Hemodynamics in a compliant hydraulic in vitro model of straight versus tapered PTFE arteriovenous graft

BACKGROUND: Hemodialysis patients require a vascular access to deliver sufficient blood flow to the artificial kidney. Of these vascular accesses, 30% are prosthetic (mainly polytetrafluorethylene [PTFE]) graft implants. These grafts are prone to the development of stenosis in the vein due to intimal hyperplasia, subsequently leading to thrombosis and graft failure. AIM: We investigated the hemodynamics in a straight and a tapered PTFE-graft and compare the hydrodynamical behavior of both grafts. MATERIALS AND METHODS: Two different vascular access geometry models were examined: a 6-mm diameter straight graft and a 4- to 7-mm tapered graft. The grafts were sutured to a compliant silicon model of an artery and vein in a loop configuration. Flow rate varied between 500 and 1500 mL/min. Two conditions were tested: 1). control: mean pressure is 100 mm Hg at the arterial inlet; and 2). low resistance condition: pressure is 20 mm Hg at the venous outlet. Pulse pressure is 60 mm Hg at the arterial inlet for both conditions. Pressure and flow velocity are measured continuously, while flow rate is measured volumetrically. RESULTS: The pressure drop at the arterial anastomosis of the tapered graft is three times higher compared to the straight graft model. Intragraft pressure drops are similar in both graft types. Mean pressure and pulse pressure in the graft and vein are decreased in the low resistance condition. Also, the difference between maximum and minimum velocity is smaller in this. CONCLUSIONS: No significant differences are noted between the graft geometries: pressure drop over the graft is almost equal. The major difference is the higher pressure drop at the arterial anastomosis of the tapered graft.     

Perivenous support reduces early changes in human vein grafts: studies in whole blood perfused human vein segments

BACKGROUND: Patency of vein grafts in coronary artery bypass grafting procedures is generally less favorable than those of selected arterial grafts. However, vein grafts still are needed in cardiac operations. It would be desirable to find measures to improve the patency of vein grafts next to antithrombotic regimens. Animal studies demonstrated that arterial pressure induces overdistention of the thin-walled vein grafts and that prevention of this overdistention with extravascular support ameliorates the arterialization process with, subsequently, more favorable patency. To evaluate whether perivenous stenting of the rather muscular human vein grafts is also beneficial, we designed an in vitro model to study the early effects of perivenous support in human vein grafts. METHODS: Seven paired segments of human vein graft obtained during coronary artery bypass grafting procedures were placed in a perfusion circuit and perfused simultaneously with autologous whole blood, with a pressure of 60 mm Hg (nonpulsatile flow). After 30 minutes of perfusion, one segment, and after 60 minutes of perfusion, the remaining segment were taken for histologic and immunohistochemical examination. In the next experiments 7 segments of human vein graft were placed in the circuit and supported with a polytetrafluoroethylene graft to prevent overdistention with 7 unstented segments as controls. RESULTS: In unsupported vein grafts perfused with autologous blood under a pressure of 60 mm Hg, a complete de-endothelialization was shown after 1 hour of perfusion. In the study vein grafts, with a perivenous polytetrafluoroethylene graft preventing overdistention (n = 7), the endothelium remained intact. Electron microscopic investigation of the media showed severe damage in the circular smooth muscle layer in the unstented group, whereas in the stented group almost no injury was found. CONCLUSION: In our in vitro closed-loop model, reproducible vessel wall changes were observed in all human vein graft specimens studied. The beneficial effect of perivenous support could also be established for the human greater saphenous vein, providing a basis for clinical application.     

Randomized comparison of 6-mm straight grafts versus 6- to 8-mm tapered grafts for brachial-axillary dialysis access

