Cryopreservation prevents arterial allograft dilation

Immunological Aspects Involved in the Degeneration of Cryopreserved Arterial Allografts

Introduction: Cryopreserved arterial allografts have remained an option in patients requiring distal revascularization or associated with vascular infection, in the absence of a valid autogenous saphenous vein. The objective of this study is to describe the different clinical, anatomopathological, and immunological findings related to vascular transplant rejection.

Methods: In a prospective trial, 35 patients who underwent cryopreserved allogeneic arterial bypass were studied, including demographics and conduit patency. Anti-HLA antibody production was stablished prior to the surgery, 7 days, 1, 3 months, and every 3 months since. Clinical and ultrasound evaluation was added after the first month. Donor HLA-typing was retrieved whenever available, allowing for the characterization and quantification of donor specific antibodies. Cytotoxic crossmatch test was also performed. A second group of patients with allograft degenerations registered during the follow up period was studied. In this group, exclusively for aneurysm description and histopathological analysis, they were included those degenerated vascular transplants from the original series, but also those implanted prior to the beginning of the study and degraded during follow up.

Results: All patients studied displayed an increase in anti-HLA antibodies one month after the intervention, regarding bypass patency. In total, 14 patients fulfilled requirements for the study of donor specific antibodies, equally showing IgG production detectable one month after surgery. The presence of complement-fixing antibodies was also confirmed. Antibody levels were not related to graft degeneration. No specific immune markers able to predict aneurysmal development and evolution were found. From the original group, 3 patients suffered aneurysmal degeneration during follow up, together with 9 bypasses previously implanted. Average time until the first degeneration was 33 ± 19.7 months, with 30.6 ± 17.7 and 54.5 ± 2.5 months for a second and third degeneration, when occurring. Therefore, subsequent vascular transplants frequently augmented the time for new degenerations, despite increasing sensibilization. Samples from eight degenerated allografts were available for analysis, unexpectedly showing inflammatory infiltrate in only four cases and immune complex deposition in 7.

Conclusions: Immune response against vascular transplants was confirmed in all cases, but chronic rejection did not necessarily provoke bypass degradation or reduced the time for new aneurysms to develop in subsequent allografts.

[The place of arterial allograft in reconstructive surgery of the main arteries of the lower extremities]

Critical limb ischemia, especially in the absence of autologous vein, prosthetic and native vascular infections are isolated diseases for which there currently doesn't have best surgical treatment. Vascular allografts may be the treatment of choice for these patients. In this analysis, we tried to reflect the directions of development of vascular allotransplantation, global trends related to indications for their use, methods of conservation, degradation and endothelial dysfunction. At the present time there doesn't have meta-analyzes on the efficiency of using arterial allografts or other options for implantation (synthetic graft, xenografts) for critical limb ischemia and graft and native infections. Now it is wrong to recommend using them always. Further studies of their performance are necessary. In addition, development of graft control techniques is also needed when rejection develops. Currently, there are no special diagnostic markers, the assessment of which could save patients with immune-mediated dilatation and dysfunction of allografts.

Treatment of popliteal artery aneurysms by means of cryopreserved homograft

BACKGROUND

Autologous saphenous vein is considered the gold standard conduit in the femoral-popliteal revascularization for popliteal artery aneurysms (PAAs). In several cases, it may be absent or unsuitable for length or diameter and so it may be considered unfit for a conduit. In such patients, a synthetic graft or the endovascular correction can be useful, but results are controversial. In this retrospective case series, we have analyzed the safety and efficacy of the cryopreserved homograft (CHg) as a conduit in the PAA revascularization.

METHODS

In the period between January 2005 and December 2013, 54 PAAs have been treated with an arterial CHg. Indications to surgery were asymptomatic aneurysm with >25-mm diameter in 30 cases (55.6%), ischemic symptoms in 20 (37%), and compressive symptoms in 4 (7.4%). An urgent treatment was performed in 8 cases (14.8%) for severe ischemic symptoms. All cases have been operated by the same vascular team: a posterior surgical approach was preferred whenever possible (33 cases, 61.1%). All patients received a clinical and radiologic follow-up, and all data were collected in a specific database. A >10-mm diameter increase of the conduit was considered significant for an aneurysmatic degeneration.

