Estimation of mitral regurgitation with a hemielliptic curve-fitting algorithm: in vitro experiments with native...

To date, studies on the mitral flow convergence method have used rigid, circular, or slit orifices to represent the regurgitant orifice. In this study, explanted porcine mitral valves, with the entire mitral apparatus preserved, were mounted in an in vitro model to reproduce the three-dimensional regurgitant orifice geometry while permitting close control and measurement of the experimental conditions. This experimental setup permitted the evaluation of the hemispheric and hemielliptic formulas under realistic physiologic conditions. In this study, a heart rate of 70 beats/min was used with cardiac outputs between 1.5 and 6 L/min. Peak regurgitant flow rates ranged from 7 to 16 L/min (regurgitant jet velocities ranged from 2 to 5.5 m/sec); peak aortic flow rates ranged from 9 to 30 L/min. Four native mitral valves were used for these studies for a total of 28 stages. Although the hemielliptic modification has previously shown success in vitro and computationally, it has not been used clinically because of difficulty imaging the flow convergence region in three orthogonal planes. A curve-fitting algorithm was developed to extract the hemielliptic dimensions from two standard ultrasound views by rotating the transducer 90 degrees. Improved agreement was obtained between true and calculated flow rates by the hemielliptic formula (y = 1.02 x + 0.29; r = 0.91) compared with the hemispheric formula (y = 1.18 x - 2.2; r = 0.66). This method provides accurate results with a realistic three-dimensional regurgitant orifice geometry and has the capability of being incorporated as a function key on an ultrasound machine for clinical application.