Thromboembolic potential of synthetic vascular grafts in baboons

We have compared in baboons the capacity of two types of synthetic vascular grafts to accumulate thrombus, activate circulating platelets, and generate occlusive platelet microemboli. Grafts were incorporated into femoral arterial-arterial shunts placed unilaterally in 10 baboons; the unoperated contralateral limbs served as controls. The accumulation of indium 111 (111In)-labeled platelets onto the grafts (expanded polytetrafluoroethylene [ePTFE] or knitted Dacron, 4 mm inner diameter) and the appearance of 111In radioactivity in distal microcirculatory beds (calf and foot) were quantified by dynamic scintillation camera imaging. After 1 hour total platelet deposition per graft was higher with Dacron (49.0 +/- 8.0 x 10(9) platelets) than with ePTFE (3.7 +/- 0.6 x 10(9) platelets, p less than 0.01). Platelet counts decreased and beta-thromboglobulin levels increased with Dacron graft placement but were unaffected by ePTFE graft placement (p less than 0.05 and p less than 0.01, respectively). Emboli shed from Dacron grafts were detected as multifocal, irregular, and changing deposits in the calves and feet. Indium 111 platelet activity in the feet distal to the Dacron grafts increased 81.1% +/- 21.4% from baseline values over 1 hour, whereas the activities in the feet distal to the ePTFE grafts were unchanged (p less than 0.05). The increase 111In-platelet radioactivity above the control limb values (excess radioactivity) was higher for the Dacron graft group than for the ePTFE group in both the feet (139.6% +/- 46.9% vs 6.2%, p less than 0.05) and the calves (86.7% +/- 21.7% vs 7.3% +/- 3.6%, p less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Simple methods for direct antibiotic protection of synthetic vascular grafts

Two simple methods for direct antibacterial protection of synthetic vascular grafts were investigated. In the first protocol the highly protein-bound antibiotics nafcillin (90% protein bound), cefazolin (80%), and cefamandole (70%) were added directly to preclotting blood. Knitted Dacron grafts preclotted in the presence of one of these drugs absorbed significant amounts. Although at high concentrations these antibiotics exhibited anticoagulant effects, significant antibacterial protection was obtained at lower antibiotic levels. Washing treated grafts for 6 hours failed to eliminate the antibacterial activity. Antibiotics remained on the grafts for at least 96 hours. In the second protocol knitted Dacron grafts were soaked in a suspension of silver-pefloxacin, a silver-nalidixic acid analogue with intense antistaphylococcic activity. Using 110Ag-labeled complexes, significant antibiotic activity was documented on the graft after 19 days of washing. Four nafcillin-treated prostheses, six silver-pefloxacin-coated grafts, and 11 control grafts were interposed in the infrarenal aorta of dogs and immediately challenged with an intravenous infusion of 1 X 10(7) Staphylococcus aureus. None of the four nafcillin-treated grafts was infected at 3 weeks. One of the six silver-pefloxacin-coated grafts grew staphylococci, and 9 of 11 controls had positive graft cultures for Staphylococcus when harvested. These studies suggest that prosthetic grafts can be simply coated at the time of implantation with antibiotics selected for appropriate binding and antibacterial characteristics to obtain an infection-resistant prosthesis.     

Prevention of neointimal proliferation by immunosuppression in synthetic vascular grafts.

OBJECTIVE: Immunosuppressive agents have been proposed to reduce neointimal hyperplasia in synthetic vascular grafts. Thus, the purpose of the present study was to evaluate the safety and efficacy of rapamycins (systemic vs. local vs. oral administration) and mycophenolate mofetil (MMF) to reduce intimal hyperplasia in infrarenal synthetic vascular grafts of the rat. METHODS: Fifty-four Wistar rats (250 g) completed the study after a synthetic vascular graft (ePTFE, Gore-tex, 2 mm diameter, 10 mm length) was implanted end-to-end in the infrarenal aorta. The animals were divided into three groups: group 1 consisted of 12 control animals, group 2 consisted of 37 rats receiving rapamycins, either per os (RAD, 1.5 or 3 mg/kg), intraperitoneally (RPM, 1.5 or 3 mg/kg) or locally (RPM soaking of the graft); and in group 3 (n=5), MMF (40 mg/kg) was administered orally. The animals were followed weekly with weight controls and signs of toxicity for 30 (n=37) and 60 (n=17) days, respectively. All animals were sacrificed and underwent histological examination at completion of the study. RESULTS: All animals survived in groups 1 and 3, but five died in group 2. The weight gain was normal in all groups, except for the subgroup 2a receiving high dose rapamycins orally. All rats in group 3 suffered from diarrhea, whereas animals receiving high dose rapamycins showed toxic signs (hair loss, wound healing problems). Histological examination showed a significant increase in intimal hyperplasia in group 1 (0.03+/-0.01 and 0.14+/-0.05 microm after 30 and 60 days, respectively; P<0.01). Rapamycins in either application or dosage had no significant effect on intimal hyperplasia. CONCLUSIONS: Local or systemic administration of rapamycins has no effect on intimal hyperplasia in synthetic vascular grafts. In contrast, toxic signs with weight loss were observed in animals treated with high dose rapamycins, but not in those treated with MMF. Thus, in the rat model, immunosuppression with rapamycins or MMF cannot be recommended for the prevention of intimal hyperplasia in the synthetic vascular graft model.     

