Bioprosthetic tissue calcification: influence of blood contact and arterial pressure. an experimental study in rats and sheep.

Several animal models are currently used to study bioprosthetic tissue calcification. The study aim was to evaluate the influence of species and environmental factors (blood contact and arterial pressure) on valve tissue mineralization.Glutaraldehyde-fixed porcine cusps and aortic wall samples were implanted subcutaneously in rats (n = 6) and sheep (n = 18). In sheep, similar samples were also implanted into the jugular vein (blood contact) and carotid artery (blood contact and arterial pressure). Tissue was explanted at intervals up to three months and evaluated macroscopically, and by X-radiography, light and electron microscopy and calcium content measurement.After eight weeks in the subcutaneous position, glutaraldehyde-fixed cusps were severely calcified in rats, but not in sheep (78.6 +/- 28.3 and 0.3 +/- 0.5 microg Ca/mg, respectively; p <0.001). Aortic wall samples were calcified in both species, but less in sheep (p <0.001). In sheep, blood contact without arterial pressure (venous implants) significantly increased the calcification of cusp and even more of aortic wall tissue. Arterial pressure had no effect on calcification of aortic wall tissue.Major inter-species inconsistencies were found in valve tissue calcification after subcutaneous implantation. In sheep, blood contact increased tissue calcification significantly, mainly in aortic wall samples. Arterial pressure did not enhance mineralization of aortic wall tissue.