Subtypes of Atrial Functional Mitral Regurgitation: Imaging Insights Into Their Mechanisms and Therapeutic Implications

Functional mitral regurgitation (MR) in patients with atrial fibrillation (AF) without left ventricular dysfunction, namely, atrial functional MR, has been increasingly recognized. Whether mitral annular dilatation causes MR in patients without left ventricular dysfunction has remained controversial; however, recent studies using novel imaging technologies, including 3-dimensional echocardiography, have shown that significant functional MR can sometimes occur in AF patients with significant dilatation of mitral annulus and left atrium. Additional contributors such as atriogenic leaflet tethering, annulus area to leaflet area imbalance resulting from insufficient leaflet remodeling and reduced annular contractility, increased valve stress by flattened saddle shape of the annulus, and left atrial dysfunction may be important triggers of atrial functional MR in the presence of dilated mitral annulus and left atrium. The prevalence of atrial functional MR is reported to be between 3% and 15% in AF patients and those with atrial functional MR are associated with worse clinical outcomes. Because there are few published data regarding therapeutic strategies of atrial functional MR, understanding the principles of therapeutic options and their target mechanisms is important with regards to clinical practice until sufficient evidence is established. In this review, the known mechanisms, clinical implications and, when possible, potential therapeutic options of atrial functional MR are discussed.