Silyl-heparin adsorption improves the in vivo thromboresistance of carbon-coated polytetrafluoroethylene vascular grafts

BACKGROUND: Expanded polytetrafluoroethylene (ePTFE) remains the most commonly utilized synthetic graft material for infrainguinal arterial reconstruction. However, patency rates of ePTFE bypass grafts are inferior to those observed with autogenous vein grafts. Modification of the luminal surface of ePTFE grafts such as coating with carbon or heparin, may prevent early graft failures and improve overall patency rates. We now report our results with a silyl-heparin adsorbed carbon-coated ePTFE graft. METHODS: Silyl-heparin was adsorbed onto carbon-coated ePTFE vascular grafts (Bard Peripheral Vascular, Tempe, Arizona), which were then evaluated for patency and platelet deposition acutely (2 hours after implantation) and 7 days after graft implantation in mongrel dogs. Dogs underwent bilateral aortoiliac grafting where one heparin adsorbed carbon-coated graft and one carbon-coated graft (control) were placed on either (alternating) side. Platelet deposition was determined by injection of autologous (111)Indium radiolabeled platelets followed by a 2-hour circulation period prior to explantation of grafts. Heparin activity of the silyl-heparin grafts (at preimplantation and explantation) was determined using an antithrombin-III based thrombin binding assay. RESULTS: Graft patency was 100% for both heparin coated (5 of 5) grafts and control (5 of 5) grafts in the acute group of dogs. In the 7-day group, patency was 87.5% for heparin coated (7 of 8) grafts and 50% for control (4 of 8) grafts (P = 0.28, Fisher's exact test). Radiolabeled platelet studies revealed a significantly lower deposition of platelets on heparin coated grafts compared with control grafts in the acute group (17.3 +/- 13.5 versus 35.2 +/- 17.9 counts per minute, per cm(2) per million platelets, mean +/- SEM; n = 5, P <0.05, paired Student t test). In the 7-day group of dogs with bilaterally patent grafts (4 of 8), a trend toward a lower deposition of platelets on heparin coated grafts compared with control grafts was observed (1.55 +/- 0.409 versus 2.14 +/- 1.13 counts per minute, per cm(2) per million platelets, mean +/- SEM; n = 4, P = 0.52, paired Student t test). Eight percent of the preimplantation heparin activity remained on the explanted silyl-heparin grafts after 2 hours and only 2% after 7 days. CONCLUSIONS: Silyl-heparin adsorption onto carbon-coated ePTFE vascular grafts resulted in improved acute thromboresistance in a canine bilateral aortoiliac model. Ongoing laboratory efforts are aimed at improving the silyl-heparin retention on vascular grafts. This graft may prove to be useful in the clinical setting.     

Reduction of platelet deposition on vascular grafts using an antiplatelet graft coating technique

The systemic use of platelet inhibitors has been shown to improve vascular graft function. In this study a biodegradable coating of polymeric polylactic acid (PLA) containing a microparticulate suspension of aspirin (ASA) 30% by weight, was applied to the lumenal surface of small diameter vascular prostheses to reduce platelet deposition on canine implanted arterial grafts. USCI 4-mm ID Dacron internal velour grafts were used. Coated and contralateral noncoated (control) prostheses were implanted in canine carotid and femoral arteries. Graft performance was assessed by determination of aspirin elution rates, in vivo red cell subtracted 111indium-labeled platelet scans, and post implant platelet aggregation studies. Eighty percent of the aspirin in the coated grafts was released during the first 24 hr of perfusion and approximately 20% of the aspirin remained in grafts after 1 month. In vivo platelet scans documented less platelet deposition on ASA-coated grafts when compared to controls 2 and 24 hr post implant (P less than 0.01, P less than 0.05, respectively). There was no significant difference in platelet deposition on ASA-coated and control grafts at 2 weeks or 1 month post implant. Post implant platelet aggregation studies indicated systemic platelet inhibition for 4-5 days. It was concluded that aspirin incorporation in a polylactic acid coating applied to 4-mm ID vascular prostheses reduced the platelet affinity of Dacron grafts and exerted a temporary local and systemic platelet inhibiting effect.     

