The fate of aortic valve homografts. An experimental study.

Segments of homograft aortic valve cusp and aortic sinus wall have been inserted as patches in the abdominal aortic wall of sheep. The donor valves were prepared in one of three ways: (1) fresh valves, (2) freeze-dried valves sterilized with antibiotics and ethylene oxide, and (3) valves which had been cooled at a controlled rate to – 70°C. in a medium containing the cryoprotective agent, dimethyl sulphoxide. Histological examination of the implanted tissue obtained at intervals up to 2 years failed to show survival of any donor cells, whichever method of preparation had been used. The elastic tissue in the freeze-dried series had become calcified by 2 years, and although valves prepared in this way appeared to elicit no immunological response, both the fresh and frozen tissue were infiltrated by lymphocytes and plasma cells by 2 weeks. This round-cell infiltration reached a peak at 4 weeks and then subsided again. The response to fresh valves was more marked and more prolonged than that to frozen valves.