One hundred percent patency of one-millimeter polytetrafluoroethylene (Gore-tex) grafts in the carotid arteries of rats

Use of Stretch Expanded Polytetrafluoroethylene as a Microvascular Graft in a Low-pressure Situation

OBJECTIVE

Microvascular reconstruction is often limited by the availability and length of the pedicle. The harvesting of autologous vein grafts adds morbidity and may not provide a good match. Expanded polytetrafluoroethylene (ePTFE) grafts have been used routinely in macrovascular surgery. However, there are no conclusive data on the performance of small-diameter PTFE grafts for pedicle lengthening in free flaps in a low-pressure situation. In this study, we evaluated the efficacy of 3-mm diameter stretch ePTFE grafts to lengthen the venous pedicle of a free flap.

METHODS

Fifteen male New Zealand white rabbits were operated on under sterile conditions. Using an operating microscope, an epigastric flap was raised and the pedicle was exposed and dissected to its origin from the superficial femoral vessels. A segment of the vein of 1 cm to 3 cm was replaced with a stretch ePTFE graft. Microsurgical anastomoses were performed using 9-0 nylon sutures. Four weeks postoperatively, the flaps were raised again with the pedicles re-explored. The graft was then removed and examined histologically.

RESULTS

All the grafts demonstrated immediate patency. There were no cases of flap loss on the control side at 4 weeks postoperatively. When re-explored, the patent ePTFE grafts appeared to be covered by connective tissue. Light microscopy showed neoendothelialization with fibrovascular in growth.

CONCLUSION

From this study, we can conclude that 3-mm diameter stretch ePTFE grafts can be used successfully as an alternative to bridging autologous vein grafts in free-flap pedicles.

Microvascular repair with 1-mm polytetrafluoroethylene (PTFE) grafts: effect of recombinant tissue-type plasminogen activator (rt-PA) on the patency rate and healing process

The present study assesses the effect of recombinant tissue-type plasminogen activator (rt-PA) on the patency rate and healing process of microvascular polytetrafluoroethylene (PTFE) grafts. Wistar rats were used, divided into four groups of 25 animals each. After dissection of the carotid artery a segment of the vessel, 1 cm long, was resected and replaced by equal length graft. Two different type fibril length (30- or 60-microm) grafts of the same wall thickness (0.18 mm) were used. Normal saline or 3 mg/kg of body weight of rt-PA was applied locally in each group of different fibril length grafts. Patency tests were performed at 15 min and 4 weeks after blood flow was reestablished. All grafts were harvested and examined histologically. The results showed that local application of rt-PA improves patency statistically significantly in both types of fibril length grafts. Patency in 60-microm fibril length grafts was statistically significantly higher than that of 30-microm fibril length grafts, whether rt-PA was used or not. The use of rt-PA had no influence on the healing process of either type of graft.

Fibroblast growth factor pretreatment of 1-mm PTFE grafts

When using microvascular polytetrafluoroethylene (PTFE) vascular grafts, the best results in terms of patency rate and neoendothelialization are obtained with prostheses with thin walls and long fibril length (i.e., 90 microm). A complete internal neoendothelial lining is usually achieved at 12 weeks after implantation. Clinically, this period can be too long. In this study, 1-mm internal diameter PTFE prostheses with optimal physical characteristics were pretreated with basic fibroblast growth factor in fibrin glue, a potent endothelial cell mitogen, and chemoattractant. Rate, speed, extent, quality, and origin of neoendothelium were compared with two control groups, using Evans Blue dye, immunohistochemical localization of factor VIII von Willebrand factor protein, and scanning electron microscopy. Prostheses (8 mm long) were implanted in the infrarenal rat aorta and harvested after 3 weeks. In treated grafts, the amount of endothelial regeneration was greater than in untreated grafts (75% of the internal surface compared with 30%). However, patency rate in the experimental group was lower than in the control groups. This study provides new data on neoendothelial regeneration in small-diameter PTFE grafts.

