Abstract Body (Do not enter title and authors here): Background: Mitral stenosis (MS) is associated with adverse left atrial (LA) structural changes. Mechanical relief of this obstruction via balloon mitral valvuloplasty (BMV) may be associated with LA reverse remodelling.

Objective: To study LA and RV remodelling in isolated severe rheumatic MS patients before and 9-12 months after successful BMV.

Methods: We included 49 patients with isolated severe rheumatic MS in sinus rhythm who underwent successful BMV. CMR was done at baseline and 9-12 months post BMV. Thirty age- and gender- matched healthy controls were included for comparison. Indexed LA volumes (V_max, V_min, & V_pre-A) were obtained from CMR cine images. LA phasic functions were evaluated using both volumetric and deformation indices. Deformation analysis including LA strain (global, passive, & active strain) & strain rate (SRs, SRe, and SRa ) measurements were performed using specialized MASS (R) software for CMR feature tracking.

Results: At baseline, there was significant impairment of LA volumes and functions in severe MS patients compared to healthy controls. Following BMV, there was statistically significant reduction in all LA indexed volumes compared to baseline (p-value <0.001 for all). There was significant improvement in LA phasic functions; Reservoir, conduit and pump functions as shown in Table. Higher mean gradient (MG) at baseline correlated significantly with passive strain and passive SR. Strain indices of reservoir and pump functions have normalized, however, the LA volumes and volumetric functions still remained significantly impaired compared to healthy controls.
RV volumes, EF and RV free wall GLS were normal at baseline. Post BMV, both RV ESVi and RV EF showed significant improvement.

Conclusion: Significant MS is associated with marked LA structural & functional changes detected by CMR. Successful BMV results in reverse LA remodelling with reduction in LA volumes and improvement in LA functions and strain indices, This reverse remodelling was evident at 9-12 months post procedure. Longer term follow-up studies are needed to assess whether improvement in LA volumetric functions and strain indices are sustained or not.