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Ann Thorac Surg 1998;66:1864
© 1998 The Society of Thoracic Surgeons
a Cryobiology Unit and Tissue Bank, Regional Blood Transfusion Center, Reina Sofía Hospital, Córdoba, Spain
b Department Cardiovascular Surgery, Reina Sofía Hospital, Córdoba, Spain
To the Editor
The usefulness of allograft aortic and pulmonary valves in the surgical management of aortic valve and aortic root disease, as well as for correction of complex congenital heart disease, is undeniable. Of particular interest has been the investigation of allograft leaflet viability and how this may be associated with valve durability.
The article by Lu and colleagues [1] has evaluated the injury resulting from postmortem cold ischemia and cryopreservation using the reduction of XTT-tetrazolium salt as a marker for metabolic sequelae. They concluded that there is progressive loss of metabolic functioning in valve leaflet cells in both noncryopreserved and cryopreserved tissue as storage time increases.
During the last few years, our group has evaluated the effects of several substances and those of cryopreservation on tissues by employing the reduction of tetrazolium salts as marker for tissue viability [2,3]. The reduction of tetrazolium salts is a specific indicator of the activity of mitochondrial dehydrogenase enzymes in living cells [3].
In this way, we have investigated possible differences in lactic dehydrogenase activity according to the source of human valves (living versus cadaveric donor) as a marker for injuries on mitochondrial activity related to the metabolic status before cardiac explant. For this purpose, a total of 15 human leaflets provided by 4 recipients of heart transplantation (living donors) as well as 15 human leaflets obtained from 4 cadaveric donors receiving less than 2 hours warm ischemia were evaluated for tetrazolium reductase activity as previously described [2,3]. Once obtained, cardiac explants were rinsed and maintained at 4°C in cold Ringer’s lactate solution until valve extraction. Semilunar leaflets from mitral and tricuspideal roots were dissected free from the hearts and tetrazolium reductase was immediately determined (fresh valves).
Human leaflets obtained from living donors showed a higher lactic dehydrogenase activity than those obtained from dead donors (59.03% versus 34.34%, p < 0.001). We can not give a clear explanation for this fact, but it can be argued that hemodynamic alterations, ie, metabolic and pH changes of which duration ranges from hours to days, produced by trauma or death from disease, can affect the metabolic activity of the valves, as reported for short periods of warm ischemia [4].
However, to our knowledge no differences in survival after implantation of valves obtained from living or dead donors have been reported, and it is also probable that a nonlethal injury does not sensitize the cells to later injury, which might lead to lower cell salvage at the time of clinical implantation.
In conclusion, we agree with Lu [1] that tetrazolium reductase activity is a sensitive, inexpensive, and efficient marker for viability in procedures of retrieval, handling, and cryopreservation of heart valves. Further studies will be necessary to analyze the effects of disease and status of the donor at the moment of donation on tissue viability.
References
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