What can CMR provide?
Until the last decade, the majority of textbooks mostly decried the use of CMR for valvular pathology. Early adopters in this field however recognized the substantial attributes attendant to CMR based on its spatial resolution, inherent physics and mathematical capabilities and, chiefly, on its non-reliance on a pure visual assessment to formally quantify mitral regurgitation. CMR innately provides highly accurate and reproducible assessment of left and right atrial and ventricular size and function with superior endocardial definition and has become the ‘gold standard’ for evaluating cardiac chamber size. (10,15-17). It is then a natural extension to apply all of the considerations of an ideal chamber volumetric capability towards a valvular volumetric challenge. (Table I)
A comprehensive CMR study is able to quantitate both atrial and ventricular remodeling, which plays a crucial role in understanding both the severity as well as the mechanism of regurgitation. Quantitative parameters include regurgitant volume, regurgitant fraction, and regurgitant orifice area. CMR offers several important advantages in the assessment of MR. (4,7,10) This includes identifying the mechanism of MR, quantifying MR severity, and determining its consequences on cardiac remodeling. CMR can provide information about the mechanism of MR by identifying morphologic abnormalities of the MV apparatus (Figure 1, Figure 2). (18) Dedicated cine imaging on a CMR study can offer insights into pathology of mitral valve leaflets including the presence of prolapse or flail leaflets. (Figure 2, Figure 3a, Figure 3b). (19,20)
Two multicenter observational studies have clearly defined the role of CMR quantification of primary MR and its use to be a better predictor for mortality than echocardiography.(21,22) In one study, there was high disagreement between echocardiography and MRI derived regurgitation volumes, especially in patients with multiple or late systolic jets of MR.(22) These studies point to a multi-modality approach in predicting mortality, follow up and interventions in MR.
In secondary MR, CMR offers accurate assessment of LV dilation and function in addition to identification of myocardial and papillary muscle scar. (23,24) Additionally, late gadolinium enhancement in CMR in patients with MR can provide additional consolidating information about features such as myocardial infarct size as well as the significance of scarring of papillary muscles and mitral valve fibrosis. (25-27)