Forskolin impregnation of small calibre PTFE grafts lowers early platelet graft sequestration and improves patency in a sheep model

Synthetic vascular grafts have a thrombogenic surface which plays a role in graft failure. Systemic pharmacologic interventions have been used to lower platelet sequestration onto the graft surface but are associated with side effects. In this communication we describe the results of a new therapeutic principle of applying forskolin, a powerful cyclic adenosine monophosphate stimulator (cAMP) to the inner surface of PTFE vascular grafts. The grafts were evaluated with Indium-III-oxine labelled platelets and by graft patency on 3 consecutive days after implantation at 1 month and 3 months. Forskolin significantly lowered early platelet sequestration onto the treated graft surface when compared with controls. Graft potency at 1 and 3 months was also significantly higher in the forskolin treated grafts.     

Silyl-heparin bonding improves the patency and in vivo thromboresistance of carbon-coated polytetrafluoroethylene vascular grafts

OBJECTIVES: Our purpose was to improve the performance of carbon-coated expanded polytetrafluoroethylene vascular grafts by bonding the grafts with silyl-heparin, a biologically active heparin analog, using polyethylene glycol as a cross-linking agent.Material and method Silyl-heparin-bonded carbon-coated expanded polytetrafluoroethylene vascular grafts (Bard Peripheral Vascular, Tempe, Ariz), were evaluated for patency and platelet deposition 2 hours, 7 days, and 30 days after graft implantation in a canine bilateral aortoiliac artery model. Platelet deposition was determined by injection of autologous, (111)Indium-radiolabeled platelets, followed by a 2-hour circulation period prior to graft explantation. Histologic studies were performed on a 2-mm longitudinal strip of each graft (7-day and 30-day groups). Heparin activity of the explanted silyl-heparin grafts was determined by using an antithrombin-III based thrombin binding assay. RESULTS: Overall chronic graft patency (7-day and 30-day groups) was 100% for the silyl-heparin bonded (16/16) grafts versus 68.75% for control (11/16) grafts (P =.043). Acute 2-hour graft patency was 100% for the silyl-heparin bonded (6/6) grafts versus 83.3% for control (5/6) grafts. Radiolabeled platelet deposition studies revealed a significantly lower amount of platelets deposited on the silyl-heparin grafts as compared with control grafts in the 30-day group (13.8 +/- 7.18 vs 28.4 +/- 9.73, CPM per cm2 per million platelets, mean +/- SD, P =.0451, Wilcoxon rank sum test). In the 2-hour group of dogs, a trend towards a lower deposition of platelets on the silyl-heparin grafts was observed. There was no significant difference in platelet deposition between the two grafts in the 7-day group. Histologic studies revealed a significant reduction in intraluminal graft thrombus present on the silyl-heparin grafts as compared with control grafts in the 30-day group of animals. In contrast, there was no difference in amount of graft thrombus present on both graft types in the 7-day group of dogs. Pre-implant heparin activity on the silyl-heparin bonded grafts was 2.0 IU/cm(2) (international units[IU]/cm(2)). Heparin activity remained present on the silyl-heparin grafts after explantation at all 3 time points (2 hours: above upper limit of assay, upper limit = 0.57, n = 6; 7 days: 0.106 +/- 0.015, n = 5; 30 days: 0.007 +/- 0.001, n = 5; mean +/- SD, IU/cm(2)). CONCLUSION: Silyl-heparin bonding onto carbon-coated expanded polytetrafluoroethylene vascular grafts resulted in (1) improved graft patency, (2) increased in vivo graft thromboresistance, and (3) a significant reduction in intraluminal graft thrombus. This graft may prove to be useful in the clinical setting.     

