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