Porcine aortic valve bioprostheses: a morphologic comparison of the effects of fixation pressure

It has been suggested that the mechanical durability of glutaraldehyde-treated porcine aortic valve (PAV) bioprostheses (BPs) may be increased if collagen crimp approximating that observed in native valvular tissue is maintained during preimplantation processing. Among the factors affecting PAV fixation, the magnitude of the pressure applied to the aortic valve during fixation influences the extent of collagen crimp. Polarized light microscopy is useful for both the qualitative assessment of collagen morphology and the quantitative measurement of collagen crimp in BPs. The purpose of this study was to determine the feasibility of using this optical method to detect quantitative differences in PAV collagen crimp following zero-, low-, and high-pressure fixation. The results of this study demonstrate the following: 1) coupling polarized light microscopy and morphometric measurements provides a quantitative method for the evaluation of the relationship between fixation pressure and collagen crimp in PAVs; 2) a significant association between increasing fixation pressure and absence of collagen crimp was observed in cords and the mid-cusp region; 3) collagen crimp length in the cords is affected by fixation pressure; 4) the alteration of collagen crimp by low- and high-pressure fixation does not uniformly affect all regions of the cusp; and, 5) collagen crimp was consistently present in all cusp regions in zero-pressure fixed PAVs.