Functional anatomy and echocardiographic assessment in secondary mitral regurgitation

Abstract

Background: Mitral valve apparatus is complex and involves the mitral annulus, the leaflets, the chordae tendinae, the papillary muscles as well as the left atrial and ventricular myocardium. Secondary mitral regurgitation is a consequence of regional or global left ventricle remodeling due to an acute myocardial infarction (75% of cases) or idiopathic dilated cardiomyopathy (25% of cases). It is associated with an increase in mortality and poor outcome. There is a potential survival benefit deriving from the reduction in the degree of severity of mitral regurgitation. So the correction of the valve defect can change the clinical course and prognosis of the patient. The rationale for mitral valve treatment depends on the mitral regurgitation mechanism.Therefore, it is essential to identify and understand the pathophysiology of mitral valve regurgitation. Aim of the Study:The aim of this review is to describe the crucial role of transthoracic and trans-esophageal echocardiography, in particular with threedimensional echocardiography, for the assessment of the severity of secondary mitral regurgitation, anatomy, and hemodynamic changes in the left ventricle.Moreover, the concept that the mitral valve has no organic lesions has been abandoned. The echocardiography must allow a complete anatomical and functional evaluation of each component of the mitral valve complex, also useful to the surgeon in choosing the best surgical approach to repair the valve.Conclusions: Echocardiography is the first-line imaging modality for a better selection of patients, according to geometrical modifications of mitral apparatus and left ventricle viability, especially in preoperative phase.

Parameters of the mitral apparatus in patients with ischemic and nonischemic dilated cardiomyopathy

“…31 Moreover, the presence of a left bundle branch block may contribute to worsening MR, since papillary muscle contraction becomes dyssynchronous, resulting in complex LV longitudinal, circumferential, and rotational LV mechanics modifications. 25 Leaflet remodeling is also hypothesized to play a role in the development of MR. 21 Patients with mild or low MR seem to have more elongated anterior leaflets, protecting them from valve regurgitation, 32 supporting the theory that the anterior leaflet may actively reshape in response to the mechanical stretching that is exerted. 21,32 This complex interplay of papillary muscle displacement, systolic symmetric or asymmetric leaflet tetherings, regional or global LV remodeling, annular dilatation and flattened shape, along with abnormal leaflet remodeling, may result in incomplete mitral leaflet closure and consequent MR after myocardial infarction, even in the absence of organic mitral valve disease.…”

“…20 Each papillary muscle distributes chordae to the ipsilateral half of both leaflets. 21 Chordae hold both leaflets in position to guarantee coaptation during systole without extrusion into the LA. 20 Normally, the LV comprises two papillary muscles one anterolateral, arising from the LV apicolateral third, and one posteromedial, arising from the middle of the LV inferior wall.…”

“…22 Annular dilation is another finding that plays an additional role in the development of ischemic MR. Post-myocardial infarction, the mitral annular shape tends to become flattened, losing its usual saddle shape and overall height. 21 Furthermore, its diameter and area tend to increase significantly, which further aggravates the insufficiency. 21 This change is frequently asymmetric and often occurs with a higher magnitude along the posterior annulus, as this is an area under increased stress and less densely fibrotic.…”

“…The increased LV sphericity index leads to radial papillary muscle displacement, symmetric mitral valve leaflet tethering, and sMR. 21,22,25 Another major influencing factor is mitral annulus dilatation and loss of annular contraction. 35 As a consequence of myocardial disease, there is increased circularization and a reduction in ring height.…”

“…25 However, in contrast to ischemic MR, the annulus enlargement is usually symmetric in non-ischemic circumstances. 21 Mitral valve leaflets also seem to readapt in response to tethering. 36 Just like in ischemic MR, the degree of remodeling may explain the differences in valve competency, despite significant ventricular dilation.…”