Heparin bonding increases patency of long microvascular prostheses

The high thrombogenicity of synthetic biomaterials has limited their use for reconstructive microsurgery. Prime factors in the thrombogenicity of synthetic materials in contact with blood include gas nuclei at the blood gas interface as well as the inherent thrombogenicity of the materials themselves. Expanded polytetrafluoroethylene (ePTFE) vascular prostheses were denucleated by placement in acetone and ethanol followed by degassed saline or by placement in degassed saline subjected to hydrostatic pressure. Heparinized grafts were prepared by coating with tridodecylmethylammonium chloride (TDMAC), followed by immersion in heparin. Grafts were installed to reconstruct the femoral artery (1 x 10 mm) or as renal-iliac bypasses (1 x 50 mm) in rats. In the femoral artery reconstruction model, control grafts thrombosed within 10 minutes of implantation. All acetone denucleated femoral grafts remained patent for 60 minutes but were occluded at day 1. All pressure denucleated femoral grafts remained patent for 60 minutes, whereas six were patent at 1 month. In contrast, 11 of 15 heparinized femoral grafts were patent at 1 month. In the renal iliac bypass model, all control grafts were thrombosed within 10 minutes, whereas all heparin bonded grafts remained patent at 1 month. This finding confirms that removal of air from small diameter ePTFE grafts decreases acute thrombogenicity and that heparin bonding further decreases thrombogenicity, suggesting that clinically useful lengths of microvascular prostheses may be possible.

The 3M precise microvascular anastomotic system for implanting PTFE microvenous prostheses into the rat femoral vein

Successful implantations of PTFE microvenous prostheses with 3M precise anastomosis systems were presented. Twelve PTFE prostheses (Gore-Tex;I.D.1.0 mm) were implanted into rat femoral veins by means of 3M precise technique to evaluated the patency rate. In the control group, PTFE prostheses (n = 12) were implanted by means of end-to-end technique. In the experimental group, patency of the PTFE prostheses was evaluated at 3 (n = 6) and 6 (n = 6) weeks after implantation by means of macroscopic inspection and scanning electron microscopy. All prostheses except one were patent at the time of removal (patency rate 91.7 percent). All the microvenous prostheses were completely covered by an endothelial layer at 3 and 6 weeks after implantation, and no stenosis was observed at the anastomotic sites. In the control group, all prostheses except one were found to be occluded 3 weeks after implantation. These results demonstrate the value of the 3M precise technique when implanting PTFE microvenous prostheses.

Neo-endothelialisation of PTFE microvascular grafts: a five-year experience

This paper presents the results of a 5-year experience of the implantation of 1 mm diameter polytetrafluoroethylene (PTFE) prosthesis in rodents. By evaluating the implanted grafts at different intervals, the process of neo-endothelial healing can be divided into six phases: Platelet Aggregation Phase (Stage I); Fibrin Network Phase (Stage II); Bridging Phase (Stage III); Progression Phase (Stage IV-A); Transmural Migration Phase (Stage IV-B) (only in optimal grafts, with thin wall and long fibril length); Intimal Closure Phase (Stage V); and Endothelial Thromboresistance Phase (Stage VI). Grafts with 60 or 90 microns fibril length offer enough "anchoring space" for the ingrowth of neo-endothelium and they act as a framework for the neo-endothelial invasion. Furthermore, this type of material allows intramural migration and penetration of cellular elements. In particular, a network of capillaries traversing the graft wall and opening eventually on the luminal surface can provide multiple sources of neo-endothelium, contributing to the development of the inner neo-endothelial lining. Scanning electron microscopy can favourably assist in the evaluation of different types of PTFE grafts, with regard to their fibril length, diameter, and wall thickness.

Study of microvascular polyester prosthesis in rat carotid arteries

The implantation of a microvascular polyester prosthesis (MPP) (internal diameter 1 mm, length 10 mm) in the carotid arteries was studied in 48 Sprague-Dawley rats. The left carotid artery was resected to 7 mm in length and replaced with MPP by means of sleeve anastomoses. Postoperatively the patency was monitored with Doppler ultrasound at 24 and 72 hr, and at 1, 2, 3, 4, 8, and 12 weeks and was confirmed either by direct inspection intraoperatively or by angiography at the time of removal. At each monitoring time, all the thrombosed and some selected patent grafts were removed and prepared for scanning electron microscopy (SEM) study. The early patency rate was 100% within 24 hr, and the cumulative long-term patency rate was 77.1% at 12 weeks. Rapid and complete endothelial lining (EL) restoration was demonstrated 3 weeks after operation, which provided a smooth and nonthrombogenic surface, and contributed to the long-term patency. Ten of the 11 failed grafts occurred within 3 weeks, that is, before EL, due to thrombosis. These observations indicate that MPP can be successfully used as arterial conduits in rats, and an enhanced patency rate may be expected with the use of anticoagulants or endothelial cell seeding for prevention of early thrombosis.

