The Pony as an Animal Model for Vascular Implants

This study evaluated the pony as a potentially suitable model for vascular implant research. Healthy, conditioned ponies were randomly assigned to one of three groups: group I, carotid artery autografts (n = 6); group II, e-PTFE carotid interpositional grafts (n = 5); and group III, e-PTFE carotid interpositional grafts plus aspirin (10 mg/kg) and dipyridamole (3.5 mg/kg) drug administration. It was found that autografts remained patent longest (mean = 396.2 days; grafts were still patent at time of writing) followed by group III grafts (157.5 days), with group II grafts remaining patent for the shortest duration (61.1 days), (p < 0.01). Patency was determined using two-dimensional real-time ultrasonography with Doppler velocimetry and/or arteriography. It was demonstrated that the pony's response to antithrombotic drugs was consistent and comparable to that in other animal models, both with respect to platelet function and affect on patency rate. The combination of the ease of surgical manipulation, drug administration, and platelet function testing, the comparable size of the pony and its heart and blood vessels to that of an adult human, the long life span of ponies, and the patency results of this study have demonstrated that the pony is a valuable animal model for vascular research.     

Patency in canine inferior vena cava grafting: effects of graft material, size, and endothelial seeding

We studied 117 inferior vena cava (IVC) replacements in dogs to determine the effects of graft material, graft size, endothelial seeding, and cultured endothelial linings on graft patency. As a control, the IVC was removed and reimplanted in 11 dogs. Dacron (n = 7) and expanded polytetrafluoroethylene (e-PTFE) grafts (n = 12) were seeded immediately with the use of enzymatically derived autogenous jugular vein endothelium. Cultured linings were prepared for e-PTFE grafts (n = 9) by inoculating the graft with jugular endothelium and nurturing the lining in tissue culture for 14 to 30 days before implantation. Unseeded grafts (n = 27) were prepared according to the manufacturer's recommendations. These six methods of preparation were tested in grafts measuring 6 mm I.D. and 60 mm in length. Other sizes were tested with a Latin square study design. After 30 to 60 days the grafts were perfusion fixed and studied with light and transmission electron microscopy. Patency was determined by contrast cavography after 7 and 30 days. Patency in the IVC reimplantation was 100% compared with 28.0% of the e-PTFE (p = 0.001) and none of the Dacron grafts that measured 6 mm I.D. and 60 mm long. e-PTFE and Dacron graft patency also differed significantly (p = 0.035). Seeded and culture-lined e-PTFE grafts in that same size were patent in 31.6% compared with 16.7% of unseeded e-PTFE. With grafts measuring 80 mm long, three of the five e-PTFE grafts were patent between 3 and 7 days. All progressed to occlusion by 30 days and compared poorly with all other graft sizes tested (2.6% progression to occlusion [p = 3 X 10(-8)]). Recanalization was not seen in 10 occluded grafts that were followed for 60 days. The histologic features of seeded grafts differed remarkably from grafts previously studied in the arterial circulation and from culture-lined and unseeded venous prostheses in that 60% had prominent large, random, endothelium-lined channels within the inner capsule. Larger graft diameters (p = 0.009) and the omission of an endothelial surface treatment (p = 0.004) were associated with anastomotic subendothelial fibrous hyperplasia. We conclude that graft material is the major determinant of patency in IVC replacements, that an extensive endothelial surface promotes patency, but that simply seeding e-PTFE or Dacron grafts with 10(5) endothelial cells does not provide sufficient endothelium to alter early patency.(ABSTRACT TRUNCATED AT 400 WORDS)     

A prospective evaluation of plasma-TFE and expanded PTFE grafts for routine and early use as vascular access during hemodialysis.

