Is It Time to Update the Definition of Functional Mitral Regurgitation?

Abstract

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. Article p 845 In the present issue of Circulation , Chaput et al5 present in vivo evidence of structural changes in the mitral leaflets of patients with functional mitral regurgitation. They employ a new 3-dimensional echocardiographic method of measuring diastolic mitral leaflet area to compare leaflet size in normal subjects with that in patients with left ventricular dysfunction on the basis of either dilated cardiomyopathy or inferior wall infarction. In the left ventricular dysfunction group, patients with mitral regurgitation are contrasted to those without. The authors report larger-than-normal leaflets in patients with both global and regional left ventricular dysfunction. Moreover, in the group of patients with dilated cardiomyopathy, the leaflets are larger in those without versus those with mitral regurgitation. By also measuring the leaflet area required to close the valve, the authors are able to demonstrate that regurgitation is associated with a reduced valve area/closing area ratio. They conclude that in functional …