EVALUATION OF MITRAL REGURGITATION USING A DIGITALLY DETERMINED COLORDOPPLER FLOW CONVERGENCE CENTERLINE ACCELERATION METHOD - STUDIES IN AN ANIMAL-MODEL WITH QUANTIFIED MITRAL REGURGITATION

Background The imaging and measurement of the proximal flow convergenc e region in the left ventricle have been reported to be useful for ide ntifying the site of mitral regurgitation (MR) and for evaluating its severity. However, the application of this method has not gained gener al acceptance. There have been few in vivo studies with quantified ref erence standards for determining regurgitant volume, and those that ha ve been reported used spectral Doppler standards and/or nonsimultaneou sly performed contrast ventriculography. The purpose of the present st udy was to evaluate the proximal flow convergence centerline velocity- distance profile method applied to chronic MR resulting from flail mit ral leaflets in an animal model in which regurgitant flow rates and re gurgitant volumes were determined simultaneously with electromagnetic flow probes and flowmeters. Methods and Results In six sheep, a total of 18 hemodynamically different states were obtained when the animals were restudied 6 months after surgical induction of MR produced by sev ering chordae tendineae to the anterior (three sheep) or posterior (th ree sheep) mitral leaflet. Echocardiographic studies with a Vingmed 75 0 were performed to obtain complete proximal axial flow acceleration v elocity-distance profiles for each hemodynamic state. The color Dopple r velocity data were directly transferred in digital format from the u ltrasound instrumentation to a microcomputer. The severity of MR was a ssessed by the magnitude of the mitral regurgitant fraction determined using both mitral and aortic electromagnetic flow probes balanced aga inst each other to yield regurgitant volume. MR was classified as grad e I when the regurgitant fraction was <20%, as grade II when it was 20 % to 35%, and as grade III to IV when it was >35%. Thus, of the 18 hem odynamic states, 4 (from two sheep) were grade I, 7 (from five sheep) were grade II, and 7 (from three sheep) were grade III to IV. All of t he velocity-distance acceleration curves showed organized acceleration fields with highly significant correlations using multiplicative regr ession fits (y=a . x(-b) r=.90 to .99, all P<.01). Grade III to IV MR resulted in rightward and upward shifts of the velocity-distance profi le curves compared with those produced by grade II and grade I MR. All of the centerline velocity-distance profiles for grade III or IV regu rgitation resided in a domain encompassed by velocities >0.5 m/s at di stances from the orifice >0.6 cm; the profiles for grade I regurgitati on resided in a domain encompassed by velocities <0.3 mis at distances from the orifice of <0.45 cm. The profiles for grade II regurgitation s resided in a domain between them. Regression analysis for the distan ce at which a velocity of 0.5 mis was first reached bore a close relat ion to regurgitant fraction (r=.92, P<.0001) and peak regurgitant flow rate (r=.89, P<.0001). In addition, an equation for quantitatively co rrelating both a and b (coefficients from the multiplicative regressio n fits) with the peak regurgitant flow rate (Q(peak) in L/min) was der ived from stepwise regression analysis: Q(peak)=12a+2.7b-2.4 (r=.96, P <.0001, SEE=.45 L/min). Conclusions In this study, using quantified MR volume, we demonstrate that the proximal flow convergence axial cente rline velocity-distance profile method can be used for evaluating the severity of MR without any assumption about isovelocity surface shape geometry.