Relative size of the effective regurgitant orifice to right ventricular cavity contributes significantly to the underestimation of 2D PISA method in tricuspid regurgitation quantitation
Authors: Liu Y , Wu Y , Meng F , Chen B , Zuo W , Dong L , Shu X , Ge J 
Published: November 2023

Abstract

Background
2D proximal isovelocity surface area (PISA) method underestimates tricuspid regurgitation (TR) severity largely due to the distortion of proximal flow geometry under low jet velocity. Previous studies demonstrated that the confining wall geometry also strained the streamline distribution in the proximal flow field. This could add to the variability when applying 2D PISA in TR as TR presents with wider range of effective regurgitant orifice area (EROA).

Purpose
We aim to examine (1) the impact of ventricular wall constraint to proximal flow region on TR quantitation and (2) its relative contribution to the underestimation of 2D PISA compared with the distortion of proximal flow field under low jet velocity.

Methods
150 pts with more than mild TR underwent comprehensive echocardiographic session. The standard 2D PISA EROA (EROASD)was derived as per guideline with angle correction applied for tethering leaflets. The underetimation caused by low jet velocity was corrected by multiplying the standard EROA (EROASD) with VOrifice/(VOrifice-VNyquist), where the VOrifice stands for the peak regurgitant velocity and the VNyquist represents the color Doppler aliasing velocity (EROAVo-VN). The volumetric EROA and vena contracta area serves as two independent reference methods. The ventricular wall constraint was quantified as the ratio of reference EROA to right ventricular end-diastolic volume (RVEDV).

Results
A consistent significant underestimation by standard 2D PISA methods, either corrected for low jet velocity or not, was observed as a function of the EROA (Figure 1). In Bland-Altman analysis, correction for low jet velocity lessened the systematic underestimation but still leaves minor while could-be-important error (VCA, bias = 19.6 and 15.1 mm2; volumetric EROA, bias = 10.1 and 5.6 mm2 for EROASD and EROAVo-VN respectively). The accuracy of both methods to differentiate severe TR was similar but the cut-off values were lower compared with guideline recommendation (AUC = 0.905 and 0.903, cut-off = 0.26 and 0.29 cm2 for EROASD and EROAVo-VN respectively). In multi-linear regression model (Table 1), the difference between standard 2D PISA EROA and reference EROA (mean of volumetric EROA and vena contracta area) was significantly related to etiology, the jet velocity-related correction coefficient, and the reference EROA/RVEDV ratio. The ventricular wall constraint contributes to the underestimation of 2D PISA to a greater extent than the low jet velocity (beta = -0.269 and 0.592 for VOrifice/(VOrifice-VNyquist) and reference EROA/RVEDV respectively).

Conclusion
Correction for low jet velocity lessens the extent of underestimation of TR severity by 2D PISA method but still leaves important measurement error. The confining wall geometry to proximal flow region contributes significantly to the understimation but is not accounted for in current recommendation. This could be especially important in massive and torrential TR.