JCMR 2021; 23.138. Direct mitral regurgitation quantification in hypertrophic cardiomyopathy using 4D flow CMR jet tracking: evaluation in comparison to conventional CMR-Article

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This study evaluated whether 4D flow CMR jet tracking can directly measure mitral regurgitation (MR) in patients with hypertrophic cardiomyopathy (HCM), instead of relying on the usual indirect volumetric CMR method. The indirect method estimates MR as left ventricular stroke volume minus forward aortic flow, but in HCM this can be error-prone because of variable ventricular contouring and abnormal outflow patterns.<br /><br />The retrospective study included 37 adults with HCM. MR severity was measured by both CMR methods and compared with clinical transthoracic echocardiography (TTE) performed near the time of CMR. The direct 4D flow approach tracked the MR jet through systole by placing reformatted planes at the jet’s peak velocity and integrating regurgitant flow over time.<br /><br />Results showed good agreement between direct jet tracking and the indirect volumetric method for MR volume, but only fair agreement for MR severity. Compared with echocardiography, direct jet tracking agreed better than the indirect method. Importantly, direct jet tracking was highly reproducible between observers and within the same observer, with excellent intraclass correlation and kappa values. It was also slightly faster to analyze than the indirect approach.<br /><br />The main source of variability in the indirect method was end-systolic volume measurement. Overall, the authors conclude that while indirect CMR quantification of MR in HCM has limited reproducibility, 4D flow CMR jet tracking is a promising alternative that directly measures MR with better reproducibility, better agreement with echo, and shorter analysis time.

Keywords

4D flow CMR

mitral regurgitation

hypertrophic cardiomyopathy

jet tracking

cardiac magnetic resonance

volumetric method

transthoracic echocardiography

regurgitant flow

reproducibility

intraclass correlation