Cryopreserved arterial allografts for limb salvage in the absence of suitable saphenous vein: two-year results in 20 cases

A novel method for long-lasting preservation of arterial grafts

BACKGROUND

Autologous venous grafts generally give best results for arterial bypass grafting in cases of arterial stenosis. When no suitable venous graft can be found, synthetic prosthetic graft may be an alternative. Prostheses are easily accessible but susceptible to infection. In these cases, the replacement of infected prosthesis by the human arterial allograft is the best treatment option. The question arises whether we could prepare a graft meeting mechanical conditions of an artery immunologically inert and resistant to bacterial infection.

MATERIALS AND METHODS

LEW and BN rat aortic segments were placed in dehydrated sodium chloride and stored for 1 to 12 mo. Then, they were transplanted orthotopically as aortic grafts for 3 to 15 mo in syngenic and allogenic combination. No immunosuppression was used. Patency, pulsation, and frequency of development of aneurysms were studied. The tensile strength and maximum intraluminal pressures were measured. Morphology of grafts was evaluated on histology and electron microscopy. The endothelial and infiltrating cells were identified.

RESULTS

Transplanted allogeneic aortic grafts preserved in anhydrous sodium chloride up to 12 mo remained patent for 15 mo. Hypertrophy of intima with endothelial cells lining the inner surface and single muscle cells between elastic fibers were seen. Normal structure of collagen and elastic fibers was maintained. Only minor-host mononuclear infiltrates were seen around the preserved allografts.

CONCLUSIONS

Rat aortas preserved in anhydrous sodium chloride retain patency and function even 15 mo after transplantation. Such grafts retain their wall structure and evoke only minor recipient reaction. Our results confirm that anhydrous sodium chloride may be used for arterial grafts preservation. Low immunogenicity is additional advantage.

Patency and structural changes in cryopreserved arterial grafts used as vessel substitutes in the rat

OBJECTIVE

To evaluate the patency and structural changes that occur in the short- and mid-term when cryopreserved syngenic arterial grafts are implanted in an experimental animal model.

MATERIAL AND METHODS

Segments of iliac artery from the Spraque-Dawley rat were cryopreserved in a biological freezer according a controlled, computerized freezing protocol whereby the specimens are cooled at a rate of 1 degrees C/min. After storage at -145 degrees C in liquid N2 vapor for 30 days, the cryografts were slowly thawed. These vessels were grafted to the common iliac artery in syngenic animals. The following study groups were established: group I (GI), non-implanted cryografts; group II (GII), autografts; and group III (GIII), cryoisografts. The control group (CG) was comprised of fresh iliac arteries. The animals were sacrificed 14, 30, or 90 days post-surgery. At each of these follow-up times, graft specimens were morphologically evaluated by light and scanning and transmission electron microscopy and immunolabeling of endothelial cells (vWf). Cell damage attributed to the cryopreservation or grafting process was also determined.

RESULTS

At the time of sacrifice, graft patency was 100% for the autografts, while 26.6% of the cryoisografts showed fully occlusive thrombosis. Among other complications, two pseudoaneurysms were detected. After cryopreservation, the grafts (GI) showed patches of endothelial denudation and good cellularity of the medial layer. The intimal hyperplasia observed in autografts implanted for 14 days (GII) was significantly delayed until day 30 when the graft was cryopreserved (GIII). Cryoisografts showed general thinning of the arterial wall and degeneration accompanied by medial layer cell loss. These grafts showed most cell damage at 90 days post-implant. Expression of the vWf in all specimens showing intimal hyperplasia was confined to the outermost graft layer.

CONCLUSIONS

Cryopreservation modified the reparative response of the grafts. Owing to faster degeneration of the medial layer and a delay in the appearance of intimal hyperplasia, arterial wall thickness was reduced relative to that of the non-cryopreserved autografts. This thinning, at least in the short-term (90 days), does not seem to give rise to aneurysms owing to the generation of a neointima that stabilizes the vessel wall.

Long-term Behaviour of Cryopreserved Arterial Grafts Versus Prosthetic Micrografts

INTRODUCTION

When a patient has no suitable vessels for use as grafts in bypass or reconstruction procedures, two of the options available are the use of a cryopreserved vessel or an expanded polytetrafluoroethylene (ePTFE) prosthesis. This study was designed to compare the long-term behaviour of these vascular substitutes.