The use of prosthetic grafts as vascular access for chronic hemodialysis is frequently necessary in patients with end-stage renal disease. Most commonly, expanded polytetrafluoroethylene (e-PTFE) has been employed because of ease of handling, tissue inertness, and acceptable long-term patency. Delay in use to allow for tissue ingrowth, however, has often required placement of temporary access devices. The authors have undertaken evaluation of a new material, plasma polymerized woven dacron Plasma-TFE, in a prospective randomized trial (Plasma-TFE VA) to compare clinical behavior against e-PTFE grafts, and we have used the Plasma-TFE grafts in an additional group of patients (Plasma-TFE AVA) as early access (within 1 week of implantation). Twenty-one Plasma-TFE grafts were implanted in 19 patients and 19 e-PTFE grafts were implanted in 17 patients in a prospective randomized fashion. Additionally, 31 Plasma-TFE grafts were implanted in 31 nonrandomized patients for early access. Primary patency rates in Plasma-TFE VA and e-PTFE grafts were equivalent at 12 months (0.471 and 0.556). When Plasma-TFE AVA primary patency was included (0.621), comparisons were not statistically significant (p = 0.50). Similarly, secondary patency rates among the three groups did not differ (cumulative proportion patent at 12 months: Plasma-TFE VA 0.403, e-PTFE 0.658, Plasma-TFE AVA 0.510). In considering after-revision patency after graft thrombosis, however, the Plasma-TFE grafts (both VA and AVA) performed significantly more poorly (p = 0.027) than e-PTFE grafts. Incidence of graft infection, wound infection, arm edema, hematoma from use, and occurrence of distal limb ischemia between Plasma-TFE (VA and AVA) and e-PTFE did not differ statistically. The authors conclude that Plasma-TFE compares favorably to e-PTFE with respect to primary and secondary patency and nonthrombotic complications, even with early use. Plasma-TFE does not perform as well as e-PTFE, however, after graft thrombosis.     

Detergent-extracted small-diameter vascular prostheses

The exact mechanism that leads to thrombosis of small-diameter vascular prostheses (<4 mm × >6 cm) is unknown. This report presents preliminary patency and healing data on a sequential detergent-extraction technique for the preparation of autogenous small-diameter microvascular grafts. Fifteen carotid interpositional allografts (3 to 4 mm × 4 to 6 cm) were implanted in 15 mixed species adult greyhounds. Ninety days after implantation grafts were perfusion-fixed in situ, harvested, and evaluated by light microscopy and scanning and transmission election microscopy. Two categories of acellular vascular matrix grafts were evaluated: non—cross-linked and cross-linked (1% carbodiimide). By objective morphologic analysis with blind random view, histologic sections were rated from 0 to 4 in five categories believed to be important for graft healing and patency. Overall graft patency was 8% (12 of 15), and there was no significant difference between cross-linked and non-cross-linked grafts. Non—cross-linked grafts were superior to cross-linked grafts in all areas of histologic evaluation except immunogenicity (p < 0.01). Most important, non—cross-linked grafts demonstrated complete endothelial coverage (p < 0.001). There was no significant difference (that is, normal) between control autografts and non—cross-linked grafts; however, there was a significant difference between control autografts and cross-linked grafts in all parameters except immunogenic reaction (p < 0.01). (J. VASC SURG 1984;1:181-91.)     

Experimental comparison of the thrombogenicity of fibrin and PTFE flow surfaces

Two types of 4 mm ID prostheses were studied in the carotid arteries of the dog. These were noncrimped polypropylene-supported filamentous velour knitted Dacron (PPSFV) and expanded polytetrafluoroethylene (e-PTFE, Gore-Tex). Thrombus-"Free" Surface TFS) areas and patency rates were determined at the end of the implant periods. One series of implants was subjected to controlled low flow rates for six hours; another was exposed to physiologic flow rates and observed at seven days, 14 days, and 12 weeks. At six hours the filamentous Dacron, preclotted according to a specific regimen utilizating heparin, performed as well as, and possibly better than, e-PTFE. The Gore-Tex developed surface coagulum in an irregular fashion which was related to graft wetting and blood soakage. Seven-day TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates of the two graft types were comparable at physiologic flow rates. At two weeks, TFS scores and patency rates dropped. This was sufficiently marked in the case of e-PTFE that longer-term implants were not done. However, PPSFV grafts were implanted for 12 weeks, and all grafts examined at that time had closed. It appears that patency of 4 mm ID grafts of this construction will not be reliably attained in the dog carotid artery without the use of platelet-inhibitory drugs until complete healing has occurred.     

