Biatrial Inflammatory and Profibrotic Remodeling in Severe Mitral Regurgitation: A Comparative Tissue and Echocardiographic Study Versus CABG Comparator Group

Background/Objectives: Severe mitral regurgitation (MR) is associated with chronic atrial stretch, chamber enlargement, pulmonary pressure elevation, and atrial fibrosis, yet the relationship between tissue inflammatory/profibrotic signaling, histologically quantified fibrosis, and echocardiographic remodeling remains incompletely characterized. This study aimed to compare biatrial tissue remodeling in patients with severe MR undergoing mitral valve surgery with a practical non-valvular surgical comparator group undergoing isolated coronary artery bypass grafting (CABG). Methods: This single-center, observational, cross-sectional comparative study included 36 elective cardiac-surgery patients: 22 with severe MR and 14 undergoing isolated CABG without significant valvular disease. Left- and right-atrial tissue samples were collected intraoperatively. IL-6, TNF-α, and TGF-β expression was assessed by quantitative real-time PCR using pooled atrial samples stratified by atrial side and study group, whereas atrial fibrosis was quantified histologically on individual tissue specimens using Masson’s trichrome staining and digital image analysis. Clinical, laboratory, and echocardiographic parameters were compared between groups, and exploratory associations were assessed with cautious interpretation. Results: Compared with the CABG comparator group, patients with severe MR showed a pooled molecular profile compatible with higher aggregate atrial expression of IL-6, TNF-α, and TGF-β; because qPCR was performed on pooled tissue preparations, these molecular findings were interpreted descriptively and were not used for patient-level inferential statistics. Histologically quantified fibrosis was significantly increased in severe MR in both the left atrium (29.69 ± 12.26% vs. 12.17 ± 4.56%, p < 0.0001) and the right atrium (25.25 ± 11.33% vs. 9.01 ± 4.46%, p < 0.0001). The MR group also showed more pronounced echocardiographic remodeling, including larger estimated left atrial volume, higher pulmonary artery systolic pressure, and greater right ventricular diameter. Exploratory individual-level analyses were restricted to histological fibrosis and echocardiographic variables. Conclusions: Severe MR was associated with marked echocardiographic remodeling and significantly greater histologically quantified biatrial fibrosis compared with a CABG surgical comparator group. Pooled qPCR findings support an aggregate inflammatory/profibrotic signal, but they should be interpreted descriptively because individual-level molecular variability could not be assessed. These findings are hypothesis-generating and do not establish causality.