MATERIAL AND METHODS

We established three study groups by grafting the following vessel substitutes to the iliac artery in Spraque-Dawley rats: arterial autografts (GI, n=12), cryopreserved syngenic arterial grafts (cryoisografts) (GII, n=12), and ePTFE micrografts (GIII, n=12). The animals were sacrificed 180 days after surgery, at which time the graft specimens were morphologically evaluated by light and electron microscopy, immunolabelling (ED1/alpha-actin) and morphometric analysis of the neointima.

RESULTS

At the time of sacrifice, graft patency was 100% for the autografts and cryoisografts, while 10% of the ePTFE micrografts showed fully-occlusive thrombosis. Intimal hyperplasia was observed in grafts in GI and GII; the neointima being thinner in the cryoisografts (54.36 +/- 2.26 microm) than the autografts (161.30 +/- 3.91 microm). The endothelium formed over the prosthetic micrografts was unstable, with areas of subendothelial thickening (9.37 +/- 3.18 microm). Cell loss and medial layer degeneration were observed in both GI and GII specimens, while the GIII grafts were colonised by cells on their luminal surface.

CONCLUSIONS

All three grafts show good long-term tolerance when used in an arterial setting. Following long-term implant, autografts and cryoisografts show similar alterations that give rise to the complete loss of the muscle component of the tunica media along with the formation of a stable neointima. This new layer takes on the role of the tunica media.

Abdominal aorta transplantation after programmed cryopreservation

AIM: To study the morphologic and cellular immunologic changes after homologous transplantation of the abdominal aorta in rats after programmed cryopreservation (-196 °C).

METHODS: Abdominal aorta was harvested from anesthetized Spraque Dawley (SD) rats for cryopreservation (group B) or immediate implantation (group A). The survival rates and apoptotic rates of aortic endothelial cells (ECs) were examined. The patency rates, histology and cellular immunologic changes of the abdominal aorta were examined on days 1, 3, 7, 14, 30, 60 after transplantation respectively.

RESULTS: The survival rate of ECs after programmed cryopreservation was 90.1% ± 1.79%, about 3.4% lower than that of uncryopreservation (93.5% ± 1.96%). The apoptotic rates of ECs was increased after cryopreservation (7.15% vs 4.86%, P < 0.05). The patency rate of group B was significantly higher than that of group A (91.6% ± 12.9% vs 62.5% ± 26.2%, P < 0.01). CD4/CD8 ratio, TCR αβ and CD11b/ CD18 ratio of group B were significantly lower than those of group A (P < 0.05). Revivification of the cryopreserved abdominal aorta showed normal adventitia and intact smooth muscle cells.

CONCLUSION: Cryopreservation can reduce homologous abdominal aortic antigenecity. Even if without administration of immunosuppressive agents, it is still feasible to implement homologous artery grafting in rats.

Cryopreservation prevents arterial allograft dilation

Historically, immune-mediated degradation and subsequent aneurysm formation have limited the usefulness of cryopreserved arterial allografts. This study tested the hypothesis that modern cryopreserved arterial allografts are protected from immune-mediated dilation. Abdominal aortas were harvested from anesthetized rats (Lewis and Brown-Norway) for immediate implantation or cryopreservation. Subsequently, Lewis rats underwent infrarenal aortic replacement with either an acutely harvested or a cryopreserved graft. There were four experimental groups: (1) acutely harvested isografts (Iso; n = 6), (2) cryopreserved isografts (C-Iso; n = 6), (3) cryopreserved allografts (C-Allo; n = 6), and (4) acutely harvested allografts (Allo; n = 6). All grafts were explanted at 8 weeks. A video camera and edge detection software were used to measure systolic and diastolic in vivo graft diameter (d). Measurement of arterial blood pressure (p) allowed calculation of compliance (Dd/Dp). Tail-cuff plethysmography was used to assess graft patency at 1 week. Graft diameter and blood pressure measurements were repeated at harvest. All harvested grafts were examined histologically. Our results showed that cryopreservation prevented immune-mediated dilation in arterial allografts in our 8-week rat implant model. Furthermore, the compliance of the cryopreserved grafts and was similar to that of controls. Further investigation is needed to delineate the exact mechanism of these potential clinically significant findings.

