Robert T. Mcnally

Cryopreserved Vein Transplantation

There have been numerous attempts to develop prosthetic conduits or utilize al‐lograft saphenous veins for arterial bypass. This article summarizes our experimental and clinical experience with cryopreserved allograft saphenous veins. During these studies, particular attention was paid to vein donor postmortem ischemia time, vein procurement technique, and tissue storage methods. Experimental cryopreserved autograft studies demonstrated that cryopreservation of the veins does not alter subsequent graft patency, the arterialization process, blood flow, or platelet deposition in vein grafts. Endothelium‐derived relaxing and contractile factors are produced by the endothelium of explanted cryopreserved autografts, and smooth muscle contractions and relaxations can be induced. In experimental cryopreserved al‐lografts, the endothelium appears to be removed by an immune response during the first 10 days after transplantation, fibrin deposition is minimal, and re‐endothelialization occurs over 6–9 months. Early clinical results using cryopreserved allograft saphenous veins are encouraging with 1‐year patency rates of 79% for peripheral grafts and 86% for coronary bypass grafts.

Factors affecting the viability of cryopreserved allograft heart valves

Allograft heart valves have been used for more than 25 years as replacements for diseased aortic valves and repair of congenital abnormalities. In many instances, particularly paediatric surgery, it is the valve of choice due to its non-obstructive flow, relative freedom from calcification and thromboembolism without anticoagulation therapy. In order to permit valve size matching for recipients, it is necessary to find methods of storage which will maintain cellular viability. The best method which allows infinite, convenient storage is cryopreservation.

Short-term follow-up of cryopreserved allograft valves and valved conduits from the CryoLife clinical registry

CryoLife, a laboratory which specializes in the cryopreservation of human tissues for transplant, first started preserving valves in Autumn 1984. The hearts which arrive at CryoLife are currently procured by 144 independent organ and tissue procurement agencies in the United States, Canada and West Germany. This procured tissue is preserved by CryoLife as a service to those agencies or doctors to whom the tissue has been assigned. In order to assure consistent quality control, all agencies follow the guidelines printed in the CryoLife (3) heart valve procurement protocol. The protocol provides information for screening for infectious diseases and diseases of the heart which would render the tissue less than ideal. For instance, when the required serum sample is returned by the procuring group, tests are performed for HIV (AIDS), hepatitis, syphilis and CMV (cytomegalovirus). These internal tests are compared with pretest data which accompanies the organ and are used as a double check to confirm that the possibility of transmission of these diseases is eliminated. The donor form also contains a detailed medical history of the donor, which helps eliminate donors of questionable standards or with a history of cardiac complications. The protocol also contains the precise details for the surgical extraction of the heart so that uniformity amongst participating centres is maintained.

Intermediate-term performance of CryoLife cryopreserved heart valve allografts

CryoLife, Inc., a tissue processing laboratory, specializes in ultra-low temperature preservation of human tissues for transplant, including aortic and pulmonary heart valve allografts. Since CryoLife’s inception in 1984, the company has processed over 18000 donated hearts, received from 150 Tissue Banks and Organ Procurement Organizations throughout the United States, and documented the implantation of more than 16000 cryopreserved allograft heart valves from 450 institutions in the United States, Canada, and Europe (Fig. 1). The following chapter provides a summary of CryoLife’s tissue processing methodology and documented clinical experience of allograft heart valves.