Aortic valve area discrepancy by Gorlin equation and Doppler echocardiography continuity equation: Relationship to flow in patients with valvular aortic stenosis

BACKGROUND: In vitro studies have shown a discrepancy between aortic valve area (AVA) measurements derived invasively by Gorlin equation (Gorlin AVA) and noninvasively by Doppler echocardiography (Doppler-echo) continuity equ ation (Doppler AVA) during low flow states. OBJECTIVE: To assess whether a flow-related discrepancy between Gorlin AVA and Doppler AVA occurs in the clinical setting in patients with isolated va lvular aortic stenosis. PATIENTS AND METHODS: Seventy-five consecutive patients with isolated valvu lar aortic stenosis, who had AVA deter mined both invasively by Gorlin equa tion and noninvasively by Doppler-echo continuity equation, were retrospect ively reviewed. RESULTS: Gorlin AVA and Doppler AVA correlated (r=0.68) over the narrow AVA range (Gorlin AVA 0.30 to 1.22 cm(2)); however, Doppler AVA was systematic ally larger than Gorlin AVA (0.80+/-0.21 versus 0.70+/-0.23 cm(2) AVA diffe rence=0.10+/-0.17 cm(2), P<0.0001). The AVA difference was inversely relate d to invasive cardiac index (r=-0.51) and was significantly greater at low flow states (cardiac index less than 2.5 L/min/m(2)) than at normal flow st ates (cardiac index 2.5 L/min/m(2) or more) (0.16+/-0.15 versus -0.03+/-0.1 5 cm(2), P<0.0001). Independent predictors of the AVA difference were the d ifference between Doppler-echo and invasive cardiac output (P<0.0001); the difference between Doppler-echo and invasive mean transvalvular pressure gr adient (P=0.0002); and the average cardiac output (Doppler-echo plus invasi ve cardiac output/2, P=0.001) at the time of the hemodynamic assessments. T he AVA difference was not related to average pressure gradient, average AVA or patient characteristics. CONCLUSIONS: A flow-related discrepancy between Gorlin AVA and Doppler AVA occurs in the clinical setting of patients with isolated valvular aortic st enosis. This discrepancy should be considered when assessing aortic stenosi s severity during low flow states, where Gorlin AVA may be significantly sm aller than Dop pier AVA.