Long-term results of infrageniculate bypass grafting using all-autogenous composite vein

Infrageniculate (below-knee) bypass using all-autogenous composite vein requires multiple incisions, venovenostomy, and prolonged operating time. The purpose of this study was to evaluate the long-term results of this procedure, with comparisons to grafts created from single-segment greater saphenous vein (GSV) or polytetrafluoroethylene (PTFE). A total of 362 consecutive infrainguinal bypass grafts with infrageniculate distal target arteries were created in 283 patients in a single institution between January 1995 and December 2000. Comorbid conditions were common, including diabetes (58%), coronary artery disease (56%), prior lower extremity revascularization (41%), end-stage renal failure (20%), and prior coronary artery bypass grafting (18%). The indication for revascularization was limb salvage in 93% of cases. The grafts were constructed from single segments of GSV (n = 239), from two or more vein segments resulting in an all-autogenous composite graft (n = 61), or from PTFE (n = 62). All-autogenous composite grafts were constructed using segments of ipsilateral or contralateral GSV (n = 49), upper extremity vein (n = 23), superficial femoral vein (n = 7), or lesser saphenous vein (n = 5). Infrageniculate all-autogenous composite vein grafts exhibited similar long-term results to those of GSV grafts, and far superior results to those of PTFE grafts. For patients with available autogenous segments, the all-autogenous composite vein graft is the conduit of choice.

The use of ischaemic vessels as prostheses or tissue engineering scaffolds after cryopreservation

OBJECTIVE

to evaluate the condition of organ donor arteries subjected to prolonged cold-ischaemia followed by cryopreservation, for their possible use as vascular grafts.

MATERIALS AND METHODS

fresh specimens of human iliac artery from organ donors were used as controls. These arteries were divided into two portions, one of which was cryopreserved in an automated freezer. A further group of arteries was immersed in Wisconsin solution and kept for 4 days at 4 degrees C (cold-ischaemia). After this period, the arteries were also cut into two, and one of these portions was cryopreserved. All the cryopreserved arterial segments were stored for a month and then subjected to automated gradual thawing. The thawed specimens were evaluated by light microscopy, scanning and transmission electron microscopy, immunohistochemical analysis (MMPs, elastin, CD31, von Willebrand factor) and the in situ detection of fragmented DNA (TUNEL method).

RESULTS

the most marked changes induced by cryopreservation were partial vessel deendothelialisation and morphological changes in cells of the intima that were in the process of detachment. No significant changes were observed in the medial layer, other than discrete elastic fibre fragmentation. Following cold-ischaemia, the endothelium was the most affected layer, with large denuded areas and exposure of the fibroelastic layer. Increased MMP-2 expression was also noted after cold-ischaemia. When subjected to both cold-ischaemia and cryopreservation, a large proportion of endothelial cells showed positivity for the TUNEL technique, however, no significant difference was observed between the ischaemic and the ischaemic/cryopreserved specimens.

CONCLUSIONS

prolonged cold-ischaemia causes some additional damage to the arterial wall compared to cryopreservation alone. However, the structural component of the ischaemic vessel remains in a condition that is suitable for subsequent cryopreservation and use as a vessel substitute or a scaffold for tissue engineering.

Effect of the thawing process on cryopreserved arteries

This study was designed to explore the changes that occur in cryopreserved pig arteries following different thawing procedures, before and after being placed in an in vitro flow circuit. Segments of minipig iliac artery were cryopreserved in complete minimal essential medium plus 10% dimethylsulphoxide and stored in liquid nitrogen at -196 degrees C for 30 days. Three study groups were established according to whether the arterial specimens were fresh (control, n = 20), cryopreserved and rapidly thawed (RT) at 37 degrees C (n = 22) or cryopreserved and subjected to controlled, automated slow thawing (ST) (n = 22). Half of the specimens of each group were subsequently placed in the flow circuit for 72 hr. Evaluation was made of morphological and ultrastructural changes. Cell damage was established using the TUNEL method. All cryopreserved specimens showed endothelial denudation that was most extensive in those subjected to rapid thawing. Slowly thawed specimens showed improved cell viability and organization of the vessel wall, compared to those thawed rapidly. Under conditions of flow, the damage induced by the freezing/thawing process was enhanced. These findings suggest that (a) slow thawing of cryopreserved arteries results in improved preservation of the structure and viability of vessels, and (b) the damage induced by freezing/thawing is enhanced when vessels are subjected to flow in an in vitro circuit.

