Effect of preservation on the elasticity of human aortic valve homografts

Measurement of postcryopreservation viability

For any tissue, there is a cell viability threshold below which the ability of the tissue to maintain itself and function will eventually be compromised. During cryopreservation and subsequent thawing of tissues there are many steps involved, each with attendant potential risks for reduction of viability. To determine the effectiveness of any cryopreservation procedure it is important to select appropriate assays. In this manuscript viability assays, in general, are reviewed from a biological viewpoint prior to review of methods employed for assessment of heart valve viability. Both in situ and in vitro assays of heart valve viability indicate that valve mechanical properties and the majority of fibroblasts, which are responsible for maintenance of the valve connective tissue, are retained after cryopreservation.

Morphological assessment of sucrose preservation for porcine heart valves

Porcine aortic valves stored in various concentrations of sucrose (50-80%) for up to 52 weeks were examined both histologically and by electron microscopy. The valves were compared with porcine aortic valves stored in a nutrient and antibiotic medium for 12 weeks. Overall preservation was better in those porcine valves stored in sucrose solution than in nutrient and antibiotic medium, the best preservation being in 50% sucrose. Despite wide separation of collagen at that concentration seen on electron microscopy (not noted histologically), tissue preservation was good after storage in sucrose solutions at concentrations up to 80%, at which clumping of collagen and distortion of fibroblasts occurred. It is suggested that sucrose solution is acceptable for the long-term preservation of biological valves.

Storage of heart valve allografts in glycerol with subsequent antibiotic sterilisation

Fresh allograft valves stored in a nutrient medium at +4 degrees C have a limited storage time of eight weeks. Dura mater has been stored in glycerol for longer periods, and this paper presents work on the glycerol storage of allograft heart valves. The elastic properties of the valve cusps showed a fall during storage in glycerol that was associated with an altered histological appearance of the cusp tissue. The loss in nuclearity in the histological sections of stored tissue was partially responsible for the observed decrease in viability during storage. All these changes during storage in glycerol, or glycerol and subsequent antibiotic treatment, were similar to the changes seen in valves stored in a nutrient medium. Glycerol therefore offers an alternative storage system to the cold nutrient medium but has no practical advantages. Glycerol alone will not sterilise the allograft tissue, and a post-storage treatment with antibiotics is essential.