Is the tricuspid position suitable for testing replacement bioprosthetic valves in the sheep model?

Background and aim of the study: Glutaraldehyde may promote calcification i n xenograft tissue by the action of toxic aldehyde group residues involved in the cross-link process. Post-fixation treatment with homocysteic acid (H A) neutralizes this toxicity by bonding aldehyde groups, and enhances bioco mpatibility on, the basis of strongly electronegative sulfonic groups. Prev ious studies in a rat subcutaneous model showed significant longterm mitiga tion of mineralization of glutaraldehyde-fixed pericardium treated with HA. This study aimed to assess the anticalcific efficacy of HA in a valvular i mplant in growing sheep, and establish if the tricuspid position is suitabl e for testing replacement bioprosthetic valves. Methods: Eleven stented 25 mm Pericarbon (R) bioprostheses (seven HA-treate d, four standard) were implanted in the tricuspid position of growing sheep . Infective endocarditis occurred in four prostheses. Among the remaining s even, three (two HA-treated, one standard) were explanted at 91 days (mid-t erm), and four (two HA-treated, two standard) at 140-141 days (long-term). All explants were studied by gross, X-ray, light, transmission and scanning electron microscopy, as well as by atomic absorption spectroscopy. Results: No histological. and ultrastructural difference in tissue preserva tion were - observed between HA-treated and standard Pericarbon (R) biopros theses, either in the mid or long term. The mean calcium content of inid-te rm, HA-treated explants was 9.55 mg/g compared with 16.26 mg/g in mid-term standard explants. Only one late standard explant failed as a result of Sev ere stenosis caused by massive dystrophic calcification. Among four late ex plants, two showed significant increase in mineralization (HA-treated, 87.4 5 mg/g.- standard, 181.20 mg/g), while two showed calcium contents similar to those in mid-term explants, (HA-treated, 11.96 mg/g; standard, 17.32 mg/ g). Conclusion: Post-fixation treatment with HA preserves structural properties , after tricuspid implantation in growing sheep, The tricuspid implant in t he sheep model failed to reproduce remarkable accelerated progressive calci fication in all xenografts so as to demonstrate a significant difference be tween HA and standard explants. The tricuspid position - for testing replac ement bioprosthetic valves should be abandoned, and investigations repeated , with the prosthesis, in, the initial position.