title: Stentless bioprosthetic heart valve research: sheep versus primate model.
abstract: BACKGROUND
  The mild inflammatory response against stented bioprosthetic heart valves in the sheep model is often opposed by a more distinct response in failing human implants. With the emergence of stentless root prostheses with their significantly larger proportion of tissue interacting with the immune system of the host, a more relevant animal model than the sheep may be needed.
  
  
  METHODS
  Valved, porcine aortic roots of 5 cm length were fixed in 0.2% glutaraldehyde and implanted in the upper descending aorta of Merino sheep (n = 5; 43+/-3 kg) and Chacma baboons (n = 5; 17+/-3 kg). After 6 weeks of tissue calcification, pannus outgrowth and inflammation were assessed by atomic absorption spectrophotometry, histologic damage scoring (0 to 3), image analysis, and transmission electron microscopy.
  
  
  RESULTS
  The main difference between the two animal models was in aortic wall calcification (64.8+/-39.8 microg/mg in the sheep model versus 4.1+/-5.9 microg/mg in the primate model; p > 0.005). In both models, leaflet calcification was negligible (2.6+/-2.4 microg/mg in the sheep versus 2.5+/-1.9 microg/mg in the primate), and the overall extent of inflammation was comparable (1.2+/-0.8 versus 0.98+/-0.7; p = 0.18 in the sheep and the primate, respectively). Qualitatively, the sheep demonstrated a macrophage-dominated reaction whereas the inflammatory demarcation often resembled a granulocyte-dominated xenograft response in the primate. Pannus outgrowth was comparable in length (8.4+/-2.3 mm versus 9.1+/-4.3 mm proximally and 7.1+/-3.4 mm versus 7.4+/-5.1 mm distally, in the sheep and baboon, respectively; p > 0.05).
  
  
  CONCLUSIONS
  Our results confirm the sheep as a significantly stronger calcification model for stentless aortic heart valves than the primate. Remaining antigenicity of porcine tissue as a result of incomplete cross-linking, however, elicits a distinctly stronger xenograft-type reaction in the primate model.
authors.affiliation: Department of Cardiothoracic Surgery, Cape Heart Centre, University of Cape Town Medical School, South Africa.
authors.forename: A
authors.initials: A
authors.lastname: Trantina-Yates
authors.forename: C
authors.initials: C
authors.lastname: Weissenstein
authors.forename: P
authors.initials: P
authors.lastname: Human
authors.forename: P
authors.initials: P
authors.lastname: Zilla
mesh_terms: D000818:Animals; D001705:Bioprosthesis; D002114:Calcinosis / Q000473:pathology; D004195:Disease Models, Animal; D019544:Equipment Failure Analysis; D006350:Heart Valve Prosthesis; D006801:Humans; D008875:Middle Aged; D010215:Papio; D011474:Prosthesis Design; D012756:Sheep; D013045:Species Specificity; D013054:Spectrophotometry, Atomic; D015607:Stents; D013552:Swine