Determinants of disproportionate functional mitral regurgitation

Abstract Funding Acknowledgements Type of funding sources: None. Background Recent studies have suggested that "disproportionate" functional mitral regurgitation (FMR) defined by greater MR than expected from the degree of left ventricular (LV) dilatation may be a good candidate for transcatheter edge-to-edge repair (TEER). Determinants of disproportionate FMR (d-FMR) is unknown. We hypothesized that additional factors such as asymmetric tethering, extreme mitral annular dilatation, and deep indentation, might worsen the severity of FMR regardless of LV volumes and lead to d-FMR. Purpose To investigate the impact of the additional factors on the proportionality of FMR. Methods We reviewed consecutive FMR patients who underwent TEER and 3D transesophageal echocardiography (3DTEE) in our institute between 2018 and 2022. d-FMR and proportionate FMR (p-FMR) were defined by the effective regurgitant orifice area (EROA)/LV end-diastolic volume (LVEDV) >0.2 and ≤0.2 mm2/mL, respectively. Results A total of 110 FMR patients (63 d-FMR and 47 p-FMR, 75±12 years old, 46.3% female) were included. Patients with d-FMR had significantly larger EROA than p-FMR (41 ± 12 vs 33 ± 11 mm2, P<0.001) despite smaller LVEDV index (100 ± 28 vs 138 ± 49 mL/m2, P<0.001), better LV ejection fraction (37 ± 10% vs 27 ± 8%, P<0.001), and lower tenting height (7.6 ±2.9 vs 9.4 ± 2.7 mm, P=0.009). The 3DTEE analysis revealed that patients with d-FMR were more likely to have asymmetric tethering (29% vs 21%), extreme mitral annular dilatation (>700 mm2/m2; 54% vs 30%), and deep indentation (22% vs 4.3%) The presence of such additional factors was independently associated with d-FMR (odds ratio 3.83, P=0.0081) after adjustment by body surface area and LVEDV index. Furthermore, EROA/LVEDV increased as the number of additional factors increased. (Jonckheere-Terpstra test, P<0.001). TEER successfully reduced FMR regardless of the presence of such additional factor (success rate 95% vs. 96%, P>0.99). Conclusions The presence of additional factors exacerbates MR independently of LV size and is an important mechanism of d-FMR. TEER is an effective therapy to reduce FMR regardless of these factors.