Influence of endothelial cell seeding on platelet deposition and patency in small-diameter Dacron arterial grafts

Serial platelet deposition, surface topography, and patency were evaluated in control (N = 28) and endothelial cell-seeded (N = 28) small-diameter (4 mm inner diameter) USCI Dacron grafts implanted in the carotid and femoral arteries of dogs. All dogs received aspirin (325 mg) daily for 2 weeks starting 24 hours prior to graft implantation. Endothelial cell seeding was performed by mixing suspensions of autologous endothelial cells that had been enzymatically harvested from segments of external jugular vein with blood that was used to preclot the prostheses. The platelet deposition on each graft was quantitated by means of indium 111-labeled platelets and technetium 99m-labeled red cells in a dual-isotope platelet-imaging technique. Platelet deposition on seeded grafts 24 hours after implantation was significantly higher than on the controls (p less than 0.05). Two weeks after implantation platelet deposition on seeded prostheses had decreased to a level significantly lower than that on the controls and continued to decline on serial studies up to 7 months. In contrast to seeded grafts, platelet accumulation on control grafts dramatically increased after the withdrawal of aspirin therapy and was associated with a sharp rise in control graft thromboses. Gross and scanning electron microscopic evaluation of endothelial cell-seeded grafts after 1 month indicated complete neointimal coverage, whereas none of the control grafts explanted at 1 month or later exhibited a continuous neointimal lining. Cumulative 7-month patency for seeded prostheses was significantly higher than for the controls (96% and 29%, respectively; p less than 0.001). We conclude that endothelial cell seeding in combination with short-term aspirin therapy is a simple, reliable diameter Dacron prostheses. Abrupt withdrawal of aspirin therapy may be contraindicated in nonseeded control grafts because it results in increased platelet deposition and thrombosis.     

Perioperative suppression of platelet adherence to small-diameter polytetrafluoroethylene (PTFE) grafts

The perioperative effect of platelet antagonists on small-diameter polytetrafluoroethylene (PTFE) grafts was evaluated in forty-six New Zealand white male rabbits receiving either dipyridamole (DPM) 100 mg/kg/day (n = 10; group 1), aspirin (ASA) 10 mg/kg/day (n = 10; group 2), a combination of ASA 10 mg/kg/day and DPM 10 mg/kg/day (n = 9; group 3) or 100 mg/kg/day (n = 10; group 4), or placebo (n = 7) as single daily doses. All regimens began 72 hr prior to insertion of a 20 x 3-mm internal diameter PTFE interposition aortic graft. Autologous indium-111 labeled platelets were injected immediately after implantation. Graft and an equivalent segment of aorta were harvested after 48 hr. Graft platelet adherence index (GPAI) was calculated as the graft:reference aorta ratio of emissions. The GPAI in the control group was 238 +/- 46 (mean +/- SD). Single regimen antiplatelet agents in groups 1 and 2 reduced mean GPAI to 47 +/- 38 and 40 +/- 12, respectively. The combination regimen in group 3 lowered mean GPAI to 43 +/- 8 and in group 4 to 21 +/- 7. Platelet uptake in PTFE grafts at 48 hr is significantly lowered to 8.8 to 19.7% of control by perioperative antiplatelet agents given as a single daily oral dose (P less than 0.001). ASA alone and DPM alone provided similar suppression of platelet uptake, but combination ASA + low dose or high dose DPM gave significantly greater (P less than 0.001) suppression of early platelet deposition than the single agent regimens. These results support perioperative administration of combination oral antiplatelet agents as adjunctive therapy in small diameter prosthetic graft implantation.     

Evaluation of platelet deposition and neointimal hyperplasia of heparin-coated small-caliber ePTFE grafts in a canine femoral artery bypass model

