Nonischemic Septal Fibrosis in Functional Tricuspid Regurgitation Provides Incremental Stratification of Adverse Remodeling and Prognosis.

BACKGROUND Functional tricuspid regurgitation (TR) arises from impaired valve integrity resulting from contractile dysfunction, chamber dilation, or myocardial tissue alterations. Whereas right ventricular (RV) dysfunction is a recognized driver of adverse outcomes in TR, the impact of myocardial tissue injury, particularly nonischemic septal fibrosis (NIsF), remains largely unexplored. OBJECTIVES This study aims to evaluate the association of NIsF with adverse right-sided chamber remodeling and to assess its incremental prognostic value for mortality in patients with functional TR. METHODS Patients with advanced (≥ moderate) functional TR underwent comprehensive cardiac magnetic resonance (CMR) evaluation. Late gadolinium enhancement (LGE) was used to identify NIsF, defined as hyperenhancement in the midmyocardial or epicardial regions of the interventricular septum. Cine CMR measured functional and geometric indices of the left and right sides of the heart. Follow-up data were obtained for all-cause mortality. RESULTS A total of 663 patients with advanced TR (mean age: 63.8 ± 16.0 years; 53% male) were studied, and 29.4% were found to have NIsF. NIsF was strongly associated with adverse chamber remodeling, including larger left ventricular and RV volumes, reduced systolic function, and increased TR severity (all P < 0.001). TR regurgitant fraction increased stepwise with NIsF extent (no NIsF, 34.9% ± 1.5%; 1 segment, 38.1% ± 13.0%; 2 segments, 40.8% ± 13.8%; P < 0.001). Over a mean follow-up of 4.3 ± 4.3 years, 25.3% of patients died. NIsF was independently associated with mortality (HR: 1.79 [95% CI: 1.26-2.56]; P = 0.001), even after adjusting for conventional risk markers, including age, TR severity, RV dysfunction, and dilation. Kaplan-Meier analysis demonstrated significantly higher mortality risk among patients with NIsF compared with patients without NIsF (P < 0.001). CONCLUSIONS Among patients with advanced TR, NIsF is an important marker of adverse right-sided chamber remodeling and provides incremental prognostic utility beyond conventional risk markers.