Adjuncts to improve patency of infrainguinal prosthetic bypass grafts

The superiority of autologous venous conduit for infrainguinal arterial bypass has been well documented, especially when the bypass extends below the knee or to the tibial arteries. Nevertheless, when adequate autologous vein is not available, prosthetic bypasses (eg, polytetrafluoroethylene [PTFE] or Dacron) are often used in limb-salvage situations. The inferior long-term patency of these infrainguinal prosthetic bypasses has been documented by a number of studies. One such study reported a prospective multicenter randomized trial with only a 12% primary patency for infrapopliteal prosthetic bypasses after 4 years. Another study reported a similar experience with infragenicular bypasses with PTFE for limb salvage even for above-knee (27%, 5 year) and below-knee (25%, 5 year) femoral-popliteal bypasses. The reported PTFE graft patency was consistently inferior to that achieved with autologous vein for limb salvage. Dacron grafts appear to have similar patency rates to PTFE. In an attempt to improve prosthetic graft patency, a number of surgical and medical adjuncts have been developed. In this review, the authors discuss these adjuncts and their impact on infrainguinal prosthetic graft patency.     

Vein graft adaptation and fistula maturation in the arterial environment

Veins are exposed to the arterial environment during two common surgical procedures, creation of vein grafts and arteriovenous fistulae (AVF). In both cases, veins adapt to the arterial environment that is characterized by different hemodynamic conditions and increased oxygen tension compared with the venous environment. Successful venous adaptation to the arterial environment is critical for long-term success of the vein graft or AVF and, in both cases, is generally characterized by venous dilation and wall thickening. However, AVF are exposed to a high flow, high shear stress, low-pressure arterial environment and adapt mainly via outward dilation with less intimal thickening. Vein grafts are exposed to a moderate flow, moderate shear stress, high-pressure arterial environment and adapt mainly via increased wall thickening with less outward dilation. We review the data that describe these differences, as well as the underlying molecular mechanisms that mediate these processes. Despite extensive research, there are few differences in the molecular pathways that regulate cell proliferation and migration or matrix synthesis, secretion, or degradation currently identified between vein graft adaptation and AVF maturation that account for the different types of venous adaptation to arterial environments.     

Access to occluded infrainguinal bypass grafts with a loopsnare

Thrombolysis for the treatment of occluded bypass grafts is used in selected clinical circumstances. Unfortunately, a minority of these procedures are technical failures because of the inability to access the occluded graft. We describe a technique that greatly increases the chances of technical success.     

Angioscopy of arm vein infrainguinal bypass grafts

Between January 1988 and December 1990, 56 patients underwent 66 arm vein infrainguinal bypass grafts for limb salvage. Thirty-nine grafts were intraoperatively monitored by the standard methods of continuous wave Doppler alone (30) and arteriography (9). Twenty-seven grafts were prepared and monitored by intraoperative angioscopy. No significant findings requiring intraoperative revision or correction were noted in the grafts monitored by the standard methods. However, in those grafts prepared and monitored by angioscopy, intraluminal abnormalities of the arm veins were detected and corrected in 20/27 (74%). None of the grafts prepared or monitored by angioscopy occluded within 30 days, whereas, in those grafts monitored by continuous wave Doppler and arteriography, 7/39 failed within 30 days, a primary patency rate of 32/39 (82%) (x² with Yates correction, p=0.055). This study shows that angioscopic preparation and monitoring of arm vein bypass grafts allows the detection and correction of unsuspected intraluminal abnormalities, which appears to improve the early primary patency of arm vein infrainguinal bypass grafts.Presented at the Fifteenth Annual Meeting of the Peripheral Vascular Surgery Society, June 2, 1990, Los Angeles, California.     

Effectiveness of surveillance of infrainguinal grafts.

OBJECTIVE: To audit the surveillance programme of infrainguinal vein graft in a tertiary vascular unit, and find out how effective it was in preventing occlusion of grafts. DESIGN: Retrospective study. SETTING: Teaching hospital, Scotland. SUBJECTS: 59 consecutive patients who had 61 vein grafts between 1996 and 1998 for critical limb ischaemia. INTERVENTIONS: Grafts scanned at 3-monthly intervals for at least a year, and clinical review. MAIN OUTCOME MEASURES: Survival with an intact limb and patency of the graft. RESULTS: 52 of the 59 patients (90%) were alive at the time of follow up, and 55 of the 61 involved limbs (90%) were intact. Median follow up was 660 days (range 180-1995). 23 stenoses were detected by the surveillance programme. 17 grafts were revised, all of which were patent at follow up, and 8 other grafts occluded requiring 6 major amputations. One-year cumulative primary, primary-assisted, and secondary patency, and limb salvage rates were 63%, 88%, 88%, and 90% respectively. CONCLUSIONS: Surveillance of infrainguinal grafts by duplex scanning is effective and has resulted in high rates of limb salvage and secondary patency in patients who presented with critical ischaemia.     