OBJECTIVE: This report presents the results of a prospective randomized study that compared 2 grafts of different diameter: 6 mm, and 8 mm tapered to 6 mm at the arterial site, placed in the upper arm for hemodialysis in a selected population of patients younger than 71 years without diabetes. METHODS: Seventy consecutive patients younger than 71 years without diabetes who required an upper arm graft between January 1997 and January 2002 and without previous access in the same limb were randomly allocated to receive either a 6-mm graft or 6- to 8-mm graft. Graft flow was measured every 3 months with the Doppler dilution technique. When access flow was less than 600 mL/min, fistulography was performed, and any stenosis was surgically treated with venous outflow replacement. Thrombectomy and associated stenosis treatment in the same stage was performed in all cases immediately after detection of thrombosis. Complication rate, and primary, assisted primary, and secondary patency rates were compared between the two groups with the Student t test and life table analysis. RESULTS: Mean access flow was 975 mL/min for 6-mm grafts (range, 600-1500 mL/min; 95% confidence interval [CI], 889-1070), and for 6- to 8-mm grafts was 1397 mL/min (range, 1122-2700 mL/min; 95% CI, 1122-1672). This difference was significant (P <.01). Complication rate was 0.45 episodes per graft-year in 6-mm grafts, and 0.19 episodes per graft-year in 6- to 8-mm grafts (P <.01). At 1, 2, and 3 years, primary patency rates were 62%, 58%, and 44%, respectively, for 6-mm grafts, and 85%, 78%, and 73% for 6- to 8-mm grafts; log-rank comparison between curves was P =.0259. At 1, 2, and 3 years, secondary patency rates were 85%, 85%, and 85%, respectively, for 6-mm grafts, and 90%, 90%, and 90% for 6- to 8-mm grafts; log-rank comparison between curves was not significant, at P =.0603. At 1, 2, and 3 years, assisted primary patency rates were 84%, 79%, and 76%, respectively, for 6-mm grafts, and 90% for 6- to 8-mm grafts; log-rank comparison was P =.0414. CONCLUSIONS: The results of this study show an advantage in terms of primary and assisted primary patency rates, and complication rate for upper arm grafts with diameter 6 mm to 8 mm over grafts with 6-mm diameter in a patient population younger than 70 years without diabetes. The finding of a similar secondary patency rate in both groups is probably due to the surveillance program with sequential measurement of access flow and prompt surgical treatment of stenosis. However, we needed twice the number of rescue procedures in 6-mm grafts to achieve a similar patency rate as with large-bore grafts. These study results must be carefully evaluated, taking into consideration the small number of patients and the selected patient population.     

Accelerated endothelialization of interpositional 1-mm vascular grafts

BACKGROUND: There is an increased need for alternative, synthetic, small-diameter vascular grafts due to a growing segment of the population who suffer from ischemic heart disease and lack suitable autologous vein grafts for use in coronary artery bypass grafting (CABG). We hypothesized that a cell-mediated extracellular matrix (ECM) modification of ePTFE would stimulate increased vascularization within the graft and thus promote lumenal endothelialization in a 1-mm rat abdomenal aortic implant model. METHODS AND RESULTS: Expanded polytetrafluoroethylene (ePTFE) vascular grafts (1 mm i.d.) were modified on the ablumenal surface with ECM deposited by the HaCaT or II-4 cell lines and implanted intrapositionally into the descending aorta of rats. Five weeks after implantation, all samples were patent and examination of the grafts demonstrated that the ECM modified samples exhibited extensive ablumenal vascularization and tissue incorporation compared to nonmodified samples. Also, ECM modified grafts had a cellular lining, while the nonmodified grafts were void of a cellular lining except for a limited pannus ingrowth. CONCLUSION: HaCaT and II-4 cell ECM modifications of ePTFE increase new blood vessel growth in association with the graft, and the II-4 cell modification results in formation of an endothelial monlayer on the lumenal surface of the graft.     

Clinical experience with autologous endothelial cell-seeded polytetrafluoroethylene coronary artery bypass grafts

OBJECTIVE: Autologous endothelial cell seeding was used to improve the patency of 4-mm polytetrafluoroethylene vascular prostheses. METHODS: Since 1995, 14 patients with coronary artery disease received 21 autologous endothelial cell-seeded polytetrafluoroethylene vascular bypass grafts for coronary artery revascularization. The polytetrafluoroethylene grafts were seeded with the endothelial cells in a multiple step procedure, including cell culture techniques before coronary bypass operation. With the use of extracorporal circulation and cardioplegic arrest, a bypass operation was performed by means of conventional surgical techniques. RESULTS: After a mean postoperative follow-up of 27.7 months (range, 7.5-48 months), the graft patency rate is 90.5%. Follow-up angiograms of the aorta-coronary polytetrafluoroethylene bypass grafts showed patent bypasses in all cases except two. Angiograms of all 19 patent endothelial cell-seeded polytetrafluoroethylene bypass grafts showed a smooth luminal borderline without stenotic regions. The percutaneous transluminal angioscopic evaluation showed a glossy white and smooth endoluminal graft surface without any fibrin, platelet, or erythrocyte deposits. Intravascular ultrasonographic examinations confirmed the results. CONCLUSION: Patency of autologous endothelial cell-seeded 4-mm polytetrafluoroethylene vascular prostheses as coronary artery bypass grafts was much better than that of unseeded polytetrafluoroethylene grafts. Further evaluations and a larger population of patients will prove whether the encouraging patency will last.     

