Experience with fresh venous allografts as an arterial substitute

Cryopreserved saphenous vein as a last-ditch conduit for limb salvage

OBJECTIVE

In patients lacking autogenous vein suitable for infrainguinal bypass, cryopreserved saphenous vein (CSV) allograft (CryoLife, Inc, Kennesaw, Ga) may be an acceptable alternative. The purpose of this study was to examine outcomes of CSV conduit for infrainguinal revascularization.

METHODS

Between February 2008 and August 2015, 70 patients underwent infrainguinal bypass grafts in 73 limbs using CSV. All patients lacked suitable arm or leg vein. Demographic data and patient outcomes were retrospectively collected using electronic medical records.

RESULTS

The mean age of our cohort was 70 ± 14 years, and 36 (51%) were male; 47 (67%) were white, 39 (56%) had coronary artery disease, 27 (39%) had diabetes, 56 (80%) had hypertension, and 50 (71%) were former or current smokers. Median follow-up was 304 days (interquartile range, 130-991 days). Indications for the index operation included rest pain (27%), tissue loss (55%), and prosthetic graft infection (18%); 62 of 73 (85%) bypasses were performed for critical limb ischemia, and 45 of 73 (62%) were redo operations. Distal targets included superficial femoral artery or popliteal (38%), tibial (55%), and pedal (7%). All grafts had a minimum diameter of 3 mm. At 30 days, 55 of 64 grafts (86%) were patent; 9 were lost to early follow-up. The only significant risk factors associated with 30-day failure were ABO mismatch (43% vs 10%; P = .05) and donor blood type B or AB (40% vs 9%; P = .03). Estimated overall 1-year primary patency was 35%. In a multivariate analysis, nonblack race (P = .05), donor B or AB blood type (P = .01), and bypass to a tibial or pedal target (P = .05) were independently associated with loss of primary patency. There were 20 (27%) major amputations, and all grafts in these limbs had occluded at the time of amputation. Of the 33 limbs with ischemic tissue loss that had long-term follow-up, 17 of 33 (52%) went on to graft occlusion, 10 of 33 (30%) had a major amputation, and 24 of 33 (73%) had complete healing of the index wound.

CONCLUSIONS

In the setting of a multidisciplinary team with aggressive wound care, CSV may be a reasonable choice for infrainguinal revascularization in patients with ischemic tissue loss who lack autogenous conduit. However, poor midterm to long-term patency suggests that optimal selection of patients is needed to derive meaningful clinical benefit.

Superior Vena Cava Reconstruction Using An Iliocaval Allograft

Successful replacements of the superior vena cava (SVC) using autogenous saphenous or superficial femoral vein or prosthetic grafts have been previously performed, but the use of allograft for treatment of SVC syndrome has not been reported. The patient treated by the authors was a forty-one-year-old woman who presented with severe venous congestion of the head and neck caused by fibrosing mediastinitis. In addition, she had sclerosing cholangitis and chronic liver failure. To treat her SVC syndrome and provide access for fluid and blood transfusion and for possible venovenous bypass, SVC reconstruction was performed concomitant to orthotopic liver transplantation. A left innominate vein-right atrial bypass was inserted using an iliocaval allograft. The patient had an uncomplicated recovery, and at six months after surgery her SVC allograft is widely patent and her transplanted liver is functioning well. The venous allograft is an excellent conduit for those patients who are receiving immunosuppression therapy to avoid rejection of a transplanted organ.

The Alternative to the Saphenous Vein as an Arterial Graft

If God created the saphenous vein for the sake of vascular surgeons, He neglected to create all men equal in respect to the presence of saphenous veins for needed revascularizations. Therefore, the burden of finding alternatives to saphenous veins reverts to the humble ingenuity of man.