Cerebral revascularization with an artificial graft: long-term follow-up and discussion of the role of graft pretreatment with modified host endothelial cells

Controversy remains regarding the effectiveness of EC/IC bypass for the prevention of stroke and the authors believe that some studies suggest that a subcategory of patients disabled by transient flow-related symptoms may benefit from surgery. The authors present a 7 1/2 year follow-up analysis of a patient who had undergone an EC/IC bypass from the proximal extracranial carotid to the middle cerebral artery using a 4 mm Gore-Tex prosthesis. Following his death from pulmonary sepsis, the graft was retrieved. Pathological and electron microscopic findings are reviewed.

Modified anastomotic technique for 1 millimeter internal diameter polytetrafluoroethylene arterial grafts in the rat

Reported patency rates after standard end-to-end anastomoses for microvascular prosthetic grafts have been inconsistent and usually disappointing. A modified anastomotic technique is described in which the prosthetic graft is invaginated inside the arterial lumen. In this study of 6 cm lengths of 1 mm internal diameter polytetrafluoroethylene femoro-femoral bypass grafts in the rat, 6 (40%) of 15 grafts with standard anastomoses were patent at 6 months compared to 28 (90%) of 31 grafts using the modified anastomotic technique (P < 0.001). With invagination of the prosthetic graft inside the arterial lumen, reliable high patency rates can be achieved with microvascular prostheses long enough for potential clinical applications.

Achieving better patency rates and neoendothelialization in 1-millimeter polytetrafluoroethylene grafts by varying fibril length and wall thickness

This study evaluates the effects of different fibril lengths and wall thicknesses on patency and neoendothelialization in 1 mm inner diameter polytetrafluoroethylene (PTFE; Gore-Tex) grafts and highlights the importance of longer fibril lengths and matching wall thicknesses. Fibril lengths tested were 30, 60, and 90 microns. The grafts had a wall thickness ranging from 0.18 to 0.34 mm. Ninety-six grafts were implanted in the infrarenal aorta of Wistar rats. Grafts were harvested at various intervals and examined macroscopically, by light microscopy, and by scanning electron microscopy. Both the highest patency rates and the best grades of neoendothelialization were observed in the 90 microns fibril length grafts, while the lowest of both were seen in the 30 microns fibril length grafts. From this study we conclude that 90 microns fibril length PTFE can be considered a valid micrograft for bridging arterial defects in microvascular reconstructive procedures.

Microarterial synthetic graft repair: interstitial cellular components

Although the histologic changes occurring during healing on the lumen surface of large vessel synthetic vascular grafts have been well characterized, the cells populating the interstices of microvascular grafts have not been examined in detail. Since microvascular grafts are required to provide vascular continuity under quite different physiological and hemodynamic conditions as compared with large vessel grafts, these interstitial cells within the synthetic graft material may also vary as a function of graft size. Monoclonal antibodies, light microscopy, and scanning and transmission electron microscopy were used in this study to identify the cells present within the 30-microns pores of 1-mm diameter polytetrafluoroethylene and replamineform silicone rubber grafts. Identified cells included few capillary endothelial cells enclosing erythrocytes, rare proliferating endothelial cells, few macrophages, rare foreign body giant cells, and a majority of fibroblasts. There was no evidence of smooth muscle cells or myofibroblasts within the interstices of these microvascular prostheses 12 weeks after implantation in the rabbit central ear artery. The graft types differed by the presence of foreign body giant cells and more densely packed collagen between cells in the replamineform silicone rubber graft interstices.

Polytetrafluoroethylene interposition grafts in vertebral to carotid artery transposition. A long-term follow-up study

Eight patients undergoing an end-to-side vertebral artery (VA) to common carotid artery transposition between August, 1979, and July, 1982, had a polytetrafluoroethylene (PTFE) interposition graft placed when a direct anastomosis was believed not to be satisfactory. Five of these patients are living; clinical and radiographic follow-up studies over periods ranging between 54 and 82 months show that their transpositions are patent. Two patients died perioperatively, one from an acute anterior myocardial infarction and the other from acute VA occlusion with a propagating thrombus. A third patient died of myocardial infarction 20 months after graft placement; the anastomosis had been found patent at 12 months. This report gives the clinical and radiographic follow-up results in a previously reported group of patients with PTFE interposition grafts. Some of these patients have been followed for over 6 years after surgery: the average radiographic follow-up period in the five survivors is 60 months, and all grafts are patent without evidence of progressive stenosis. Expanded PTFE appears to be an acceptable material for short interposition grafts in operations involving the VA; however, direct artery-to-artery anastomosis is preferred. The results of longer PTFE grafts in reconstructive cerebrovascular surgery have not been adequately studied.

