Geometric differences of the mitral valve apparatus in atrial and ventricular functional mitral regurgitation

Background: Functional mitral regurgitation (FMR) occurs in patients with annular dilation (atrial, aFMR) or patients with left ventricular (LV) disease (ventricular, vFMR). Meticulous understanding of the mechanisms underpinning regurgitation is crucial to optimize therapeutic strategies. Methods: Patients with moderate-severe FMR were identified from a registry of patients referred for transcatheter mitral valve intervention. In addition, controls without cardiovascular disease were identified. Differences in the geometry of the LV and mitral valve apparatus (including leaflet and tenting geometry, papillary muscle displacement and movement, annular dimensions, and dynamism) between atrial and ventricular FMR, and control subjects, were assessed using multiphasic cardiac CT. Results: Of 183 FMR patients, 18 patients (10%) were found to have aFMR. The remaining patients had either ischemic or non-ischemic ventricular FMR. In aFMR, both increasing LV end-systolic volume (rho 0.701, p ​< ​0.01) and left atrial volume (rho 0.909, p ​< ​0.01) were associated with larger annular area. By contrast, in vFMR larger annular area was most strongly associated with larger left atrial volume (rho 0.63, p ​< ​0.01). In controls, increased annular area was associated with larger LVEDV (rho 0.78, p ​< ​0.01) and LVESV (rho 0.824, p ​< ​0.01), but not left atrial size (rho 0.16, p ​= ​0.45). Ventricular FMR comprised apicolaterally displaced, akinetic posteromedial papillary muscles, resulting in pronounced leaflet tethering, leaflet elongation compared to controls, and only modest relative LA dilatation. Compared to vFMR, aFMR was characterised by marked relative annular dilation, smaller but discernible mitral valve tenting, shorter leaflet lengths when related to annular size, but normal papillary geometry. Conclusion: FMR is characterised by multiple changes within the mitral valve complex. Atrial and ventricular FMR differ significantly in terms of the drivers of annular size, and geometry and function of the subvalvular apparatus. This highlights the need to consider these as separate disease entities.