Mineralization and organic phase modifications as contributory factors of accelerated degeneration in homograft aortic valves.

BACKGROUND AND AIM OF THE STUDY

The study aim was to assess histological and mineralogical properties of leaflets in human, antibiotic-preserved aortic homograft valves (recovered during surgical replacement) in order to identify factors accounting for pathological changes leading to accelerated graft dysfunction. A comparison was made with aortic valves prepared for grafting, with a view to assessing morphological and mineralogical characteristics as a potential preimplantation risk factor.

METHODS

Valve leaflets were examined with light and scanning electron microscopy. Mineralization was assessed histochemically, and also physicochemically by atomic absorption spectroscopy (AAS).

RESULTS

All explanted homograft valve leaflets revealed prominent degenerative changes seen as decreased surface area, fibrosis, mineralization and focal thrombosis. Substantial loss of endothelium and fibroblasts, reduced collagen bundles crimping, inflammation (81%) and disappearance of layered structure (59%) was identified. The elastic elements were relatively stable, though a gradual age-dependent loss was observed in both groups. Accelerated mineralization was seen in all explanted homografts; inorganic deposits were composed mainly of hydroxyapatite. Two types of mineralization were identified: large limited nodular structures, and diffuse mineral deposits. Homografts with moderately elevated mineralization, well-preserved layered structure and sporadic infective changes proved to have the greatest durability. Homograft durability was also affected by the difference in host and donor age.

CONCLUSION

Preimplantation factors affecting pathological changes determining homograft durability included morphological status of the graft itself and donor age; host-related factors included recipient age, endocarditis, native valve calcification, and host-donor matching (age difference between host and donor). A limited molecular mineralization may increase valvular durability, provided that no focal nodular calcifications exist that might adversely affect overall homograft integrity.