The junction between the leaflet tissue and the atrium, or so-called the atriovalvular junction, is well-visualized from an atrial view. The motion of the leaflets is initiated at the level of this junction or leaflet hinge. This video shows the mitral valve from an atrial view. A hook is used to show the atriovalvular junction.

From an anatomic point of view, the mitral annulus is located deeper and 2 mm external to the hinge. Therefore, it is important to emphasize that the mitral annulus is an anatomic structure which is not visible from an atrial view. Classically, the mitral annulus is divided into anterior and posterior portions. The anterior mitral annulus is situated between the left and the right fibrous trigones and is anatomically related to the aortic annulus via the aorto-mitral curtain. The right fibrous trigone is a dense junctional area between the mitral, tricuspid, non-coronary cusp of the aortic annuli and the membranous septum. The left fibrous trigone is situated at the junction of both left fibrous borders of the aortic and the mitral valves.

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This anatomic drawing was inspired from the original work of Antoine Portal (1742-1832) (See inset).


The posterior annulus is composed of a discontinuous band of fibrous tissue that exists in some areas of the attachment of the posterior leaflet . This segment of the annulus is not attached to any rigid structures, and it is at this area that annular dilatation occurs predominantly in the setting of mitral regurgitation.

The mitral annulus is a nonplanar structure which has a three-dimensional saddle-shape configuration.The peaks are located anteriorly and posteriorly at the midpoints of the mitral annulus. The valleys are located medially and laterally at the trigones. This saddle-shape has been shown to decrease stress exerted on the mitral leaflets during valve closure. In pathologic situations, the mitral annulus shape becomes more planar.

The motion of the mitral annulus is determined by the contraction and relaxation of atrial and ventricular musculature and the central displacement of the aorto-mitral curtain. Three distinct types of annular motions are described and consist of apical displacement during systole, circumferential contraction, and a folding motion in intercommissural axis. During systole, these different annular motions facilitate the closure of the valve by creating a large surface of coaptation while exerting minimal stress on leaflets structure.