8.7 Mitral Subvalvular Apparatus

Mitral Subvalvular Apparatus is a complex anatomical structure located beneath the mitral valve leaflets of the heart. It plays a crucial role in maintaining proper mitral valve function by anchoring the valve leaflets to the left ventricular myocardium, ensuring valve competence during the cardiac cycle and preventing prolapse or regurgitation. This apparatus comprises the mitral chordae tendineae, papillary muscles, and their spatial relationships, which together support the dynamic opening and closing of the mitral valve leaflets.

Components of the Mitral Subvalvular Apparatus

Mitral Chordae Tendineae

The mitral chordae tendineae are strong, fibrous cords that connect the mitral valve leaflets to the papillary muscles. They are classified into three main types based on their attachment and function:

• Primary Chordae Tendineae: These are thin, delicate chordae that attach directly to the free edges of the mitral valve leaflets. Their primary function is to prevent leaflet prolapse into the left atrium during ventricular systole, maintaining valve coaptation.

• Secondary Chordae Tendineae: These chordae are thicker and attach to the ventricular surface of the mitral leaflets, away from the free edge. They provide structural support to the leaflet body, distributing mechanical stress during valve closure.

• Tertiary Chordae Tendineae: Present mainly on the posterior mitral leaflet, these chordae attach to the basal portion of the leaflet and the ventricular wall. They contribute to leaflet stabilization and ventricular geometry.

The chordae tendineae exhibit a branching pattern that increases their tensile strength and allows even force distribution across the valve leaflets.

Papillary Muscles

The papillary muscles are muscular projections from the left ventricular wall that serve as the anchoring site for the chordae tendineae. There are two main papillary muscles associated with the mitral valve:

• Anterolateral Papillary Muscle: Located on the anterolateral wall of the left ventricle, this muscle typically receives dual blood supply and is less prone to ischemic damage. It attaches chordae to both anterior and posterior mitral leaflets.

• Posteromedial Papillary Muscle: Positioned on the posteromedial wall of the left ventricle, this muscle generally has a single blood supply, making it more vulnerable to ischemia. It also anchors chordae to both leaflets.

The coordinated contraction of these muscles during ventricular systole tenses the chordae tendineae, preventing mitral valve leaflet prolapse.

Functional Anatomy and Spatial Relationships

Cross-Leaflet Papillary Support

Each papillary muscle sends chordae tendineae to both mitral valve leaflets, creating a cross-leaflet support system. This arrangement ensures balanced tension across the leaflets, optimizing leaflet coaptation and minimizing leaflet stress.

Mitral Leaflet-Chordal Distribution

The distribution of chordae tendineae to the anterior and posterior leaflets varies, with the anterior leaflet typically receiving more primary chordae due to its larger size and greater excursion during valve motion. The chordal branching pattern contributes to the flexibility and durability of the valve leaflet structure.

Three-Dimensional Architecture

The mitral subvalvular apparatus forms a three-dimensional complex that integrates with the left ventricular geometry. The papillary muscles, chordae, and leaflets operate in synchrony to accommodate changes in ventricular shape during the cardiac cycle, preserving valve competence and ventricular function.