DYNAMICS OF MITRAL REGURGITANT FLOW AND ORIFICE AREA - PHYSIOLOGICAL APPLICATION OF THE PROXIMAL FLOW CONVERGENCE METHOD - CLINICAL-DATA AND EXPERIMENTAL TESTING

Background The proximal how convergence method, a quantitative color D oppler flow technique, has been validated recently for calculating reg urgitant flow and orifice area. We investigated the potential of the m ethod as a tool to study different pathophysiological mechanisms of mi tral valve incompetence by assessing the time course of regurgitant fl ow and orifice area and analyzed the implications for quantification o f mitral regurgitation. Methods and Results Fifty-six consecutive pati ents with mitral regurgitation of different etiologies were studied. T he instantaneous regurgitant flow rate Q((t)) was computed from color M-mode recordings of the proximal flow convergence region and divided by the corresponding orifice velocity V-(t) to obtain the instantaneou s orifice area A((t)). Regurgitant stroke volume (RSV) was obtained by integrating Q((t)). Mean regurgitant flow rate Qm( )was calculated by RSV divided by regurgitation time. Peak-to-mean regurgitant flow rate s Q(p)/Q(m) and orifice areas A(p)/A(m) were calculated to assess the phasic character of Q((t)) and P-(t) In the first 24 patients (group 1 ), computation of Q(m) and RSV from the color Doppler recordings was c ompared with the conventional pulsed Doppler method (r=.94, SEE=29.4 m L/s and r=.95, SEE=9.7 mL) as well as with angiography (r(s)=.93 and r (s)=.94, P<.001). The temporal variation of Q((t)) and A((t)) was stud ied in the next 32 patients (group 2): In functional regurgitation in dilated cardiomyopathy (n=12), there was a constant decrease in A((t)) throughout systole with an increase during left ventricular relaxatio n; A(p)/A(m) was 5.49+/-3.17. In mitral valve prolapse (n=6), A((t)) w as small in early systole, increasing substantially in midsystole, and decreasing mildly during left ventricular relaxation; A(p)/A(m) was 2 .48+/-0.26. In rheumatic mitral regurgitation (n=14), a roughly consta nt regurgitant orifice area during most of systole was found in 4 pati ents. In the other patients there was significant variation of A((t)) and the time of its maximum; A(p)/A(m) was 1.81+/-0.56. ANOVA demonstr ated that the differences in A(p)/A(m) were related to the etiology of mitral regurgitation (P<.0001). To verify that the calculated variati on in regurgitant orifice area during the cardiac cycle reflects an ac tual variation, the ability of the method to predict a constant orific e area throughout systole was tested experimentally in a canine model of mitral regurgitation. Five flow stages were produced by implanting fixed grommet orifices of different sizes into the anterior mitral lea flet. A constant regurgitant orifice area was correctly predicted thro ughout systole with a mean percent error of -1.8+/-4% (from -6.9% to 5.8%); the standard deviation of the individual curves calculated at 1 0% intervals during systole averaged 13.3% (from 3.6% to 19.6%). In ad dition, functional mitral regurgitation caused by ventricular dysfunct ion was produced pharmacologically in five dogs, and the color M-mode recordings of the proximal flow convergence region were obtained with the transducer placed directly on the heart instead of the chest, thus ruling out a significant effect of translational motion on the observ ed flow pattern. The pattern of regurgitant how variation was identica l to that observed in patients. Conclusions The proximal flow converge nce method demonstrates that regurgitant flow and orifice area vary th roughout systole in distinct patterns characteristic of the underlying mechanism of mitral incompetence. Therefore, in addition to the poten tial of the method as a tool to quantify mitral regurgitation, it allo ws analysis of the pathophysiology of regurgitation in the individual patient, which may be helpful in clinical decision making. Calculating mitral regurgitant flow rate and volume from the time-varying proxima l how field tie, without assuming a constant orifice area that would p roduce overestimation in individual patients) provides excellent agree ment with independent techniques and agrees well with angiography.