Incomplete biochemical adaptation of vein grafts to the arterial environment in terms of prostacyclin production

Biochemical (or functional) adaptation of venoarterial grafts has been demonstrated recently. We reexamined one aspect of this biochemical "arterialization" process: prostacyclin (PGI2) production by canine venoarterial autologous grafts and the responsiveness of this biosynthetic pathway to maximal stimulation with substrate enhancement. Four reversed autologous grafts (femoral vein) were interposed into both carotid and femoral arteries in eight dogs. After 12 weeks, the grafts were removed, and radioimmunoassay was used to determine luminal surface production of 6-keto-PGF1 alpha (the stable metabolite of PGI2) in both the basal and stimulated (27 mumol/L arachidonic acid [AA]) states. PGI2 production by the venous autologous grafts was compared with that of control native artery and vein. We confirmed that PGI2 production (measured in nanograms per milliliter) by control artery was greater than vein under both basal conditions (5.8 +/- 0.4 [+/- SEM] vs. 2.7 +/- 0.5, p less than 0.001) and stimulated conditions (8.8 +/- 0.8 vs. 5.5 +/- 0.4, p = 0.002); moreover, AA stimulation significantly increased PGI2 production in both native artery and vein compared with basal PGI2 production. Under basal conditions, graft PGI2 production (6.3 +/- 1.6 ng/ml) was not significantly different than basal arterial levels (p = 0.8) but was higher than basal venous levels (p = 0.05). However, in marked contrast to both native artery and vein, the vein graft flow surface showed no significant response to substrate enhancement with AA: basal (6.3 +/- 1.6 ng/ml) vs. stimulated (5.9 +/- 0.9 ng/ml) (p = 0.8). These observations confirm that canine venoarterial autologous grafts undergo biochemical "arterialization"; however, this process appears to be an incomplete one.(ABSTRACT TRUNCATED AT 250 WORDS)     

Clinical results of common strategies used to revise infrainguinal vein grafts

Purpose: Patients who have failing infrainguinal bypass grafts or failed grafts reopened with lytic therapy represent a group at high risk of subsequent failure. Previous studies suggest that vein patch angioplasty and jump grafting may be less durable than interposition grafting as a method of correcting graft lesions. Our objective was to assess the value of various technical strategies for graft revision in a series of autogenous infrainguinal bypass grafts and to assess how these variables might affect cumulative graft patency (CGP) rates.Methods: We retrospectively reviewed the clinical course, anatomic sites of revision, and type of revision performed on 67 grafts in 58 patients who underwent at least one revision from 1991 to 1995. Results were assessed with regression analysis and Kaplan-Meier estimates of CGP rates ( p < 0.05 was considered significant).Results: Sixty-seven vein grafts underwent revision of 112 anatomical sites in 95 operations. Forty-nine of 67 grafts were single-segment greater saphenous vein grafts and 18 were composite (>1 segment) grafts, with an overall 5-year CGP rate of 72%. No difference was observed between the 4-year CGP rate in grafts with hemodynamically significant distal anastomotic stenoses repaired primarily with jump grafts (n = 20, 71% CGP rate) and those with stenoses found only in the graft body (n = 41, 89% CGP rate). Vein patch angioplasty was used primarily, but not exclusively, for focal graft body stenoses (n = 35), whereas interposition grafts (n = 11) were reserved for more diffuse strictures; no significant difference in 3-year CGP rates was observed (94% and 73%, respectively).Conclusion: Using an appropriate revision strategy that favors vein patch angioplasty for graft body lesions and jump grafts for distal anastomotic lesions, acceptable assisted patency rates can be achieved in grafts that are at risk for repeated failure. (J Vasc Surg 1996;24;909-19.)     