Does bacteremia pose a direct threat to synthetic vascular grafts?

This study was undertaken to determine the significance of graft lumen exposure to blood-borne organisms in the development of graft infection. Three groups of dogs were studied. In group I (n = 20), the infrarenal aorta was dissected from surrounding tissue, divided, and reconstructed with a Dacron tube interposition graft. In group II (n = 9) the aorta was similarly isolated, but Dacron graft material was wrapped around the intact aorta. In group III (n = 13) the infrarenal aorta was isolated, but no graft material was placed. All dogs were given intravenous 1 X 10(7) Staphylococcus aureus at the completion of surgery. Group I grafts were harvested 8 hours, 1 day, or 21 days after bacterial challenge. Group II and III grafts were harvested 1 day or 21 days after infusion. At the time of harvest, selective cultures of the periaortic tissue (PAT), periaortic graft (PAG), and interposition graft lumen (GL) were taken. The overall infection rates were similar, with 17 of 20 (85%) dogs in group I, 6 of 9 (67%) in group II, and 11 of 13 (85%) in group III found to be culture positive. In group I, 3 of 3 dogs at 8 hours, 2 of 2 on day 1, and 12 of 15 on day 21 had positive PAT cultures. Only 4 of 15 on day 21 had positive GL cultures. In group II, 4 of 5 dogs on day 1 and 2 of 4 on day 21 had positive PAT and PAG cultures. In group III, 9 of 9 animals on day 1 and 2 of 4 on day 21 had positive PAT cultures. All aortic lumen cultures were negative in groups II and III. The difference between GL and PAT cultures was statistically significant in all groups (I, p = 0.01; II, p = 0.05; III, p = 0.01). Serial quantitative blood cultures revealed a mean bacterial load of 10.5 +/- 4.5 CFU/ml at 15 minutes postinfusion, which fell steadily until no bacteria were detected at 3.5 hours. Lymphangiography demonstrated periaortic pooling of lymph in the immediate postoperative period. These data suggest that the bacteremia in this model is transient and rapidly clears. Periaortic tissues quickly sequester bacteria, possibly because of lymphatic leakage. The GL appears to be secondarily infected.     

血管移植三种术式修复四肢血管损伤的疗效评价

[目的]分析和评价显微缝合自体大隐静脉移植、吻合器自体大隐静脉移植与人工血管移植三种术式对四肢血管损伤的疗效。[方法]2014年1月~2015年12月,对89例(146条血管)肢体血管损伤行血管移植修复术。其中30例患者采用显微缝合自体大隐静脉移植术(显微缝合组),33例采用吻合器自体大隐静脉移植术(吻合器组),26例采用缝合人工血管移植术(人工血管组)。对3组围手术期相关指标及术后3个月随访结果进行对比分析。[结果]总手术时间分别为显微缝合组(353.13±6.49)min,吻合器组(217.27±8.30)min,人工血管组(288.64±4.53)min,三组间比较差异有统计学意义(F=596.91,P<0.001)。总输血量分别为显微缝合组(2435.2±153.08)ml,吻合器组(1271.07±87.47)ml,人工血管组(1522.60±103.0)ml,三组间比较差异有统计学意义(F=141.909,P<0.001)。吻合器组用时最短,输血量最少,差异有统计学意义(P<0.001)。吻合器组和显微缝合组的术后并发症基本相当,均少于人工血管组,但三组血管术后通畅及血管危象比较差异无统计学意义(P>0.05)。[结论]对肢体血管伤的处理须考虑患者的全身状况、局部伤情、供体条件、血管口径等因素。采用吻合器进行血管移植手术用时最短。自体大隐静脉移植时,血管直径>4 mm,宜选择显微缝合术式;直径在1~4 mm之间,优先选用吻合器。人工血管仍可安全使用。     

Biological vascular grafts

Biological bypass graft material has been used as an alternative to autogenous vein since the first lower extremity revascularization procedures were performed. Both immunogenicity and biodegradation can contribute to the failure of these grafts and must be addressed. Cryopreservation at ultralow temperatures (-196 degrees C) after pretreatment with dimethylsulfoxide has been successful in preserving viable vein graft endothelium. Both rejection and deterioration of the cellular elements may contribute to the relatively high failure rates. The umbilical vein graft has become an effective alternative to autogenous material. The glutaraldehyde tanning procedure increases tensile strength, masks antigenicity, and sterilizes the tissue. Recent results with excellent 5-year patency (67%) and cumulative limb salvage (80%) confirm the utility of this graft.     

