Mitral Valve

The mitral valve separates the left atrial chamber from the left ventricle and prevents blood flowing backwards from the left ventricle into the left atrium. There are several components for the mitral valve: leaflets, annulus, chordae tendinae and papillary muscles.

The mitral valve has two leaflets: anterior and posterior. The anterior leaflet has a semi-circular shape and attaches to two fifths of the annular circumference. The posterior leaflet of the mitral valve has a quadrangular shape and is attached to approximately three fifths of the annular circumference. The posterior leaflet typically has two well defined indentations which divides the leaflet into three individual scallops identified as P1 (anterior or medial scallop), P2 (middle scallop), and P3 (posterior or lateral scallop).

The mitral annulus constitutes the anatomical junction between the ventricle and the left atrium, and serves as insertion site for the leaflets. It is often divided segmentally according to the site of leaflet insertion (the anterior or posterior annulus). The mitral annulus is less well developed at the insertion site of the posterior leaflet. This segment is not attached to any fibrous structures and is prone to increase its circumference in the setting of mitral regurgitation in association with left atrial or left ventricle dilation. Correction of the annular dimension to normal is therefore an essential part of reconstructive mitral valve surgery.

There are two papillary muscles arising from the left ventricular wall and providing chordae tendinae to both leaflets. The chordae are responsible for the correct positioning of the leaflets.
Because the annulus resides in the left atrioventricular groove, and the chordae are connected to the ventricle via the papillary muscles, mitral valve function is integrally related to the ventricle. Chronic or acute left ventricular dilatation can lead to papillary muscle displacement with increased leaflet tethering due to tension on chordae tendinae as well as annular dilatation, leading to the axiom “that mitral regurgitation begets mitral regurgitation.”