Mechanism of dynamic regurgitant orifice area variation in functional mitral regurgitation - Physiologic insights from the proximal flow convergence technique

OBJECTIVES We used the Doppler proximal flow convergence technique as a phy siologic-tool to explore the effects of the time courses of mitral annular area and transmitral pressure on dynamic changes in regurgitant orifice are a. BACKGROUND In functional mitral regurgitation (MR), regurgitant flow rate a nd orifice area display a unique pattern, with peaks in early and late syst ole and a midsystolic decrease. Phasic changes in both mitral annular area and the transmitral pressure acting to close the leaflets, which equals lef t ventricular-left atrial pressure, have been proposed to explain this dyna mic pattern. METHODS In 30 patients with functional MR, regurgitant orifice area was obt ained as flow (from M-mode proximal flow convergence traces) divided by ori fice velocity (v) from the continuous wave Doppler trace of MR, transmitral pressure as 4v(2), and mitral. annular area from two apical diameters. RESULTS All patients had midsystolic decreases in regurgitant orifice area that mirrored increases in transmittal pressure, while mitral annular area changed more gradually. By stepwise multiple regression analysis, both mitr al annular area and transmitral pressure significantly affected regurgitant orifice area; however, transmitral pressure made a stronger contribution ( r(2) = 0.441) than mitral annular area (added r(2) = 0.008). Similarly, the rate of change of regurgitant orifice area more strongly related to that o f transmitral pressure (r(2) = 0.638) than to that of mitral annular area ( added r(2) = 0.003). A similar regurgitant orifice area time course was obs erved in four patients with fixed mitral annuli due to Carpentier ring inse rtion. CONCLUSIONS In summary, the time course and rate of change of regurgitant o rifice area in patients with functional MR are predominantly determined by dynamic changes in the transmitral pressure acting to close the valve. Thus , although mitral annular area helps determine the potential for MR, transm itral pressure appears important in driving the leaflets toward closure, an d would be of value to consider in interventions aimed at reducing the seve rity of MR. (C) 1999 by the American College of Cardiology.