Gradual thawing improves the preservation of cryopreserved arteries

This study was designed to test a slow, controlled, automated process for the thawing of cryopreserved arteries, whereby specimen warming is synchronized with the warming of its environment. Segments of minipig iliac artery, 4-5 cm in length, were subjected to controlled, automated cryopreservation in a biological freezer at a cooling rate of 1 degrees C/min to -120 degrees C, followed by storage in liquid nitrogen at -196 degrees C for 30 days. Following storage, the arterial segments were subjected to rapid (warming rate of approximately 100 degrees C/min) or gradual (1 degrees C/min) thawing. Thawed specimens were processed for light microscopy and for scanning and transmission electron microscopy, Cell death was determined by the TUNEL method. Metalloproteinase (MMP) expression was estimated by immunohistochemical analysis. Most of the cryopreserved vessels subjected to rapid thawing showed spontaneous fractures, mainly microfractures, whereas these were absent in slowly thawed specimens. In rapidly thawed vessels, the proportion of damaged cells was double that observed in those thawed more gradually. Increased intensity and extent of MMP-2 expression was shown by rapidly thawed specimens. The slow-thawing protocol tested avoids the formation of spontaneous fractures and microfractures and the accumulation of fluid within the arterial wall tissue. This results in improved tissue preservation.

Experimental small bowel transplantation using newborn intestine in rats: III. Long-term cryopreservation of rat newborn intestine

BACKGROUND

If long-term organ cryopreservation can be attained, a significant achievement will have been made to address the problem for donor shortage. Fetal intestine has been known to revascularize naturally without vascular anastmosis. The authors have confirmed previously that the newborn intestine also could develop to maturity in the host omentum. Here, the authors examined whether the cryopreserved newborn intestine could revascularize in the syngeneic combination using the 2 different solutions and whether cryopreservation affect their antigenicity in the allogeneic combination.

METHODS

Inbred rat strains of LEW (MHC haplotype; RT1(l)) and BN (RT1(n)) were used. LEW newborn intestinal grafts were stored in RPMI-1640 or University of Wisconsin solution with 10% DEMSO (n = 10 in each group). The grafts were placed into a cold (4 degrees C) preservation solution for 30 minutes and then placed into a freezing chamber and cooled to -80 degrees C at -1 degrees C/min after 12 hours quenched to -180 degrees C in liquid nitrogen for longer than 30 days. Then, the cryopreserved grafts under the 2 different solutions were transplanted syngenicaly (LEW to LEW). The cryopreserved BN grafts also were implanted into the LEW omentum pouch. The allotransplantation was received with a 14-day high-dose course of tacrolimus (0.64 mg/kg, intramuscularly). The grafts were evaluated histologically at 4 weeks after transplantation. Fresh newborn intestines implanted in this syngeneic and allogeneic combination were evaluated as each control group.

RESULT

In the syngeneic combination, more than 90% of the mature intestine were obtained. There was no significant difference among the different solution and the fresh group. However, in the allogeneic combination, both fresh and cryopreserved grafts were histologically poor.

CONCLUSIONS

This is the first report showing that long-term cryopreservation was not harmful for neovascularization of newborn intestine. Long-term cryopreservation did not reduce the antigenicity of the newborn intestine. J Pediatr Surg 36:602-604.

Long-term assessment of cryopreserved vein bypass grafting success

PURPOSE

When autogenous vein is unavailable, cryopreserved veins have been used in patients as a means of attempted limb salvage. We evaluated the long-term patency and limb salvage rates for patients undergoing bypass grafting with cryopreserved veins.

METHODS

Medical records were reviewed for patients undergoing cryovein bypass grafting at two hospitals from 1992 to 1997. Follow-up data were obtained from subsequent admissions and office records. Primary outcomes were death, amputation, and primary patency. Skin integrity and additional bypass grafting procedures were assessed when data were available. Analysis was performed by means of life-table and chi(2) analyses with the Statistical Package for Social Sciences (SPSS).

RESULTS

Seventy-six patients (mean age, 70 +/- 11 years) underwent 80 procedures. Indications for surgery were tissue loss (63%), rest pain (24%), acute ischemia (11%), and other (2%). Early complications included 3 deaths (4%), 14 acute thromboses (18%), and 7 major amputations (9%). The mean follow-up period was 17.8 +/- 20.89 months (range, 0-77 months). The primary patency rate was determined to be 36.8% at 1 year and 23.6% at 3 years by means of life-table analysis. The limb salvage rate was 65.5% at 1 year and 62.3% at 3 years. Skin integrity was found to be compromised in 17 (55%) of 31 patients who were available to follow-up. Nine patients (11.3%) underwent additional ipsilateral revascularization or revisions, with one of three of these patients eventually requiring a major amputation.

