Aortic valve morphology influences regurgitant volume in aortic regurgitation: In vivo evaluation

Study objective - According to the Gorlin hydraulic orifice equation, aortic regurgitation volume can be determined by the regurgitant orifice cross sectional area, diastolic filling period, mean pressure gradient between the aorta and left ventricle, and a constant relating the coefficients of contraction (C_c) and velocity (C_v). This study was performed to determine whether variation in aortic valve morphology affects regurgitant flow volume, C_c and C_v.Design - Four aortic valve templates, modelled after circular, rheumatic, degenerative, and bicuspid lesions, were constructed with equal orifice cross sectional areas in two sizes, 0.2 and 0.7 cm². These valves were studied in vitro in a flow model of aortic regurgitation, wherein aortic pressure was regulated by varying the height of a column of fluid. Flow, pressure, and velocity were measured, and the coefficient C_c and C_v were calculated from standard equations.Measurements and main results - Regurgitant volume was assessed at diastolic filling periods of 0.5 and 1.0 s and averaged 15% greater for bicuspid and degenerative as compared to circular or rheumatic valve shapes (p=0.0001). This difference was accentuated at the shorter diastolic filling time and higher pressure gradient, such that bicuspid lesions allowed 29% more regurgitant flow across the 0.2 cm² orifice at fluid height of 120 cm over 0.5 s. This difference in regurgitant volume between valve shapes was due to an increased C_c for the bicuspid and degenerative valve shapes, suggesting that they are more efficient orifices than rheumatic or circular valve shapes.Conclusions - Aortic valve morphology influences regurgitant volume in aortic regurgitation. Specifically, degenerative and bicuspid orifice shapes have a higher contraction coefficient and allow more regurgitant flow than rheumatic or circular orifices at a given driving pressure and diastolic filling time.