Long-term histological changes in 1 millimeter polytetrafluoroethylene (Gore-Tex) prosthetic arterial grafts

Vein grafts are used extensively to repair blood vessels. However, when suitable vein segments are unavailable, alternative graft materials must be used. This study tested the suitability of 1 mm diameter polytetrafluoroethylene (PTFE) grafts for small-calibre arterial replacements. Grafts of 4 mm length were inserted microsurgically into the iliac arteries of 26 rats. The grafts were removed between 3 and 22 months postoperatively and examined with light microscopy and scanning and transmission electron microscopy (SEM:TEM). Anastomotic intimal hyperplasia was minimal, consisting of a few smooth muscle cells extending 100-200 microns onto the graft. The rest of the PTFE was covered with endothelium. In a few isolated areas, there was a subendothelial layer of smooth muscle, 2-10 cells thick. The short segments used in this study were highly successful, with an overall long-term patency rate of 80%. These grafts showed no evidence of excessive neo-intimal hyperplasia.

The use of long synthetic microvascular grafts to vascularise free flaps in rabbits

A 5 cm length of 2 mm internal diameter (i.d.) synthetic, expanded polytetrafluoroethylene (PTFE, or Gore-Tex) vascular graft was used to connect 25 rabbit inferior epigastric flaps to the contralateral femoral vessels. In 15 animals an expanded PTFE graft connected the opposite femoral artery to the flap while the ipsilateral venous drainage remained intact. In the remaining 10 animals an expanded PTFE graft was used to replace the venous drainage of the flap and connected to the opposite femoral vein while the ipsilateral femoral artery supplied the flap. Flap survival and graft patency were evaluated over 3 weeks. Ten of 15 flaps with intra-arterial grafts survived at 3 weeks (67%). Only 27% (4/15) of their supplying grafts remained patent for 3 weeks, although 67% (10/15) were patent at 10 days. All 10 flaps, where expanded PTFE grafts replaced venous outflow, failed within 36 hours. At exploration these grafts were thrombosed or collapsed. In conclusion, currently available 2 mm (i.d.) expanded PTFE vascular graft cannot maintain patency in a low blood flow circulation supplying an isolated free flap.

Vascular grafts in microvascular surgery. An experimental study

The patency of microvascular grafts depends on the luminal diameter, which is determined by the amount of fibrin and platelets deposited on the intraluminal surface and the anastomotic site, and the extent of pseudointimal formation. An experimental microvascular model in rats has been developed in our laboratory using Indium-111-labeled platelets to measure the amount of deposition on grafts inserted into the infrarenal aorta. This study was designed to assess the patency rates in these grafts and the pathologic maturation as determined by light and electron microscopy. Our study suggests that substantial patency rates can be achieved in aspirin-treated rats, although there was little influence on the pathologic maturation. Indium-111 oxine-labeled platelets can be used to document platelet aggregation, and the technique can be a valuable adjunct in the study of microvascular grafts.

The use of long synthetic microvascular grafts in dogs with a view to clinical application

Five centimetres long segments of 3 mm internal diameter synthetic expanded polytetrafluorethylene (E-PTFE) vascular graft (Gore-Tex) were implanted into the femoral arteries, proximal to the origin of the saphenous artery, of 10 mongrel dogs. In five cases saphenous island flaps were raised and the femoral artery was ligated distal to the saphenous origin so that a low flow system was created through the graft. In 10 femoral vessels the Gore-Tex graft was inserted without raising a flap and the distal femoral artery not ligated so that the graft acted purely as a conduit for blood flow to the distal limb. This created a high flow rate model compared to the reduced flow in the former group. In the first group flap survival was evaluated daily by direct observation of the flaps and graft patency was assessed every 48 h by means of Doppler ultrasound. None of these flaps survived longer then 48 h. In the second group, graft patency was monitored every 48 h with Doppler ultrasound and exploration of Gore-Tex grafts at 3 weeks showed that all had thrombosed.