CONCLUSION

Cryopreserved vein may be a reasonable alternative conduit for limb salvage when no autogenous tissue is available; it has an acceptable limb salvage rate (62.3%) at 3 years. Long-term patency remains relatively poor, with only 23.6% of originally placed grafts patent at 3 years. The use of cryopreserved veins should be strictly confined to limb salvage after a thorough search for autogenous tissue has been exhausted.

New concepts and materials in microvascular grafting: prosthetic graft endothelial cell seeding and gene therapy

Microsurgical free tissue transfer is currently associated with very high success rates and few complications. While interposition vein grafting is clearly an important adjunct to the microsurgeon's armamentarium, it has been associated with higher free flap/replantation failures and complication rates. With appropriate flap planning and surgical techniques, the need for interposition vein grafting should be quite infrequent and hopefully avoided if at all possible. Nevertheless, when necessary, the vein graft remains the gold standard, with virtually all alternative interposition grafts demonstrating lower patency rates. One of the more promising areas of research is the concept of genetic manipulation of the endothelial cell via molecular biological techniques. It is likely that in the near future this may become a clinical reality, not only improving the patency of microsurgical anastomoses and interposition vein grafts, but quite possibly altering the target organ functionally as well.

Cellular repopulation of human vein allograft bypass grafts

PURPOSE

Vein allografts are an alternative conduit for patients lacking available autogenous vein. The ability to develop a neoendothelium is a potential advantage of allografts over other nonautogenous grafts, because endothelial cells have been shown to play numerous essential roles in vessel survival. However, repopulation by endothelial cells has not previously been demonstrated or characterized in human subjects.

METHODS

In our prospective trial, 40 patients (20 men, 20 women) underwent cryo- preserved saphenous vein bypass grafting procedures for limb salvage. Several patients underwent multiple grafting procedures. All grafts were sampled at implantation. During the 31 month follow-up interval, 22 allografts were explanted at the time of revision or subsequent surgical procedure. All grafts (22 of 22) demonstrated intact endothelium at implantation and explantation. Seventeen explantation biopsy samples (seven from men, 10 from women) from 16 patients (seven men, nine women) were adequate for further histologic and immunofluorescent analysis. Explants were stained with hematoxylin-eosin and immunohistochemical markers to quantitate rejection and also underwent fluorescence in-situ hybridization, with probes for X and Y chromosomes and counterstain for nuclear envelope. Cells were counted as XX, XY, XO, YO, or unstained. The endothelium and vessel walls were analyzed for origin of cells based on sex-mismatched transplants, with sex-matched transplants serving as controls.

RESULTS

Evidence of cellular damage was noted in all explanted allografts, and moderate or severe rejection (lymphocyte infiltrate, +CD3, +CD8, +CR3, cytotoxic granules) was noted in six explanted allografts (29%). All allografts demonstrated intact endothelium (complete or partial), at the time of both implantation and explantation. Sex-matched (male to male) control explants showed only male cells, as expected. Male donor-female recipient transplants showed complete repopulation by recipient (female) cells in nine of 10 cases (90%), whereas one case (10%) demonstrated partial repopulation (a mosaic of male and female cells). One patient's slides were unreadable. Findings in cells of the allograft wall were identical to those of the endothelium (nine recipient-only cells and one mosaic). Complete absence of donor cells was noted as early as 1 week after implantation, but mosaicism was demonstrated in one patient 3 months after grafting. No relationship could be demonstrated between repopulation and time (P >.05), quantity of rejection (P >.05), or donor age (P >.05).

CONCLUSION

Both the endothelial lining and vessel wall of venous allografts repopulate with cells of recipient origin, resulting in either a completely novel cellular constituency or a mosaic of host and donor cells. The loss of donor cells may be mediated by apoptosis or rejection, and the rate of migration of repopulating host cells is, at this point, unclear. Although the development of a completely endothelial-lined conduit offers a potential advantage over other alternative conduits, the functional status of the neoendothelium and repopulated vessel wall and their role in maintenance of allograft patency require further investigation.

