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J Thorac Cardiovasc Surg 2002;123:333-340
© 2002 The American Association for Thoracic Surgery

Surgery for Acquired Cardiovascular Disease (ACD)

Aortic valve cusp vessel density: Relationship with tissue thickness

From The Heart Valve Laboratory,^a The John P. Robarts Research Institute, The Department of Medical Biophysics,^b University of Western Ontario, and The Division of Cardiology,^c London Health Sciences Centre, University Campus, London, Ontario, Canada.

Supported by a grant-in-aid T3573 from the Heart and Stroke Foundation of Ontario and the Medical Research Council of Canada. K.L.W. was supported in part by the Ontario Graduate Student for Science and Technology Scholarship Programme.

Received for publication March 9, 2001. Revisions requested April 13, 2001; revisions received June 22, 2001. Accepted for publication Aug 15, 2001. Address for reprints: Derek R. Boughner, MD, PhD, London Health Sciences Centre, University Campus, 339 Windermere Rd, London, Ontario N6A 5A5, Canada (E-mail: derek.boughner{at}lhsc.on.ca).

Objectives: The presence of a microvasculature within aortic cusps implies that tissue oxygen requirements exceed the amount deliverable by diffusion from the tissue surfaces alone. For the design of a successful tissue-engineered valve replacement, the effect of diffusion distance (tissue thickness) on oxygen delivery must be considered. We therefore examined in normal aortic valve cusps the relationship between the presence of microvessels and the tissue thickness.
Methods: Thirty porcine aortic valve cusps were excised and examined after cusp microvessels were pressure filled with a carbon particle solution. Cusp images were captured for stereographic vessel density analysis, and cusp thickness was determined with a radiographic technique. Histologic cross-sections were evaluated to determine vessel depth from the cusp surface.
Results: Cusp basal regions measured 0.69 to 0.86 mm in thickness, significantly thicker (P = .001) than the rest of the cusp, which measured 0.36 to 0.48 mm. In general a vascular bed was present when cusp thickness exceeded 0.5 mm, with a median value of 5.16 vessels/mm³.
Conclusions: From published values of arterial wall oxygen consumption and diffusivity, we predicted that the probable maximum oxygen diffusion distance for valve tissue would be about 0.2 mm. This was consistent with our physical findings, which implies that central tissue anoxia is avoided by the capillary bed. An avascular tissue-engineered valve metabolically similar to an aortic valve should therefore not exceed a thickness of approximately 0.40 mm.

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