Cryopreserved Allografts for Limb Salvage

Over a nineteen-month period, 17 patients (8 men, 9 women) underwent revascularization for limb salvage with cryopreserved saphenous vein allografts when autogenous saphenous vein was not available and prosthetic material was felt to be inappropriate. Their mean age was sixty-seven years. Risk factors included hypertension (88%), diabetes mellitus (63%), cigarette smoking (44%), and hypercholesterolemia (44%). All patients had multiple previous vascular operations including coronary artery bypass grafting (3.9 procedures per pa tient). Indications for operations were rest pain (8), ischemic necrosis (3), or both (6).

All cryopreserved allografts were obtained from the same procurement source and prepared by a standardized protocol. Combinations of prosthetic material and cryopreserved allograft were used to make composite grafts (5 cases) when adequate length of autogenous saphenous vein was not available. Upper limb veins were not utilized. All patients received antiplatelet therapy or were anticoagulated postoperatively.

Current follow-up is two to fifteen months. There were 1 death and 3 major amputations (including the 1 patient who died) in the postoperative period. Fol low-up noninvasive vascular studies were obtainable in 13 patients whose limb was salvaged; 71 % of assessable grafts were patent. Cryopreserved saphenous vein allografts provide a viable option for a selected group of patients when autogenous saphenous vein is not available.

Limb salvage with CryoVein cadaver saphenous vein allografts used for peripheral arterial bypass: role of blood compatibility

Patients suffering from limb-threatening ischemia often have scarce or inadequate autogenous veins for complex lower limb revascularization. One option for such patients is to use conduit consisting of cadaver saphenous vein allograft (CSVA) as a final surgical option before limb amputation. This study reviewed retrospectively the patency of CryoVein CSVA allografts, processed by CryoLife, Inc., in 54 implant cases of lower extremity arterial bypass over a span of 6 years. Patient demographics, graft patency, limb salvage, and blood type matching of donor to recipient were analyzed. Kaplan-Meier analysis showed postoperative primary patency rates of 89, 63%, 30%, 17%, and 9% at 1, 3, 6, 12, and 18 months, respectively. Secondary patency rates were 89%, 74%, 63%, 63%, and 54% at 1, 3, 6, 12, and 18 months, respectively. Limb salvage rates were 67% at 12 months and 54% at 18 months. Median follow-up was 467 days. Of the 34 cases where the patient received a blood-group compatible CSVA, 30 had limb salvage and only six of 20 noncompatible grafts offered limb salvage (p = 0.05). Although primary patency rate was poor at 1 year, high secondary patency and limb salvage rates support the use of CSVA as a peripheral bypass conduit alternative. Cases with donor-recipient ABO blood type compatibility had significantly better limb salvage.

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.

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.

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.

Venous allografts for infrainguinal vascular bypass

Between 1978 and 1993, 107 patients received venous allografts for infrainguinal revascularization because autogenous material was unavailable. These operations comprised 7.4% of 1442 reversed vein bypass procedures performed during the same period. Alloveins were harvested during varicose vein stripping and stored up to 10 days in saline solution containing heparin and antibiotics. Veins with or without minimal degenerative changes were used and when necessary segments were sutured end-to-end to obtain a convenient length. The patients comprised 95 men and 12 women of age range 44-87 years. All operations were performed for limb salvage (rest pain and gangrene); 40 femoropopliteal and 67 femorocrural bypasses were performed; 66 were primary reconstructions and 41 secondary reconstructions. The operative mortality rate was 3.7%. Early thrombosis occurred in 18 patients (16.8%), nine of whom were successfully reoperated upon. The cumulative patency rates for all bypass operations was 82.9%, 38.7% and 21.3% at 30 days, 3 and 5 years, respectively, the limb salvage rates being 84.8%, 48.0% and 29.2%, respectively. Allografts may have a place in lower-limb bypass surgery in the absence of veins, polytetrafluoroethylene or human umbilical vein.

