Q. What are the Components of mitral valve apparatus?

1) Annulus: Annulus is a saddle shaped structure with medial and lateral portions forming the basal points and anterior and posterior aspects forming the apical points of the saddle. Anteriorly it merges with aortic annulus while posteriorly there is a C shaped discrete fibrous annulus. The normal diameter is about 2.5 - 3.5 cm. and circumference is about 8 - 9 cm. Normal motion and contraction contribute to the normal mitral valve function.

2) Posterior Left Atrial Wall: Change in the posterior left atrial wall distort mitral annulus and its contraction. Also sequential atrial and ventricular contraction that occurs in sinus rhythm is important for normal mitral valve closure as loss of sinus rhythm can cause mitral regurgitation.

3) Leaflets: Anterior leaflet is longer than wider and posterior leaflet is wider but shorter. Anterior leaflet occupies about one third and posterior about two thirds of annulus. Total combined area of the leaflet is more than double that of annulus. The posterior leaflet has three scallops-medial, central and lateral. Redundancy, loss or restricted motion of leaflets results in mitral regurgitation.

4) Chordae: There are 12 primary chordae that subdivide in to secondary and tertiary chordae attaching leaflets to the papillary muscles. Anterior papillary muscle supplies chordae to lateral aspects while posteromedial papillary muscle supplies to medial aspects of the leaflets. Rupture, fusion or redundancy of chordae can lead to regurgitation.

5) Papillary Muscle: Two papillary muscles are situated at two thirds of the long axis from the base. Their systolic contraction helps leaflets to overcome the systolic pressure and remain closed during systole without prolapse. Impaired contraction of these due to any cause like ischemia, infarction, necrosis, fibrosis or altered geometry will lead to mitral regurgitation.

6) Left Ventricle: Global as well as regional contraction of ventricular muscle is important for normal mitral valve closure. Impaired contractility leads to mitral regurgitation by one or more mechanisms.