Comparison of the flow capacity of free arterial grafts and saphenous vein grafts for coronary bypass surgery

There is controversy regarding the flow reserve and capacity of arterial conduits to meet the needs of the myocardium. This study compared flow in 22 free arterial bypasses to 15 saphenous vein grafts in procedures involving twenty patients. To assess the maximal flow possible, (flow capacity) graft flow was measured using a calibrated pump while perfusing blood cardioplegia through the conduit and distal anastomosis during cardiac arrest (no competitive flow). This assessment was subsequently confirmed with whole blood during myocardial contraction while on cardiopulmonary bypass. Twenty-two free arterial grafts were used; 15 right internal mammary artery grafts, 4 right gastroepiploic grafts, 3 inferior epigastric artery grafts, and 3 sequential bypasses. Free arterial conduit flow ranged from 50 to 180cc/ml, with an average flow of 102.5+/-28.5ml/min as compared to saphenous vein graft flow, 102+/-28 ml/min. No correlation of flow with the conduit size was found. Arterial graft flow demonstrated a mild correlation with the size of the native coronary artery bypassed (R=0.47, P相似文献   

Intraoperative flow measurement in composite Y arterial grafts.

OBJECTIVE: Total arterial myocardial revascularization may be achieved by using the 'Y-graft' techniques with different free arterial conduits anastomosed off the side of an in situ internal thoracic artery to reach distal coronary segments. This study was assessed to measure intraoperative graft flow, resistance and clinical outcomes. METHODS: Seventy-six patients who underwent coronary artery bypass grafting during a time period of 27 months were enrolled in this prospective study. All patients received sequential grafting by using both internal thoracic arteries, inferior epigastric and right gastroepiploic artery joined as a composite Y graft. Intraoperative graft flow, resistance and derived variables were measured. RESULTS: All patients except one showed good flow (ml/min and waveform) in either branch of composite graft. In one case, a low-flow situation through the graft was registered requiring surgical correction. Temporary occlusion of either branch did not significantly affect flow in the other side of the arterial Y. Mid-term follow-up (3 and 15 months) and angiographic studies showed a high graft patency rate. CONCLUSION: Composite arterial grafts provide excellent early and mid-term clinical results. Flow reserve of the left internal thoracic artery did not affect blood flow and resistance on either branch of the Y graft when temporary occlusion on the other side of the arterial Y was performed.     

Composite arterial Y graft has less coronary flow reserve than independent grafts

BACKGROUND: It is not known whether a composite Y graft of the left internal thoracic artery can provide sufficient blood flow to the whole left coronary system. The aim of this study was to compare regional myocardial blood flow (MBF) and coronary flow reserve after coronary artery bypass grafting using arterial composite Y graft or independent arterial grafts. METHODS: Positron emission tomography was performed at rest and after dipyridamole infusion using oxygen-15-labeled water 2 weeks after coronary artery bypass grafting. Regional MBF was calculated in seven segments of the left ventricle. Coronary flow reserve was defined as the ratio of MBF after dipyridamole infusion to MBF at rest. In the Y graft group (n = 22), a free arterial graft to obtuse marginal arteries was anastomosed to the proximal side of in situ left internal thoracic artery, which was anastomosed to the left anterior descending artery. In the independent graft group (n = 13), left anterior descending and obtuse marginal arteries were independently revascularized using in situ left internal thoracic artery and a free arterial graft. RESULTS: There was no difference between the groups in MBF at rest. Coronary flow reserve in the Y graft group was lower than that in the independent group in the anterobasal (1.43 +/- 0.07 versus 1.90 +/- 0.13, p = 0.038), apical (1.24 +/- 0.06 versus 1.64 +/- 0.12, p = 0.003), septal (1.34 +/- 0.05 versus 1.75 +/- 0.13, p = 0.023), and lateral regions (1.19 +/- 0.04 versus 1.66 +/- 0.09, p = 0.001). CONCLUSIONS: Although arterial composite Y graft improved MBF at rest, it was not as effective as independent grafts for improving coronary flow reserve soon after coronary artery bypass grafting.     

