Since Général Baron Nicolas Corvisart, Napoléon’s physician, recognized that heart failure may be due to mitral valve regurgitation following chordae rupture, multiple studies have emphasized the extreme complexity of the pathophysiology of the mitral valve. The pathophysiological triad and functional classification, briefly introduced in Chapter 2 , can help overcome this complexity. According to the triad, the description of mitral valve disease is facilitated by a clear separation between etiology, lesions, and dysfunction ( Table 6-1 ). This separation is important because prognosis depends upon etiology, repair strategy depends upon dysfunction, and techniques depend upon lesions.
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ETIOLOGY
Numerous diseases can affect the mitral valve ( Table 6-2 ). Some directly involve the mitral valve itself, while others affect primarily the myocardium. The mitral valve is the primary target in rheumatic valve disease, degenerative valve disease, bacterial endocarditis, and other uncommon diseases. Mitral valve regurgitation may also result from primary myocardial diseases, such as ischemic cardiomyopathy, dilated cardiomyopathy, or hypertrophic obstructive cardiomyopathy. The determination of etiology is important for at least three reasons: the long-term prognosis, the expected complexity of the operation, and the proper medical therapy that precedes or follows valve reconstruction. Several factors may contribute to determining the etiology of valve disease, such as age, medical history, geographical considerations, socioeconomic conditions, and clinical presentation. In many cases, however, the etiology remains uncertain until echocardiography is performed or the surgical operation is undertaken, which allows assessment of the usually characteristic gross morphology of the valve. Uncertainty may persist, however, because secondary lesions such as fibrosis or calcification may significantly change the initial characteristic features in areas of valve dysfunction or blood turbulence. These morphological characteristics with their clinical presentation and surgical indications will be extensively described in Section 5. They are briefly depicted in Figure 6-1 .
| Primary Valve Diseases |
Secondary to Myocardial Diseases
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* Bacterial endocarditis and calcification may complicate a preexisting valve disease.
Secondary lesions may mask the characteristic pathological features and therefore confuse recognition of the primary etiology.
VALVULAR LESIONS
Any of the diseases previously mentioned can cause one or several lesions, which may affect one or several components of the valvular apparatus: the annulus, the leaflets, the chordae, the papillary muscles, and the ventricular wall ( Table 6-3 ).
| Annulus: | Dilatation |
| Abscess | |
| Calcification | |
| Leaflets: | Excess leaflet tissue |
| Thickening | |
| Vegetations | |
| Abscess, perforation | |
| Tear | |
| Calcification | |
| Commissures: | Fusion |
| Thickening | |
| Calcification | |
| Papillary muscles: | Rupture |
| Elongation | |
| Calcification | |
| Ventricle: | Infarction |
| Fibrosis | |
| Dilatation | |
| Aneurysm | |
| Myocarditis | |
| Calcification |
These lesions may be multiple or complex, and they are often associated. For example, annular dilatation is usually associated with other valvular or subvalvular lesions. Some of these lesions are easily identified while the predominant lesion may mask others: for example, a chordae rupture recognized by echocardiography is often associated with an unrecognized chordae elongation that should be corrected as well.
Since a comprehensive description of the lesions is often difficult for the echocardiographer, the surgeon must complete the inventory of the lesions by a systematic analysis of all components of the valve apparatus during the operation.
VALVULAR DYSFUNCTION: THE “FUNCTIONAL CLASSIFICATION”
As the understanding of the pathophysiology of mitral valve dysfunction progressed, it became apparent that the classical separation between valve stenosis, valve regurgitation, and combined valve stenosis and regurgitation of various degrees was insufficient to describe the multiple aspects of mitral valve disease.
On the other hand, describing all the possible lesions was too complex to be practical. This complexity was overcome by concentrating on the valve dysfunction resulting from valve lesions. This led to the “Functional Classification” of mitral valve disease based on leaflet motion.