Microvascular polytetrafluoroethylene (Gore-Tex) grafts in the infrarenal rat aorta

To evaluate the use of microvascular prosthetic grafts, the infrarenal aorta in 33 male Sprague-Dawley rats was replaced by an interposition graft of PTFE (polytetrafluoroethylene, Gore-Tex). Three groups of experimental animals were studied: Group A consisted of rats with 7-mm-long grafts, group B consisted of rats with 20-mm-long grafts, and group C consisted of rats with 20-mm-long grafts and ligatures of one patent after varying observation periods (6-92 days, median value 28 days, mean value 49 days). In group B all grafts but one (13/14) were patent (0-201 days, median value 198 days, mean value 118 days). In group C two grafts occluded immediately postoperatively, whereas the remaining six were patent (0-24 days, median and mean values 9 days). Twelve of 13 grafts observed for 3 months or more remained patent. There were no signs of infection. Angiography did not reveal any stenosis in the anastomoses of patent grafts. Light microscopy demonstrated a good adaptation between the grafts and the aorta in all animals. In the short grafts observed for 3 months and in the long grafts observed for 6 months, the luminal surfaces were completely covered by endothelial-like cells. In the occluded graft in group B, a stenosis was demonstrated in one of the anastomoses. This was not found in any other specimen. The results of this study document the possibility of using PTFE grafts of 1 mm diameter in experimental microvascular position.

Nerve regeneration through a synthetic microporous tube (expanded polytetrafluoroethylene): experimental study in the sciatic nerve of the rat

Nerve grafts made of expanded polytetrafluoroethylene (PTFE) were used to bridge 10-mm gaps in the sciatic nerves of rats. The most prominent gross and histological finding was abundant neovascularization and capillary ingrowth through the microporous PTFE wall. Organized, myelinated nerve tissue was observed. After 4 months, regeneration through hollow PTFE tubes (N = 16) was equivalent to autogenous nerve grafts (N = 12) as measured by gastrocnemius muscle weights (P = 0.33). Nerve conduction velocity in the hollow PTFE tubes was 21.7 m/sec as compared to 50.6 m/sec in the control nerves (P less than 0.001).

The inner prosthetic surface structure and re-endothelialization: an experimental study in the rat using two types of microvascular prostheses for aortic implantation

Two types of microvascular prostheses were implanted in the rat infrarenal aorta. Operations were carried out with clean, nonsterile instruments under ether anesthesia. Anastomoses were made with a continuous 8-0 suture. In group A, a 1-cm-long piece of expanded polytetrafluorethylene (PTFE) and in group B a 1-cm-long fibrous polyurethane prosthesis were implanted. Both groups consisted of 18 rats. Three rats from each group were killed at days 3, 5, 10, 20, 40, and 60 postimplantation. Prostheses were examined by scanning electron and light microscopy for the re-endothelialization. All prostheses in both groups were patent at the time of death. Re-endothelialization started in both types of prostheses the fifth day after implantation and had advanced 1-3 mm in the PTFE prostheses at day 60. However, in the fibrous polyurethane prostheses, re-endothelialization progressed and a complete new lining was achieved between days 20 and 40 postimplantation. The endothelium/neointima in the fibrous prosthesis was firmly anchored onto the prosthetic wall by means of cellular protrusions between the polyurethane fibers. In contrast to this observation, the endothelium/neointima developed in the PTFE prostheses was not anchored to the wall of the prosthesis. It is emphasized that the development of a new lining in a prosthesis may reduce the risk of endogenous, hematogenous infections. From the results of this study, we have concluded that there is a correlation between the inner surface structure and the extent of the re-endothelialization of a prosthesis. A prosthesis with a fibrous structure is much more rapidly and completely re-endothelialized than an expanded PTFE prosthesis.

Microvascular silicon replamineform grafts of 2- and 5-cm lengths: experimental studies

Replamineform silicone microvascular grafts 1 mm in diameter were cut to clinically useful lengths (2 and 5 cm) and used to reconstruct segments of the femoral artery in the rabbit. Despite initial patency and flow rates comparable to flow seen in vein graft repairs and primary repair, no long-term patency was observed. The theoretical biomechanical advantages of this kind of graft material have not solved the problem of long microvascular grafting.