INTRODUCTION: Bypass graft failure due to acute thrombosis and intimal hyperplasia remains a major challenge in small-diameter vascular prosthetic graft reconstruction. Heparin has been shown to prevent thrombus formation and inhibit intimal antithrombotic in animal studies. In this study, we evaluated the effect of small-caliber heparin-coated expanded polytetrafluoroethylene (ePTFE) grafts on platelet deposition and intimal hyperplasia in a canine model of femoral artery bypass grafting. METHODS: Nine adult greyhound dogs underwent placement of bilateral femorofemoral artery bypass grafts with ePTFE grafts (4 mm diameter and 7 cm long). In each animal, a heparin-coated ePTFE graft was placed on one side while a noncoated graft was placed on the contralateral side which served as the control. Platelet deposition was measured by autologous (111)indium-labeling and scintillation camera imaging analysis in 24 h. The graft patency was assessed at 4 weeks following the bypass. The effect of intimal hyperplasia was assessed with histological and morphometric analysis. RESULTS: Platelet deposition on the heparin-coated grafts at 24 h was significantly reduced by 72% as compared to controls (P = 0.001). The patency rate was 44% in control grafts and 89% in heparin-coated grafts. There was a significant reduction of graft intimal hyperplasia at both proximal (0.38 +/- 0.21 mm(2)) and distal (0.19 +/- 0.06 mm(2)) anastomoses in the heparin-coated grafts as compared with proximal (1.01 +/- 0.28 mm(2)) and distal (0.42 +/- 0.01 mm(2)) anastomoses in the untreated control grafts, respectively (P < 0.05). Heparin coating significantly reduced graft neointimal hyperplasia at patent graft anastomoses by 55-72% as compared to controls. CONCLUSIONS: These data demonstrate that heparin coating of ePTFE significantly reduced early platelet deposition and inhibited anastomotic neointimal hyperplasia. Moreover, small-caliber heparin-coated ePTFE graft significantly increased graft patency in a canine femoral artery bypass model. This may represent a promising treatment strategy for improving the clinical performance of small-caliber prosthetic vascular grafts.     

A quantitative and qualitative comparison of fibrin glue, albumin, and blood as agents to pretreat porous vascular grafts

Recent reports suggest that fibrin glue can be used to seal porous vascular grafts prior to insertion, but this ability has not been quantitatively compared to existing methods. We compared blood loss from and handling characteristics of grafts pretreated with either fibrin glue (FG) (Tisseel), albumin autoclaving (AA), or blood preclotting (BP). Five 6-cm segments of 6-mm internal diameter grafts, both knitted and woven double velour Dacron were treated in each group (30 specimens). Human blood was forced through the BP group until clotted; AA segments were soaked in 25% human albumin and autoclaved for 10 min; FG segments were treated with a topical application of Tisseel (0.5 ml/graft) followed by treatment with topical thrombin + CACl (0.5 ml/graft). Graft ends were sealed and attached to a transducer/syringe pump mechanism which pumped heparinized human blood into the graft at 100 mm Hg intraluminal pressure. All blood that leaked through the grafts over 2 min was collected and the amount was averaged for the five grafts in each group. Graft handling was characterized as either pliable or stiff. Blood pretreatment caused 21 +/- 2 and 13 +/- 4 cc/2 min of leak in knitted and woven grafts, respectively. Albumin autoclaving resulted in 9 +/- 2 and 1 +/- 0.5 cc of leak (P less than 0.01 compared to blood), while fibrin glue produced 2 +/- 2 and 0.4 +/- 0.5 cc leaks (P less than 0.01 compared to blood). Both blood and fibrin glue produced soft pliable grafts, while albumin pretreatment resulted in stiff grafts.(ABSTRACT TRUNCATED AT 250 WORDS)     

Platelet Consumption by Arterial Prostheses: The Effects of Endothelialization and Pharmacologic Inhibition of Platelet Function

The thrombogenic mechanism of arterial grafts has been studied by determining the relative utilization of platelets, fibrinogen and plasminogen by human arterial prostheses, and by direct examination of arterial grafts in a baboon model. Forty-one survival and turnover measurements of (51)Crplatelets, (131)I-fibrinogen and (125)I-plasminogen in ten patients with aortofemoral knitted Dacron prostheses demonstrated platelet consumption after graft placement (platelet survival 4.2 days +/- 0.5 and turnover 68,000 plat/ul/day +/-10,000 compared with 8.2 days +/- 0.3 and 35,000 plat/ul/day +/- 5,000 respectively for control subjects with stable vascular disease, p < 0.01). In vitro platelet function test results were normal. Platelet consumption was interrupted by dipyridamole or a combination of dipyridamole and acetylsalicylic acid, and platelet survival normalized spontaneously during nine months postoperatively. No significantly increased consumption of fibrinogen or plasminogen was found in these patients with arterial grafts.Placement of impervious knitted Dacron velour aortic grafts in baboons reproduced platelet consumption that progressively normalized over six weeks postoperatively. Platelet survival measurements correlated directly with endothelial cell coverage of the graft luminal surface in these animals implying that endothelialization of the graft surface was also occurring postoperatively in patients.     

