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 of chordae beyond the marginal rough zone. However, thick chordae originating from either papillary muscle, inserting well beyond the rough zone, have been reported. The significance of recognizing them during reconstruction of the mitral valve is discussed later (see section Chordae Transposition).

It is also important to distinguish between commissural chordae and leaflet chordae (Figure 8–1).

Commissural Chordae

A single chord branches in a fan-like manner into five to seven small chordae, which then insert into the free edge of the commissural segment of each leaflet. The arrangement is similar for both commissures, but with a wider lateral spread in the posteromedial commissural area. The average length of the chordae of the anterolateral commissure is 1.2 to 1.4 cm and that of the posteromedial commissural chordae is 1.4 to 1.7 cm. Knowledge of the commissural chordae is essential to understanding the pathophysiology and management of ischemic mitral regurgitation.

Leaflet Chordae

From each papillary muscle three groups of chordae insert in an oblique manner into the corresponding half of the anterior leaflet, on either side of the midline: paramedial, central (strut), and paracommissural. The strut chordae are the thickest, and arise at the very summit of the papillary muscle and insert into the ventricular surface of the rough zone, usually away from the edge of the leaflet. They appear to constitute the “cornerstone” of the chordal system of the anterior leaflet, whereas the paramedial and paracommissural chordae play an accessory role in the support of the leaflet. Typically, each of them divides into three branches that insert directly or, after further branching, into the free edge, limit of the rough zone, and intermediate area of the leaflet, respectively, and act together as a functional unit. Chordae similar to those described for the anterior leaflet reach the free edge and the ventricular surface of the posterior leaflet in a parallel alignment. However, the basal and cleft chordae are unique to this leaflet. The former originate in the papillary muscles or ventricular wall and attach into the base (annular region) of the central scallop of the posterior leaflet. The latter always originate from the papillary muscle and insert into the margins and adjacent areas of the central and lateral scallops. The typical fan-shape attachment of the chordae to the ventricular surface of the posterior leaflet has pathologic and surgical implications that are discussed later. The mitral valve has an average of 25 primary chordae. Nine of these insert into the anterior leaflet, 14 into the posterior leaflet, and two into the commissures. Most of the “variations from normal” are characterized by the absence of one or a group of chordae, leaving a portion of the leaflet unsupported.

Papillary Muscles

The left ventricle has two papillary muscles: anterior (or anterolateral) and posterior (or posteromedial). Both originate from the ventricular free wall, at or near the junction between the apical and middle thirds. The anterior papillary muscle is attached to the anterior wall of the ventricle, close to its lateral border. The posterior papillary muscle originates from the posterior wall, near the junction with the ventricular septum. Both papillary muscles have equal anatomic and functional importance and have the same volume. However, there are also notable variations of form. Acar and coworkers established a classification based on the ways that the papillary muscles relate to the leaflets via the chordae.5 Four types are described (Figure 8–2). In type I, the papillary muscle is single. In type II, the papillary muscle has two heads, one of which sends chordae exclusively to the posterior leaflet. In type III, the papillary muscle is also divided, with one head supporting the commissural area exclusively. Type IV papillary muscle resembles but is distinct from type III in that the head supporting the commissure is very short. In type IV, the different heads also originate at different levels on the ventricular wall from the apex to the base.

The blood supply to the papillary muscles is provided by septal branches of the right and left coronary arteries. The anterior papillary muscle usually is supplied by several branches of the left coronary artery, including the second septal branch of the anterior descending (interventricular) artery and branches of the circumflex artery. Conversely, the posterior papillary muscle receives its supply from one of the septal branches of the posterior descending artery and/or another branch directly from the circumflex artery. In approximately two-thirds of the population, the posterior papillary muscle is perfused by only one vessel. Within the papillary muscles, each artery divides into two branches that course centrally and subendocardially throughout the length of the muscle and usually are interconnected by multiple anastomoses. However, the supply may be from a single central artery. The highly variable anatomy of the posterior descending artery renders the posterior papillary muscle more susceptible to rupture, secondary to occlusion of the right coronary artery, circumflex artery, or both. Although the major contribution is from the intramural arteries, the most peripheral portions of the papillary muscles are perfused by oxygen diffusion from intracavitary blood.

