Introduction
Coronary atherosclerotic heart disease (CHD) is a common disease in the elderly. IMR is a functional mitral regurgitation secondary to the chronic coronary heart disease and LV remodeling. Up to 60% of patients with myocardial infarction have IMR[1]. The typical reason is that the geometric changes in the left ventricle following myocardial injury impede sufficient coaptation of normal mitral leaflets[2]. The MV, as a one-way valve, ensures a certain blood volume circulating from left atrium to left ventricle. The MV apparatus is a complicated structure consisting of anatomic components (leaflets, fibromuscular annulus, chords, papillary muscles and the underlying myocardium). The MV apparatus interact to maintain the MV competent during the cardiac cycle[3]. During systole, MV closure includes a dynamic interaction between anatomical and physiological factors (preload, afterload and contractility) to reach the maximum mitral coaptation so as to prevent regurgitation. The intraoperative MV function analysis should start with the quantification of mitral regurgitation (MR) and the diagnosis of related mechanism[4]. IMR is a common complication of the left ventricular global or local pathological remodeling caused by acute or chronic coronary artery disease[5]. It is a form of systolic incompetence, that is, the consequence of progressive annular dilation or leaflet retraction with gradual reduction and failure of systolic leaflet apposition[2]. It often represents the pathological results of increased tethering forces and decreased MV leaflets coaptation[6]. Therefore, the degree of apposition serves as a “mitral valve reserve” function that allows the apparatus to sustain further remodeling without overt systolic incompetence[7,8]. Ring annuloplasty is usually performed to reduce the annular area, increase the valvular coaptation zone, and reduce the severity of MR[9]. However, the remodeling of the MV apparatus in IMR can be heterogeneous that there may be a variable degree of apposition/reserve along the line of coaptation[10,11]. Depending upon the available reserve, the upper limit of the normal mitral annular diameter is MV specific and perhaps region specific within the same MV. The appreciation of spatial variation of MV reserve brings into question the utility of normative values of mitral annular diameter routinely used for patient selection for annuloplasty[12,13]. The “mitral valve reserve” function is determined by the pathophysiology of the underlying disorder, and an extensive discussion about these changes is beyond the scope of this review. However, a brief introduction of “mitral valve reserve” function is important for surgical decisions making from the intraoperative echocardiographic perspective.
Intraoperative Mitral Regurgitation Assessment