RESULTS

The primary outcomes were complications and reoperation rate, limb salvage, and primary and secondary patency. Secondary outcome was the incidence of aneurysmatic degeneration of the CHg. Mean diameter of the homografts was 6.3 mm (range, 4-8 mm). In the 30-day postoperative period, 7 PAAs (13%) developed a complication: 3 wound infections, 3 graft thrombosis, and 1 anastomotic bleeding. Six cases needed a reoperation: 2 surgical revascularizations, 2 wound debridement, and 1 anastomotic hemostasis; 1 major amputation was necessary for graft failure after the revascularization. Mean follow-up was 34.8 months (range, 1-96). Five cases (9.3%) developed a graft complication with 4 reoperations necessary (7.4%): 2 grafts required a percutaneous transluminal angioplasty for a perigraft stenosis and 2 underwent a femorodistal bypass in CHg for severe ischemic symptoms after CHg occlusion. Another one CHg occlusion was treated conservatively because it was clinically asymptomatic. Primary patency was 96.3%, 93.9%, and 88.3% at 12, 36, and 60 months, respectively; secondary patency was 98.1% at 12, 36, and 60 months. Freedom from amputation resulted in 98.1%. No aneurysmatic degeneration was observed. Univariate and multivariate analysis showed urgent surgery to be independent risk factors for complications, reoperations, and CHg occlusion (P < 0.05).

CONCLUSIONS

In this retrospective study, the use of CHg showed to be safe and effective in the surgery of PAAs, either in the short or in the long-term follow-up. Urgent surgery can be considered predictive of graft failure. In our experience, CHg can be considered a good alternative conduit to the autologous saphenous vein.

The Influence of Cryopreservation on Changes in Diameter and Compliance of Allografts in an Animal Experimental Model

OBJECTIVE

The purpose of this study was to analyze the influence of cryopreservation on changes in diameter and compliance of allografts.

METHODS

Sixty aortic allografts implanted in situ in rats were analyzed. The animals were divided into four groups that received fresh or cryopreserved isogenic (Lewis to Lewis) grafts, or fresh or cryopreserved allogenic (Lewis to DA) grafts, respectively. The diameter and compliance of the grafts were then visually evaluated with the digital video camera recorder after 15, 30, 60, 90 and 120 days.

RESULTS

Gradual increase in diameter and decrease in compliance in case of all allogenic and cryopreserved isogenic grafts were observed. The observed changes in cryopreserved grafts were smaller when compared with fresh grafts, however, the differences did not reach statistical significance.

CONCLUSION

Cryo preservation does not protect allografts from stiffening and dilatation.

Cardiovascular tissue engineering: state of the art

In patients requiring coronary or peripheral vascular bypass procedures, autogenous arterial or vein grafts remain as the conduit of choice even in the case of redo patients. It is in this class of redo patients that often natural tissue of suitable quality becomes unavailable; so that prosthetic material is then used. Prosthetic grafts are liable to fail due to graft occlusion caused by surface thrombogenicity and lack of elasticity. To prevent this, seeding of the graft lumen with endothelial cells has been undertaken and recent clinical studies have evidenced patency rates approaching reasonable vein grafts. Recent advances have also looked at developing a completely artificial biological graft engineered from the patient's cells with surface and viscoelastic properties similar to autogenous vessels. This review encompasses both endothelialisation of grafts and the construction of biological cardiovascular conduits.

Effects of cryopreservation on the immunogenicity of porcine arterial allografts in early stages of transplant vasculopathy

BACKGROUND

The number of revascularization procedures including coronary and lower extremity bypass, have increased greatly in the last decade. It suggests a growing need for vascular grafts. Cryopreserved allografts could represent a viable alternative but their immunologic reactivity remains controversial.

METHODS

71 pigs (40 recipients and 31 donors) were used. Two femoral grafts per recipient animal were implanted for 3, 7, and 30 days. Types of grafts: fresh autograft as a control graft (n=19), fresh allograft (n=31) and cryopreserved allograft (n=30). Histological and immunohistochemical studies were performed.