Does 111indium-platelet deposition predict patency in prosthetic arterial grafts?

The relationship between the rate of 111In-platelet deposition on vascular grafts and subsequent thrombosis has been examined in patients undergoing femoropopliteal by-pass. Sixty-seven patients undergoing femoropopliteal by-pass using vein, Dacron or PTFE were randomized to aspirin plus dipyridamole (ASA/DPM) or placebo. Autologous 111In-platelets were injected in the second postoperative week and Thrombogenicity Index (TI) calculated as the mean daily rise in the ratio of radioactivity graft/contralateral thigh. Graft patency was assessed to 1 year. Mean (+s.e.m.) TI at 1 week in 21 grafts that occluded within 12 months was 0.19 +/- 0.018 compared with 0.07 +/- 0.009 in the 38 that remained patient (P less than 0.001). Grafts with a TI less or greater than the median had a 90 per cent or 39 per cent cumulative 1-year patency, respectively (P less than 0.001). In the prosthetic grafts ASA/DPM reduced mean TI from 0.17 +/- 0.02 to 0.11 +/- 0.01 (P less than 0.02) and enhanced 1-year patency from 36 to 67 per cent (P less than 0.05). Following femoropopliteal by-pass TI related to subsequent graft patency. Radiolabelled platelet deposition therefore provides a guide as to how new materials or antithrombotic drugs may influence clinical graft thrombosis. Platelet inhibition reduced both graft thrombogenicity and subsequent occlusion.     

Small-caliber heparin-coated ePTFE grafts reduce platelet deposition and neointimal hyperplasia in a baboon model

PURPOSE: Intimal hyperplasia and graft thrombosis are major causes of graft failure. Heparin prolongs graft patency and inhibits neointimal hyperplasia in animal models. The purpose of this study was to evaluate the effect of a heparin-coated expanded polytetrafluoroethylene (ePTFE) graft on platelet deposition and anastomotic neointimal hyperplasia after aortoiliac bypass grafting in a baboon model. METHODS: Heparin-coated ePTFE grafts (4-mm diameter) were incorporated into exteriorized femoral arteriovenous shunts placed in five baboons. Platelet deposition was analyzed by measuring the accumulation of indium 111-labeled platelets on the grafts, with dynamic scintillation camera imaging. Eight adult male baboons (mean weight, 9.3 kg) underwent bilateral aortoiliac bypass grafting with ePTFE grafts (4-mm internal diameter). In each animal a heparin-coated ePTFE graft was placed in one aortoiliac artery, and an uncoated graft, which served as the control, was placed in the contralateral aortoiliac artery. All grafts were harvested at 4 weeks, and were analyzed quantitatively for neointimal hyperplasia at graft-vessel anastomoses. RESULTS: Early platelet deposition on heparin-coated grafts after 1 to 4 hours of ex vivo circuitry was significantly reduced. All the harvested aortoiliac grafts were patent at 4 weeks. There was a significant reduction in neointimal area at both proximal (0.26 +/- 0.11 mm(2)) and distal (0.29 +/- 0.14 mm(2)) anastomoses in the heparin-coated grafts, compared with proximal (0.56 +/- 0.18 mm(2)) and distal (0.63 +/- 0.21 mm(2)) anastomoses in the untreated control grafts (P <.05). In addition, neointimal cell proliferation assayed with bromodeoxyuridine (BrdU) incorporation was reduced in the graft neointima (3.47% +/- 0.43%) in heparin-coated grafts compared with the graft neointima (6.21% +/- 0.59%) in untreated control grafts (P <.05). CONCLUSIONS: Small-caliber heparin-coated ePTFE grafts significantly reduce platelet deposition and anastomotic neointimal hyperplasia and cell proliferation, without measurable side effects, in baboons. Surface coating with heparin in small-caliber ePTFE grafts is useful for improving prosthetic bypass graft patency. Clinical relevance: An autologous vein graft is the ideal bypass conduit in peripheral arterial reconstruction; however, many patients who undergo bypass grafting do not have adequate or available autologous vein graft. As a result surgeons often must rely on prosthetic grafts as an alternative conduit in arterial bypass procedures. Clinical outcomes with prosthetic grafts in peripheral arterial reconstruction are generally inferior to those with autologous vein bypass grafts, in part because of anastomotic neointimal hyperplasia. This study evaluated the effect of small-caliber heparin-coated expandable polytetrafluoroethylene (ePTFE) grafts in aortoiliac reconstruction in a baboon model. The study found that heparin-coated ePTFE grafts resulted in less intimal hyperplasia and less platelet deposition after implantation, compared with noncoated control ePTFE grafts.     

