricuspid Regurgitation

BACKGROUND: Right atrioventricular coupling index (RACI), defined as the ratio of right atrial (RA) to right ventricular end-diastolic volume on cardiac magnetic resonance, is a novel parameter that reflects RA–right ventricular (RV) hemodynamic interplay. Its prognostic value in functional tricuspid regurgitation (TR) is unknown. METHODS: This study included 633 consecutive patients with moderate or greater functional TR undergoing cardiac magnetic resonance. Patients were stratified into 2 groups based on the optimal cutoff by the Youden index (normal: RACI<0.62 versus high: RACI≥0.62). The primary outcome was all-cause mortality. RESULTS: Patients with high RACI (n=147) were older (74.1±10.7 years versus 60.6±16.1 years, P <0.001) with larger RA volumes (RV end-systolic volume index: 96.7 [interquartile range, 77.5–121.2] mL/m 2 versus 55.4 [interquartile range, 42.6–69.0] mL/m 2 ; P <0.001), smaller RV size (RV end-diastolic volume index: 106.2±33.5 versus 114.8±37.2 mL/m 2 ; P =0.012), and no difference in RV function (RV ejection fraction: 46.3±9.8% versus 45.4±12.7%; P =0.43). Over a median follow-up of 2.9 years (interquartile range, 0.7–6.9), a high RACI was associated with increased mortality risk (25% versus 15%; hazard ratio, 2.06 [95% CI, 1.47–2.90]; P <0.001). In multivariable Cox regression analysis adjusting for age, right and left heart size and function, and clinical markers of right-sided congestion (glomerular filtration rate <30, total bilirubin), RACI remained an independent predictor of all-cause mortality (adjusted hazard ratio, 1.16 per 0.10 increase, 95% CI, 1.03–1.32, P =0.014). In addition, RACI provided incremental prognostic value for predicting the primary outcome over conventional right heart indices (RA and RV volumes, RV ejection fraction, TR severity), improving model performance (χ 2 increased from 28.5 to 37.6; P =0.003). CONCLUSIONS: RACI is a novel parameter that effectively integrates RA and RV remodeling, and independently predicts all-cause mortality in functional TR. Incorporating RACI into clinical assessment may help with improving risk stratification and guiding the timing of intervention in patients with functional TR.