RESULTS

Fresh allografts compared to autografts showed intimal inflammatory infiltration at 3 days (328 vs. 0 macrophages/mm2; P<0.05) and 7 days (962 vs. 139 T lymphocytes/mm2; P<0.05) post-transplantation. At 30 days, there was a loss of endothelial cells, presence of luminal thrombus and aneurismal lesions (total area=15.8 vs. 8.4 mm2; P<0.05). Cryopreservation did not reduce these lesions nor modify endothelial nitric oxide synthase (eNOS) expression nor modify the number of animals that developed anti-SLA antibodies. Moreover, at 7 days, cryopreserved allografts compared to fresh allografts showed a higher expression of P-selectin (5 out of 5 vs. 1 out of 5; P<0.05) and, at 30 days, a greater inflammatory reactivity (2692 vs. 1107 T lymphocytes/mm2 in media; P<0.05) with a trend towards a higher presence of multinucleated giant cells than in the fresh ones.

CONCLUSIONS

The cryopreservation method used maintained immunogenicity of allografts and increased the inflammatory reactivity found in fresh allografts up to 30 days of vascular transplantation.

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.

Allograft replacement for infrarenal aortic graft infection: early and late results in 179 patients

OBJECTIVES

We evaluated early and late results of allograft replacement to treat infrarenal aortic graft infection in a large number of patients and compared the results in patients who received fresh allografts versus patients who received cryopreserved allografts.

METHODS

From 1988 to 2002 we operated on 179 consecutive patients (mean age, 64.6 +/- 9.0 years; 88.8% men). One hundred twenty-five patients (69.8%) had primary graft infections, and 54 patients (30.2%) had secondary aortoenteric fistulas (AEFs). Fresh allografts were used in 111 patients (62.0%) until 1996, and cryopreserved allografts were used in 68 patients (38.0%) thereafter.

RESULTS

Early postoperative mortality was 20.1% (36 patients), including four (2.2%) allograft-related deaths from rupture of the allograft (recurrent AEF, n = 3), all in patients with fresh allografts. Thirty-two deaths were not allograft related. Significant risk factors for early mortality were septic shock (P <.001), presence of AEF (P =.04), emergency operation (P =.003), emergency allograft replacement (P =.0075), surgical complication (P =.003) or medical complication (P <.0001), and need for repeat operation (P =.04). There were five (2.8%) nonlethal allograft complications (rupture, n = 2; thromboses, which were successfully treated at repeat operation, n = 2; and amputation, n = 1), all in patients with fresh allografts. Four patients (2.2%) were lost to follow-up. Mean follow-up was 46.0 +/- 42.1 months (range, 1-148 months). Late mortality was 25.9% (37 patients). There were three (2.1%) allograft-related late deaths from rupture of the allograft, at 9, 10, and 27 months, respectively, all in patients with fresh allografts. Actuarial survival was 73.2% +/- 6.8% at 1 year, 55.0% +/- 8.8% at 5 years, and 49.4% +/- 9.6% at 7 years. Late nonlethal aortic events occurred in 10 patients (7.2%; occlusion, n = 4; dilatation < 4 cm, n = 5; aneurysm, n = 1), at a mean of 28.3 +/- 28.2 months, all but two in patients with fresh allografts. The only significant risk factor for late aortic events was use of an allograft obtained from the descending thoracic aorta (P =.03). Actuarial freedom from late aortic events was 96.6% +/- 3.4% at 1 year, 89.3% +/- 6.6% at 3 years, and 89.3% +/- 6.6% at 5 years. There were 63 late, mostly occlusive, iliofemoral events, which occurred at a mean of 34.9 +/- 33.7 months in 38 patients (26.6%), 28 of whom (73.7%) had received fresh allografts. The only significant risk factor for late iliofemoral events was use of fresh allografts versus cryopreserved allografts (P =.03). Actuarial freedom from late iliofemoral events was 84.6% +/- 7.0% at 1 year, 72.5% +/- 9.0% at 3 years, and 66.4% +/- 10.2% at 5 years.

CONCLUSIONS

Early and long-term results of allograft replacement are at least similar to those of other methods to manage infrarenal aortic graft infections. Rare specific complications include early or late allograft rupture and late aortic dilatation. The more frequent late iliofemoral complications may be easily managed through the groin. These complications are significantly reduced by using cryopreserved allografts rather than fresh allografts and by not using allografts obtained from the descending thoracic aorta.

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.