Morphology of heart valves preserved by liquid nitrogen freezing

As a preliminary to establishing a frozen valve bank for replacement surgery, the possible effects of the proposed freezing and thawing procedure on tissue structure were assessed in 16 human pulmonary valves removed from cadavers at necropsy and nine dog valves obtained fresh. The valves were frozen and stored in liquid nitrogen for intervals ranging from 23 to 380 days. Blocks of tissue cut from the central area of one leaflet, and including some adjacent arterial wall and ventricular myocardium, were obtained both before freezing and after thawing and examined by a large specimen resin embedding technique for light and electron microscopy, with histochemical staining for matrix material. Control and thawed tissue from all valves appeared similar, indicating good preservation irrespective of storage time. Fine structural alterations in the cellular elements correlated with the total interval of autolysis (from death to freezing) rather than the cause of death or other variables and were not uniform in any of the specimens.