Degeneration of bioprosthetic heart valve cusp and wall tissues is initiated during tissue preparation: an ultrastructural study.

OBJECTIVE

Chronic tissue degeneration is a major factor in the failure of porcine bioprosthetic heart valves. Stabilization with glutaraldehyde (GA) has become the standard in preparation of bioprosthetic heart valves, but there is increasing evidence that GA does not effectively stabilize all tissue structures, specifically glycosaminoglycans (GAGs). The study aim was to establish the status of GAGs in bioprosthetic heart valves and to ascertain whether degeneration of the extracellular matrix (ECM) is initiated during preparation of porcine tissues for use as bioprosthetic heart valves.

METHODS

Stentless porcine bioprosthetic heart valves were prepared by tissue harvesting, 24 h of storage in cold saline, and 14 days' fixation in buffered 0.6% GA. Tissue samples obtained from fresh and fixed aortic cusps and wall conduit were analyzed for ECM integrity and GAG localization by transmission electron microscopy combined with toluidine blue staining.

RESULTS

Major degenerative changes occurred in the ECM ultrastructure of both porcine cusp and wall during tissue preparation for use as bioprosthetic heart valves. Modifications in the aortic cusp included loss of GAGs from the interfibrillary space and from the surface of the collagen fibers. In the aortic wall, GAGs were lost from the interfibrillary space and from the surface of collagen fibers. In addition, the surface of wall elastic fibers exhibited marked paucity of GAGs and elastin-associated microfibrils.

CONCLUSIONS

The typical steps involved in the preparation of porcine aortic bioprosthetic heart valves induce, or cannot fully prevent, degeneration of some components of the ECM. Controlling the extent of this pre-implantation deterioration will open new gateways for improvement of the quality and durability of future cardiovascular bioprostheses.