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CLINICAL RESEARCH: CARDIAC ULTRASOUND

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

Lyes Kadem, PhD, Eng^_*,, Régis Rieu, PhD^_*, Jean G. Dumesnil, MD, Louis-Gilles Durand, PhD, Eng and Philippe Pibarot, DVM, PhD^_*,_*

^_* Cardiovascular Biomechanics Team (IRPHE-CNRS), Université de la Méditerranée, Marseille, France
Biomedical Engineering Laboratory, Institut de recherches cliniques de Montréal, Montreal, Quebec, Canada
Research Center of Laval Hospital/Quebec Heart Institute, Laval University, Quebec, Canada

Manuscript received February 18, 2005; revised manuscript received May 5, 2005, accepted May 18, 2005.

^_* Reprint requests and correspondence: Dr. Philippe Pibarot, Laval Hospital, 2725 Chemin Sainte-Foy, Sainte-Foy, Quebec, Canada, G1V-4G5 (Email: philippe.pibarot{at}med.ulaval.ca).

OBJECTIVES: We sought to determine whether the flow-dependent changes in Doppler-derived valve effective orifice area (EOA) are real or due to artifact.

BACKGROUND: It 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 (EOA_Dop) may underestimate the actual EOA at low flow rates.

METHODS: One bioprosthetic valve and three rigid orifices were tested in a mock flow circulation model over a wide range of flow rates. The EOA_Dop was compared with reference values obtained using particle image velocimetry (EOA_PIV).

RESULTS: There was excellent agreement between EOA_Dop and EOA_PIV (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 EOA_Dop and EOA_PIV were observed when stroke volume increased from 20 to 70 ml both in the 1.5 cm² rigid orifice (+52% for EOA_Dop and +54% for EOA_PIV) and the bioprosthetic valve (+62% for EOA_Dop and +63% for EOA_PIV); such changes are explained either by the presence of unsteady effects at low flow rates and/or by an increase in valve leaflet opening.

CONCLUSIONS: The flow-dependent changes in EOA_Dop are 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 EOA_Dop can be relied on for clinical judgment making.

Abbreviations and Acronyms   AS = aortic stenosis   EOA = effective orifice area   EOADop = EOA estimated by Doppler-echocardiography   EOAPIV = EOA estimated by particle image velocimetry   GOA = geometrical orifice area   LV = left ventricular   Qmean = mean flow rate during the systolic phase   Qmax = peak flow rate during the systolic phase   St = Strouhal number   SV = stroke volume   T = left ventricular ejection time   V = velocity vector