Flow dynamics of stenotic aortic valves assessed by signal processing of Doppler spectrograms

Clinical assessment of aortic stenosis (AS) is sometimes challenging, becau se all hemodynamic indexes of severity are modified by flow rate. However, the mechanisms underlying flow dependence remain controversial. Analysis of instantaneous flow dynamics has provided crucial information in a number o f cardiovascular disorders and may add new insight into this phenomenon. Th is study was designed to analyze in vivo the effects of flow interventions on instantaneous valvular dynamics of stenotic valves. For this purpose, a custom algorithm for signal processing of Doppler spectrograms was develope d and validated against a control population. Digital Doppler recordings at the aortic valve and left ventricular outflow tract were obtained in 15 pa tients with AS, at baseline and during low-dose dobutamine infusion; 10 nor mal subjects were studied as controls. Spectrograms were processed by signa l averaging, time alignment, modal-velocity enhancement, envelope tracing, and numerical interpolation. Instantaneous relative aortic valve area (rAVA ) was obtained by the continuity equation and plotted against normalized ej ection time. Curves were classified as either type A (rapid, early-systolic opening) or type B (slow, end-systolic opening). Curves from controls clos ely matched prior knowledge of normal valve dynamics, but curves from patie nts were clearly different: all controls except 2 (80%) had type A, whereas all patients except 3 (80%) had a type B pattern (p = 0.03). Dobutamine in fusion in patients increased and slightly anticipated peak rAVA by accelera ting valve opening. Despite similar values of area and pressure difference, type B dynamics were associated with lower blood pressure (p = 0.01) and w orse long-term outcome (>3 years) than type A flow dynamics (p = 0.02). Sig nal processing of Doppler spectrograms allows a comprehensive assessment of aortic flow dynamics. Differences in timing of valve aperture and in maxim al leaflet excursion account for flow-mediated changes in valve area, sugge sting complementary effects of inertia and elasticity on the kinetics of st enotic aortic valves. Flow-dynamic analysis provides novel clinical informa tion regarding physiology of AS unavailable to conventional indexes. (C)200 0 by Excerpta Medica, Inc.