Color Doppler jet area overestimates regurgitant volume when multiple jets are present

Color Doppler jet area (CDJA) is an important measure used to classify mitral regurgitation (MR) severity. The investigators hypothesized that the presence and configuration of multiple regurgitant jets can alter CDJA quantification for fixed regurgitant volumes. This has relevance to MR assessment prior to the treatment of valves with multiple regurgitant orifices or after surgical or percutaneous double-orifice mitral valve repair.

An in vitro model was developed to create jets flowing through a simulated mitral orifice into an imaging chamber. The flow loop was driven with a pulsatile pump at 60 beats/min containing a water-glycerol solution approximating the viscosity of blood. At the orifice, simulated regurgitant stroke volumes of 2.5 to 25 mL were created through plates having either single openings with orifice areas from 0.125 to 0.50 cm(2) or two to four openings with total orifice area of 0.25 cm(2) and varied linear spacing. An 8-MHz transthoracic two-dimensional ultrasound probe was used to acquire jet velocities by continuous-wave Doppler as well as color Doppler for offline analysis. CDJA values were obtained with custom automated pixel-counting software.

Peak jet velocities ranged from 30 to 550 cm/sec. For single jets, normalized average CDJA values increased nonlinearly as a function of average Reynolds number. Peak CDJA values were up to 62% higher for multiple jets compared with single jets with similar total orifice areas and simulated regurgitant stroke volumes. The presence or absence of multiple jets, rather than the total number of jets, appeared to have a greater effect on maximum CDJA. In addition, peak CDJA values for multiple jets increased with increased linear spacing.

A fixed regurgitant volume involving multiple jets will have a larger CDJA value than the same total volume from a single jet. The source of this discrepancy appears to be increased ambient fluid entrainment from adjacent regurgitant jets. This potential overestimation of MR severity using color Doppler flow jets should be taken into consideration when assessing MR prior to treatment or when assessing residual MR after double-orifice mitral valve repair.