M-mode proximal iso-velocity surface area-based dynamics of instantaneous flow rate and its implications for degenerative mitral regurgitation quantification

Abstract

Abstract Background Instantaneous flow rate of degenerative mitral regurgitation (DMR) showed dynamic changes. However, inconsistencies exist across literatures about the timing of measurements for flow convergence in proximal iso-velocity surface area (PISA) calculation. While the 2017 ASE guideline suggested measurement of PISA radius and velocity should be performed at simultaneous moments of the regurgitant phase (PISApair), a few studies used max PISA radius (PISAmax) to calculate regurgitant volume and showed poor agreement with cardiac magnetic resonance (CMR) results. Purpose This study aimed to compare the above methods with M-mode PISA, thus to investigate the effect of instantaneous flow rate on the agreement of the diagnosis of severe mitral regurgitation (sMR). Methods We prospectively enrolled 75 DMR patients with a) at least mild MR, b) single and non- eccentric MR jet. Regurgitant volume (RVol) was calculated using three PISA methods, respectively. In 25 patients who received CMR, RVol was calculated using volumetric method. The correlation and agreement of RVol among three PISA methods and CMR were compared. The agreements of the diagnosis of sMR between PISA methods and ASE multi-parameter algorithm were analyzed using Cohen’s kappa analyses. Results The curve of instantaneous flow rate of DMR displayed unimodal pattern with at the mid-late systolic phase. The correlation of RVol between PISA methods and CMR were moderate for PISAmax (r = 0.77) and strong for PISApair and M-mode PISA ( r = 0.80 and 0.87, respectively). PISAmax derived RVol was larger than that of CMR (69.1 ± 37.1 mL versus. 49.0 ± 29.0 mL, P = 0.002). Compared to the ASE algorithm, only PISAmax significantly overestimated the percentages of sMR (74.7% versus 54.7%, P =0.010), but both PISAmax and PISApair showed moderate consistency (Kappa coefficient (k): 0.496 and 0.525, respectively). A strong agreement was found between M-mode PISA and the ASE algorithm with regard to the diagnosis of sMR (k = 0.867, P <0.05). Conclusion Based on the unimodal pattern of instantaneous flow rate in DMR patients, PISAmax significantly overestimated RVol and may expose a significant proportion of DMR patients to MR surgery.