Arterial homografts

Arterial allografts, formerly called homografts, came into limited use in the 1940s and 1950s as arterial substitutes. Fresh allografts underwent rapid rejection. Preserved allografts had a longer but still limited clinical life. Allografts demonstrated that arterial replacement was a valid concept and led to the development of synthetic substitutes. Recent renewed interest is based on the need for graft replacements in re-do procedures and in an infected field. Even the best methods of graft procurement and preservation do not preserve normal endothelial and smooth muscle cell functions nor eliminate antigenicity. The biologic and economic costs of immune suppression to obtain a successful allograft for an ischaemic limb are presently unjustifiable. Transplantation between species (xenotransplantation) may be attainable via selective inhibition of the complement system avoiding full immunosuppression now required for organ transplantation. At present allografts may be an acceptable choice for the patient with (1) a critical need for revascularisation and with a life expectancy not exceeding that of the graft, (2) in urgent vascular trauma, and (3) where immunosuppression is contraindicated as in an infected surgical field. Except in most unusual circumstances allografts should not be used for (1) relief of claudication, (2) in the above mid-calf location and (3) anatomic locations where synthetic grafts are superior.

Human allograft vein failure: immunohistochemical arguments supporting the involvement of an immune-mediated mechanism

The aim of this study was to search for signs suggestive of an ongoing immune-mediated reaction in failed human cryopreserved venous allografts. In 15 samples, the authors analyzed: (1) the pattern of morphological changes; (2) the density, distribution, and phenotype of leukocytic infiltrate; and (3) the expression of class II major histocompatibility complex (MHC) antigens and inducible adhesion molecules. Two groups of samples could be recognized. In samples explanted before 3 months after grafting, the structure of the vessel wall was preserved. A dense leukocytic infiltrate was present within the intima and around the numerous vasa vasorum located in medial and adventitial layers. Class II MHC antigens and cytokine-dependent molecules were induced on endothelial cells lining the vasa vasorum and on residual smooth muscle cells. In samples explanted after 3 months of evolution, the vessel wall has lost its normal structure and contained few vasa vasorum. A few leukocytes were detected around capillary vessels located in the peripheral connective tissue surrounding the graft. Class II MHC antigens and adhesion molecules were induced on endothelial cells lining the peripheral capillary vessels. These results suggest the involvement of an immune-mediated mechanism at the early stage of the evolution of failed human venous allografts.

Fresh venous allografts as arterial substitutes in dogs: the importance of donor-recipient tissue compatibility

Fresh venous allografts were investigated in dogs matched according to donor-recipient tissue compatibility, either originating from the same litter or chosen at random (pound dogs). Five centimeter long segments of femoral vein were interposed as carotid substitutes in an autografting and allografting manner between paired dogs. During a 5-month implantation period, donor-specific antibody development was measured in the recipient serum by a flow-cytometric assay using cultured donor vascular endothelial cells. Autografts and allografts were investigated in terms of patency, histopathology, and endothelial cell function. Fifteen of 16 autografts remained patent. Allografts between littermate dogs, whether compatible or incompatible, showed no donor-specific antibody development and were all patent at retrieval. Compatible and incompatible allografts in littermates did not show any difference in prostacyclin (PGI2)/thromboxane A2 (TXA2) ratios. In pound dogs, both compatible allografts were patent and one dog developed donor-specific antivascular endothelial cell antibodies. Among incompatible dogs, antibody formation was detected at 1 month in five of six recipients and graft patency was as follows: two partial thromboses, two stenoses, and two patent grafts. The PGI2/TXA2 ratio was significantly lower in incompatible allografts than in compatible ones (p = .028). These results show the importance of donor-recipient histocompatibility matching in improving the outcome of vein allografts.

