Axial centerline flow convergence and vena contracta methods for evaluation of aortic regurgitation: A chronic animal study

Objectives: The aim of the present study was to validate a digital color Doppler based centerline velocity/distance acceleration profile method and a color Doppler imaged vena contracta method for evaluating the severity of aortic regurgitation. Background: Recently applications of the flow convergence methods have been used for estimating regurgitant flow rates and regurgitant volumes. However, the angle between the Doppler interrogation and the blood flow direction can cause serious errors in evaluating flow rates. Methods: In 6 sheep, a total of 22 hemodynamic states were obtained pharmacologically 14 weeks after a portion of the aortic non-coronary (n = 3) or right coronary (n = 3) leaflet was incised to produce aortic regurgitation. Echocardiographic studies were performed to obtain complete proximal axial flow acceleration velocity/distance profiles during the time of peak regurgitant flow and to obtain the maximal size of the vena contracta in diastole for each hemodynamic state. For each steady state, the severity of aortic regurgitation was assessed by measurement of the magnitude of the regurgitant flow volume/beat, regurgitant fraction and regurgitant flow rates determined using both aortic and pulmonary artery electromagnetic flow probes. Results: All of the velocity/distance curves had highly significant correlations using multiplicative regression fits; y = ax^-b, where y = centerline velocity and x = distance from the regurgitant orifice; r = 0.94 0.99; all p < 0.01. The coefficient 'a' correlated well with regurgitant volumes/beat and peak regurgitant flow rates (r = 0.87 and r = 0.95, both p<0.0001). Importantly, grade I regurgitation (regurgitant volume/beat< 15 ml), grade II regurgitation (regurgitant volum/beat between 16 ml and 30 ml) and grade III-IV regurgitation (regurgitant volume/beat>30 ml) were clearly separated using the color Doppler centerline velocity/distance profile domain technique. There was also a good correlation between the width of the color Doppler imaged vena contracta and aortic regurgitant volumes (r = 0.88, p<0.0001, SEE = 0.09 cm). Conclusions: This study, using quantified aortic regurgitation, demonstrates that both the flow convergence axial centerline velocity/distance acceleration profile method and the vena contracta method can be used for evaluating the severity of aortic regurgitation.