Anastomotic tissue response associated with expanded polytetrafluoroethylene access grafts constructed by using nonpenetrating clips.

PURPOSE: The gross, light microscopic, and scanning microscopic appearance of arterial and venous anastomoses in expanded polytetrafluoroethylene (ePTFE) access grafts constructed with nonpenetrating clips were compared with that of those constructed with polypropylene suture. We hypothesized that clip-constructed anastomoses would provide controlled approximation of native vessel intimal and medial components with the ePTFE grafts. We further hypothesized that anastomotic healing with clips would involve primarily an intimal cellular response, as compared with suture-constructed anastomoses in which cells within the media and adventitia walls participate. METHODS: Femoral artery to femoral vein arteriovenous (AV) grafts were constructed in five dogs using 4-mm internal diameter ePTFE graft material. Each animal received one AV graft with anastomoses constructed by using polypropylene sutures in one leg and one AV graft with anastomoses constructed with Vascular Closure System clips in the contralateral leg. Animals were given aspirin for the duration of the study, and grafts were explanted at 5 weeks. At the time of explantation, graft segments were grossly evaluated and then underwent light and scanning electron microscopic analysis. RESULTS: At the time of explantation, all access grafts were patent. Joining the ePTFE grafts to the native vessels with clips resulted in minimal vessel wall damage. The lumenal contours of the discontinuous approximation were smooth and without gross endothelial disruption. These observations are in contrast to the lumenal compromise and endothelial disturbance associated with the sutured anastomoses. Furthermore, hemostasis was achieved immediately in the clipped grafts, decreasing the incidence of perianastomic hematoma. Finally, cellular reconstitution occurred at the anastomotic cleft in both the sutured and the clipped junctions. The neointima exhibited an endothelial cell lining on the lumenal surface and the presence of alpha-smooth muscle cell actin positive cells within the subendothelial layer. CONCLUSION: Vascular Closure System clips are a viable alternative to suture for the approximation of ePTFE AV access grafts to native blood vessels. The use of the clips resulted in a more streamlined anastomosis, with decreased vessel wall damage, immediate hemostasis, and a trend toward shorter procedure times.     

Blood flow in composite arterial grafts and effect of native coronary flow

BACKGROUND: Total arterial coronary revascularization can be achieved by joining arteries together as a composite graft with the proximal left internal mammary artery as the only source of blood inflow. Proof of the capacity of this composite conduit to provide adequate blood flow to the coronary circulation is required. METHODS: The radial artery was anastomosed to the left internal mammary artery as a Y graft in 17 patients and all coronary arteries grafted. Intraoperative blood flow through the composite grafts was evaluated by the transit-time Doppler technique. RESULTS: Against no resistance, blood flow in the left internal mammary artery alone was 99 +/- 9 mL/min and rose to 173 +/- 16 mL/min when the radial artery was anastomosed as a Y graft. Composite-graft flow following grafting was 88 +/- 9 mL/min, 49 +/- 6 mL/min when the aortic clamp was removed and native coronary flow restored and 82 +/- 13 mL/min following weaning from cardiopulmonary bypass. The maximal potential flow through the composite graft was 2.3-fold (95% CI 1.6 to 3.2) greater than that after cardiopulmonary bypass. CONCLUSIONS: Total arterial revascularization, using a composite graft, provided a 2.3-fold reserve of blood flow to the coronary vascular bed through the grafts.     

Supraceliac aortic pseudoaneurysms after liver transplantation in infants

BACKGROUND: Reconstruction of the hepatic artery in infants undergoing liver transplantation presents challenging vascular situations. Microvascular techniques ensure arterial blood flow via small caliber vessels but are insufficient when inflow is poor. In these situations, the use of allogeneic grafts to the supraceliac aorta have been advocated. The development of a pseudoaneurysm at the supraceliac aortic suture line requires urgent repair and restoration of arterial flow to the graft. METHODS: Our study was based on case reports and review of the literature. RESULTS: Definitive diagnosis and successful repair of supraceliac pseudoaneurysm was accomplished in two infants after transplantation. CONCLUSION: We advocate a thoracoabdominal retroperitoneal approach, which provides safe control of the aorta and primary repair or patching of the diseased aortic segment, and also provides access for hepatic revascularization via placement of an infrarenal graft. Thrombosis of the artery and subsequent liver necrosis are indications for retransplantation.     

