Background and aims of the study: 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).