Surgical treatment of threatened reversed infrainguinal vein grafts

Purpose: Current information concerning the results of surgical revision of threatened infrainguinal vein grafts is largely limited to in situ conduits. Infrainguinal grafts may be threatened by intrinsic graft lesions or significant stenosis in the adjacent inflow or outflow arteries. To assess the results of operative revision of infrainguinal reversed vein grafts, we reviewed our experience with surgical revision of threatened infrainguinal reversed vein grafts identified through a program of postoperative clinical and vascular laboratory graft surveillance. Methods: All patients who underwent surgical revision of a threatened but patent infrainguinal reversed vein graft from January 1987 through April 1993 were identified through review of our vascular registry. Data were analyzed for type of vein used, date of original reversed vein graft, clinical and vascular laboratory findings leading to reversed vein graft revision, results of preoperative angiography, patient risk factors, operative techniques and complications, and long-term assisted primary graft patency and limb salvage. Results: Ninety-six patients with 100 infrainguinal reversed vein grafts (69) femoral-popliteal, 31 femoral-tibial) underwent 117 surgical vein graft revisions or inflow procedures during the study period. Eighty-one percent of the original reversed vein grafts consisted of a single segment of greater saphenous vein. All revised grafts had at least a 50% stenosis in the graft itself or the proximal or distal artery. A single revision was performed in 85 grafts, two revisions in 13 grafts, and three revisions in two grafts. There were nine (8%) isolated inflow procedures, eight (7%) vein patch angioplasties, 62 (53%) interposition vein grafts, and 29 (25%) vein graft extensions to a new distal anastomotic site. The remaining nine (8%) procedures consisted of combinations of the above. Median time to primary graft revision after initial graft implantation was 15 months (range 2 days to 316 months). Mean time to secondary revision after primary revision was 21 months. Operative mortality was 0.9%. Cumulative assisted primary patency of the original grafts revised for stenotic lesions was 99%, 96%, and 92% at 1, 3, and 5 years, respectively. Limb salvage was 99%, 97%, and 97% at 1, 3, and 5 years, respectively. Conclusions: Although surgical revision of reversed vein graft requires much use of alternative vein sources, these procedures can be performed with minimum mortality and provide excellent assisted primary graft patency and limb salvage. (J VASC SURG 1994;20:558-65.)     

静脉指纹分子EphB4在移植静脉适应动脉血流环境中的调控机制

目的:探讨EphB4在移植静脉适应动脉血流过程中的调控作用及机制。方法:静脉移植重建动脉模型采用将供体大鼠上腔静脉端端吻合移植到受体大鼠腹主动脉的方式构建,实验分为单纯模型组(供体、受体均为野生型大鼠)、EphB4增强组(供体、受体均为野生型大鼠,移植静脉外膜以EphB4的配体ephrinB2持续刺激)、EphB4减弱组(供体EphB4+/-型转基因大鼠,受体为野生型大鼠),各组分别在建模后1、4周取移植静脉行组织病理学检测;分离并培养野生型及EphB4+/-型大鼠静脉内皮细胞,比较两种细胞在相同浓度ephrinB2刺激下,EphB4膜受体(EphBR)及下游传导通路ERK1/2的磷酸化程度及细胞迁移能力。结果:与大鼠正常上腔静脉比较,各实验组移植静脉的内膜+中膜厚度、平滑肌肌动蛋白、胶原纤维含量均明显并逐渐增加(均P0.05);建模后1周,以上指标的增加程度在各实验组间差异无统计学意义(均P0.05),但建模后4周,EphB4增强组以上指标的增加程度均明显低于另两组(均P0.05)。相同浓度ephrinB2刺激下,EphB4+/-型大鼠静脉内皮细胞的EphBR与ERK1/2磷酸化程度、EphB4 mRNA转录活性、迁移能力均明显低于野生型大鼠内皮细胞(均P0.05)。结论:静脉分子指纹EphB4的表达量可能对移植静脉重塑的走向起关键作用,机制可能与其通过ERK1/2途径影响内皮细胞功能有关。     