Inhibition of experimental neointimal hyperplasia by recombinant human thrombomodulin coated ePTFE stent grafts

OBJECTIVES: The goal of this study was to evaluate the ability of recombinant human thrombomodulin (rTM) to inhibit neointimal hyperplasia when bound to expanded polytetrafluoroethylene (ePTFE) stent grafts placed in a porcine balloon injured carotid artery model. METHODS: The left carotid artery of male pigs, weighing 25 to 30 Kg, was injured with an angioplasty balloon. Two weeks later either a non-coated standard ePTFE stent graft (Viabahn, 6 x 25 mm, W. L. Gore & Associates) or a rTM coated stent graft was implanted into the balloon-injured segment using an endovascular technique. Carotid angiography was performed at the time of the balloon injury, two weeks later and then at 4 weeks to assess the degree of luminal stenosis. One month after stent graft deployment, the grafts were explanted following in situ perfusion fixation for histological analysis. The specimens were then cross-sectioned into proximal, middle and distal segments, and the residual arterial lumen and intimal to media (I/M) ratios were calculated with computerized planimetry. RESULTS: rTM binding onto ePTFE-grafts was confirmed by functional activation of protein C and histopathology with immuno-scanning electron microscopy, backscatter electron emission imaging and x-ray microanalysis. All seven of the rTM coated stent grafts and six of the seven uncoated stent grafts were patent at the time of explantation. The mean luminal diameter of the rTM coated stents was 93% +/- 2.0% of the original diameter, compared with 67% +/- 23% (P = .006) in the control group. Histological analysis demonstrated that the area obliterated by intimal hyperplasia at the proximal portion of the rTM stent was -27% compared with the control group: (2.73 +/- 0.69 mm(2), vs 3.47 +/- 0.67 mm(2), P <.05). CONCLUSIONS: Neointimal hyperplasia is significantly inhibited in ePTFE stent grafts coated with rTM compared with uncoated grafts, as documented by improved luminal diameter by angiography and by computerized planimetry measurements of residual lumen area. These findings suggest that binding of recombinant human thrombomodulin onto ePTFE grafts may improve the long-term patency of covered stents grafts. CLINICAL RELEVANCE: Decrease of neointimal hyperplasia of the magnitude observed in this study could significantly improve blood flow and patency of small caliber prosthetic grafts. If the durability of these results can be confirmed by long-term studies, this technique may prove useful in preventing graft stenosis and arterial thrombosis following angioplasty or vascular bypass procedures.     

Hemodynamic profiles during piggyback liver grafts using arterial or portal revascularization

BACKGROUND: The order of revascularization in human liver grafts is still discussed. This study tries to answer this question in terms of hemodynamic data. STUDY DESIGN: Fifty-nine patients were randomized in this study to compare hemodynamic data just before and 15 minutes after revascularization of liver grafts in relation to first hepatic artery (n = 29) or first portal vein (n = 30) revascularization procedure. RESULTS: Hemodynamic variations were significantly greater in the portal vein group than in the hepatic artery group in terms of mean arterial pressure, cardiac index, central venous pressure, pulmonary capillary pressure, and systemic vascular resistance. The latter decreased from 741.8 +/- 390.3 to 659.9 +/- 411.1 dynes/ cm5 (NS) in the hepatic artery group versus 807.7 +/-336.7 to 439.7 +/- 215 dynes/cm5 (p < 0.05) in the portal vein group. Clinical results and postoperative complications, graft characteristics, patient survival, and graft survival were not significantly different between the groups. CONCLUSIONS: Initial arterial revascularization of the liver graft leads to a more stable hemodynamic profile during revascularization of the liver graft after vascular unclamping. This technique is always feasible and has become our reference procedure.     

Free flow capacity of skeletonized versus pedicled internal thoracic artery grafts in coronary artery bypass grafts.