A normal mitral valve typically has a kidney-shaped orifice, a perfect relationship between the orifice area and the amount of leaflet tissue, fully mobile leaflets, and a large surface of coaptation with the free edge positioned low below the plane of the orifice ( Fig. 6-2 ).
Any anomaly of these characteristic features may produce a valve dysfunction. In mitral valve regurgitation, this dysfunction may present four functional types according to leaflet motion: normal leaflet motion (type I), excess leaflet motion (type II), or restricted leaflet motion (type III) during diastole (IIIa) or systole (IIIb) ( Table 6-4 ) ( Fig. 6-3 ).
“Functional Classification” and “Segmental Analysis” are the foundations for performing valve reconstruction.
The functional classification of valvular disease was refined by the addition of the “Segmental Analysis,” which allowed precise localization of the leaflet dysfunction. The valve is divided into eight segments, using the scallops of the posterior leaflet as a reference ( Fig. 6-4 ). The anterior scallop of the posterior leaflet is termed P1 and the corresponding anterior segment A1. The middle scallop of the posterior leaflet is named P2 and the corresponding anterior segment A2. The posterior scallop is referred to as P3 and the corresponding anterior segment A3. The anterolateral and posteromedial commissures are termed AC and PC, respectively. Both transthoracic ( Fig. 6-5, a ) and transesophageal echocardiography ( Fig. 6-5, b ) have been of paramount importance in the analysis of these different segments.
In the operating room, using transesophageal echocardiography, surgeons can easily recognize the different leaflet segments and their occasional dysfunctions ( Fig. 6-6 ).
DYSFUNCTIONS AND LESIONS
The functional classification complements the usual assessment of hemodynamic consequences of valvular lesions. It allows the echocardiographer to assess and localize the valvular dysfunction resulting from the lesions. In addition, it provides valuable information to the surgeon, who, in the operating room, can proceed to a full inventory of the lesions in the area where a dysfunction has been identified.
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Type I: Mitral valve regurgitation with normal leaflet motion . In type I mitral regurgitation, the course of the leaflets between systole and diastole has a normal amplitude and the free edges of the two leaflets are well positioned 5 to 10 mm below the plane of the orifice. The regurgitation is due either to a lack of coaptation between leaflets or to an annular dilatation or a leaflet perforation, tear, or vegetation ( Fig. 6-7 ).
FIGURE 6-7
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Type II: Mitral valve regurgitation with excess leaflet motion: “leaflet prolapse.” Typically, a leaflet prolapse is a valve dysfunction in which the free edge of a leaflet overrides the plane of the mitral valve orifice during systole. The resulting lack of leaflet apposition produces a regurgitant jet, which runs obliquely over the nonprolapsing leaflet. A mitral valve prolapse is due either to chordae rupture or elongation or to papillary muscle rupture or elongation ( Fig. 6-8 ). In leaflet prolapse, two important features should be assessed: the degree of prolapse and the extent of prolapse. Echocardiography measures the degree of prolapse in millimeters by comparing the level of the prolapsed free edge to a reference segment. The extent of prolapse is assessed by measuring the length of the margin of the prolapsed area, thus permitting the distinction between limited prolapse and extensive prolapse. A limited prolapse involves less than one fourth of the free margin of the anterior leaflet and less than one third of a segment of the posterior leaflet. An extensive prolapse involves more than one fourth and one third, respectively.
FIGURE 6-8
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Type III: Restricted leaflet motion . In type III mitral regurgitation ( Fig. 6-9 ), the motion of one or two leaflets is limited primarily during diastole (type IIIa) or during systole (type IIIb). Type IIIa is typically seen in rheumatic valve disease. The valve motion is limited mostly during diastole but also to some extent during systole as a result of commissure fusion, chordae thickening, and chordae fusion. Type IIIb mitral regurgitation displays a leaflet tethering caused by papillary muscle displacement resulting either from a localized ventricular wall dyskinesia, as seen in ischemic cardiomyopathy, or from a global dilatation of the ventricle, as seen in end-stage cardiomyopathy.
