A juvenile sheep model for the long-term evaluation of stentless bioprostheses implanted as aortic root replacements

Background and aim of the study: Orthotopic valve replacement in large anim als is an important component of the preclinical assessment of bioprostheti c valves. To provide the most useful preclinical information, the developme nt of models that parallel clinical practice patterns is essential. Therefo re, we sought to develop a technically feasible and reproducible model for chronic evaluation of stentless bioprosthetic aortic valves implanted as ao rtic root replacements in juvenile sheep. Methods: Juvenile domestic sheep (mean age 21 2.28 weeks; range: 17-26 week s) underwent aortic root replacement using standard cardiopulmonary bypass (CPB) and surgical techniques. Animals were implanted with 19 mm (n = 21), 21 mm (n = 18) or 23 mm (n = 4) bioprostheses from two different manufactur ers, and followed for 150 days. Animals surviving at least 150 days were co nsidered long-term survivors; those which died prior to postoperative day ( POD) 31 were considered operative deaths. Results: Forty-three animals underwent aortic root replacement. The mean CP B time was 91 +/- 20 min (range: 62-149 min); mean cross-clamp time was 63 +/- 13 min (range: 39-95 min). Thirty-five animals (81%) survived the first 30 days of the study period. Five deaths occurred at POD 0 due to anastomo tic complications. One death occurred each on POD 3, 6, and 26 as a result of prosthesis size mismatching, thromboembolic complications, and endocardi tis, respectively. There were five late deaths. Twenty animals survived the minimum 150-day study period, and 12 were sacrificed at 183 +/- 17 days. S ix animals remain alive at 151 +/- 0.98 days, and one animal died each on P OD 184 and 190. The remaining 10 animals are not yet 150 days from their op eration. Currently, all are well at 102 +/- 34 days (range: 33-140) days. Conclusion: These data suggest that long-term evaluation of stentless aorti c bioprostheses implanted as aortic root replacements can be accomplished u sing juvenile sheep.