Surgical repair of infected peripheral graft and abdominal aortic aneurysm using arterial homograft

We report a case of combined surgical repair including lower limb revascularization (below-knee bypass) and abdominal aortic aneurysm repair using cryopreserved arterial homograft. The patient experienced lower limb ischemia due to repeated thrombosis of a long-infected polytetrafluoroethylene (PTFE) graft, and was also shown to have a complicating abdominal aortic aneurysm. Infection was eradicated with total graft excision and intravenous antibiotics. Two-year patency of the in situ arterial homograft revascularization was demonstrated with hemodynamic and tomographic controls; no degenerations have been found to date. Benefits of the use of in situ arterial homograft for arterial reconstruction may include improved hemodynamics and greater resistance to infection compared to when alloplastic materials are used. Because of the risk of allograft deterioration, close follow-up of the patient is required.

Bacterial resistance of refrigerated and cryopreserved aortic allografts in an experimental virulent infection model

PURPOSE

The bacterial resistance of refrigerated and cryopreserved aortic allografts in a highly virulent infection in a dog model was studied.

METHODS

The infrarenal aorta of 12 dogs was replaced with either a cryopreserved aortic allograft (group I, n = 6) or a refrigerated aortic allograft (group II, n = 6) in infected sites. Allografts were harvested from dogs and stored for 1 week, either by cryopreservation (-140 degrees C) or refrigerated method (4 degrees C), in a preservation medium. At the time of implantation, induction of infection was achieved with an infected piece of knitted Dacron placed just beneath the allograft. The Dacron was contaminated in vitro by soaking it in a solution with Staphylococcus aureus PR209. All 12 dogs received no adjunct antibiotic or antithrombotic therapy. Four weeks after implantation, the animals were killed to recover the grafts for bacteriological and histological analyses. Bacterial results were expressed as colony-forming units (CFU)/cm2 of graft material.

RESULTS

In group I, only one allograft grew bacteria at 2. 16 x 10(6 )CFU/cm2, with a blood culture positive for S aureus. In group II, one dog died at 3 weeks from a false septic aneurysm rupture, all the allografts were infected (P <.05) with a mean bacterial count of 9.41 +/- 6.8 x 10(4) CFU/cm2, and three blood cultures were positive for S aureus. The patency of the grafts was analyzed at the time of recovery. Three laminar thrombi without occlusion were present in group I; none were present in group II. A better preserved endothelium in group I was revealed by means of histologic analysis staining with factor VIII antibody before implantation. After 4 weeks of implantation in the infected site, infected allografts presented polynuclear infiltrates in the media with a high degree of inflammatory reaction, and endothelial recovery was more significant in group I, with numerous young plump cells.

CONCLUSION

This study demonstrates that cryopreserved allografts implanted in infected sites in a dog model can produce greater bacterial resistance.

Cryopreserved arterial homografts: preliminary results in infrageniculate arterial reconstructions

The aim of this report is to present our preliminary experience using cryopreserved arterial homografts in below-knee revascularization. We carried out a retrospective study at the Public Health Hospital of the Servicio Galego da Saude (SERGAS) from October 1995 to March 1997 in which cryopreserved arterial homografts were used for revascularization of 17 lower limbs in 16 patients. The clinical indications were limb-threatening ischemia in 15 lower extremities (7 with rest pain and 8 with ischemic ulcers or gangrene), and large aneurysms of femoropopliteal arteries in 2. In addition, 75% of the patients had undergone previous surgical procedures for revascularization on the involved extremity. No patient had a suitable greater saphenous vein in the ipsilateral extremity and all patients required a below-knee arterial reconstruction procedure. There was just one runoff vessel in 11 of 17 extremities (65%). A histological exam was performed in four patients who died (1 case) or had homograft-related complications (3 cases). The results of this study indicated that cryopreserved arterial homografts could be a promising alternative when below-knee revascularization is required in patients lacking suitable greater saphenous vein, especially in those with limited life expectancy, but despite early acceptable results, many aspects must be clarified. Close follow-up is mandatory.

Early experience with cryopreserved arterial allografts in below-knee revascularization for limb salvage

BACKGROUND

Below-knee revascularization for limb salvage in the absence of a suitable autogenous saphenous vein is a frequent challenge associated with a high amputation rate. The aim of this prospective study was to evaluate the usefulness of cryopreserved arterial allografts in such cases.

