Flow-Dependent Changes in Doppler-Derived Aortic Valve Effective Orifice Area Are Real and Not Due to Artifact

ObjectivesWe sought to determine whether the flow-dependent changes in Doppler-derived valve effective orifice area (EOA) are real or due to artifact.BackgroundIt has frequently been reported that the EOA may vary with transvalvular flow in patients with aortic stenosis. However, the explanation of the flow dependence of EOA remains controversial and some studies have suggested that the EOA estimated by Doppler-echocardiography (EOADop) may underestimate the actual EOA at low flow rates.MethodsOne bioprosthetic valve and three rigid orifices were tested in a mock flow circulation model over a wide range of flow rates. The EOADopwas compared with reference values obtained using particle image velocimetry (EOAPIV).ResultsThere was excellent agreement between EOADopand EOAPIV(r2= 0.94). For rigid orifices of 0.5 and 1.0 cm2, no significant change in the EOA was observed with increasing flow rate. However, substantial increases of both EOADopand EOAPIVwere observed when stroke volume increased from 20 to 70 ml both in the 1.5 cm2rigid orifice (+52% for EOADopand +54% for EOAPIV) and the bioprosthetic valve (+62% for EOADopand +63% for EOAPIV); such changes are explained either by the presence of unsteady effects at low flow rates and/or by an increase in valve leaflet opening.ConclusionsThe flow-dependent changes in EOADopare not artifacts but represent real changes in EOA attributable either to unsteady effects at low flow rates and/or to changes in valve leaflet opening. Such changes in EOADopcan be relied on for clinical judgment making.