Cryopreserved arterial homografts: preliminary study

The use of arterial or venous allografts for vascular reconstruction was first reported in 1951, but long-term results have been disappointing. Rejection and inappropriate methods of preservation are the main reasons for failure. A successful solution to this problem could be achieved by programmed cryopreservation with cryoprotectant. Our study had two aims: to define the biomechanical properties of cryopreserved arterial allografts and to study their histologic appearance. Arteries were removed as part of a protocol for multiorgan harvesting for transplantation. Cryopreservation was performed within the first 24 hours after harvesting. Programmed cryopreservation with 15% dimethyl sulfoxide (cryoprotectant) was used. Mechanical testing was done immediately after thawing. Two groups were tested: a control group of fresh aortas and a group of cryopreserved aortas. Axial and circumferential strips were tested. High strain modulus and stress and strain characteristics were calculated for each strip. There was no statistically significant difference between the mechanical properties of fresh and cryopreserved human descending thoracic aortas. Biochemical tests were performed in the preservative solution at 1 and 7 days in both groups. There was no statistically significant difference between the two groups at day 1 or day 7 (p > 0.05). Histologic studies before and after arterial cryopreservation included standard and electron microscopy and showed that arteries had normal structure after cryopreservation. These results confirm that programmed cryopreservation with cryoprotectant does not alter the molecular or geometric configuration of collagen or elastic fibers. Endothelial cells were still present, however, their viability and function were not assessed.(ABSTRACT TRUNCATED AT 250 WORDS)

Cryopreserved vein transplantation

There have been numerous attempts to develop prosthetic conduits or utilize allograft 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 allografts, 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.

Development of an ovine collagen-based composite biosynthetic vascular prosthesis

The search for an ideal vascular prosthesis to bypass peripheral vascular obstructive lesions is necessary where autologous tissues are either unavailable or unsuitable. This paper will outline the development and use of vascular conduits, principally of biological origin. The clinical benefits and limitations of these materials are discussed. The development of a composite biosynthetic prosthesis (Omniflow¿) is described, together with the testing methods used to determine and predict its suitability for use as an arterial substitute. The ovine biosynthetic prosthesis has significantly improved surface and mural properties over previous attempts at producing prostheses for vascular reconstruction. Immunohistological studies on samples recovered from dogs after 4 years show that the original ovine collagen is still present after 4 years, and it is further augmented by the deposition of new, host-derived connective tissue.

Immunosuppressive treatment of venous allografts

In order to evaluate whether temporary immunosuppressive therapy is able to improve the results obtained with viable venous allografts and achieve better results than with synthetic grafts, 142 arterial reconstructions were performed in mongrel dogs bypassing their ligated femoral arteries. Histological as well as immunological studies were performed and patency determined by weekly palpation and regular angiography. The 6-month cumulative patency rates were: Group I: synthetic grafts (a) Dacron: 48%, (b) plasma-TFE: 53%. Group II: fresh grafts (a) autografts: 100%, (b) allografts: 37%, (c) allografts treated with cyclosporin 4 mg kg-1 daily for 1 month: 74% (100% after 1 month). Group III: grafts preserved in Hanks' solution with 15% DMSO at -160 degrees C for 1 month (a) autografts: 77%, (b) allografts: 35%, (c) allografts treated with methylprednisolone 1 mg kg-1 daily: 38%, (e) allografts treated with cyclosporin and methylprednisolone: 83%. Group IV: human saphenous veins implanted as xenografts and treated with cyclosporin and methylprednisolone: 18%. Immunosuppressive therapy with cyclosporin seems to be able to prevent early thromboses due to rejection seen after implantation of viable fresh or cryopreserved venous allografts, and the results are significantly better than those obtained with synthetic grafts. Tissue matching might further improve these results. This study suggests that cryopreserved venous allografts could be used for the creation of a vein-bank and their use, in combination with tissue typing and temporary immunosuppressive therapy may be warranted for arterial reconstructions when autologous saphenous vein is not available.

Three years experience with denaturated venous homografts as an arterial substitute: a clinical, pathological and immunological study

Over a three-year-period 105 peripheral arterial reconstructions were performed using a denaturated venous homograft in a group of patients with no suitable autologous vein. A retrospective analysis has been carried out to investigate the patency rate of this graft. After three years 64% of all grafts are functioning well (according to the Life Table Method, Kaplan & Meyer). No significant differences in patency rates were found between reversed autologous veins and the material tested in this study but analysis of grafts removed after failure showed obstruction due to thrombosis or aneurysmal dilatation. No evidence of an immune response to the grafts was seen.

