Right Atrioventricular Coupling Index (RACI): A Novel Prognostic Marker in Functional Tricuspid Regurgitation
TL;DR
RACI is a novel parameter that effectively integrates RA and RV remodeling, and independently predicts all-cause mortality in functional TR, and incorporating RACI into clinical assessment may help with improving risk stratification and guiding the timing of intervention in patients with functional TR.
Abstract
Background: Right atrioventricular coupling index (RACI), defined as the ratio of right atrial (RA) to right ventricular (RV) end diastolic volume on cardiac magnetic resonance (CMR), is a novel parameter that reflects RA-RV hemodynamic interplay. Its prognostic value in functional tricuspid regurgitation (TR) is unknown. Methods: This study included 633 consecutive patients with ≥ moderate functional TR undergoing CMR. Patients were stratified into two groups based on the optimal cutoff by the Youden index (normal: RACI<0.62 vs. 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 vs. 60.6±16.1 years, p<0.001) with larger RA volumes (RAESVi: 96.7 [IQR 77.5, 121.2] ml/m2 vs. 55.4 [IQR 42.6, 69.0] ml/m2, p<0.001), smaller RV size (RVEDVi: 106.2±33.5 ml/m2 vs. 114.8±37.2 ml/m2, p=0.012), and no difference in RV function (RVEF: 46.3±9.8% vs. 45.4±12.7%, p=0.43). Over a median follow-up of 2.9 years (IQR 0.7, 6.9), a high RACI was associated with increased mortality risk (25% vs 15%; HR: 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 (GFR<30, total bilirubin), RACI remained an independent predictor of all-cause mortality (adjusted HR: 1.16 per 0.10 increase, 95% CI: 1.03–1.32, p=0.014). Additionally, RACI provided incremental prognostic value for predicting the primary outcome over conventional right heart indices (RA and RV volumes, RVEF, TR severity), improving model performance (χ2 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.