Pericardial heterografts. Toward quality control of the mechanical properties of glutaraldehyde-fixed leaflets.

The mechanical properties of five different, equally distributed, and randomly oriented sites in natural and glutaraldehyde-fixed calf pericardial sacs were investigated. Identical sites in different sacs were obtained by placing a template over each sac and using the ligaments still attached to the pericardium as a reference frame. Mean maximum extension of the fixed tissue was statistically significantly greater than that of natural tissue at the same degree of stress. There was no significant difference in thickness from position to position within a sac, from sac to sac, or from the natural to fixed pericardium. However, the extensibility of one particular site was significantly greater than that of other positions in the pericardial sac. This position lay entirely in a well-defined sector that emanated radially from the pericardial ligaments. Light and electron microscopy showed no difference in collagen structure in the five positions studied. In contrast, both the content and ultrastructure of the tissue elastin differed in the region of high extensibility compared with those sites studied in the remainder of the sac. This region contained coarse condensed elastin whereas the other sites had fine elastin dispersed diffusely throughout the tissue. These results suggest that pericardial heterografts of uniform thickness may be harvested from any position in calf pericardium. However, unless the region of coarse condensed elastin is excluded, leaflets with significantly different mechanical properties may be produced.