Secondary/functional MR can occur due to which mechanism?

• A. Afib
• B. Significant AR
• C. Large VSD
• D. Severe dilation of the ventricle

Answer: (D)

Functional (secondary) mitral regurgitation happens when the mitral leaflets are structurally normal, but the left ventricle changes size and shape in a way that pulls on the mitral apparatus. When the ventricle dilates and remodels, the mitral annulus enlarges and the papillary muscles are displaced laterally and downward. This increased leaflet tethering prevents the leaflets from coapting fully during systole, so blood leaks back into the left atrium even though the valve itself isn’t intrinsically diseased.

The most direct mechanism among the options is severe dilation of the ventricle, because the geometric distortion from the enlarged ventricle is what creates poor leaflet coaptation. Other factors, like atrial fibrillation, can contribute to MR through secondary annular dilation in some scenarios, but the classic driver of functional MR is LV dilation. Large VSD or significant aortic regurgitation can lead to LV volume overload and eventual dilation as well, but the fundamental cause of the regurgitation in this context is the ventricle’s dilated geometry affecting the mitral apparatus.