Is it time to update the definition of functional mitral regurgitation?: structural changes in the mitral leaflets with left ventricular dysfunction.

Functional mitral regurgitation has traditionally been defined as a disorder of regional or global left ventricular remodeling in which anatomically normal leaflets fail to coapt adequately.1 The abnormal closure pattern, most easily appreciated with echocardiography, is one of apical tethering of one or both leaflets. Based on a series of in vitro,2 animal,3 and human studies,4 we have embraced the concept that pathological tethering and concomitant regurgitation occur when an imbalance is present between closing and tethering forces. Tethering forces are increased when increased traction on the leaflets exists through a combination of annular dilation and geometric remodeling of the left ventricle. Closure forces are reduced as a consequence of left ventricular systolic dysfunction. The leaflets have largely been viewed as passive participants in this disease process. Consequently, therapies to reduce or eliminate mitral regurgitation have focused on annular and ventricular remodeling.