Transplantation of tissues and organs. Review of the first 100 years of the Southern Surgical Association

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Long microvenous allografts in rabbit femoral arteries and veins

In this study the patency of long microvenous allografts in rabbits with and without immunosuppressive drug therapy was investigated. Eighty-two microvenous autografts (controls) and allografts were transplanted into rabbit femoral vessels. Veno-venous autograft controls were 100% patent at 3 weeks. Rejection of non-immunosuppressed veno-venous allografts consistently produced occlusion between 15-20 days. Thrombus filled the lumen, and a leucocyte invasion destroyed the graft wall. In contrast vein allografts into arteries were 100% patent at 3 weeks; this was reduced to 50% at 4 weeks. Low (5 mg/kg/day) and high (20 mg/kg/day) doses of hydrocortisone over 21 days improved the 3 week patency in veno-venous allografts to 28.5% and 57.0% respectively. Cyclosporin A (15 mg/kg/day) over 8 or 22 days significantly increased the patency rate of veno-venous allografts to 100%. Only cyclosporin A treated rabbits maintained allografts of normal vein morphology to 3 weeks.

Vein to artery allografts: experimental evidence of immunological sensitivity in rats

Vein allografts were studied in rats using the major histocompatibility complex-incompatible DA (RTIa) and LEW (RTI1) inbred strains. Allografts from DA rats were inserted in to 22 LEW hosts, and vice versa, by interposing a 5 mm segment of donor iliolumbar vein into a defect in the host's iliac artery (1 mm in diameter), using microsurgical techniques. Grafts were left in situ for 6 weeks and were then tested for evidence of sensitization by the insertion of an allogeneic fetal heart from the donor strain into the host's foot pad. The fetal heart beat was recorded with an ECG and the time of rejection determined by the cessation of ECG activity. As controls, allogeneic donor fetal hearts were implanted into 40 host rates (20 of each strain) which had not previously received a donor vein allograft. These were monitored by ECG, as above. Control LEW host rats rejected DA fetal hearts in a mean time of 8.45 days. Control DA hosts rejected LEW fetal hearts in 8.70 days. DA hosts with LEW vein allografts did not reject donor fetal hearts significantly sooner (mean 8.33 days) than the controls. However, LEW host rats with allografted DA veins rejected subsequent DA fetal hearts in 7.18 days, which was significantly sooner than in controls (8.45 days). These data provide evidence of sensitization of the rejection response by vein allografts.

Cryopreserved homologous saphenous vein: early and late patency in coronary artery bypass surgical procedures

Autologous saphenous vein has proved to be a satisfactory conduit for use in coronary artery bypass grafting. Unfortunately, it is not always available, and substitute material must sometimes be used. When satisfactory autologous veins were not available and the internal mammary arteries were unsuitable, cryopreserved homologous saphenous veins were used in 28 patients. A total of 76 grafts were constructed. Cryopreserved homologous veins were used for 61 grafts, autologous saphenous veins for 11 grafts, and the internal mammary artery for 2 grafts. Coronary angiography was performed 8 to 12 days postoperatively in 16 patients. Of the 31 homografts studied, 8 were occluded (26%), 3 were stenotic (9%), and 20 were normal (65%). The one internal mammary artery and six autologous veins studied were all patent. Six patients underwent late catheterization 6 to 12 months postoperatively. Thirteen homografts were studied at late catheterization: 11 were occluded, 1 was severely stenotic, and 1 was mildly stenotic. At late catheterization, the one internal mammary artery studied was patent, and the one autologous saphenous vein was 95% occluded. Results of both early and late catheterization performed on 18 patients demonstrated that of the 35 homografts studied, 17 (49%) were occluded, 3 (9%) had greater than 70% stenosis, 1 (3%) had mild disease, and 14 (40%) were free of disease. One year follow-up data obtained on 26 patients revealed that 4 patients (15%) died of cardiac causes, 2 patients (8%) died of noncardiac causes, 11 patients (42%) have recurrent angina, and 9 (35%) are asymptomatic. It is concluded that use of cryopreserved homologous saphenous veins for coronary artery bypass grafting should be avoided if at all possible.

