This anatomic drawing was inspired from the original work of Antoine Portal (1742-1832) (See inset).
The mitral valve is composed of an anterior leaflet and a posterior leaflet. They are separated by the anterolateral and posteromedial commissural leaflets. Mitral valve tissue is inserted around the entire circumference of the mitral orifice.
The Anterior Mitral Leaflet
The anterior mitral leaflet has a trapezoidal shape and attaches to approximately one third of the circumference of the mitral orifice. The base of the anterior leaflet is attached to the cardiac skeleton with the left coronary cusp and half of the non-coronary cusp of the aortic valve. From functional point of view, the anterior leaflet constitutes an important boundary dividing the inflow and outflow tracts of the left ventricle.
From an atrial view, the leaflet surface is composed of two zones. The proximal zone is regular, often thin and clear. The distal third of the leaflet surface, rough zone, is irregular and thicker and receives the insertion of the chordae tendinae on its ventricular surface. The superior margin of the rough zone is marked by a ridge which corresponds to the line of leaflet coaptation. During systole, the rough zones of the anterior and posterior leaflets come into apposition forming a large surface of coaptation.
The Posterior Mitral Leaflet
The posterior mitral leaflet has a quadrangular shape and attaches to two thirds of the circumference of the mitral valve. Although the height of the posterior leaflet is less than that of the anterior leaflet, they have a similar surface area.
Two indentations on the posterior leaflet divide this structure into 3 anatomically individualized scallops. The three scallops of the posterior leaflet are identified as P1 (anterior scallop), P2 (middle scallop), and P3 (posterior scallop). The P2 segment is the largest scallop while P1 and P3 are two comparably sized scallops. Occasionally, P1 is smaller than P3. The three corresponding segments of the anterior leaflet are A1 (anterior segment), A2 (middle segment), and A3 (posterior segment). This anatomical nomenclature is the basis of Carpentier’s segmental valve analysis allowing a precise location of valve dysfunction, which is of critical importance while performing reconstructive surgery.
Similar to the anterior leaflet, the posterior leaflet is composed of the proximal zone and the distal or rough zone with the insertion of chordae tendinae on its ventricular surface. During valve closure, the apposition between the rough zones of the posterior and anterior leaflets creates a large area of coaptation preventing the regurgitation of the blood from the left ventricle into the left atrium.
The Commissural Leaflets
The mitral valve has two commissures namely the anterolateral and posteromedial commissures. The commissural leaflet provides continuity between the anterior and posterior leaflets and consists of several millimeters of tissue. Its base is attached to the mitral annulus and its free edge is supported by a specific type of fan-shaped chordae called the commissural chordae tendinae.
During valve reconstruction, it is important to preserve or restore the commissural area in order to prevent residual valve regurgitation.