Insights into functional mitral regurgitation using the average pixel intensity method

Previously we introduced and validated the average pixel intensity (API) method for grading mitral regurgitation (MR) in a heterogeneous MR population. We now investigated the feasibility and added value of the API method more specifically in patients with functional MR (FMR). We consecutively enrolled 283 patients with pure FMR. Transthoracic echocardiography was performed and MR was assessed using the API method and guideline-recommended parameters, including color Doppler, vena contracta width (VCW) and proximal isovelocity surface area (PISA)-based methods. The API method had an applicability of 98% in this FMR cohort, which was significantly higher than VCW (84%) and PISA-based methods (75%). Overall, the API method had significant correlations with direct parameters of FMR severity, ejection fraction, atrial and ventricular dimensions, pulmonary pressures and New York Heart Association class. Analysis of the API dynamics during MR revealed a typical pattern with early and late systolic peaks in API and a midsystolic nadir, which matched the temporal changes of the effective regurgitant orifice (ERO) during FMR. Based on ROC curves of established FMR severity cut-offs, an API value of 125 au was considered the optimal cut-off to determine severe MR. Interestingly, this API severity cut-off is similar to the API severity cut-off for MR in degenerative MR (DMR), despite different EROA/RV cut-offs in current ESC guidelines for FMR and DMR. The API method is an easy, fast and feasible parameter for grading FMR and may complement the multiparametric assessment of FMR in daily clinical practice.