Anatomy of the coronary arteries with resepct to chronic ischemic mitral regurgitation
Chronic mitral regurgitation is an important complication among patients with obstructive coronary artery disease. Approximately 30% of patients considered for coronary bypass surgery show some degree of mitral valve incompetence [5]. Mitral regurgitation
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Introduction
Chronic mitral regurgitation is an important complication among patients with obstructive coronary artery disease. Approximately 30% of patients considered for coronary bypass surgery show some degree of mitral valve incompetence [5]. Mitral regurgitation, moreover, has a tendency to increase steadily because of dilation of the mitral valve annulus. The left ventricular cavity dilates to accomodate the increase in diastolic volume and remodels itself by reactive hypertrophy of the non-ischemic wall segments [2]. A rise in end-diastolic pressure may develop, creating a further impediment to transmural myocardial perfusion in an already compromised myocardium because of obstructive coronary artery disease [3]. Within this setting papillary muscle dysfunction is generally accepted as the prime mechanism underlying chronic mitral regurgitation [4, 8]. The present survey will focus on some of the anatomic factors involved in this functional disorder. Mitral valve anatomy
The mitral valve is composed ofleaflets, chordae tendineae, and papillary muscles. The latter are direct continuations of ventricular myocardium and, for that reason, are dependent on coronary perfusion. The position of the papillary muscles, with respect to the overlying mitral valve leaflets, is crucial to guarantee an optimal support (Fig. 1). Changes in left ventricular geometry may affect the position of one or both papillary muscle groups and, hence, may result in a potentially inadequate support of the leaflets. Global distension to the left ventricular cavity, for instance, due to left ventricular volume overload, may cause lateral displacement of the papillary muscle groups and mitral regurgitation. Local dilation in case of regional myocardial infarction may cause neighboring papillary muscle groups to be displaced, thus interfering with proper valve functioning. In this context it is important that considerable variations may exist in the architecture of both papillary muscle groups. The anterolateral group usually is formed by a conglommerate of papillary muscles. The posteromedial papillary muscle group, on the other hand, is tethered to the left ventricular wall over a wide area and usually contains multiple heads. It is obvious that proper mitral valve function is jeopardized once the papillary muscles or adjacent left ventricular myocardium are affected by ischemia. From a functional point of view , therefore, the papillary muscles and left ventricular 17 H. O. Vetter et al. (eds.), Ischemic Mitral Incompetence © Springer-Verlag Berlin Heidelberg 1991
Fig. 1. Left ventricular view showing the anterolateral and the posteromedial papillary muscle groups (PMs) directly underneath the mitral valve leaflets .
myocardium are considered part of the mitral valve . The term "mitral valve apparatus" is based on this concept [7]. Mitral valve anatomy is even more complex, at least from a functional point of view, since the fibrous core of the leaflets usually is directly continuous with the fibrous annulus, while the atrial lining
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