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CLINICAL STUDY: ECHOCARDIOGRAPHIC METHODS

Effect of three-dimensional valve shape on the hemodynamics of aortic stenosis

Three-dimensional echocardiographic stereolithography and patient studies

Dan Gilon, MD, FACC^*,*, Edward G. Cape, PhD, Mark D. Handschumacher, BS^*, Jae-Kwan Song, MD, FACC, Joan Solheim, Michael VanAuker, BS, Mary Etta E. King, MD, FACC^* and Robert A. Levine, MD, FACC^*

^* Cardiac Ultrasound Laboratory, Massachusetts General Hospital, Harvard Medical School, Boston, Massachusetts, USA
Children’s Hospital, School of Medicine and Engineering, University of Pittsburgh, Pittsburgh, Pennsylvania, USA
Santin Engineering, Peabody, Massachusetts, USA

Manuscript received October 29, 2001; revised manuscript received June 6, 2002, accepted July 2, 2002.

^* Reprint requests and correspondence: Dr. Dan Gilon, Cardiac Ultrasound Laboratory, VBK508, Massachusetts General Hospital, 32 Fruit Street, Boston, Massachusetts, USA 02114.
gilond{at}cc.huji.ac.il

OBJECTIVES: This study tested the hypothesis that the impact of a stenotic aortic valve depends not only on the cross-sectional area of its limiting orifice but also on three-dimensional (3D) valve geometry.

BACKGROUND: Valve shape can potentially affect the hemodynamic impact of aortic stenosis by altering the ratio of effective to anatomic orifice area (the coefficient of orifice contraction [Cc]). For a given flow rate and anatomic area, a lower Cc increases velocity and pressure gradient. This effect has been recognized in mitral stenosis but assumed to be absent in aortic stenosis (constant Cc of 1 in the Gorlin equation).

METHODS: In order to study this effect with actual valve shapes in patients, 3D echocardiography was used to reconstruct a typical spectrum of stenotic aortic valve geometrics from doming to flat. Three different shapes were reproduced as actual models by stereolithography (computerized laser polymerization) with orifice areas of 0.5, 0.75, and 1.0 cm² (total of nine valves) and studied with physiologic flows. To determine whether valve shape actually influences hemodynamics in the clinical setting, we also related Cc (= continuity/planimeter areas) to stenotic aortic valve shape in 35 patients with high-quality echocardiograms.

RESULTS: In the patient-derived 3D models, Cc varied prominently with valve shape, and was largest for long, tapered domes that allow more gradual flow convergence compared with more steeply converging flat valves (0.85 to 0.90 vs. 0.71 to 0.76). These variations translated into differences of up to 40% in pressure drop for the same anatomic area and flow rate, with corresponding variations in Gorlin (effective) area relative to anatomic values. In patients, Cc was significantly lower for flat versus doming bicuspid valves (0.73 ± 0.14 vs. 0.94 ± 0.14, p < 0.0001) with 40 ± 5% higher gradients (p < 0.0001).

CONCLUSIONS: Three-dimensional valve shape is an important determinant of pressure loss in patients with aortic stenosis, with smaller effective areas and higher pressure gradients for flatter valves. This effect can translate into clinically important differences between planimeter and effective valve areas (continuity or Gorlin). Therefore, valve shape provides additional information beyond the planimeter orifice area in determining the impact of valvular aortic stenosis on patient hemodynamics.

Abbreviations and Acronyms   Aanat   anatomic orifice area   Aeff   effective orifice area   Cc   coefficient of contraction   PG   pressure gradient   3D   three-dimensional   Q   flow rate

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