Modified vein allograft for small arterial reconstruction in dogs

The ideal graft for peripheral arterial reconstruction has yet to be developed. We evaluated on the effectiveness of porosity to intimization of the graft. Modified vein allografts newly constructed through digestion of vein allografts with elastase, glutaraldehyde tanning and lyophilization were implanted in thirty-nine canine femoral arteries. These grafts had a higher porosity than conventional vein allografts and the overall patency rate was 70 per cent at 6 months after implantation. Microscopic examination showed that graft interstitial healing and subsequent intimization were completed by ingrowth of connective tissue from outside through the graft wall at 3 weeks and later. Aneurysmal change of the modified vein allografts was never evident. These results indicated that porosity of the graft is indeed an important factor for intimization and durability of grafts, even in bioderivative substitutes.

Preparation of venous allografts. A comparison of techniques

In order to evaluate alternate techniques of preparing veins for use as homografts, 102 femoral veins were harvested from adult mongrel dogs. The veins were treated in four different ways, then transplanted into recipient animals bypassing their ligated femoral arteries. Group I--24 veins (6 cm each) were harvested and immediately transplanted. Group II--24 veins were stored in 15% dimethyl sulfoxide (DMSO) solution at -120 C for 21 days prior to transplantation. Group III--26 veins were stored for 21 days in plasminate solution at -60 C prior to use as allografts. Group IV--28 veins were stored in 0.5% gluteraldehyde solution for 21 days prior to implantation. Animals were randomly sacrificed at 1-month, 2-month, 6-month, and 12-month intervals. Patency of the transplant was determined weekly by ultrasound. Specimens were sent for light and scanning electron microscopy at the time of harvest, prior to implantation, and at sacrifice. Endothelial damage was graded on a scale of 0-16. Veins in Group II had a significantly higher patency rate (68% at 1 year) than Group III (35%) and Group IV (11%) (p less than 0.05). The intimal layer of all patent vessels was replaced by an organized mural thrombus. Partial endothelialization of the luminal surface was most prevalent in Group II. Intimal damage related to storage technique was significant in Group III (p less than 0.01). At sacrifice, severe endothelial damage was present in all groups (p less than 0.01). In conclusion, veins stored in 15% dimethylsulphoxide (DMSO) solution at -120 C have immunologic and physical characteristics that yield patency rates acceptable for clinical use when autogenous tissue is not available.

Coronary artery bypass with glycerol-preserved saphenous vein allografts

Over a 2-year period, 19 patients whose autologous saphenous veins were either unsuitable or unavailable underwent myocardial revascularization with saphenous vein allografts (SVAs) at our institution. All SVAs had been preserved in 98% glycerol at room temperature for at least 3 weeks (average, 7 weeks); before use, they were rinsed with saline and antibiotic solution. One operative death (5.2%) and three late deaths (16.6%) occurred. Fourteen of the long-term survivors have been observed for 24 to 48 months (average 32.2 months) postoperatively. Nine are asymptomatic, whereas four complain of angina, and one reports exertional dyspnea with-out chest pain. Only three patients have been restudied (7, 10, and 18 months after surgery, respectively); in each of these patients, angiography has shown occlusion of all SVAs. However, histologic examination of glycerol-preserved SVAs has not revealed pathologic changes that would suggest potential graft failure. Despite fairly satisfactory clinical results, preliminary hemodynamic data indicate that glycerol-preserved SVAs are unsuitable for myocardial revascularization in the absence of autologous saphenous veins.