Evaluation of neointimal hyperplasia on tranilast-coated synthetic vascular grafts: an experimental study.

Tranilast is an antiallergic drug that interferes with proliferation and migration of vascular smooth muscle cell induced by platelet-derived growth factor (PDGF) and transforming growth factor-beta1 (TGF-beta1). We investigated the local effect of tranilast on neointimal hyperplasia using tranilast-coated prosthetic grafts. The inner sides of the thin-walled polytetrafluoroethylene (PTFE) grafts were coated with chitosan and tranilast containing chitosan solution. Wistar albino rats (32) were used in the study. Patches (1 x 2 mm) for vascular grafts were prepared. Three groups were tested: group 1 (n = 12; tranilast coated), group 2 (n = 10; adhesive-only film-layer-coated), and group 3 (n = 10; normal ePTFE patch grafts sutured to the carotid arteries of the rats). Recipient sites of the carotid arteries were excised 4 weeks after surgery. All sections were examined histologically for graft patency, thrombus formation, and neointimal thickness. Expression of PDGF, fibroblast growth factor, and TGF-beta1 on cross-sections of the neointima were evaluated by immunohistochemistry. No significant differences were found regarding mean neointimal thicknesses. PDGF and TGF-beta-1 expressions were significantly lower in group 1. Although a decrease in local effect of tranilast was observed for growth factor expressions at a drug concentration of 0.05 mg/cm(2), a significant reduction in neointimal hyperplasia was not achieved. The coating concentration of 0.05 mg/cm(2) may have been too low to produce an antiproliferative effect. Given our promising results, further studies are recommended and planned using different drug concentrations and time intervals.     

Administration of granulocyte colony-stimulating factor enhances endothelialization and microvessel formation in small-caliber synthetic vascular grafts

OBJECTIVE: The purpose of this study was to determine whether systemic administration of granulocyte colony-stimulating factor (G-CSF) would promote endothelialization for small-caliber Dacron vascular grafts. METHODS: We implanted 4-mm preclotted Dacron grafts in both carotids of 12 dogs. For a fair comparison, all dogs had a comparable platelet aggregation profile with platelet aggregation scores less than 30. Five dogs served as controls, and the others were given 7-day subcutaneous injections of G-CSF (10 microg/kg per day), starting on the seventh postoperative day. The effect of G-CSF was evaluated by white blood cell count, which showed a 3.7-fold (+/- 2.7-fold) increase at the end of treatment. Grafts were harvested at 4 weeks. All G-CSF grafts were patent, and one control occluded. Endothelial-like cell coverage averaged 80.8% on G-CSF grafts, but only 35.6% for control grafts (P <.0004). With the exclusion of the anastomotic pannus healing factor, the difference in endothelial-like cell coverage was even greater (68.5% vs 9.8%; P <.0001). Immunocytochemical staining and electron microscopy studies demonstrated endothelial cells. Light microscopy also showed that there were more microvessels on and in the G-CSF grafts than in the control grafts. This study suggests that G-CSF can enhance early endothelialization of small-caliber vascular grafts. Further studies to determine the proper dosage and timing are needed before clinical application can be recommended.     

Mechanisms of healing in synthetic grafts

In previous baboon studies we have shown that porous (60 micron mean internodal distance) polytetrafluoroethylene (PTFE) grafts heal by ingrowth of endothelium and smooth muscle cells from the adjacent artery and from capillaries penetrating through the interstices of the graft. However, porous grafts (principally made of Dacron) in humans do not heal. This has been attributed to a wound healing deficiency in humans; however, it might be due to an inhibitory effect of the Dacron itself. To examine the latter possibility, we undertook this study to compare the healing of 4 mm internal diameter porous Dacron grafts (USCI, Sauvage Filamentous Knitted) with that of Gore-Tex 60 micron PTFE grafts in baboons (the latter graft not available for clinical use). The grafts were harvested at 2, 4, and 12 weeks and assessed for (1) percentage of endothelial coverage, (2) endothelial cell (EC) proliferation (thymidine labeling index), (3) intimal area, and (4) smooth muscle cell (SMC) proliferation (thymidine labeling index). The PTFE grafts at all three time points were fully covered, whereas only one of five Dacron grafts was completely covered at 12 weeks. The intima of the PTFE grafts consisted of ECs and SMCs, whereas that of the Dacron grafts contained ECs and SMCs as well as focal accumulations of thrombus. The intimal cross-sectional areas in the Dacron grafts (3.0 +/- 1.2 mm2) were significantly greater than in the PTFE grafts (0.8 +/- 0.6 mm2) at 4 weeks; there was no difference at 12 weeks (Dacron, 2.6 +/- 2.3 mm2 and PTFE, 3.0 +/- 2.5 mm2).(ABSTRACT TRUNCATED AT 250 WORDS)