Challenges and pitfalls in classification of disproportionate mitral regurgitation

The concept of disproportionate mitral regurgitation (dispropMR) has been introduced to identify patients with functional mitral regurgitation (MR) who benefit from percutaneous treatment. We aimed to examine echocardiographic characteristics behind this entity. We retrospectively included 172 consecutive patients with reduced left ventricular ejection fraction (LVEF), and more than mild MR referred to clinically indicated echocardiography. According to the proportionality ratio (effective regurgitant orifice area (EROA)/left ventricular end-diastolic volume (LVEDV)) patients were divided into dispropMR and proportionate MR (propMR) group. Potential factors which might affect proportionality definition were analyzed. 55 patients (32%) had dispropMR. Discrepant grading of MR severity was observed when using regurgitant volume (RegVol) by proximal isovelocity surface area (PISA) method or volumetric method, with significant discordance only in dispropMR (p < 0.001). Patients with dispropMR had more frequently left ventricular foreshortened images for LVEDV calculation than patients with propMR (p = 0.003), resulting in smaller LVEDV in dispropMR group. DispropMR group had more substantial dynamic variation of regurgitant flow compared to propMR. Accordingly, EROA was consistently overestimated by standard single-point PISA method compared to serial PISA method. This was more pronounced in dispropMR (bias:10.5 ± 28.3 mm²) compared to propMR group (bias:6.4 ± 12.8 mm²). DispropMR may be found in roughly one third of clinically indicated echocardiographic studies in patients with reduced LVEF and more than mild MR. EROA overestimation due to dynamic variation of regurgitant flow and LVEDV underestimation due to LV foreshortening were more frequently found in dispropMR. Our results indicate that methodological limitations of echocardiographic MR grading could not be neglected in classifying the proportionality of MR.