Three-Dimensional Field Optimization Method: Clinical Validation of a Novel Color Doppler Method for Quantifying Mitral Regurgitation

Background Assessment of mitral regurgitation (MR) severity by echocardiography is important for clinical decision making, but MR severity can be challenging to quantitate accurately and reproducibly. The accuracy of effective regurgitant orifice area (EROA) and regurgitant volume (RVol) calculated using two-dimensional (2D) proximal isovelocity surface area is limited by the geometric assumptions of proximal isovelocity surface area shape, and both variables demonstrate interobserver variability. The aim of this study was to compare a novel automated three-dimensional (3D) echocardiographic method for calculating MR regurgitant flow using standard 2D techniques. Methods A sheep model of ischemic MR and patients with MR were prospectively examined. Patients with a range of severity of MR were examined. EROA and RVol were calculated from 3D color Doppler acquisitions using a novel computer-automated algorithm based on the field optimization method to measure EROA and RVol. For an independent comparison group, the 3D field optimization method was compared with 2D methods for grading MR in an experimental ovine model of MR. Results Fifteen 3D data sets from nine sheep (open-chest transthoracic echocardiographic data sets) and 33 transesophageal data sets from patients with MR were prospectively examined. For sheep data sets, mean 2D EROA was 0.16 ± 0.05 cm2 , and mean 2D RVol was 21.84 ± 8.03 mL. Mean 3D EROA was 0.09 ± 0.04 cm2 , and mean 3D RVol was 14.40 ± 5.79 cm3 . There was good correlation between 2D and 3D EROA ( R = 0.70) and RVol ( R = 0.80). For patient data sets, mean 2D EROA was 0.35 ± 0.35 cm2 , and mean 2D RVol was 58.9 ± 52.9 mL. Mean 3D EROA was 0.34 ± 0.29 cm2 , and mean 3D RVol was 54.6 ± 36.5 mL. There was excellent correlation between 2D and 3D EROA ( R = 0.94) and RVol ( R = 0.84). Bland-Altman analysis revealed greater interobserver variability for 2D RVol measurements compared with 3D RVol using the 3D field optimization method measurements, but variability was statistically significant only for RVol. Conclusions Direct automated measurement of proximal isovelocity surface area region for EROA calculation using real-time 3D color Doppler echocardiography is feasible, with a high correlation to current 2D EROA methods but less variability. This novel automated method provides an accurate and highly reproducible method for calculating EROA.