Mitral Leaflets

The normal mitral valve has two leaflets: the anterior leaflet (AML), which covers 80% of the orifice area, and the posterior leaflet (PML), which covers the remaining 20% of the orifice area. Disease of the mitral valve leading to mitral regurgitation (MR) rarely involves the whole leaflet, but is usually confined to specific segments. To unify the language between cardiologists and surgeons and among the surgeons themselves, Carpentier proposed a nomenclature that would allow clear identification of the anatomic segment(s) involved. He designated the posterior leaflet segments as P1, P2, and P3. P1 is adjacent to the anterolateral commissure, P2 is the middle scallop, and P3 is adjacent to the posteromedial commissure. The anterior leaflet has less clearly defined segments designated as A1, A2, and A3, corresponding to the adjacent posterior leaflet segments (Figure 8–3). The transesophageal echocardiographic (TEE) transgastric basal short-axis view of the left ventricle, with some anteflexion, provides the “fishmouth” view of the mitral valve (MV), in which the A3 and P3 segments are at the top of the screen and the A1 and P1 segments are at the bottom (anterior leaflet to the left). In the surgeon’s view, A3 and P3 are to the right, and A1 and P1 are to the left (anterior leaflet superior).

One of the most important breakthroughs in the management of MR was the introduction by Carpentier in the early 1980s of the functional classification of MR.6 This classification describes mitral valve disease in terms of the pathophysiologic triad of type of valve dysfunction, lesion, and etiology. It is based on the opening and closing motions of the mitral leaflets (Figure 8–4):

• Type I has normal motion of the leaflets and MR is due to leaflet perforation (endocarditis) or to annular dilatation (LV dysfunction).
  
• Type II has increased leaflet motion with the free edge of the leaflet traveling above the plane of the mitral annulus during systole (leaflet prolapse). This is due to chordal elongation or rupture as seen in degenerative valve disease.
  
• Type III has restricted leaflet motion.
  
• Type IIIa dysfunction implies restricted leaflet motion during diastole and systole due to rheumatic changes.
  
• Type IIIb dysfunction correlates to restricted leaflet motion during systole secondary to papillary muscle displacement in ischemic or dilated cardiomyopathy.

Diseases of the mitral valve responsible for MR are numerous. The most common causes of MR include degenerative mitral valve disease, ischemic mitral regurgitation, endocarditis, and dilated cardiomyopathy. Other less frequent causes include rheumatic heart disease, traumatic MR, and systemic inflammatory diseases.

Degenerative Mitral Valve Disease

Although the most common cause of MR is degenerative disease, it is interesting to note the confusing terminology, typical of the literature, used to define degenerative mitral valve disease (eg, “myxomatous degeneration,” “floppy leaflets,” “billowing leaflets,” “Barlow’s disease,” “flail leaflets,” and “leaflet prolapse”). Patients with degenerative mitral valve disease most commonly have type II dysfunction, which corresponds to the overriding of the free edge of the leaflet above the plane of the mitral annulus during systole (leaflet prolapse). This is usually related to chordal elongation or chordal rupture. Associated annular dilation is a common finding in these patients; however, isolated annular dilatation (type I dysfunction) with normal motion of both leaflets has been reported. Of note is the fact that leaflet restriction (type III dysfunction) is not observed in patients with degenerative disease.

Controversy continues as to the pathologic types of degenerative mitral valve. Some investigators have claimed that this is a single disease diagnosed at different stages, and others have described multiple subtypes. For the sake of clarity, we distinguish three types of degenerative mitral valve disease: fibroelastic deficiency (first described by Carpentier), Barlow’s disease (characterized by myxoid degeneration with excess leaflet tissue), and Marfan’s disease.

Fibroelastic deficiency is most common in elderly patients with a relatively short history of valve dysfunction. Intraoperative analysis typically shows transparent leaflets with no excess tissue except in the prolapsing segment, and elongated, thin, frail, and often ruptured chordae. The annulus is often dilated and may be calcified. In contrast, Barlow’s disease appears early in life, and patients typically have a long history of a systolic murmur. The valve leaflets are typically thick with marked excess tissue. The chordae are thickened, elongated, and may be ruptured. Papillary muscles also are occasionally elongated. The annulus is dilated and sometimes calcified. Marfan’s disease with MR is characterized by excess leaflet tissue, which may be thickened (without myxoid degeneration), and a dilated annulus that is rarely calcified. In some patients with degenerative mitral valve disease, the exact etiology of valvular regurgitation remains undetermined. The most common lesions encountered in all types of degenerative mitral valve disease are posterior leaflet prolapse secondary to elongation and rupture of the corresponding chordae, and annular dilatation and deformation.