Dacron arterial grafts: the influence of porosity, velour, and maturity on thrombogenicity

It has been claimed that the neointimal healing of Dacron arterial prostheses can be enhanced by increasing porosity and including both an internal and an external velour layer. To test this, 24 patients received at random either woven (USCI, DeBakey, C. R. Bard, Inc.) or more porous, double-velour, knitted (Microvel, Meadox Medicals, Inc.) Dacron aortobifemoral prostheses. Graft thrombogenicity was measured using autogenous 111In-labeled platelets shortly following surgery and 6 to 9 months later. The thrombogenicity index was defined as the mean daily rise in the ratio of emissions over the graft to emissions over a reference area (aortic arch) and is a measure of platelet deposition. At early study the mean (+/- SE) thrombogenicity index was similar in woven and knitted graft patients at 0.19 +/- 0.4 and 0.14 +/- 0.2, respectively. In both groups it was lower (P less than 0.05) 6 to 9 months later at 0.06 +/- 0.2 (woven( and 0.08 +/- 0.1 (knitted), with again no difference between materials. Although platelet survival was restored to near normal values in both groups by 6 to 9 months, only one woven graft failed to demonstrate continued platelet accumulation by gamma-imaging. Thrombogenicity in Dacron grafts diminishes in the early months of maturation but is not affected by porosity and velour. Moreover, this thrombogenicity persists beyond the period of altered platelet survival.     

Effect of a selective thromboxane synthase inhibitor on arterial graft patency and platelet deposition in dogs

This study examined the effect of selective thromboxane synthase inhibition and nonselective cyclooxygenase inhibition on vascular graft patency and indium 111-labeled platelet deposition in 35 mongrel dogs undergoing carotid artery replacement with 4 mm X 4 cm polytetrafluoroethylene (PTFE) (one side) and Dacron (opposite side) end-to-end grafts. Aspirin-dipyridamole therapy improved one-week graft patency, from 46% in untreated dogs to 93% in treated dogs. Thromboxane synthase inhibition (U-63557A) improved graft patency in these dogs to 81%. Both drug treatments reduced platelet deposition on Dacron and PTFE grafts by 48% to 68% compared with control dogs. Dacron grafts accumulated significantly more platelets than PTFE grafts but had comparable patency rates. Low-dose aspirin therapy had no significant effect on either graft patency or platelet deposition. All treatment groups showed a 60% to 76% reduction in serum thromboxane B2, but only thromboxane synthase inhibitor treatment increased plasma 6-keto-prostaglandin F1 alpha by 100%. Selective thromboxane synthase inhibition improved small-caliber prosthetic graft patency to the same extent as did conventional cyclooxygenase inhibition in this preliminary study.     

The influence of platelet-graft interaction on platelet survival in patients with aortobifemoral Dacron grafts.

