Fixation-Related Autolysis and Bioprosthetic Aortic Wall Calcification
Paul Human MD, Christoph Weissenstein MD, Ameli Trantina MD, Peter Zilla MD

Immediate fixation and increased glutaraldehyde (GA) concentrations are required to prevent severe autolytic tissue damage during bioprosthetic aortic root production. The study aim was to verify that structure-preserving fixation also reduces aortic wall calcification. Porcine aortic roots were fixed either at the abattoir or after being kept on ice for 48 h. Two concentrations of GA (0.2% and 3.0%) were chosen (4°C, seven days). Discs of aortic wall tissue (1.2 cm diameter) were implanted subcutaneously in rats for 60 days (n = 10 per group); aortic roots were implanted in the distal aortic arch of sheep for six weeks (n = 3 per group) and six months (n = 4 per group). Calcification was assessed by atomic absorption spectrophotometry and light microscopy. Fixation-related tissue damage was determined by transmission electron microscopy, and correlated with calcification. No significant difference in calcification was found between immediate and delayed fixation if tissue was fixed with 0.2% GA. With 3.0% GA, both animal models showed a significantly lower level of calcification if tissue was fixed immediately. In the subcutaneous rat model, immediate fixation reduced calcification by 26% (p <0.0001); in the sheep model immediate fixation did not affect calcification in the short-term six-week implants, but markedly lowered it by 37% (p = 0.035) after six months. Ultrastructurally, there was a significant correlation between membrane damage, vacuolization and vesicle shedding on the one hand, and calcification on the other.