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Correspondence

Long-Term Storage of Human Heart Valves Above the Glass Transition at –80°C

Research and Development, CryoLife, Inc., 1655 Roberts Blvd NW, Kennesaw, GA 30144

(Email: heacox.al{at}cryolife.com).

To the Editor:

Drs Heacox and Goldstein disclose that they have financial relationships with CryoLife, Inc.

 

The article by Brockbank and colleagues [1] identifies a streamlined method of storing heart valves. Because porcine valves were used as the model, we find the title misleading. Furthermore, the model may be inappropriate because differences in the stability of cryopreserved porcine and human aortic valve matrix have been noted [2–4].

Although systems maintaining –80°C are widely available, suitability of this environment for long-term storage is questionable. Solutions with high cryoprotectant concentrations are not stable above their glass transition temperature [5] and tend to accumulate crystalline ice over time, which is potentially damaging to biologic structures. There is evidence for this phenomenon with the suggested storage medium as the authors report viable cells in valves stored at –80°C for 30 days. However, sheep valves stored in the same solution and conditions for 1 year were not viable [6]. This temporal difference could indicate cryoprotectant toxicity or matrix instability during storage.

The safety and simplicity of this solution and process are also questionable. Formamide is a known teratogen, and valves stored in it might not be suitable to implant in women of childbearing age. Ultracold mechanical freezers are expensive, are subject to temperature fluctuations, recover slowly, and require liquid nitrogen backup against power outages. Tighter restrictions on airline transport of dry ice may limit distribution. Finally, the proven shelf life of such tissues is critical, as the time required to obtain clearance on donor and tissue safety factors generally exceeds 30 days.

Stable long-term storage of heart valve allografts is necessary. Cryopreserved valves retain structure and cellular activity for more than 5 years [7], and their use has been shown over the past 30 years to provide for comparable long-term functional outcomes and patient survival when compared with nonfrozen, antibiotic-stored valves. The method presented by Brockbank and colleagues needs verification.

	References

Top References

 

1. Brockbank KGM, Wright GJ, Yao H, et al. Allogenic heart storage above the glass transition at –80°C Ann Thorac Surg 2011;91:1829-1835.[Abstract/Free Full Text]
2. Gerson C, Goldstein S, Heacox AE. Retained structural integrity of collagen and elastin within cryopreserved human heart valve tissue by two-photon laser scanning confocal microscopy Cryobiology 2009;59:171-179.[Medline]
3. Schenke-Layland K, Madershanian N, Riemann I, et al. Impact of Cryopreservation on Extracellular Matrix structures of Heart Valve Leaflets Ann Thorac Surg 2006;81:918-926.[Abstract/Free Full Text]
4. Brockbank KGM, Heacox AE, Schenke-Layland K. Guidance for the removal of fetal bovine serum from cryopreserved heart valve processing Cells Tissues Organs 2011;193:264-273.[Medline]
5. Vigier G, Vassoille R. Ice nucleation and crystallization in water-glycerol mixtures Cryobiology 1987;24:345-354.
6. Lisy M, Pennecke J, Brockbank KGM, et al. The performance of ice-free heart valve allografts in an orthotopic pulmonary sheep model Biomaterials 2010;31:5306-5311.[Medline]
7. Mirabet V, Carda C, Solves P, et al. Long-term storage in liquid nitrogen does not affect cell viability in cardiac valve allografts Cryobiology 2008;57:113-121.[Medline]

This article has been cited by other articles:

				K. G. M. Brockbank, U. A. Stock, and K. Schenke-Layland Reply Ann. Thorac. Surg., February 1, 2012; 93(2): 695 - 695. [Full Text] [PDF]

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