Morphological Analyses of Ice-free and Frozen Cryopreserved Heart Valve Explants

Kelvin G. M. Brockbank, Ying C. Song
Organ Recovery Systems, Charleston, South Carolina, USA
 

Background and aim of the study: The pathophysiology of allogeneic heart valve failure is not fully understood. It is hypothesized that the rapid deterioration seen in some allograft heart valve recipients is due to disruptive interstitial ice damage that occurs during cryopreservation by freezing.
Methods: The hypothesis was tested by comparing a standard commercial heart valve freezing and ice-free, vitrification cryopreservation methods with fresh controls in: (i) a subcutaneous, juvenile rat implant model of calcification; and (ii) a descending thoracic aorta implant rat model for histopathology. Calcium concentrations in one- to six-week explants were determined using atomic absorption spectroscopy; calcification rates were also determined.

 Results: The calcification rate of frozen valves was significantly greater (p <0.01) than that of vitrified valves in both syngeneic and allogeneic recipients, supporting prior observations that ice-free cryopreservation reduces allogeneic heart valve calcification. Cryopreservation by freezing and vitrification resulted in mild morphological changes in two- and four-week explants, a slight decrease in leaflet cellularity, and a more rapid onset of intimal hyperplasia than in fresh valve explants. The allograft explant groups exhibited similar changes, regardless of how the valves were processed.
Conclusion: These findings provide only weak support for the tested hypothesis, and further studies in a large animal model are warranted.
 
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