Aortocoronary bypass with homologous saphenous vein: long-term results

Between February 1973, and February, 1979, 27 homologous saphenous veins were used in 20 patients (mean age, 54 years). Seven fresh grafts were used less than 24 hours after severance. They were kept at a temperature of 4 degrees C in saline solution containing penicillin. Twenty cryopreserved grafts were used within a period of eight days to 2 months from severance. They were preserved in glycerol at a temperature of -40 degrees C. One patient (5%) died postoperatively. A perioperative myocardial infarction developed in 3 patients (15%). Average follow-up is 27 months. No late mortality was registered. Fifteen patients are free from symptoms, and 3 patients have residual angina with exercise. Control angiograms were made in 13 patients 1 to 68 months after operation; 17 homografts were seen. Early occlusion of 1 graft and late occlusion of 8 grafts were registered. The poor late patency rate does not seem to be related to either histocompatibility or technical conditions. Conversely, microscopic examination of several cryopreserved grafts showed that the mode of preservation resulted in deterioration of intimal and medial tissues of the vein. Therefore, it appears to us that the use of homologous saphenous veins should be avoided for coronary bypass.

The role of graft material in femorotibial bypass grafts

"Newer" graft substitutes are being widely used in arterial reconstructive procedures in the infrafemoral region. A retrospective study of 101 consecutive femorotibial bypass grafts compares autogenous saphenous vein (ASV), polytetrafluoroethylene (PTFE), and glutaraldehyde tanned (GA) human umbilical cord vein. Symptoms prompting arterial reconstruction was rest pain or tissue necrosis in 90%. Asv (57 bypasses) was the material of choice, but when inadequate or unavailable PTFE, (29 bypasses) or GA (15 bypasses) were used. The immediate and one year patency in ASV was 92--82%. A high incidence of failure occurred in both the PTFE and GA grafts so that patency at one year was 24 and 10% respectively. An overwhelming statistical significance occurs with respect to patency in the three groups of grafts (p = 0.0002). This extremely high incidence of failure in these graft materials has prompted us to use cephalic and basilic veins in those patients which we feel require arterial reconstruction for relief of symptoms.

Antigenicity of venous allografts

With isolated exceptions, the clinical use of venous allografts has been disappointing. Considerable evidence indicates that allograft antigenicity plays a major role in the failure of venous allografts when used as arterial replacements. Recent reports suggest that DMSO-cryopreservation of venous allografts may reduce allograft antigenicity while preserving allograft viability. The present study examines the effect of modifications of vein allografts on subsequent allograft antigenicity. Skin grafts were transplanted from ACI to Lewis inbred strains of male rats. Primary skin graft rejection occurred in 9.0 +/- 1.0 days. Subcutaneous implantation of fresh inferior vena cava from ACI rate into Lewis rats resulted in subsequent skin graft rejection in 5.0 +/- 1.0 days, confirming the antigenicity of venous tissue. Cryopreservation of ACI inferior vena cava for seven days prior to implantation, with or without 15% DMSO, resulted in subsequent skin graft rejection in 5.0 +/- 1.0 days. Treatment of ACI inferior vena cava with 0.30% gluteraldehyde for 20 minutes prior to implantation in Lewis rats resulted in skin graft rejection in 9.0 +/- 1.0 days, the same time as a first set rejection. This study indicates that unmodified veins are normally antigenic and that this antigenicity is not eliminated by cryopreservation with or without DMSO. Gluteraldehyde treatment appears to reduce allograft antigenicity, but results in a nonviable graft. At the present time, there is no known way to reduce the antigenicity of viable venous allografts.

Clinical experience with the expanded polytetrafluoroethylene vascular prosthesis

Expanded polytetrafluoroethylene grafts were used in 44 patients in the last 18 months. In 13 patients the graft was used for various types of peripheral vascular reconstructive procedures, as a substitute of the autogenous saphenous veins. In 31 patients the prosthesis was used for the construction of vascular access for hemodialysis. Results of the use of this new vascular prosthesis are comparable to those achieved with the autogenous saphenous vein when used for the same purposes. A much longer period of observation is necessary before a definitive verdict can be reached on the safety and clinical applicability of any new vascular prosthetic material. But preliminary clinical results with the PTFE vascular prosthesis are encouraging and seem to justify continued cautious application of this vascular substitute.

