RACI: A Novel Prognostic Marker in Functional Tricuspid Regurgitation

Right atrioventricular coupling index (RACI), defined as the ratio of right atrial (RA) to right ventricular (RV) end-diastolic volume on cardiac magnetic resonance, is a novel parameter that reflects RA-RV hemodynamic interplay. Its prognostic value in functional tricuspid regurgitation (TR) is unknown.

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.

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 (RA end-systolic volume index: 96.7 [interquartile range, 77.5-121.2] mL/m² versus 55.4 [interquartile range, 42.6-69.0] mL/m²; P<0.001), smaller RV size (RV end-diastolic volume index: 106.2±33.5 versus 114.8±37.2 mL/m²; 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 (χ² increased from 28.5 to 37.6; P=0.003).

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.