Chapter 7

The evaluation of valvular heart disease has become increasingly dependent on echocardiography. Since its introduction to the operating room, transesophageal echocardiography (TEE) has played a major role in surgical decision making and anesthetic management of patients undergoing mitral valve surgery. Mitral valve replacement has its own implications and is not free of risk, leading surgeons to develop techniques for mitral valve repair, which are becoming more and more intricate as our understanding of valve function expands. Recent outcome literature indicates strong support for repair relative to replacement in patients with organic, nonischemic mitral valve pathology,1 and the role of intraoperative TEE in mitral valve repair2 and replacement surgery3 is well established. A good knowledge of mitral valve anatomy and its assessment by TEE is therefore vital to any successful intraoperative echocardiographer.

The mitral valve is located between the left atrium and the left ventricle and allows unidirectional flow of blood towards the left ventricle, prevents backward flow of blood into the left atrium during left ventricular systole, and allows unobstructed flow of blood to the left ventricle during diastole, maintaining low left atrial pressures. The anterior mitral valve leaflet also forms part of the left ventricular outflow tract and allows for unimpeded left ventricular ejection during systole. For the mitral valve to function normally, it relies on the integrated function of a number of structures, which are collectively referred to as the mitral valvar complex. This complex consists of the anterior (aortic) and posterior (mural) leaflets, together with the annulus, chordae tendineae, papillary muscles, and left ventricle. Abnormalities of any of these structures can result in valvular dysfunction, and should therefore be included in the comprehensive evaluation of the mitral valve.4

### Mitral Valve Leaflets and Commissures

Two leaflets separated by two commissural areas cover the mitral valve area during systole. The anterior or aortic leaflet is situated anteriorly and to the right, adjacent to and in continuum with the aortic valve, and occupies approximately one-third of the annular circumference. Both the aortic and mitral valves contribute to the so-called fibrous skeleton of the heart, and the connection between the two is sometimes described as the aortomitral continuity. The posterior or mural leaflet occupies the remaining two-thirds of the annular circumference and is much narrower than the anterior leaflet. Although the posterior leaflet appears to have less height than the anterior leaflet, they are similar in surface area. The posterior leaflet is subdivided into three scallops by clefts. The scallop adjacent the anterolateral commissure is named P1, with P3 situated on the other end of the posterior leaflet in close relation to the posteromedial commissure. P2 is the middle scallop in between P1 and P3. Even though the anterior leaflet is not anatomically divided into scallops, the areas opposing the posterior leaflet are correspondingly referred to as the A1, A2, and A3 segments (Figure 7–1).5 Closure of the valve requires apposition ...

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