Evaluation of stentless kangaroo aortic valves in the mitral position of juvenile sheep.

BACKGROUND AND AIM OF THE STUDY The performance and longevity of bioprosthetic heart valves are limited by tissue calcification and degeneration after implantation. Experimental valve replacement in large animal models forms an important component of the preclinical evaluation of these bioprosthetic heart valves. The study aim was to assess the feasibility of a mitral model for stentless valves and to evaluate the calcification behavior of stentless glutaraldehyde-preserved kangaroo heart valves in the mitral position of a sheep model. METHODS Medtronic Freestyle (n = 10) and kangaroo (n = 11) stentless aortic valves were implanted in the mitral position of juvenile sheep and retrieved after a maximum of 200 days. Retrieved stentless valves were examined for morphological changes and calcification of the valve tissue, using radiological screening, Von Kossa's staining and atomic absorption spectrophotometry. RESULTS Four sheep (40.0%) with Medtronic Freestyle and 10 sheep (90.9%) with kangaroo valves could be weaned from bypass and mechanical ventilation. Two animals (20.0%) with Medtronic Freestyle and six animals (54.5%) with kangaroo prostheses survived more than 30 days postoperatively. No significant difference (p >0.05) was seen between the calcification potential of Medtronic Freestyle valve leaflets (3.21 +/- 1.67 microg/mg) after 93 days and kangaroo valve leaflets (2.39 +/- 0.80 microg/mg) after 200 days. CONCLUSION The present results suggest that implantation of a stentless valve in the mitral position of sheep is possible, but technically difficult. The calcification potential of kangaroo valve tissue is comparable to that of Freestyle valve tissue in the mitral position of sheep.