Combined arachidonic acid and ADP platelet inhibition maximizes patency of small-diameter vascular grafts

Arachidonic acid (AA) and adenosine diphosphate (ADP) are potent stimuli of platelet aggregation. Each agonist may act through separate platelet pathways. In order to evaluate inhibition of ADP and AA on platelet aggregation, we studied the effect of ticlopidine (TC) and aspirin (ASA) alone and in combination on plasma thromboxane levels, platelet deposition, and patency of small-diameter vascular grafts in a canine model. Thirty-four mongrel dogs were classified as thrombosis prone (TP) or thrombosis resistant (TR) on the basis of in vitro platelet aggregation to AA. Four groups were studied: group I, control; group II, TC (100 mg/kg/day); group III, ASA (3 mg/kg/day); and group IV, TC/ASA (same doses). PTFE grafts were implanted bilaterally in the carotid and femoral arteries Ticlopidine inhibited in vitro platelet aggregation to both ADP and AA but had no significant effect on plasma thromboxane (Tx) B2 production. Aspirin inhibited AA-induced platelet aggregation and significantly decreased TxB2 production. Aspirin inhibited AA-induced platelet aggregation and significantly decreased TxB2 levels in both TP and TR animals (p less than 0.01). Although TC and ASA significantly inhibited platelet deposition and improved 1-month patency in both TP and TR animals, maximal patency was achieved in the group in which TC and ASA were combined. We conclude that platelet ADP and AA pathways are important determinants of the thrombogenic potential in vascular graft performance in dogs and that combined inhibition of both pathways achieves maximal vascular graft patency.     

Pseudointimal thrombogenicity changes in small arterial grafts

Prosthetic grafts are rapidly covered by blood proteins after implantation. Cellular ingrowth and accumulation of interstitial proteins such as collagen complete the development of graft pseudointima. To investigate the effect of these changes on graft platelet reactivity, indium 111-labeled platelet accumulation on two grafts of differing porosity and thrombogenicity (polytetrafluoroethylene [PTFE] and Dacron) was measured 1, 7, and 21 days after graft implantation in canine carotid arteries. Pseudointima structure, weight, and collagen content were also determined at each measurement interval. In addition, platelet accumulation on carotid autografts and dissected carotid arteries was determined for comparison. Platelet accumulation on all grafts and arteries diminished significantly (p less than 0.05) between 1 and 7 days. Platelet accumulation on autografts and dissected arteries decreased further between 7 and 21 days and approached baseline. In contrast, platelet accumulation on Dacron grafts increased significantly (p less than 0.05) between 7 and 21 days to levels above those measured at 1 day, whereas platelet accumulation in PTFE grafts increased minimally and remained significantly below 1-day levels. A thick pseudointima that contained significant amounts of collagen developed in Dacron grafts during this time period, and a thin, incomplete pseudointima containing minimal collagen covered PTFE grafts. These differences in pseudointimal platelet reactivity and composition were associated with decreased patency of Dacron grafts (78%) compared to PTFE grafts (89%).     

Cell seeded decellularised allogeneic matrix grafts and biodegradable polydioxanone-prostheses compared with arterial autografts in a porcine model.

BACKGROUND: small diameter vascular grafts are limited by their restricted availability, early thrombosis, and requirement for anticoagulants. OBJECTIVE: to evaluate different approaches to biocompatible vascular grafts. METHODS: sixteen allogeneic acellularised arteries seeded with autologous endothelial cells were implanted to replace a segment of the common carotid artery (group I). Other animals received polydioxanone prostheses (group II: inner diameter, i.d. 4 mm, n=18; group III, i.d. 5 mm, n=20) or arterial autografts (group IV, n=8). Graft patency was evaluated by means of ultrasound duplex scanning, angiography and histology. RESULTS: patency was 54% (71%), 17% (0%), 50% (50%), and 100% (100%) in group I, II, III, and IV after 1 week (4 months), respectively. Significant differences (p<0.05) were found for group IV versus all other groups at 1 week, as well as for group IV versus groups II and III, for group II versus III, and group I versus II at 4 months. CONCLUSION: small diameter vascular grafts can be engineered from an acellular allogeneic matrix seeded with autologous cells. Patency is superior to polydioxanone prostheses but inferior to the arterial autograft.     