Small arterial reconstruction using modified cadaveric saphenous veins

Human saphenous veins removed from cadaver donors were subjected to proteolytic enzymatic digestion, cross bonding, and heparin bonding. They were tested as small arterial substitutes in dogs. Eight of eleven were successful, persisting without development of stenosis or aneurysm, the longest for eighteen months. In humans, similarly prepared veins were used as arterial bypasses to revascularize ischemic limbs in eleven patients and aneurysmal degeneration of an earlier unmodified allograft bypass in one patient. Distal arterial anastomoses were to the tibial and peroneal arteries. Nine patients who had not undergone previous reconstructive surgery involving the vessel used for distal anastomosis were treated successfully; all remain with healed limbs between three and twelve months after surgery, eight with functioning bypasses. In three patients who had undergone previous operations on the same artery used for distal anastomosis, long bypasses failed, although amputation was avoided in one patient by additional bypass with modified vein to the profunda femoris artery. We conclude that modified saphenous vein allografts are suitable small arterial substitutes. It remains to be seen whether veins will maintain patency for long periods without development of complications.

Studies of the modified venous allograft

Segments of rat inferior vena cava were modified by proteolytic digestion and dialdehyde starch tanning in an attempt to alter their antigenic nature and increase their tensile strength. These tissues were found to retain their ability to sensitize allogeneic recipients in both the intradermal and intra-aortic positions in all 50 experimental animals. Furthermore, these grafts had a very high aneurysm formation (100%), and aneurysm rupture (54%) rate even in isogeneic recipients, suggesting that the modification procedure so damages the structural integrity of venous tissue that its use in clinical situations may have disastrous consequences. Histologic evidence of intimal thickening, elastic disruption, and often severe acute and chronic inflammation supported the gross evidence of mechanical and immunologic damage and suggests that a mild brief course of immunosuppression may be indicated in clinical trials in situation in which autogenous saphenous vein in unavailable. Although the use of prosthetic mesh support for the graft may help to avoid structural changes, the introduction of synthetic materials may offset the theoretical advantages of the venous tissue.

Long-term patency of vein grafts preserved in liquid nitrogen in dimethyl sulfoxide

Autogenous canine jugular veins were stored in 15% dimethyl sulfoxide (DMSO) in liquid nitrogen vapor for one to 28 days and then implanted in the carotid artery as autografts. The patency rate at one year was 62.5-87.5%. The patency rate of fresh jugular vein autografts placed in the carotid artery for one year was 75%. Similar autografts stored in liquid nitrogen vapor for one to 28 days without the cryopreservative DMSO exhibited a zero to 12.5% patency rate at one year. Scanning electron microscope studies revealed preservation of theendothelium in DMSO protected veins and a damaged or sloughed endothelium in veins frozen without DMSO cryopreservation.

Nonanastomotic aneurysms in venous homologous grafts and bovine heterografts in femoropopliteal bypasses

In the absence of a suitable autologous vein for a long distal femoropopliteal bypass, the homologous vein appears to be a good substitute. However, the patency rate after one year is less than 50 per cent and nonanastomotic aneurysms occurred in one third of our patients followed for more than one year. These two complications may be related to an immune response which may be lessened by preservation of the graft in the frozen state. Bovine heterografts function well when placed subfascially for femoropopliteal bypasses ending above the knee. Failure rate is high when the distal end of the graft extends across the knee joint. In our experience nonanastomotic aneurysms have developed in 50 per cent of patent grafts followed for more than one year, although other surgeons have reported an incidence of only 3 to 20 per cent. In the follow-up of twenty-three venous homografts and twenty bovine heterografts placed as femoropopliteal bypasses, eight nonanastomotic aneurysms appeared and required replacement. This occurrence was noted in more than 33 per cent of grafts patent beyond one year. When an adequate autologous vein is not available, the composite Dacron-vein graft is the best substitute.