Muscle Matters: CMR Tissue Characterization for Mechanistically Tailored Risk Stratification of Functional Mitral Regurgitation

Functional Mitral Regurgitation; Cardiac Magnetic Resonance (CMR); Cardiomyopathy Functional mitral regurgitation (FMR) is a leading cause of valvular heart disease that markedly increases risk of heart failure, arrhythmia, and death.1,2 FMR stems from maladaptive left ventricular (LV) remodeling that leads to malcoaptation of intrinsically normal mitral leaflets.While FMR broadly refers to mitral incompetence stemming from adverse LV remodeling, mechanism for this varies.In ischemic cardiomyopathy (ICM), localized myocardial injury (ischemia or infarction) in regions underlying the mitral valve can result in mitral valve tethering and insufficiency.3,4 In non-ischemic cardiomyopathy (NICM), diffuse myocardial fibrosis augments LV stiffness, which can increase mitral afterload and contribute to FMR.Myopathic contributors to FMR can also be mixed, with both infarction and non-ischemic fibrosis co-existing.Given differences in mechanism and imprecision of clinical assessment, myocardial tissue characterization imaging is well-suited to improve clinical decision-making and prognostic outcomes for patients with FMR.Cardiac MRI (CMR) enables assessment of myocardial tissue properties that can provide a nidus for mitral dysfunction, modify therapeutic response, and drive adverse outcomes in FMR.Infarct transmurality on late gadolinium enhancement (LGE) CMR has been shown to predict LV remodeling response to revascularization. 5 LGE-CMR evidenced focal non-ischemic fibrosis is known to occur with FMR, and increase with LV dilation.6,7 Regarding MR, current guidelines rely primarily on echocardiography-based thresholds that are uniform irrespective of MR etiology.8 While guidelines encompass LV performance and dimensions as criteria for mitral repair or replacement, 9 CMR enables quantification of myocardial tissue characteristics that provides incremental prognostic value beyond LV function and geometry.10,11 It is also known that mortality in FMR increases at lower thresholds due to underlying cardiomyopathy; even mild MR is associated with adverse outcomes with myocardial injury contributing to risk.12,13 These concepts highlight the importance of refining current algorithms to grade and risk stratify FMR in order to account for mechanistic etiology of mitral valve dysfunction.