Biaxial strain properties of elastase-digested porcine aortic valves.

OBJECTIVE

Previous studies have suggested that elastin in porcine aortic valve cusps is responsible for restoring collagen fibers to their original configuration between loading-unloading cycles.

METHODS

Biaxial loading tests were performed on intact aortic valves before and after elastase treatment to further investigate the role of elastin.

RESULTS

Degradation of elastin caused an increase in the radial dimensions of the cusps (mean increase in gauge length, 29%), which corresponded to a significant decrease in radial extensibility (mean decrease, 61%) and a threefold increase in radial stiffness. Changes in circumferential extensibility and stiffness were smaller and, for most cusps, were not statistically significant. Control experiments, in which the valves were treated with buffer only, resulted in the opposite changes in radial dimensions and extensibility (7% decrease in gauge length and doubling of extensibility).

CONCLUSIONS

Changes in the mechanical properties of the aortic valve cusps following incubation in elastase were due to elastin damage, and not incidental to soaking in buffer. As many explanted bioprosthetic valves have mechanical characteristics similar to those of the elastase-treated valves, elastin damage may be a factor in the progressive degeneration and ultimate failure of bioprosthetic heart valves.