Functional mitral regurgitation (FMR) is MR that occurs in the absence of structural abnormalities in the mitral leaflets, annulus, chordae, or papillary muscles. It is most commonly seen in patients with poor myocardial function, whether from ischemia, infarction, or cardiomyopathy. Its presence is associated with a worse prognosis; improving survival depends on identifying the root cause more than on repairing the leak; however, at this time the direct cause(s) of FMR are uncertain.
Previous studies attributed FMR to left ventricular (LV) or papillary muscle (PM) dysfunction alone, but now implicate mitral apparatus shape distortion. Aikawa et al. at the CVRTC previously related the development and severity of FMR to the widening of the angle between the anterior and posterior chordae. Additional parameters of mitral apparatus geometry are now studied as determinants of FMR severity (below).
METHODS: Transthoracic 3D echo scans were obtained in 8 normal and 13 pts. with dilated cardiomyopathy (DCM), 5 with mild and 8 with moderate-severe FMR.
The mitral annulus was traced at end diastole, end systole, and midsystole and reconstructed in 3D. The chordae originating from the ant. and post. papillary heads were traced to measure interchordal angle.
LV shape was measured as distance from the long axis to 16 regions on the LV wall.
RESULTS: The ant. and anterolateral (antlat) wall was more displaced in pts. with mod/severe FMR (p<0.05 vs mild FMR for 6 basal, mid, and apical ant and antlat segments).
Chordae were nearly orthogonal to the leaflets in normals; in DCM pts. chordal-valve plane angle was acute; they also had a greater interchordal angle (p<0.001 for nl vs. mild vs. mod/sev FMR).
In addition, interchordal angle correlated with LV dilatation (p<0.05).
CONCLUSION: In pts. with DCM the mechanism of FMR is displacement of the antlat wall with attendant ant. papillary displacement, widening of the interchordal angle, and lateral retraction of the leaflets3.