Chapter 8

The superiority of mitral valve repair over replacement in patients with mitral valve disease is now widely accepted. This is mainly due to better preservation of left ventricular (LV) function, greater regression of left heart dimensions, resistance to endocarditis, avoidance of long-term anticoagulation (mechanical valves) or reoperation (bio-prosthetic valves), fewer valve-related complications (mechanical and bioprosthesis), and improved survival.1–4

The mitral valve is comprised of three distinct components: the mitral annulus, the subvalvar apparatus, and the mitral leaflets.

### Mitral Annulus

Two structures from the cardiac skeleton form part of the mitral valve ring: the right and the left fibrous trigones. The most prominent is the right fibrous trigone, also known as the central fibrous body, which is located between the mitral (left), tricuspid (right), and aortic (anterior) orifices in a triangular form that justifies its name. The left fibrous trigone has a similar structure but is less prominent and is situated ventrally and to the left, between the left margins of the mitral and aortic valves. The two fibrous trigones are interconnected to form the “curtain” of fibrous tissue between the aortic valve and the anterior leaflet of the mitral valve (mitral-aortic fibrous continuity). In this region, the left fibrous trigone extends superiorly to form part of the scalloped aortic root. This concentration of fibrous tissue helps prevent dilatation of the correspondent segment of the mitral annulus. Laterally, bands of connective tissue (the left filum coronarium) extend from the two fibrous bodies but fade out progressively and leave the posterior third of the mitral annulus completely devoid of collagen fibers. This segment of the annulus is therefore ill defined and without true anatomical substance. The two fibrous bodies act as the fixed points on which the contraction of the myocardial fibers is based. Thus, the annulus is dynamic, and its motion is coordinated by the cardiac cycle. Mitral annular dysfunction occurs mainly in the posterior and medial portions of the valve.3

### Chordae Tendineae

The chordal system is the most extensively studied component of the mitral apparatus, yet it remains the most controversial because of the wide variations of number and form of the chordae and their attachments. As the name indicates, the chordae tendineae are tendinous structures that originate from the tip of the papillary muscles on one side and insert into the valve leaflets on the other. However, chordae originating directly from the ventricular wall, and muscular chordae (chorda muscularis) have been described in a number of normal hearts. After a short but variable course, the chordae tendineae usually branch before insertion, but a small number of unbranched chordae may insert directly into the leaflet. The insertion into the posterior leaflet occurs at any point between the free edge and the base. The mode of insertion into the anterior leaflet is different, with most descriptions referring to the ventricular surface of the anterior leaflet as being devoid ...

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