METHODS

Arterial allografts were harvested from multiple organ donors and cryopreserved at -80 degrees C. From March 1993 to December 1997, 35 cryopreserved arterial allografts were used as below-knee bypasses for repeated limb salvage in 32 patients. There were 15 men and 17 women with a mean age of 75 years (+/-10.7). Seven patients had rest pain and 25 patients (78%) had gangrene or nonhealing ulceration. Runoff was through a single tibial vessel in 25 cases (71%) and two vessels in 10 cases. Previous ipsilateral bypasses had been done in 26 of 35 limbs (74%). Patients were followed up prospectively for an average period of 18 months (range 2 to 56).

RESULTS

Aneurysmal dilatation occurred in two patent grafts, requiring segmental replacement at 13 and 18 months, respectively. The overall primary patency rate was 75% at 6 months, 57% at 12 months, and 39% at 18 months. The overall secondary patency rate was 75% at 6 months, 75% at 12 months, and 59% at 18 months. Overall limb salvage rate was 80% at 12 months, 73% at 18 months.

CONCLUSIONS

These early data indicate that below-knee bypass with arterial allografts results in acceptable patency and limb salvage. Arterial allografts may be a useful alternative to other arterial substitutes in a difficult group of patients with critical ischemia and no suitable saphenous vein.

Arterial damage induced by cryopreservation is irreversible following organ culture

OBJECTIVES

The aim of the present study was to investigate the changes which occur to the arterial wall following cryopreservation and thawing and to determine whether these changes are reversible after a week of culture in an organ bath.

MATERIALS AND METHODS

Rat iliac arterial segments were cryopreserved. Once thawed, the arterial segments were cultured for a period of 0, 1, 2, 4 or 7 days. Freshly isolated rat iliac vessels cultured for 7 days served as the control group. Evaluation was made of ultrastructural changes, the expression of metalloproteinase activity (MMP-1, MMP-3 and MMP-9) and the apoptotic state of cells.

RESULTS

The freezing-thawing process induced damage to the arterial segments compared to fresh control vessels. After 1 week of culture, arteries showed a high degree of tissue degeneration. Only a few individual endothelial cells remained on the luminal surface. There was a gradual increase in the proportion of apoptotic cells. The sequential expression of MMP-1 during the first 2 days and subsequent expression of MMP-3 and MMP-9 were of most significance.

CONCLUSIONS

Cryopreservation induced damage to the vessels which could not be reversed by organ culture. The changes observed in the expression of metalloproteinases may be indicative of the degenerative process which occurs in the extracellular matrix.

The histo-blood group ABO system and tissue transplantation

In general, one might expect that ABO incompatibility of donor and recipient would be important to some degree if viability of the transplanted allograft is important for graft incorporation and function. This is true for some recipients of organs. However, ABO incompatibility appears to play a minor role, if any, in the clinical success of viable cornea and viable skin allografts. Even though A and B antigens may be present on the transplanted tissue, other factors that can contribute include the strength of the immune response, the avidity of the antibody, and the dose of the antigen presented, which may vary from donor to donor. Although A and B antigens are present on endothelium, the use of ABO-incompatible heart valves is successful, as they carry out their mechanical function by using the strength of the connective tissue rather than the viability of the donor endothelium. The presence, immunogenicity, and significance of A and B antigens in human vessel transplants have not been well studied. With the more commonly transplanted tissue, such as bone and tendon, posttransplant success does not depend on cellular viability or ABO compatibility.

Functional assessment of human femoral arteries after cryopreservation

PURPOSE

An established method of cryostorage that might preserve the vascular and endothelial responses of human femoral arteries (HFAs) to be transplanted as allografts was studied.

METHODS

HFAs were harvested from multiorgan donors and stored at 4 degrees C in Belzer solution before cryostorage. One hundred eleven HFA rings were isolated and randomly assigned to 1 control group of unfrozen HFAs and 2 groups of HFAs cryopreserved for 7 and 30 days, respectively. Cryopreservation was performed in Elohes solution containing dimethyl sulfoxide (1.8 mmol/L), and the rate of cooling was 1.6 degrees C/min, until -141 degrees C was reached. The contractile and relaxant responses of unfrozen and frozen/thawed arteries were assessed in organ bath by measurement of isometric force generated by the HFAs.