Inhibition of vessel allograft rejection by endothelial removal. Morphologic and ultrastructural changes.

The vascular endothelium plays an important and complex role in vascular allograft rejection. Antigens expressed by the endothelium can act to promote and be the target of rejection reactions, which often lead to thrombosis and ischemic necrosis of the allograft. In this study, segments of femoral artery and femoral vein with or without endothelium were grafted between allogenic or autologous control rats. Immunocompetent Lewis (RT1(1] recipient rats were randomly selected for groups (N = 14 for each) receiving the following: ACI- (RT1a) allografts with intact endothelium, allografts with endothelium removed before operation, autografts with endothelium, and autografts with endothelium removed. Rejection was assessed by graft patency as well as morphologic and ultrastructural changes. At 5 days, the allografts with intact endothelium were totally occluded, whereas allografts without endothelium remained patent, as did autologous control grafts with or without endothelium. Two additional groups (N = 14 each) receiving the de-endothelialized allografts or autografts were examined at 120 days after operation, revealing that grafts in both groups were still patent and had been re-endothelialized. These findings indicate that physical removal of vascular endothelium may depress vessel allograft rejection without immunosuppressive therapy.     

Thrombogenicity of a fibronectin-coated, experimental polytetrafluoroethylene graft

To determine if pretreatment of polytetrafluoroethylene (PTFE) vascular grafts with fibronectin (FN) increased platelet adherence to them and adversely affected their patency, we labeled autologous canine platelets with indium III-oxine and interposed a FN-coated, experimental, 4 mm inner diameter, 10 cm long PTFE prosthesis into one carotid artery of 10 dogs. An identical graft, lacking only the FN coating, was implanted as a control in the contralateral carotid artery. A second group of 10 dogs was similarly treated, but each animal received 2 grains of aspirin and 50 mg of dipyridamole (Persantine) daily, beginning 3 days before surgery and continuing for the duration of the experiment. By means of a quantitative, gamma-camera, platelet adherence to the grafts was studied for 5 days after implantation. Graft patency was assessed with the Doppler velocity meter and was confirmed by surgical reexploration when thrombosis was suspected. FN coating increased platelet adhesion to the grafts in animals untreated with aspirin by a factor of threefold to fivefold. In those animals receiving antiplatelet drugs, patency of FN-coated grafts at 5 days was significantly (p less than 0.05) higher (80%) than in untreated animals (27.2%). In addition, mean platelet deposition on the grafts in these animals was reduced compared with untreated controls. Thus although FN coating of PTFE grafts significantly increases their affinity for platelets, this effect can be effectively abolished by pretreatment with aspirin and dipyridamole.     

New Regenerative Vascular Grafts for Hemodialysis Access: Evaluation of a Preclinical Animal Model

The purpose of this study was to evaluate a suitable animal model for the in vivo evaluation of patency and vascular tissue regeneration in small intestinal submucosa (SIS) vascular grafts for hemodialysis access. First, a 4-mm U-shaped SIS vascular graft was implanted between the internal carotid artery (CA) and the external jugular vein (JV) in five sheep and six swine. The U-shape grafts remained functional for 53 ± 4 days in sheep and 32 ± 2 days in swine. The sheep model presented exaggerated inflammation, so the swine model was selected for the in vivo study. Based on these initial results, a 4-mm C-shape SIS vascular graft with SIS circumferential reinforcement was developed to mechanically improve the vascular graft and manage complications identified during surgery in both sheep and swine. The C-shape vascular graft was implanted in a swine model (n = 3) between the CA and JV. GORE-TEX® vascular grafts were used as controls in the contralateral side of the neck. C-shape grafts remained patent for 47 ± 4 days, whereas the GORE-TEX® grafts were patent for 30 ± 15 days. The C-shape vascular graft was easier to handle during surgery, and its circumferential reinforcement improved in vivo patency, avoiding kinks in the graft after implantation. Histological results showed neovascularization and some regeneration with the alignment of endothelial cells in the vascular wall of the grafts. The model developed may be helpful in other research involving in vivo studies of vascular grafts for hemodialysis access.     

