Prediction of aneurysm formation in vascular grafts of biologic origin

Abstract

Other than review of clinical experience, no assay exists that can reliably predict the longterm potential for aneurysm formation in an arterial prosthesis of biologic origin. Since mural degeneration probably results from proteolytic digestion, an in vitro assay was devised that used graft perfusion with 1% collagenase to induce rapid changes in mechanical properties. The effect of enzyme on graft diameter, compliance, permeability, and burst pressure was measured in ficin-digested, adipoyl chloride and glutaraldehydetanned bovine carotid artery and glutaraldehyde-tanned human umbilical vein. Both grafts have recently been reported to have a significant incidence of aneurysm within several years of implantation. Compliance and diameter were also measured noninvasively in patients with bovine carotid artery and human umbilical vein for more than 40 weeks after implantation. In vitro, the response to enzyme could be categorized into three groups. In group III, a diameter increase of more than 14% was associated with a significantly decreased compliance, and this paralleled the results found in aneurysmal grafts in vivo. In both grafts there was a strong correlation between postenzyme compliance change and initial compliance, loss of compliance being significantly greater in grafts with group III responses (p < 0.01). This response may be a good predictor of a graft's overall susceptibility to aneurysmal degeneration, and initial compliance measurement may effectively identify inadequate fixation. Thus measurement of compliance may prove useful in quality control of a fixation process used in mass production. In conclusion, measurement of mechanical properties of biologic vascular grafts before and after collagenase exposure forms the basis for an effective in vitro assay of aneurysm susceptibility.