In patients with arterial grafts, platelet consumption may be due either to platelet interaction with the graft, and/or concomitant platelet consumption in the rest of the arterial tree. This hypothesis was tested by quantifying the kinetics and platelet-graft interaction of indium-111-labelled platelets with double velour Dacron grafts in 13 patients with arterial insufficiency ascribed to atherosclerosis. Mean platelet lifespan (MPLS), 149 +/- 46 hours, was significantly shorter (P = 0.001) than normal. Labelled platelets were transiently deposited onto the graft surfaces. Peak 111In deposition on the grafts, 1.33 +/- 1.02% of injected labelled platelets, was reached at 70 +/- 33 hours. Thereafter the graft-platelet radioactivity decreased in parallel with platelet radioactivity in the circulation. There was no statistical correlation between MPLS and the factors known to be associated with graft platelet deposition: graft size; peak graft radioactivity; and the time to attain peak graft radioactivity. It is therefore concluded that in patients with arterial disease requiring graft implantation, the observed increased platelet consumption cannot only be ascribed to the interaction of platelets with the graft. Concomitant atherosclerosis is probably the important modifier of platelet consumption. The significant contribution of this factor to the shortening of the MPLS should be taken into account when assessing, by measuring platelet lifespan, the thrombogenicity of grafts.     

Preservation of compliance in a small diameter microporous, silicone rubber vascular prosthesis

Compliance is believed to be a significant factor in maintaining the patency of small diameter vascular grafts. This study evaluated the compliance changes with time of microporous Replamineform silicone rubber prostheses. The compliance of 15 canine femoral artery interpositions (4 mm internal diameter X 6 cm length) was measured by in-vivo electromagnetic rheoangiometry immediately following implantation and at intervals to eight months. At implantation, silicone rubber grafts were overcompliant (15.0 +/- 1.1% radial change/mmHg X 10(-2); mean +/- S.E.) compared to the proximal artery (7.7 +/- .6%). The compliance of the prostheses decreased within two weeks (6.3 +/- .9%) and remained isocompliant to the proximal artery for eight months. The compliance determinations for the silicone rubber grafts were compared with those from PTFE prostheses and vein grafts acquired by the same method in a previous study. The analysis demonstrates the preservation of isocompliance of the silicone rubber prostheses compared to the native arteries. In contrast, the minimally compliant vein grafts and PTFE prostheses continued to decrease in compliance following implantation. This microporous silicone rubber graft may improve the success of small internal diameter arterial reconstructions by eliminating failures caused by compliance mismatch between the artery and the prosthesis.     

Platelet deposition on vascular grafts. The accuracy of in vivo quantitation and the significance of in vivo platelet reactivity.

An in vivo platelet imaging system utilizing indium-111-labeled platelets and technetium-99m-labeled red cells was used to serially study and compare platelet deposition on autologous external jugular vein grafts, autologous arterial grafts, polytetrafluoroethylene (Gore-tex) and two Dacron (Meadox and USCI) small diameter (4mm) vascular grafts implanted end-to-end in canine carotid and femoral arteries. This method of quantitating platelet deposition was validated by correlating deposition measured in vivo with deposition measured directly on explanted grafts (r = 0.94, p less than 0.01). Platelet accumulation on all grafts was greatest immediately after implantation and declined over time. None of the artery or vein grafts thrombosed, and they had the lowest level of platelet deposition at all times. Platelet deposition on Gore-tex grafts was significantly less than on USCI Dacron grafts from 24 hours to 1 month after implantation. There was no statistical difference in 1-month patency among the synthetic graft groups. Synthetic grafts that thrombosed during the first month accumulated significantly more platelets immediately after operation than did those grafts that remained patent. Patent Dacron grafts with low levels of platelet deposition had less thrombotic debris at explantation on the luminal surface than did those grafts with high levels of platelet deposition. Differences in initial platelet deposition appeared to be more a function of platelet reactivity within each dog rather than the material used in graft construction.     

