EDITORIAL Changes in functional mitral regurgitation after cardiac resynchronization therapy

This editorial refers to ‘Impact of reduction in early- and late-systolic functional mitral regurgitation on reverse remodelling after cardiac resynchronization therapy,†, by Y.-J. Liang et al., on page 2359 Functional mitral regurgitation (MR) is a common finding in patients with global left ventricular (LV) dilatation and dysfunction.1 In these patients, the mitral leaflets are structurally normal and leaflet coaptation failure results from an imbalance between valve closing forces and valve tethering forces.2,3 Impaired LV con-tractility, global LV dyssynchrony, and reduced mitral annulus sys-tolic contraction lead to a significant reduction in valve closing forces. In turn, valve tethering forces are increased due to mitral annulus dilatation, LV remodelling, and papillary muscle displace-ment.4 Furthermore, MR per se induces additional adverse ventri-cular remodelling through volume overload, and plays a