Computational Analysis of Virtual Echocardiographic Assessment of Functional Mitral Regurgitation for Validation of Proximal Isovelocity Surface Area Methods

Abstract

Mitral regurgitation (MR) quantification by the proximal isovelocity surface area (PISA) method remains challenging. Using computer models, the authors evaluated the accuracy of different PISA methods and quantified their errors. Five functional MR computer models of different geometric and tethering abnormalities were created, validated, and treated as phantom models, from which the reference values were directly obtained. Virtual two-dimensional (2D) PISA and three-dimensional (3D) PISA (both peak and integrated values) were performed on these phantom models. By comparing virtual PISA results with reference values, the accuracy of different PISA methods was evaluated, and their sources of errors were quantified. Compared with reference values of regurgitant flow rate, excellent correlations were found for true PISA (r=0.99, bias=32.3±35.3mL/sec), 3D PISA (r=0.97, bias=-24.4±55.5mL/sec), followed by multiplane 2D hemicylindrical PISA (r=0.88, bias=-24.1±85.4mL/sec) and hemiellipsoidal PISA (r=0.91, bias=-55.7±96.6mL/sec). Weaker correlations were found for single-plane 2D hemispherical PISA (parasternal long-axis: r=0.71, bias=-77.6±124.5mL/sec; apical two-chamber: r=0.69, bias=-52.0±122.0mL/sec; apical four-chamber: r=0.82, bias=-65.5±107.3mL/sec). For regurgitant volume quantification, integrated PISA was more accurate than peak PISA. The bias of 3D PISA improved from -12.7±7.8mL (peak PISA) to -2.1±5.3mL (integrated PISA). For functional MR quantification, 2D hemispherical PISA had significant underestimation, multiplane 2D hemiellipsoidal and hemicylindrical PISA showed improved accuracy, and 3D PISA was the most accurate. The PISA method is subject to both systematic underestimation due to the Doppler angle effect and systematic overestimation when regurgitant flow is not perpendicular to PISA contour. Integrated PISA is able to capture dynamic MR and is therefore more accurate than peak PISA. The sum of regurgitant flow rates is the most feasible way to perform integrated PISA.