OBJECTIVE: The internal thoracic artery (ITA) is the ideal conduit for coronary artery bypass grafting (CABG). The skeletonization technique of this arterial conduit has been proposed to reduce chest wall trauma, increase graft length and facilitate construction of sequential anastomoses. Nevertheless, some surgeons decline this technique because of potentially increased trauma to the ITA with impairment of flow. In this investigation we compared the free flow of skeletonized with that of pedicled ITA grafts. METHODS: Two surgeons operated on 80 consecutive patients with coronary artery disease for elective CABG. In group I (n = 40), the left ITA was dissected using the skeletonization technique. In group II (n = 40), it was harvested as a pedicled graft. In 23 patients of group I both ITA's were dissected in skeletonized fashion for complete arterial revascularization. Diluted papaverine was instilled into the lumen of the ITA after distal transection of the vessel in both groups. Free flow of the ITA was registered before and 15 min after intraluminal application of diluted papaverine. Mean arterial pressure was maintained at 70 mmHg. RESULTS: Before the application of papaverine, free flow of skeletonized and pedicled ITA grafts was identical between the two groups. After treatment with papaverine maximum free flow was significantly higher in the skeletonized ITA's (group I 197.2 (+/-66.6) ml/min; group II 147.1 (+/-70.5) ml/min; P < 0.05). There was no significant difference between free flow after dilatation of the left and right ITA in group I (left 197.2 (+/-66.6) ml/min; right 198.9 (+/-61.8) ml/min). CONCLUSIONS: Preparation of the ITA with the skeletonization technique results in significantly, higher free flow capacity than in pedicled grafts. This may increase the safety of arterial revascularization by reducing the risk of ITA hypoperfusion syndrome.     

Effects of intra-aortic balloon pump on coronary artery bypass grafts blood flow: differences by graft type and coronary target

The intra-aortic balloon pump (IABP) is used worldwide as an anti-ischemic strategy. However, little is known about the modifications of the graft blood flow during IABP. A retrospective study aimed at analyzing transit-time flow measurements during 1:1 IABP and during its cessation in 401 consecutive patients receiving IABP before coronary artery bypass grafting (n = 880 graft segments) was reported. All normally functioning grafts were considered. Mean diastolic and mean blood flow improved significantly during 1:1 IABP compared with during IABP cessation (P < 0.001), although mean and end-diastolic arterial pressures were significantly lower (P = 0.001). Arterial and sequential saphenous vein (SV) grafts showed greater improvements in mean diastolic and mean flow compared with single venous grafts. Higher flows were also observed in the grafts directed to the circumflex territory. Surplus graft flow (SGF, defined as mean flow during 1:1 IABP/mean flow with IABP off) was recruited (SGF >1) during 1:1 IABP, with higher values in single arterial or sequential SV grafts versus single venous grafts (both P < 0.001). Y-conduit radial artery (RA) grafts showed higher maximum diastolic flow, mean flow, and SGF compared to aortocoronary RA or SV grafts. In this retrospective analysis, IABP was associated with improved diastolic and mean blood flow in bypass grafts. Arterial, sequential, and Y-conduit grafts were associated with greater improvements in blood flow and SGF than aortocoronary SV grafts.     

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.     

Evaluation of 4-mm to 7-mm versus 6-mm prosthetic brachial-antecubital forearm loop access for hemodialysis: results of a randomized multicenter clinical trial

OBJECTIVE: Prosthetic arteriovenous fistulas for hemodialysis vascular access have a high incidence rate of thrombotic occlusions that result in graft failure. This randomized multicenter study was performed to assess the patency rates and the effect of 4-mm to 7-mm grafts on the development of stenoses. METHODS: A total of 109 patients who needed vascular access for hemodialysis were randomized to receive either 6-mm (n = 57) or 4-mm to 7-mm prosthetic brachial-antecubital forearm loop accesses (polytetrafluoroethylene). Duplex scanning, with measurement of blood flow and peak systolic velocity and detection of stenoses (>50%), was performed at 1, 6, and 12 months after surgery. Clinical data were obtained in a prospective manner and primary, assisted primary, and secondary patency rates were calculated with the Kaplan-Meier life-table analysis. Statistical analysis was performed with the independent samples t test and chi(2) test. RESULTS: At 1 year, patency rates were similar for both 4-mm to 7-mm and 6-mm prostheses (primary, 46% versus 43%; assisted primary, 62% versus 58%; secondary, 87% versus 91%). The incidence rate of thrombotic occlusion was comparable for both groups (0.74/patient-year versus 0.88/patient-year; P >.05). Mean graft flow at 1, 6, and 12 months was 1416 versus 1415 mL/min, 1345 versus 1319 mL/min, and 1595 versus 1265 mL/min (P >.05) for 4-mm to 7-mm and 6-mm grafts, respectively. Also, no differences in peak systolic velocities in any part of the grafts were observed. The percentage of stenoses detected was equal in both groups at 1 year after surgery (27% versus 20%; P >.05). CONCLUSION: A 4-mm to 7-mm tapered prosthetic brachial-antecubital forearm loop access did not reduce the incidence rates of stenoses and thrombotic occlusions compared with a 6-mm prosthetic conduit. Moreover, no differences in patency rates were observed. Therefore, we believe that the 4-mm to 7-mm graft should not be used routinely for hemodialysis vascular access.     

