795–2 Dynamic Changes in Aortic Regurgitant Orifice Area: A Chronic Animal Model Study

Abstract

Our aim was to determine dynamic changes in aortic regurgitant (AR) orifice size using calibrated electromagnetic flow meters (EM) and color Doppler (CD) flow convergence (FC) methods. In 6 sheep AR was surgically induced by right or “non coronary” leaflet edge resection, and after 20 weeks recovery, a total of 21 hemodynamic steady states were obtained pharmacologically. Instantaneous regurgitant flow rates were obtained with aortic and pulmonary EM flow meters balanced against each other and instantaneous AR orifice areas were determined by dividing flows by the corresponding CW velocities (over 25–40 points in a diastole) (Figure), Echo studies were performed to obtain maximal aliasing distances of FC, in ranges of aliasing velocities (AV) 0.20 – 0.32 m/sec and 0.56–0.72 m/sec; and the corresponding maximal FC AR flow rates were calculated using the hemispherical assumption and were divided by the maximal CW Doppler velocities. Maximal and time averaged AR orifice areas during diastole obtained by EM ranged from 0.06 to 0.33 cm and from 0.05 to 0.30 cm 2 , respectively. AR orifice sizes obtained using EM showed little change during diastole (Figure). Regression analysis between the regurgitant volume and mean regurgitant flow rates determined by EM and the time-averaged regurgitant orifice areas demonstrated excellent correlations (r = 0.84 and 0.88, respectively. Maximal CD AR orifice areas by FC using low AV overestimated reference orifice areas, but at high AV, FC predicted the reference areas more reliably (0.20 ± 0.12 cm 2 vs 0.18 ± 0.12 cm 2 by EM). Our study demonstrated little dynamic change in AR orifice size and suggests that when high AV are used, FC estimation of effective AR orifice size is possible.