A Juvenile Sheep Model for the Long-Term Evaluation of Stentless Bioprostheses Implanted as Aortic Root Replacements
John F. Grehan MD, Ivan Casagrande MD, Elaine L. Oliveira DVM, Paulo C. Santos MD, Clodualdo J. Pessa MD, Luis R. Gerola MD, Enio Buffolo MD, John Mrachek BA, Margaret E. Norris MLAS, Matthew T. Lahti, Richard W. Bianco BS

The purpose of this investigation was to develop a technically feasible and reproducible model for the evaluation of stentless aortic bioprosthetic valves implanted as aortic root replacements in juvenile sheep. Forty-three juvenile sheep underwent aortic root replacement using standard cardiopulmonary bypass and surgical techniques. Thirty-five animals (81%) survived the first 30 days of the study period. Five deaths occurred at the time of operation due to anastomotic complications. One death occurred each on postoperative days (POD) 3, 6, and 26 as a result of thromboembolic complications, prosthesis size mismatching, and endocarditis, respectively. Twenty (80%) of 25 animals survived the minimum 150-day study period, 12 were sacrificed at 183 ± 17 days. Six animals remain alive at 151 ± 0.98 days, and one animal died each on POD 184 and 190. The remaining 10 animals are not yet 150 days from their operation. All are well at 102 ± 34 days (range: 33-140 days). These data suggest that long-term evaluation of stentless aortic bioprostheses implanted as aortic root replacements can be accomplished using juvenile sheep.