Graft material, length, and diameter determine in patency of small arterial prostheses in dogs

Thirty-two dogs were studied to determine the effects of graft material, length (L), and diameter (i.d.) on the patency of small arterial prostheses. Knitted Dacron (n = 15) and expanded polytetrafluoroethylene (e-PTFE, n = 17) were installed in the common carotid and common femoral arteries of dogs. The grafts were removed one month after implantation and their patency noted. Two of three Dacron grafts measuring 4 mm i.d. and 20 mm in length were patent, whereas none of the eight measuring 40 mm or more in length remained open (P = 0.01). With 4-mm e-PTFE grafts, 80% of the 40-mm and none of the 60-mm lengths of graft remained patent (n = 8, P = 0.03). When the grafts measured 4 mm i.d. and 40 mm in length, no Dacron grafts (n = 4) and 80% of the e-PTFE grafts (n = 5) remained patent (P = 0.016). With 3-mm grafts, the lengths had to be much shorter to insure that any grafts remained open, and even small differences approached significance: 60% of those 4 mm long were patent compared to 14% of those 8 mm long (P = 0.07). There was no difference between Dacron and e-PTFE. Given the clinical observation that much longer grafts made of both of these materials generally remain patent when i.d. = 6, equations predicting the maximum critical length consonant with a reasonable incidence of graft patency may be derived for each material. For e-PTFE: $\text{L}{}_{\mathrm{c}}\text{=}\text{r}{}^4\text{(2.41 - 1.05r)}$, and for knitted Dacron: $\text{L}{}_{\mathrm{c}}\text{=}\text{r}{}^4\text{(1.60 - 0.53r)}$, where L_c = maximumcriticallength of a particular graft and r = radius. We conclude that the patency of small arterial prostheses in dogs is a function of their length, the fourth power of their radius, and the material from which they are constructed.     

In vivo h-VEGF165 gene transfer improves early endothelialisation and patency in synthetic vascular grafts.

OBJECTIVES: Small-diameter synthetic vascular graft performance is inferior to autologous vein grafts. This study tested the hypotheses that local in vivo administration of plasmids encoding for human vascular endothelial growth factor (VEGF), or co-administration of plasmids encoding for human vascular endothelial growth factor/plasmids encoding for fibroblast growth factor-2 in the tissues surrounding a porous synthetic vascular graft would enhance graft endothelialisation and, consecutively, graft patency. METHODS: First, optimal gene for small-diameter synthetic graft endothelialisation was studied in rat abdominal aorta model (n=132): plasmids encoding for human vascular endothelial growth factor; co-administration of plasmids encoding for human vascular endothelial growth factor/plasmids encoding for fibroblast growth factor-2; or control plasmids were injected around 60 microm ePTFE graft. Second, optimal small-diameter synthetic graft design for endothelialisation was explored in rabbit abdominal aorta model (n=90). Various ePTFE grafts or pre-clotted polyester grafts were used with/without plasmids encoding for human vascular endothelial growth factor. Third, clinically used medium-size synthetic grafts were investigated with/without plasmids encoding for human vascular endothelial growth factor in dog carotid (n=20) and femoral arteries (n=15). Endothelialisation was assessed in midgraft area with scanning electron microscopy. RESULTS: In rats, plasmids encoding for human vascular endothelial growth factor enhanced endothelialisation; whereas co-administration of plasmids encoding for human vascular endothelial growth factor/plasmids encoding for fibroblast growth factor-2 had worst outcome at 1 week (NS), 2 weeks (P=0.01) and 4 weeks (P=0.02). In rabbits, pre-clotted polyester grafts had a trend for faster endothelialisation than ePTFE grafts (P=0.08); whereas plasmids encoding for human vascular endothelial growth factor enhanced endothelialisation compared to controls at 2 weeks (P=0.06), however, the effect reversed at 4 weeks (P=0.03). In dogs, synthetic graft patency was improved by plasmids encoding for human vascular endothelial growth factor in femoral position (P=0.103); whereas all carotid grafts were patent at 6 weeks. CONCLUSIONS: Thus, these data suggested that endothelialisation was fastest in pre-clotted polyester grafts; and that local application of plasmids encoding for human vascular endothelial growth factor had a potential to improve early endothelialisation and patency in synthetic vascular grafts.     