Ischemic Mitral Valve Disease

In the acute phase after myocardial infarction, massive ischemic MR usually is secondary to a ruptured papillary muscle, a catastrophic event that in most cases requires emergency replacement of the mitral valve. However, in the vast majority of patients, MR can develop after a myocardial infarction without papillary muscle rupture as a consequence of LV remodeling, due to the apical and inferior displacement of the papillary muscles producing incomplete coaptation of leaflets. In these cases, ischemic MR may be due to one of the following reasons:

1. 
   

   Simple annular dilatation (secondary to LV enlargement), which causes incomplete mitral leaflet coaptation associated with type I (normal) leaflet motion.

   
   
2. 
   

   Local LV remodeling with papillary muscle displacement producing apical tethering or tenting of the leaflets (with type IIIb restricted systolic leaflet motion).

   
   
3. 
   

   Both mechanisms.

   
   
4. 
   

   Recent studies show that mitral leaflets in functional MR are stiffer than normal leaflets with altered extracellular matrix composition.7

Endocarditis

In the setting of bacterial endocarditis, MR can develop due to:

1. 
   

   Leaflet prolapse secondary to rupture or destruction of marginal chordae

   
   
2. 
   

   Leaflet perforation due to abscess formation

   
   
3. 
   

   Leaflet destruction with giant vegetations

Dilated Cardiomyopathy

Mitral valve regurgitation is a common finding in end-stage cardiomyopathy caused by dilatation of the mitral annulus (type I) and of the left ventricle (type IIIb). Mitral insufficiency leads to a vicious circle, with increasing volume overload of the dilated left ventricle, leading to further annular and ventricular dilatation, worsening of mitral valve regurgitation, and volume overload. The resulting mitral valve insufficiency is often refractory to medical therapy and predicts poor survival in this patient group. Surgical correction of MR can interrupt this vicious cycle.

Rheumatic Valve Disease

Once the most frequent cause of mitral valve disease, rheumatic disease has been almost eradicated in the Western world. However, physicians practicing in Africa and in some parts of Asia still face the difficult problem of rheumatic mitral valves in children and young adults.

Rheumatic fever causes severe changes in all components of the mitral valve. The chordae are thickened, fused, and shortened; the leaflets become rigid and calcified; the commissures are fused; and with time, the annulus and the entire valve calcify.

Since the mid-1970s considerable efforts have been made to develop and standardize surgical techniques for mitral valve reconstruction. Techniques of mitral valve repair were developed and adapted to treat specific anatomic lesions leading to MR. There is no doubt that Carpentier pioneered a large number of these advances, and hence deserves the paternity of mitral valve repair. However, other groups from around the world have brought considerable insight into mitral valve pathology, its treatment, and the results of surgical repair.

Annuloplasty

Annuloplasty is used to treat annular dilation or deformation (type I MR), which is often encountered in association with other anatomic lesions. Annuloplasty is therefore used as an adjunct to other surgical techniques. It has been demonstrated that annuloplasty is an indispensable technique to ensure long-term durability of the repair in the vast majority of cases. Several techniques and prosthetic devices have been used to perform annuloplasty, but there is some evidence showing the superiority of prosthetic rings (complete or incomplete) over stitch reduction of the annulus or localized reinforcements.

Leaflet Resection

Leaflet resection is used to treat leaflet prolapse, most frequently at the level of the PML. In fact, quadrangular resection of the posterior leaflet is the most common technique used in degenerative mitral valve disease (Figure 8–5). It is the most predictable technique, yielding the best results postoperatively and in the long term. Triangular resections with less extensive resections at the level of the annulus of the PML offer equivalent results without the need for a wide plication of the posterior annulus to prevent kinking or damage of a dominant circumflex artery. Results of leaflet resection of the anterior leaflet are less favorable than those observed with posterior leaflet resection. Therefore, resection of the AML should be avoided and replaced by alternative techniques. However, in rare cases with excessive leaflet tissue (Barlow’s disease), localized resections have been used with good results.

Sliding Leaflet Technique

This technique is a variation of the quadrangular resection of the posterior leaflet. It was introduced in 1989 by Carpentier to address the problem of systolic anterior motion (SAM) of the AML after mitral valve repair.8 The rationale behind this technique resides in the understanding of the pathophysiology of SAM in this setting. The sliding leaflet technique aims to reduce the height of a tall posterior leaflet, which is one of the major risk factors for SAM. Results with this technique (Figure 8–6) have been extremely favorable, with virtually total eradication of significant SAM after mitral repair.8,9