Intraoperative color duplex scanning for infrainguinal vein grafts

We compared the findings of intraoperative color duplex scanning and completion arteriography in patients undergoing infrainguinal vein bypasses to identify hemodynamic abnormalities that could result in a predisposition to early or late graft failure. We reviewed the records of 72 patients who underwent 81 vein bypass graft procedures. Three intraoperative diagnostic methods were used. In 28 procedures (group I) both color duplex and completion arteriography were used, in 21 procedures (group II) only color duplex was used, and in 26 procedures (group III) only completion arteriography was used. Grafts were followed using a duplex surveillance protocol for a mean interval of 16.1 months. Nine grafts in group I showed an abnormality on the duplex scan but not on the completion arteriogram. Seven grafts had a peak systolic velocity (PSV) greater than 200 cm/sec and two had a PSV less than 45 cm/sec. These findings led to six immediate repairs, one early revision, and two late revisions. Arteriography demonstrated additional defects in two procedures but repairs were not performed. In group II duplex scans showed an abnormality in eight procedures (seven grafts with PSV 200 to 250 cm/sec and one graft with a retained valve) resulting in three immediate repairs and five late revisions. In the remaining 13 procedures in group II, duplex scans were normal and no revisions were required during follow-up. In group II defects were detected by arteriography in four procedures (>50% stenosis in three grafts and one arterial spasm) leading to three immediate repairs. In the remaining 22 studies arteriograms were interpreted as normal; however, seven of these grafts required late revisions. Our data suggest that grafts that appear normal on intraoperative duplex scans are not likely to develop a stenosis requiring revision. Intraoperative duplex ultrasound may be superior to completion arteriography.Presented at the Fourteenth Annual Meeting of the Southern California Vascular Surgical Society, September 15–17, 1995, La Jolla, Calif.     

Risk factors for occlusion of infrainguinal bypass grafts.

OBJECTIVES: to identify risk factors for infrainguinal bypass occlusion and quantify the predictive value of data available before and after surgery. Design: prospective study of 2650 patients who participated in a randomised trial of oral anticoagulants or aspirin after infrainguinal bypass surgery. MATERIALS AND METHODS: risk factors were determined by univariate Cox regression analysis, and entered in multivariate analyses which distinguished two models: analysis of factors available from history and clinical examination, completed by radiological and surgical data in the second model. To compare the information content of the two models, receiver-operator characteristic (ROC) curves were computed. RESULTS: in all patients female gender, critical ischaemia, femorocrural bypass grafting and non-venous graft material were independent risk factors. In patients with femoropopliteal bypasses female gender, critical ischaemia, poor run-off and non-venous graft material, the latter even in patients with supragenicular bypasses, were independent risk factors. The only significant risk factor in patients with femorocrural bypass grafts was use of a non-venous graft. The information contained in the first model was poor, whereas the second model had a higher predictive value. CONCLUSIONS: the major risk factor, even in above-knee bypasses, is non-venous graft material. The venous bypass graft should be offered to patients whenever possible.     

Outflow resistance and early occlusion of infrainguinal bypass grafts

Distal outflow vascular resistance (VR) has been measured intra-operatively during 67 infrainguinal bypass procedures to establish whether it might have a role as a predictive test for early graft thrombosis. The graft outflow was popliteal artery above the knee (48), popliteal artery distal to the knee (6) or a single calf vessel (13). VR was measured before anastomosis of the graft, calculated from the relationship between pressure and flow in the outflow artery during infusion of the patient's own blood at a constant rate. VR was measured before and after vasodilation with papaverine. Primary graft patency at 30 days was documented. In the 10 limbs in which graft thrombosis occurred, VR was 1167 +/- 367 mPRU, significantly higher than VR in 57 limbs with a patent graft, 850 +/- 310 mPRU (P = 0.02, Mann-Whitney U test). After papaverine, VR was 823 +/- 368 mPRU in the limbs with a thrombosed graft, significantly higher than that of limbs with a patent graft, 463 +/- 211 mPRU (P = 0.001). VR appeared to show most promise as a predictor of early thrombosis in the group of femoro-tibial and femoro-peroneal grafts. In this group, the value of 800 mPRU after papaverine was 92% efficient and was 80% sensitive, 100% specific and had a predictive value of 100% for early thrombosis. Distal outflow VR is an important factor in early graft thrombosis and might have a practical application as a predictor of early thrombosis of femoro-distal bypass grafts.     