History of (micro) vascular surgery and the development of small-caliber blood vessel prostheses (with some notes on patency rates and re-endothelialization)

The historical development of vascular surgery is reviewed from ancient times (Ruphus of Ephesus, Aëtius of Amida) to recent developments (sutured anastomosis by Carrel). Attempts to anastomose blood vessels by means of nonsuturing technique, using a ring or short tube of diverse materials called prostheses, were undertaken at the start of this century and continued until shortly after World War II. With the advent of modern polymeric materials, prostheses of different types, sizes, structures, and fabrics have been used to substitute for blood vessels, both experimentally and clinically. Recently, blood vessel prostheses with small (1-1.5 mm) internal diameters became available and have been implanted experimentally. Patency rates, biophysical and structural properties, the re-endothelialization and the neointima formation of several types of microvascular prostheses are briefly reviewed.

Evaluation of patency of synthetic and autogenous venous and arterial micrografts in rats

Long-term patency rates of synthetic and autogenous venous and arterial microvascular grafts in rats were compared. The grafts were interposed between the carotid arteries. The geometry of the anastomoses was designed in a manner intended to be comparable to the situation commonly encountered in cerebral revascularization procedures in man. Patency rates were 37.5% for synthetic grafts, 90% for venous grafts, and 60% for arterial grafts. Venous grafts are the best currently available microvascular prostheses.

Three years experience with experimental implantation of fibrous polyurethane microvascular prostheses in the rat aorta

The results of a 3-year study in which a series of 355 implantations of 1-cm-long fibrous polyurethane microvascular prostheses into the infrarenal aorta of the rat (group A) were evaluated with respect to patency and formation, structure, and fate of the neo-intima. Rats were sacrificed at various intervals from 1 day to 2 years in order to obtain a time-related impression of the re-endothelialization and stability of the neo-intima. A second series of 51 implants was done with prostheses 10 cm in length, placed in a 1.5-cm loop in the abdominal aorta (group B). An overall patency rate of 92.7% was achieved in group A. Initially, eight technical failures caused early thrombosis of the prostheses. Sixteen prostheses became infected and subsequently occluded. The overall patency in group B was 52.9%, due to kinking from adhesion formation and normal growth of the rat. In both the long and short prostheses, a continuous multilayered neo-intima developed, growing from the aortic stumps into the prosthesis from both sides. According to the growth rate of 0.3 mm/day, a 1-cm prosthesis was re-endothelialized after +/- 20 days and a 10-cm prosthesis after +/- 9 months. Once developed, the neo-intima, consisting of myofibroblasts and smooth muscle cells covered with a flat endothelium, remained stable and continuous, throughout the observation period. The neo-intima was firmly anchored onto the prosthetic wall by means of cellular protrusions extending between the polyurethane fibres. The significance of rapid healing of an implanted prosthesis is emphasized with respect to preventing (late) hematogenous, endogenous infection of the prosthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat epigastric pedicle model: a clinically relevant evaluation of 1-mm PTFE grafts

Twenty-eight Sprague-Dawley rats had 1.0-mm polytetrafluoroethylene (PTFE) interposition grafts placed in their femoral artery that supplied a 3.0 X 3.0 cm epigastric pedicle flap. The model is the first to evaluate 1.0-mm PTFE under rigorous, clinically simulating conditions. Anastomoses employed a new, continuous telescoping suture technique. Grafts were selected for histological and electron microscopic evaluation, which confirmed the development of a cellular neointimal lining. Viability of the flap model had a 90% correlation with graft patency. Overall graft patency was 50%. Patency was documented in some specimens harvested at 200 days. The flap model is a good indicator of graft patency. PTFE grafts of 1.0-mm internal diameter are not yet equivalent to autologous veins. Future refinements, particularly aseptic technique, are expected to result in even higher patency rates.

Microsurgical application of freeze-dried venous allografts

Freeze-dried venous interposition allografts with an internal diameter of 1.0 mm and a length of 1.0 cm were placed into the femoral arteries of 17 Sprague-Dawley albino male rats in order to investigate patency and host tissue response. The immediate patency rate was 88%. The epigastric island flap was monitored as a sign of patency in the early postoperative period (defined as 1 to 3 days). Twelve of the 17 subjects were observed for 2 months, at which point 66% (8/12) remained patent. There were two aneurysmal dilatations. Histopathological studies and transmission electron microscopy demonstrated that freeze-dried veins undergo complete remodeling in vivo by a normal reparative process and that they do not induce a cellular immune response in the host.