Vergleichende in vivo Untersuchung verschiedener Konservierungsverfahren von allogenen Herzklappen

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Human heart valves or allografts represent nearly perfect heart valve substitutes. They have optimal hemodynamic characteristics and are resistant to infections. Disadvantages particularly in pediatric patients are limited availability, an inability to grow, degeneration and long-term failure. Potential culprits for the latter include immunological responses and an increased calcium metabolism. The first clinical use of allograft heart valves was as homovitals that were transplanted after antibiotic incubation without any preservation. Since 1968 standard frozen cryopreservation (SFC) has been employed including storage in vapour phase liquid nitrogen. Application of multiphoton imaging analysis (MIA) enables three dimensional visualization of elastin and collagen by induction of autofluorescence without fixation, embedding and staining in fresh tissue. MIA allowed for the first time detection of partial destruction of elastic and collagenous matrix in SFC porcine valves ex situ. As the overall amount of collagen and elastin remains unchanged the etiology of the above described destruction is postulated as freezing induced extracellular matrix (ECM) damage due to ice crystals. Disruptive interstitial ice damage that occurs during cryopreservation can be avoided by promoting vitrification, glass formation, instead of ice formation below the cryopreservation solutions glass transition temperature. As the preservation and warming is accomplished without any tissue destruction, vitrification enabled for the first time complete preservation of extracellular matrix in heart valves. In order to simplify the required infrastructure, we have further developed ice free cryopreservation (IFC), which permits storage above the solutions glass transition temperature in a 80C freezer. We applied IFC in a recent sheep study and were able to demonstrate that maintaining ECM results in better valve function and diminished degeneration. Furthermore, IFC is antiinflammatory preventing CD3 positive T cell mediated responses. The exact mechanism of this attenuated adaptive immune response remains unknown. Recent studies in a porcine tissue to human responder peripheral blood leukocyte combination have shown that treatment of valve tissue with IFC preservation medium reduces leaflet immunogenicity and induces responder monocyte differentiation towards endothelial like cells. Accordingly application of IFC for xenogeneic heart valves might overcome organ scarcity. Simplification by omitting controlled rate freezing and liquid nitrogen storage will improve cost effectiveness and allow application in third world and developing countries with limited financial resources.