title: A juvenile sheep model for the long-term evaluation of stentless bioprostheses implanted as aortic root replacements.
abstract: OBJECTIVE
  Orthotopic valve replacement in large animals is an important component of the preclinical assessment of bioprosthetic valves. To provide the most useful preclinical information, the development of models that parallel clinical practice patterns is essential. Therefore, we sought to develop a technically feasible and reproducible model for chronic evaluation of stentless bioprosthetic aortic valves implanted as aortic root replacements in juvenile sheep.
  
  
  METHODS
  Juvenile domestic sheep (mean age 21+/-2.28 weeks; range: 17-26 weeks) 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 manufacturers, and followed for 150 days. Animals surviving at least 150 days were considered 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 CPB 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 anastomotic complications. One death occurred each on POD 3, 6, and 26 as a result of prosthesis size mismatching, thromboembolic complications, and endocarditis, respectively. There were five late deaths. Twenty animals survived the minimum 150-day study period, and 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. Currently, all are well at 102+/-34 days (range: 33-140) days.
  
  
  CONCLUSIONS
  These data suggest that long-term evaluation of stentless aortic bioprostheses implanted as aortic root replacements can be accomplished using juvenile sheep.
authors.affiliation: Department of Surgery, University of Minnesota, Minneapolis 55455, USA.
authors.forename: J F
authors.initials: JF
authors.lastname: Grehan
authors.forename: I
authors.initials: I
authors.lastname: Casagrande
authors.forename: E L
authors.initials: EL
authors.lastname: Oliveira
authors.forename: P C
authors.initials: PC
authors.lastname: Santos
authors.forename: C J
authors.initials: CJ
authors.lastname: Pessa
authors.forename: L R
authors.initials: LR
authors.lastname: Gerola
authors.forename: E
authors.initials: E
authors.lastname: Buffolo
authors.forename: J
authors.initials: J
authors.lastname: Mrachek
authors.forename: M E
authors.initials: ME
authors.lastname: Norris
authors.forename: M T
authors.initials: MT
authors.lastname: Lahti
authors.forename: R W
authors.initials: RW
authors.lastname: Bianco
mesh_terms: D000818:Animals; D001021:Aortic Valve / Q000637:transplantation*; D001705:Bioprosthesis; D005500:Follow-Up Studies; D019918:Heart Valve Prosthesis Implantation / Q000379:methods*; D023421:Models, Animal; D011182:Postoperative Care; D011300:Preoperative Care; D012756:Sheep; D015607:Stents; D016019:Survival Analysis; D013997:Time Factors