title: Improved ultrastructural preservation of bioprosthetic tissue.
abstract: OBJECTIVE
  Poor ultrastructural tissue preservation of bioprosthetic heart valves is associated with a higher propensity for calcification. In spite of this realization, commercial valve fixation remains suboptimal.
  
  
  METHODS
  In an attempt to maintain tissue integrity through improved cross-linking procedures, transmission electron microscopy and a 21-point damage score were applied to assess the ultrastructural preservation of aortic wall tissue-the main component of contemporary aortic valve bioprostheses. An ideal glutaraldehyde (GA) concentration was assessed by immediate tissue fixation at 4 degrees C comparing 0.2%, 0.5%, 0.65%, 1.0%, 2.0%, 3.0% and 4.0% GA in phosphate-buffered saline (PBS). Subsequently, an optimal concentration of 3.0% GA was used to determine the effect of fixation temperature (4 degrees, 22 degrees and 37 degrees C). Finally, the superior glutaraldehyde concentration (3.0%) and cross-linking temperature (4 degrees C) were used to assess tolerance towards delayed fixation.
  
  
  RESULTS
  When different GA concentrations were used almost identical damage scores of 6.3 and 5.8 were found for 0.2% and 0.65% fixation. The first significant improvement was found at a concentration of 1.0% (score 3.3; p < 0.01) followed by a further improvement at 3.0% (score 2.6; p = 0.05). The optimal fixation temperature was 4 degrees C (3.7) with the worst results obtained at room temperature (score 9.2; p < 0.03). When fixation was delayed, the most significant damage occurred during the initial 30 min after slaughter (from 2.3 to 7.4; p < 0.02) followed by another significant deterioration between 4 and 16 h (from 5.6 to 9.7; p < 0.02).
  
  
  CONCLUSIONS
  In summary, the prerequisites for an ideal ultrastructural preservation of bioprosthetic aortic wall tissue are immediate fixation (within 30 min), high GA concentrations (> 1.0%) and cold-temperature fixation (4 degrees C).
authors.affiliation: Department of Cardiothoracic Surgery, University of Cape Town, South Africa.
authors.forename: P
authors.initials: P
authors.lastname: Zilla
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: P
authors.initials: P
authors.lastname: Human
authors.forename: W
authors.initials: W
authors.lastname: Koen
authors.forename: U
authors.initials: U
authors.lastname: von Oppell
mesh_terms: D000818:Animals; D001021:Aortic Valve / Q000187:drug effects / Q000648:ultrastructure; D001705:Bioprosthesis; D003080:Cold Temperature; D005404:Fixatives / Q000494:pharmacology; D005976:Glutaral / Q000494:pharmacology; D006350:Heart Valve Prosthesis; D006801:Humans; D008854:Microscopy, Electron; D011474:Prosthesis Design; D015607:Stents; D013552:Swine; D013997:Time Factors
chemical_list: D005404:Fixatives; D005976:Glutaral