Background and aims:
Atrial functional tricuspid regurgitation (atrial TR) has received growing recognition as a distinct TR phenotype. However, a universal definition is lacking. We aimed to improve the characterization of atrial TR.

Methods and results:
Overall, 1164 patients with significant functional TR were analyzed, including 856 conservatively treated individuals and 308 patients that received transcatheter tricuspid valve repair (TTVR). Echocardiographic exams were analyzed for the predominant TR mechanism (non-atrial vs. atrial TR, n=138) and served as the derivation cohort. Midventricular right ventricular (RV) diameter, TR tenting height and left ventricular ejection fraction (LV-EF) were identified as parameters that defined atrial TR (q<0.05). Therefore, atrial TR was defined as tenting height ≤10 mm, midventricular RV diameter ≤38 mm and LV-EF ≥50%. These findings were validated in a larger cohort (n=856) with all three variables being associated with atrial TR. Atrial TR patients were more often females, had better RV function, higher LV-EF and lower tricuspid valve tenting area and height, but lower right atrial (RA) areas and lower TV effective regurgitant orifice area (EROA) (all p<0.05).

Patients with atrial TR had better long-term survival than non-atrial TR patients in the conservatively treated cohort (p<0.001, n=611). Atrial TR was associated with a lower rate of the combined endpoint of mortality and heart failure hospitalization at one-year follow-up in the TTVR cohort (p<0.05, n=304). TR degree was significantly reduced after TTVR in non-atrial and atrial TR (p<0.01).

Conclusion:
An echocardiography-based atrial TR definition is associated with prognostic relevance in patients with functional TR in conservatively treated TR and after TTVR.