Transplantation of cryopreserved canine venous allografts

Local vascular reconstructions frequently require the use of vein grafts to bridge arterial or venous defects. Most previous studies on the use of cryopreserved veins have used relatively large caliber vessels. There have been few studies on the effectiveness of cryopreserved micro- or small-venous allografts. Here, we tested two types of cryopreserved venous allografts: (1) 1.5- to 1.9-mm diameter microvenous grafts (MVG); and (2) 4- to 5-mm diameter small venous grafts (SVG). Cryopreserved MVG allografts were placed into saphenous arteries of six experimental dogs and SVG cryopreserved allografts were placed into femoral arteries of six experimental dogs for 3 to 6 weeks. Two fresh MVG autografts were also transplanted into experimental dogs as controls and autografts were transferred to the contralateral side in SVG dogs as controls. None of the six cryopreserved MVG grafts retained patency but three/six cryopreserved SVG allografts were patent at harvest. Histological examination of grfts revealed control autografts were undergoing arterialization with an intact intima. Experimental cryopreserved allografts showed extensive medial fibrosis, significant lymphocytic infiltrates, and sporadic areas of intact intima for both patent and nonpatent grafts.     

Microarterial grafting into the carotid artery of the rabbit: some considerations concerning species-dependent thrombogenicity

This study was undertaken to obtain more insight into the performance of microarterial prostheses in an experimental animal that resembles the human thrombogenically more closely than the rat. Therefore, microarterial polyurethane-based (PU) prostheses and polytetrafluoroethylene (PTFE) prostheses were implanted into the carotid artery of the rabbit and were compared with regard to patency and thrombus formation at 1 hour (n = 4), 1 day (n = 4), 2 days (n = 4), 1 week (n = 4), 2 weeks (n = 6), 3 weeks (n = 6) and 6 weeks (n = 6) after implantation. Arterial autografts (n = 22), followed up for 2 weeks after implantation, served as a control for the surgical procedure. All arterial autografts were patent at the time of harvesting. In contrast, although all microarterial prostheses were patent at 1 hour and some were patent at 1 day, 2 days and 1 week, none of them were patent at 2, 3 and 6 weeks. The patent PTFE prostheses showed remarkably less thrombus accumulation on the graft surface when compared to the patent PU prostheses. However, all prostheses had the same amount of thrombus formation at the distal anastomosis.     

Glutaraldehyde-preserved venous valve transplantation in the dog

Transplantation of femoral vein grafts was performed on 33 mongrel dogs to assess graft patency and valvular function after storage in glutaraldehyde. The grafts were removed from the donor, flushed with room temperature heparinized lactated Ringer's solution, and then stored in a 0.2% glutaraldehyde solution for 16 hr. At the time of grafting, the veins were again flushed with lactated Ringer's and anastomosed orthotopically to the recipient. An arteriovenous fistula was also created. Postoperatively the animals received daily doses of aspirin (2 mg/kg) and dipyridamol (50 mg). The following groups were studied: Group I (n = 10) served as controls and received fresh autografts. Group II (n = 13) received autografts stored for 16 hr in 0.2% glutaraldehyde. Group III (n = 10) received allografts stored similarly in glutaraldehyde for 16 hr. The grafts were monitored for evidence of patency. All grafts were removed for histological evaluation when patency was no longer detected or at the end of 7 weeks. Of the fresh and glutaraldehyde-preserved autografts (Group 1), 100% were patent at 7 weeks, and generally retained valve function. Patency of allografts was only slightly inferior but valve function was disappointingly poor at 7 weeks.     

Usefulness of bovine pericardium as interpositional graft in the surgical repair of nasal septal perforations (experimental study).

