Atrial functional mitral regurgitation: Insufficiently understood and recognized.

Atrial functional mitral regurgitation (AFMR) is a form of functional mitral regurgitation that is still insufficiently recognized and characterized. The driving cause of AFMR is atrial, not ventricular dilatation, usually due to long-standing atrial fibrillation, and often in association with left ventricular diastolic dysfunction and heart failure with preserved ejection fraction (HFpEF). An increase in mitral annular area leads to a loss of central coaptation of the leaflets, often resulting in an "override" configuration and flattening of the annulus, as well as a loss of annular contraction. The left ventricle (LV) has a normal size; thus, there is usually only minor tenting of the leaflets. The regurgitant jet is mostly central, although posterior jet direction also occurs, frequently in a subform with posterior leaflet tethering and a marked localized dilatation of the posterior annulus. Because of the normal-sized and normally or nearly normally contracting LV, the amount of regurgitation is typically not more than moderate (or moderate-to-severe). Over time, functional mitral regurgitation may become mixed atrial and ventricular, with remodeling of the LV. However, the time course and the relation to symptoms have yet to be elucidated. This review presents current concepts and published insights into this form of mitral regurgitation.