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Quantification of regurgitant fraction in mitral regurgitation by cardiovascular magnetic resonance: comparison of techniques.

BACKGROUND AND AIM OF THE STUDY
Cardiovascular magnetic resonance (CMR) assessment of mitral regurgitant volume from the subtraction of the right ventricular stroke volume (RVSV) from left ventricular stroke volume (LVSV) has commonly been performed using volumetric techniques. This is sensitive to errors in RVSV visualization and regurgitation of other heart valves, and therefore subtracting aortic flow volume from LVSV may be preferable. The study aim was to compare both techniques in a single CMR examination.


METHODS
Twenty-eight patients with isolated mitral regurgitation underwent left ventricular (LV) and right ventricular (RV) volumetry and aortic flow volume measurements. Mitral regurgitant fraction (RF) was calculated as either RF(VOL) = [LVSV - RVSV] or RF(FLOW) = [LVSV - aortic flow volume], both expressed as a fraction of LVSV. The agreement of the measurements was assessed as a measure of robustness in clinical practice.


RESULTS
There was good agreement between aortic and pulmonary flow (mean +/- SD difference -0.8 +/- 8.1 ml), and aortic flow volume and RVSV by volumetry (mean difference -2.6 +/- 11.8 ml). Intra- and interobserver variability (SD) of aortic flow volume (+/-6.6 ml and +/-5.3 ml) was superior to that of the RVSV (+/-8.5 ml and +/-12 ml). The intra- and inter-observer variability (SD) of RF(FLOW) was lower (+/-4.8% and +/-7.7%) than by RF(VOL) (+/-6.7% and +/-8.8%).


CONCLUSION
The RF(FLOW) technique maximized intra- and inter-observer agreement, and is the optimal CMR technique to quantify mitral regurgitation. RF(FLOW) also has the advantage of allowing correction for aortic regurgitation when it is present, and is potentially independent of the effects of tricuspid and pulmonary regurgitation.