A 2.5-cm nasal septal perforation was performed in 18 pigs and repaired as follows: group I (n = 6), septal perforation without treatment; group II (n = 6), surgical repair with interpositional graft of glutaraldehyde-preserved bovine pericardium (GPBP); group III (n = 6), surgical repair with interpositional graft of lyophilized GPBP (LGPBP). The animals were evaluated clinically and radiologically (x-ray and CT scan) 2 days before surgery, daily during the first postoperative week, and weekly during the next 6 months. At the end of the study the animals were euthanized with an overdose of pentobarbital. Macroscopic and microscopic examination of the grafts and nasal septum was performed. All the animals survived the surgical procedure. Five pigs in group I showed persistence of the septal perforation. All the animals in groups II and III showed total closure of the septal perforation, with the presence of fibrotic tissue on the pericardial grafts as well as in the septal cartilage, and overall good healing. In conclusion, GPBP and LGPBP are adequate materials that can be used as interpositional grafts in the surgical closure of septal perforations in pigs     

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.     

Prostaglandin production and platelet reactivity of small-diameter grafts

This article examines the relationship of platelet deposition to thromboxane and prostacyclin (PGI₂) production in arterial autografts (n = 8), para-anastomotic native artery (n = 40), nonseeded control (n = 6), and endothelial cell-seeded (n = 17) small-diameter Dacron grafts implanted in the carotid and femoral arteries of dogs. Platelet deposition was measured by a dual-isotope subtraction platelet-imaging technique that expresses platelet deposition as percent indium excess (%IE). PGI₂ and thromboxane assays were performed with the use of an immunoreactive assay. The %IE in the nonseeded grafts was significantly higher than in the seeded prostheses (p < 0.001). Arterial autografts accumulated significantly less platelets than did seeded grafts (p < 0.05) or nonseeded grafts (p < 0.001). The thromboxane A₂ (TXA₂) production in nonseeded grafts was significantly higher than in seeded grafts (p < 0.001), arterial autografts (p < 0.001), or in para-anastomotic native artery (p < 0.001). The PGI₂ production by the arterial autografts was significantly higher than by the nonseeded grafts (p < 0.005), seeded grafts (p < 0.001), or para-anastomotic native artery (p < 0.025). The PGF_1α/TXB₂ ratio was significantly higher in the arterial autografts when compared with the nonseeded grafts (p < 0.001), endothelial cell-seeded grafts (p < 0.001), or para-anastomotic native artery (p < 0.025). We conclude that platelet deposition can be significantly decreased by endothelial cell seeding of small-diameter grafts. The transmural production of TXA₂ by native arteries and prosthetic grafts may have an important influence on platelet deposition and patency. The balance between the production of TXA₂ and PGI₂ in the graft wall may be the best determinant of platelet deposition and possibly of long-term patency. (J VASC SURG 1984;1:774-781.)     

Ticlopidine versus aspirin and dipyridamole: influence on platelet deposition and three-month patency of polytetrafluoroethylene grafts

In an attempt to establish a specific drug regimen that would retard neointimal fibrous thickening (NFT) and promote patency of small arterial grafts, we studied acute platelet accumulation and 3-month patency of 4 mm polytetrafluoroethylene (PTFE) grafts in dogs treated with oral aspirin (2 mg/kg/day) in combination with dipyridamole (5 mg/kg/day) (ASA/D) or ticlopidine (25 mg/kg/day) (T). After 3 days of treatment, 15 dogs were given indium 111-labeled autologous platelets and then had bilateral femoral artery grafts placed (control, 10 grafts; each drug group, 10 grafts). The calculated graft radioactivity expressed as average counts per 10 minutes +/- standard error of the mean (SEM) was as follows: control = 542,003 +/- 63,991; ASA/D = 135,163 +/- 14,443 (p less than 0.001, Student's t test); T = 104,650 +/- 14,004 (p less than 0.001). Bilateral femoral artery and carotid artery grafts were placed in 15 other dogs (control, 20 grafts; each drug group, 20 grafts). Three months later the 60 grafts were excised and their patency recorded: control = 20% (4 of 20 grafts); ASA/D = 70% (12 of 17 grafts) (p less than 0.01, chi-square analysis); T = 30% (6 of 20 grafts) (p greater than 0.05). Mean anastomotic NFT +/- SEM of each graft was measured with an ocular micrometer: control = 1.6 +/- 0.2 mm; ASA/D = 0.7 +/- 0.2 mm (p less than 0.001, Student's t test); T = 1.3 +/- 0.2 mm (p greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)