An anatomic study of vascularized fibular grafts

Objective： To study the applied anatomy of the vascular and muscular innervations related to vascularized fibular grafts. Methods： Thirty-four cadaveric lower extremities were dissected for this study. The observations included fibular length, fibular nutrient artery, arcuate arteries, and innervation of fibular muscles. The fibulas were averagely divided into four segments and the locations of relevant vessels and nerves were ascertained. Results： All specimens had 1 fibular nutrient artery and 4-9 arcuate arteries except 1 specimen which had only 1 arcuate artery. The fibular nutrient artery and the first threearcuate arteries were constantly located between the distal half of the 1/4 segment and 2/4 segment of the fibula. The muscular branch of the superficial peroneal nerve passed through the surface of the periosteum in the 2/4 segment of the fibula.
Conclusions： The most proximal osteotomy point locates at the midpoint of the 1/4 segment by which it ensure the maximal potential for preserving the nutrient vessels. The muscular branch of the superficial peroneal nerve is fragile to injury at the 2/4 segment of the fibula.     

Management of infected prosthetic dialysis arteriovenous grafts

BACKGROUND: Hemodialysis access is one of the most common vascular procedures that is performed by vascular and general surgeons. Prosthetic arteriovenous graft (AVG) infections pose potentially life-threatening septic and bleeding complications, as well as loss of dialysis access. Strategies employed to preserve some grafts, prevent morbidity in those with major infections, and maintain access are presented. METHODS: Between July 1, 1995 and August 1, 2002, 1441 AVG procedures were performed at a single institution. Fifty-one (3.5%) prosthetic AVG infections in 45 patients were identified. Twenty-seven graft infections occurred at a prior incision for placement or revision of a graft. The other 24 infections were located within the body of the graft, and 14 of these were documented to be at a recent puncture site for hemodialysis access. The most common presentation (47% [24/51]) was an exposed graft or a draining sinus tract. Management included total graft excision (TGE) when patients presented with sepsis or the entire graft was bathed in pus; subtotal graft excision (SGE), when all of the graft was removed except an oversewn small cuff of prosthetic material on an underlying patent artery; and partial graft excision (PGE), when only a limited infected portion of the graft was removed and a new graft was rerouted through adjacent sterile tissue to maintain patency of the original graft. RESULTS: None of the 45 patients died or developed hand ischemia. A uniformly successful outcome was achieved in all patients who were treated with TGE (13/13: 8 vein patches, 4 primary closure, 1 arterial ligation) or SGE (15/15). However, these treatments necessitated placement of a central venous catheter for temporary dialysis access and a new AVG later. All of these 28 wounds healed by secondary intention, including all 15 cases in which an oversewn cuff of prosthetic material remained. Graft patency and wound healing were achieved in 74% (17/23) of infections treated with PGE, and placement of a temporary dialysis access catheter and new AVG were avoided. The 6 failures of PGE ultimately required TGE because of nonhealing wounds, but there were no acute hemorrhagic or septic events. CONCLUSIONS: Systemic sepsis caused by prosthetic AVG infections mandates TGE. SGE and PGE can be safely employed in selected patients with infected prosthetic AVGs. SGE maintains patency of the underlying artery and avoids a difficult and time-consuming dissection. PGE offers the advantage of minimizing extensive dissection of well-incorporated uninfected graft segments and allows continued dialysis access at the incorporated portion of the graft.     

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.