RESULTS

After thawing, the maximal contractile responses to all the contracting agonists tested (KCl, U46619 [a thromboxane A2-mimetic], norepinephrine, serotonin, and endothelin-1) were in the range of 7% to 34% of the responses in unfrozen HFAs. The endothelium-independent relaxant responses to forskolin and verapamil were weakly altered, whereas the endothelium-independent relaxant responses to sodium nitroprusside were markedly reduced. Cryostorage of HFAs also resulted in a loss of the endothelium-dependent relaxant response to acetylcholine. The vascular and endothelial responses were similarly altered in the HFAs cryopreserved for 7 and 30 days.

CONCLUSION

The cryopreservation method used provided a limited preservation of HFAs contractility, a good preservation of the endothelium-independent relaxant responses, but no apparent preservation of the endothelium-dependent relaxation. It is possible that further refinements of the cryopreservation protocol, such as a slower rate of cooling and a more controlled stepwise addition of dimethyl sulfoxide, might allow better post-thaw functional recovery of HFAs.

Human saphenous vein allograft bypass grafts: immune response

Although it has been claimed that allografts of blood vessels might be successful because of minimal immunogenicity, they are subject to frequent and early failure, the cause of which has not been thoroughly investigated. We sought to define the immune response to allograft bypass. In a prospective trial, 40 patients underwent cryopreserved venous allograft bypass. Allograft biopsies were performed at implantation and at allograft explantation in instances of graft failure. Tissues were evaluated in a blinded manner by means of standard histologic examination and paraffin immunohistochemical analysis with monoclonal antibodies against a variety of immune markers. During the 31-month follow-up period, 22 allografts were removed, and 19 were suitable for immunohistochemical study. Of these 19, 6 (32%) had moderate or severe infiltrates, which were evenly distributed throughout the intima, media, and adventitia. Immunohistochemical study of the explants demonstrated all of these infiltrates to be leukocytes (+LCA), which were predominantly activated T lymphocytes (+CD3, CD8, CR3) containing cytotoxic granules (+TIA-1). Macrophages were uncommon (+CD68); B cells (+L26, CD79) and natural killer cells (+CD56) were rare. Immunosuppression was associated with decreased presence of cytotoxic granules (TIA-1). Human venous allografts are immunogenic and prompt a T cell-mediated response. Allografts also fail without strong evidence of rejection, presumably because of local injury, hypercoagulability, or stasis. It may be possible to modify the contribution of rejection to venous allograft failure by means of immunosuppression and to modify the contribution of local hypercoagulability by means of anticoagulation.

Immunosuppression for human saphenous vein allograft bypass surgery: a prospective randomized trial

PURPOSE

Vein allografts are an alternative bypass conduit for patients who lack adequate autogenous vein. Animal studies have demonstrated that patency can be augmented by low-dose immunosuppression with azathioprine.

METHODS

In a prospective trial, 40 patients (20 men, 20 women) were randomly assigned to receive (17) or to not receive (23) azathioprine (1 mg/kg/day) after cryopreserved vein allograft bypass grafting. Patients had pain or tissue loss that required bypass grafting to pedal or crural outflow and lacked adequate autogenous saphenous vein. Anti-HLA antibody screens were obtained before and after surgery. Biopsies of allografts were performed at implantation and at all subsequent opportunities. Postoperative physical and vascular laboratory examinations occurred every 3 months.

RESULTS

During the 31-months follow-up interval (mean, 15.7 months) there were 10 deaths (none immunosuppression-related). The primary graft patency rate at 12 months was 13%, and the limb salvage rate was 42%. No significant difference (p > 0.05) was noted between immunosuppressed and control groups for mortality rate, primary graft patency rate, or limb salvage rate. As a predictor of graft failure, positive preoperative anti-HLA antibody screen (8 patients) approached significance (p = 0.09). Of 22 explanted grafts, 13 (59%) had histologic evidence of rejection (six immunosuppressed, seven control). Seven patients who had negative results of preoperative anti-HLA antibody screens converted after surgery, and six patients had positive results of preoperative screens that became more strongly positive.

CONCLUSION

Vein allograft failure is in part mediated by rejection, which is not eliminated by low-dose azathioprine. Both humoral (antibody) and cellular responses to vein allografts develop. The poor patency rates of vein allograft bypass grafts may be improved by more potent immunosuppression as well as improvement in allograft procurement, preservation, and matching.