Mitral Valve Coaptation Reserve – Identifying the at-Risk Valve

LEAFLET APPOSITION maintains systolic competence of the mitral valve (MV), and although the absence of regurgitation is often considered evidence of normal MV function, valves may, in fact, be at varying degrees of risk for developing mitral regurgitation (MR) based on the coaptation reserve. In primary MR, the structural derangements of the MV are clearly identifiable; however, the assessment of changes in MV geometry in patients with functional MR is complicated and not as well-understood, possibly because of the heterogeneous remodeling of the MV apparatus in response to ischemia.1Shakil O Jainandunsing JS Ilic R et al.Ischemic mitral regurgitation: An intraoperative echocardiographic perspective.J Cardiothorac Vasc Anesth. 2013; 27: 573-585Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar The assessment of geometric indices of MV remodeling previously has been considered an offline research technique; however, with advances in computational power, complex dynamic geometric analysis of the valvular apparatus can now be performed in near real-time.2Warraich HJ Shahul S Matyal R et al.Bench to bedside: Dynamic mitral valve assessment.J Cardiothorac Vasc Anesth. 2011; 25: 863-866Abstract Full Text Full Text PDF PubMed Scopus (15) Google Scholar Consequently, this has led to an increasing interest in attempting to understand the geometric changes of the MV apparatus in response to ischemic insults. Regardless of its nature, the endpoint of remodeling results in the depletion of the zone of apposition between the anterior and posterior MV leaflets. The extent of apposition, known as coaptation reserve or coaptation depth, is the measurable final endpoint for maintaining systolic competence of the MV.3Zoghbi WA Adams D Bonow RO et al.Recommendations for noninvasive evaluation of native valvular regurgitation: A report from the American Society of Echocardiography Developed in Collaboration with the Society for Cardiovascular Magnetic Resonance.J Am Soc Echocardiogr. 2017; 30: 303-371Abstract Full Text Full Text PDF PubMed Scopus (1868) Google Scholar Therefore, coaptation depth can be used to predict the likelihood of the MV apparatus of sustaining ischemia-related remodeling. This implies that a nonregurgitant MV with reduced coaptation reserve, although considered normal, is at a greater risk of developing future regurgitation than a valve with a larger coaptation reserve. Ischemia-related remodeling of the MV apparatus results in apical displacement of the coaptation point, leading to a reduction in coaptation reserve. Traditional geometric indices to assess the degree of remodeling include measurement of tenting height and tenting area, which act as surrogates for the assessment of coaptation reserve. Although not directly measured, depletion of coaptation is implied with more apical displacement of the coaptation point. Since the measurement of tenting height and tenting area are based on single tomographic sectional planes, they do not represent the entire topography of the MV. Predictably, Mufarrih et al. recently have demonstrated 3-dimensionally (3D)-derived tenting volume to have a stronger negative correlation with coaptation area.4Mufarrih SH Sharkey A Mahmood F et al.Geometric indices for predicting ischemic mitral regurgitation: Correlation of mitral valve coaptation area with tenting height, tenting area and tenting volume.J Cardiothorac Vasc Anesth. 2023; 37: 8-15Abstract Full Text Full Text PDF PubMed Scopus (2) Google Scholar Technologic advances in 3D echocardiographic imaging have made it possible to measure the individual coaptation depths at different points along the closure line, as described by Jainandunsing et al.5Jainandunsing JS Massari D Vos JJ et al.Mitral valve coaptation reserve index: A model to localize individual resistance to mitral regurgitation caused by annular dilation.J Cardiothorac Vasc Anesth. 2023; 37: 690-697Abstract Full Text Full Text PDF Scopus (1) Google Scholar The results of this study are in congruence with traditional thinking that patients with structurally normal valves will have maximal depth at the central coaptation point (ie, A2-P2 region). However, this fails to explain the central jet of regurgitation often seen in patients with functional MR. It is possible that clinicians have been considering absolute values of coaptation depths at different points as a sole function of coaptation reserve at those points, whereas coaptation reserve is also a function of circumferential expansion of the annulus and indexing to account for annular dilation is paramount. The article published by Jainandunsing et al. is a significant advance in this context. Using a sophisticated algorithm, they have attempted to identify a certain structural reserve in individual MVs. They have described that structural remodeling is a heterogeneous phenomenon, with consequent variations in the structural reserve, and there are specific indices that explain the sustainability of MV leaflets at different locations in relation to progressive annular dilatation. This study challenged conventional thinking that in a structurally normal MV, the A2-P2 segment has the highest coaptation reserve relative to the more commissural segments. Interestingly, in their study, the least coaptation reserve index in most patients was at A2-P2, which further explained the larger proportion of patients with a central jet of functional MR. It is also noteworthy that the coaptation reserve index exactly correlated with the location of MR jets in 66% of their patients with trace-to-mild MR. Although this is a huge leap forward in understanding the heterogeneity of cardiac remodeling, this model certainly has some limitations. Firstly, the idea presented was largely based on the assumption that the mitral annulus is a planar structure, whereas annular dilatation is a circumferential phenomenon. Secondly, this mathematical rendition of coaptation reserve index between MV leaflets is a cumbersome process in its current form, and implementation in real-time would be a challenge. Also, a clearer definition of coaptation reserve requires accurate measurement of the degree of apposition of leaflets across the line of coaptation, which necessitates 3D imaging with higher frame rate and line density, and cannot be assessed accurately with R-wave-gated images. Moving forward, it will be a significant challenge to define the indices of the changing morphology of the mitral annulus, leaflets, and papillary muscles during different phases of the cardiac cycle and determine their impact on valvular integrity. This is indeed a very interesting time when advancements in noninvasive imaging have taken the field this far in understanding the complex geometry of MV. On the other hand, artificial intelligence has made it possible to incorporate complex algorithms all in one place to predict the future and change its course. In its current format, the coaptation area is calculated manually, with significant user input, and is an offline technique. To be clinically feasible, this technique has to be available online with significant workflow enhancements. However, this should not take away the clinical value of this concept. Jainandansing et al. have opened the door to preemptively identify, with a degree of precision, MVs at the risk of coaptation failure. Dr Feroze Mahmood receives financial compensation for the production of educational material for GE Medical. Mitral Valve Coaptation Reserve Index: A Model to Localize Individual Resistance to Mitral Regurgitation Caused by Annular DilationJournal of Cardiothoracic and Vascular AnesthesiaVol. 37Issue 5PreviewThe objective of this study was to develop a mathematical model for mitral annular dilatation simulation and determine its effects on the individualized mitral valve (MV) coaptation reserve index (CRI). Full-Text PDF Open Access