Proportionality concept of mitral regurgitation-truly valid?

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): University Medical Centre Ljubljana, Slovenia. Background The results of studies of transcatheter mitral valve repair introduced a new conceptual framework that categorized mitral regurgitation (MR) into proportionate (propMR) and disproportionate (dispropMR) according to the relationship between effective regurgitant orifice area (EROA) and left ventricular (LV) end-diastolic volume (EDV). However, pathophysiological mechanisms behind these entities have not been well defined. Purpose To identify the echocardiographic characteristics which could explain the underlying mechanism of dispropMR. Methods We retrospectively included 179 consecutive patients (age: 69±12 years, male: 132 [74%]) with HFrEF and more than mild MR referred to clinically indicated echocardiography. The disproportional cut-off value specific for our group was calculated from the theoretical line of proportionality based on the ratio EROA/EDV, considering the clinical characteristics of the study group. Correspondingly, the cut-off value for disproportionality was 0.126. Potential factors which might affect proportionality scheme were analysed: factors affecting EDV measurements (LV foreshortening) and factors affecting EROA calculation (dynamic variation of MR flow rate (MRFR) and different PISA approaches for EROA calculation: standard single-point PISA method vs. serial PISA method). Results In our cohort, 55 (32%) patients had dispropMR. Patients with dispropMR had more frequent LV foreshortened images for EDV calculation than patients with propMR (31 patients (56.4%) vs. 37 patients (32.7%); p = 0.003), resulting in smaller EDV in dispropMR group. DispropMR group had more substantial dynamic variation of regurgitant flow compared to propMR (Figure A), resulting in a more significant overestimation of MRFR in dispropMR than propMR when using instantaneous MRFR from standard single-point PISA (p = 0.001). EROA was consistently overestimated by standard single-point PISA method compared to serial PISA method (Figure B). Consequently, 73% of patients classified as dispropMR had either a foreshortened image or overestimation of EROA measurement. Conclusion Our results suggest that higher EROA/EDV ratio in dispropMR could be explained by underestimation of EDV due to LV foreshortening and overestimation of EROA by standard single-point PISA method due to more substantial dynamic variation of regurgitant flow. The data suggest that methodological limitations have an important impact on echocardiographic measurements used in the definition of proportionality. The proportionality concept is questionable and may not support the patients’ selection for treatment strategies.