4D Flow cardiac magnetic resonance quantification of mitral regurgitation, comparison with transthoracic echocardiography

Background Mitral valve regurgitation (MR) is primarily assessed by a multiparametric approach with transthoracic echocardiography (TTE) that can be further completed by 2D Cardiac Magnetic Resonance (2D CMR) in case of doubt or poor acoustic window. TTE and 2D CMR have nevertheless imperfect agreement for MR quantification. Time-resolved phase-contrast CMR with flow-encoding in three spatial directions (4D Flow CMR) could help in MR quantification. Purpose Compare 4D Flow CMR quantification of MR with TTE using a multiparametric approach. Methods We conducted a prospective study at the Institut Mutualiste Montsouris in Paris between November 2016 and 2017 including patients with chronic primitive MR. MR was evaluated with a multiparametric approach by two cardiologists with TTE and quantitatively by two radiologists with 4D Flow CMR. MR was classified as mild, moderate or severe and evaluated blindly with consensus in case of disagreement. 4D Flow CMR quantified MR regurgitant volume (RV) and MR regurgitant fraction (RF). 4D anterograde mitral flow was compared to left ventricular stroke volume using 2D-cine CMR. Results Thirty-three patients were included. Inter-observer agreement was good in TTE (kappa = 0.75 95%CI [0.57–0.92]) and excellent in 4D Flow CMR (ICC = 0.94 95%CI [0.79–0.95]). Agreement with TTE was excellent using optimized thresholds (Mild: RV ≤ 20 mL RF ≤ 20%, Moderate: RV = 21–39 mL RF = 21–36%, Severe: RV ≥ 40 mL RF ≥ 37%): kappa = 0.93 95%CI [0.8–1] for RV and kappa = 0.90 95%CI [0.7–0.9] for RF. A validation cohort confirmed that the 4D flow thresholds as determined were accurate for MR grading. Agreement between 4D anterograde mitral flow and 2D-cine CMR left ventricular stroke volume was also excellent (ICC = 0.92 95%CI [0.85–0.96]). Conclusion 4D Flow CMR is a reliable tool for MR quantification. Providing direct quantitative evaluation of MR with low inter-observer variability, it may therefore be used as a gatekeeper before therapeutic decisions such as surgery.