DYNAMIC CHANGE IN MITRAL REGURGITANT ORIFICE AREA - COMPARISON OF COLOR DOPPLER-ECHOCARDIOGRAPHIC AND ELECTROMAGNETIC FLOWMETER-BASED METHODS IN A CHRONIC ANIMAL-MODEL

Objectives. The aim of the present study was to investigate dynamic ch anges in the mitral regurgitant orifice using electromagnetic flow pro bes and flowmeters and the color Doppler how convergence method. Backg round. Methods for determining mitral regurgitant orifice areas have b een described using flow convergence imaging with a hemispheric isovel ocity surface assumption. However, the shape of how convergence isovel ocity surfaces depends on many factors that change during regurgitatio n. Methods. In seven sheep with surgically created mitral regurgitatio n, 18 hemodynamic states were studied. The aliasing distances of flow convergence were measured at 10 sequential points using two ranges of aliasing velocities (0.20 to 0.32 and 0.56 to 0.72 m/s), and instantan eous flow rates were calculated using the hemispheric assumption. Inst antaneous regurgitant areas were determined from the regurgitant how r ates obtained from both electromagnetic flowmeters and flow convergenc e divided by the corresponding continuous wave velocities. Results. Th e regurgitant orifice sizes obtained using the electromagnetic how met hod usually increased to maximal size in early to midsystole and then decreased in late systole. Patterns of dynamic changes in orifice area obtained by flow convergence were not the same as those delineated by the electromagnetic flow method. Time-averaged regurgitant orifice ar eas obtained by flow convergence using lower aliasing velocities overe stimated the areas obtained by the electromagnetic pow method ([mean /- SD] 0.27 +/- 0,14 vs. 0.12 +/- 0.06 cm(2), p < 0.001), whereas flow convergence, using higher aliasing velocities, estimated the referenc e areas more reliably (0.15 +/- 0.06 cm(2)). Conclusions. The electrom agnetic how method studies uniformly demonstrated dynamic change in mi tral regurgitant orifice area and suggested limitations of the Row con vergence method.