Choice, Isolation, and Preparation of Cells for Bioartificial Vascular Grafts

Preparation of cells and tissues for bioartificial vascular grafts is discussed from the viewpoint of tissue engineering. In general, a neointima is not formed on vascular prostheses except at the anastomotic sites. Graft surfaces do not heal and are covered with fresh thrombi for a long period of time after implantation. The delayed healing is, so to speak, an intractable ulcer of the vascular wall. To overcome this problem, we have developed a tissue fragment transplantation method. We consider that neointima formation of vascular prostheses after implantation is a product of tissue engineering in vivo. Therefore, 3 essential elements for tissue engineering, i.e., cells, extracellular matrices, and cytokines, are required for neointima formation. Synthetic vascular prostheses lack one or more of these elements. In this study we demonstrated a standard healing process of fabric vascular prostheses and an antithrombogenic polymer graft using animal models. Then we showed the tissue fragment transplantation method using venous tissues, adipose tissues, and bone marrow. This method provided the 3 essential elements to the prostheses. To allow these elements to be actively engaged in neointima formation, we treated cells and tissues as clumps without enzymatic digestion. We also took advantage of the in vivo environment. With the results we demonstrate our way of thinking in relation to bioartificial vascular grafts.     

Sartorius transposition to protect vascular grafts in the groin

Fifty-two patients who required reexploration through the groin incision within seven days of an arterial procedure were studied to assess the value of sartorius transposition. Twenty-four group I patients had the sartorius muscle used to cover the vascular graft at reoperation while 28 group II patients had a standard closure. The groups were similar with respect to age, initial arterial operation, incidence of diabetes, and use of antibiotics and postoperative anticoagulation. Wound complications were frequent in both groups (62.5% vs. 57.1%, respectively) but outcome of these wound problems was quite different. Graft infection and anastomotic disruption were significantly less frequent in group I patients. Because fewer infected prostheses had to be removed group I patients were less likely to require high level amputations. Sartorius transposition is an effective method of protecting vascular grafts jeopardized by the high frequency of wound problems associated with early reoperation.     

An experimental study to examine the patency and tissue response of two types of biosynthetic graft used as a replacement for porcine inferior vena cava.

This experimental study has been carried out to evaluate biosynthetic grafts as vascular substitutes. Tubular segments of 35 x 8 mm made of (1) tanned ovine collagen and integral polyester mesh, either of the first (Omniflow I) or second generation (Omniflow II), or (2) polytetrafluoroethylene (e-PTFE), have been sutured in the infrarenal inferior vena cava of pigs, and removed 1 hour, 7, 14, 28, 56 and 112 days after implantation. The patency rate of biosynthetic grafts was higher than that of e-PTFE grafts (p < 0.01). There was no significant difference between the patency of the first generation and second generation collagen grafts. These results indicate that biosynthetic prostheses may be suitable vascular substitutes in low flow and low pressure systems. Improvements in the collagen inner cover structure (Omniflow II vs. Omniflow I), producing greater mechanical endurance, did not enhance long-term patency or the healing patterns of biosynthetic grafts.     

Implantation of in vitro endothelialized polytetrafluoroethylene grafts in human beings. A preliminary report.

To assess the impact of in vitro endothelialization on prosthetic graft patency, we performed femorotibial reconstruction in four patients. Polytetrafluoroethylene grafts (6 mm), lined with cultivated autologous endothelial cells, harvested from the veins of the forearm, were used. Autologous endothelial cells were harvested enzymatically and characterized by morphology and factor VII staining. After a cultivation period of 17 to 23 days, the cell count increased from 27 +/- 3 x 10(4) endothelial cells to 5.4 +/- 1.1 x 10(6). Endothelial cell seeding on polytetrafluoroethylene prostheses was then performed. To improve endothelial cell attachment to the graft surface, polytetrafluoroethylene grafts (60 to 70 cm; 6 mm diameter) were precoated with fibrin glue containing fibrin and fibronectin and the fibrinolysis inhibitor aprotinin. Seeding density of 49 +/- 10 x 10(3) endothelial cells per square centimeter yielded a preconfluent monolayer immediately after seeding, as demonstrated by scanning electron microscopy. A second cultivation period of 6 days, after seeding and before implantation, was necessary for establishment of a confluent monolayer and to allow for maturation of the endothelial cell cytoskeleton as well as production and excretion of extracellular matrix. Grafts endothelialized in vitro were implanted in four patients requiring femorotibial reconstruction. Scintigraphic studies with indium 111-labeled platelets demonstrated little or no platelet deposition, indicating persistent endothelialization. All grafts remained patent at 3 months after implantation.