Intraoperative flow predicts the development of stenosis in infrainguinal vein grafts

OBJECTIVE: There are data to suggest that the development of myointimal hyperplasia is affected by long-term alterations in blood flow. However, the clinical relevance of these findings has not been demonstrated. METHODS: In this retrospective clinical study, intraoperative volume flow measurement with transit time flowmeter was performed in 257 infrainguinal vein grafts carried out in 241 patients. The patients were enrolled in an intensive duplex scanning-based surveillance program. The relationship between the intraoperative graft flow and subsequent occlusion or development of stenosis was evaluated and controlled for other pertinent risk factors. RESULTS: The median follow-up time was 13.6 months. A graft stenosis was found in 58 grafts. The mean graft flow for event-free grafts was 98 mL/min, which was significantly higher compared with 78 mL/min for stenosed or 69 mL/min for occluded grafts. The patients were divided into four groups according to quartiles of the sample distribution of graft flow measurements. The respective 2-year primary and assisted primary patency rates in the lowest to the highest graft flow groups were 39%, 49%, 47%, and 72% (P =.003) and 55%, 67%, 71%, and 84% (P =.01). Analogous significant differences were observed for maximal flow capacity measurements. Female sex (P =.009) and low graft flow in maximal flow capacity measurements (P =.003) were independent predictors of stenosis development in the multiple regression model. CONCLUSION: Intraoperative graft volume flow is a predictor of bypass occlusion after infrainguinal bypass. In addition, this study verifies an association between the development of clinically evident graft stenoses and low graft flow.     

Hemodynamics of stenotic infrainguinal vein grafts: Theoretic considerations

We developed a theoretic model of arterial stenosis to study the relationship between perfusion pressure and regional hemodynamics in stenotic infrainguinal vein grafts in an attempt to identify grafts at high risk for failure. Our model was based on the concept of energy and mass conservation of the flowing blood. We used the modified Bernoulli equation (P=4V²) to calculate the maximum possible intrastenotic peak systolic velocity (PSV) from the systolic blood pressure. PSV was measured by means of duplex ultrasonography in infrainguinal bypasses up to the time of revision (nine grafts) or spontaneous thrombosis (two grafts). We related arm systolic blood pressure, intrastenotic PSV, and prestenotic PSV obtained from duplex examinations conducted prior to graft thrombosis or revision and applied our model to these stenotic vein grafts. Intrastenotic PSV was consistently lower than maximum PSV predicted from the Bernoulli equation. The highest measured intrastenotic PSV of 600 cm/sec would require a minimum perfusion pressure of 144 mm Hg. The lowest measured PSV (20 cm/sec) was considered the minimum thrombotic threshold velocity. This model predicts that for parabolic profile flow in an 80% diameter-reducing axisymmetric stenosis (96% cross-sectional area reduction), a prestenotic PSV of 20 cm/sec would produce an intrastenotic PSV of 500 cm/sec requiring the equivalent potential energy of 100 mm Hg systolic blood pressure. Our theory implies that in patients with nocturnal hypotension thrombosis of stenotic vein grafts may occur.Supported by grant HL 42270 from the National Institutes of Health, Bethesda, Md.     

Distal percutaneous transluminal angioplasty through infrainguinal bypass grafts.

AIM: to evaluate the results of transluminal angioplasty (PTA) performed through infrainguinal bypass grafts for stenotic or occlusive lesions at the distal anastomosis and/or in the runoff arteries. Design: retrospective clinical study. MATERIAL AND METHODS: forty-one patients underwent 57 procedures at the distal anastomosis (n=13), in the runoff arteries (n=32) or at both locations (n=12) at a median of 9.6 months (range, 2-76 months) after infrainguinal bypass grafting. Nineteen procedures were on the popliteal artery, the rest on the crural arteries. Eleven procedures related to occlusions less than 5 cm in length. RESULTS: technical success was achieved in 91%. Primary and primary assisted graft patency rates at 3 years were 32% and 53%, respectively. There were no significant differences in patency rates with regard to the graft material, the type of lesion, the level of PTA, the status of runoff and the use of thrombolysis before PTA. No patients underwent amputation as a direct consequence of failed PTA or graft occlusion. One patient underwent acute surgical intervention due to graft occlusion at the time of attempted PTA. CONCLUSION: the results of PTA at the distal anastomosis and/or in the runoff arteries in limbs with infrainguinal bypass seemed to be inferior to the results of surgical revisions reported in literature. However, as failed PTA did not jeopardise vein-patch angioplasty or jump grafting, it is a reasonable alternative to surgical intervention in selected cases.     

Mortality and limb loss with infected infrainguinal bypass grafts

A recent experience with infrainguinal graft infections was reviewed in an effort to identify factors related to limb loss and mortality. The records of 32 patients who had operative treatment of 33 episodes of infrainguinal graft infection between 1978 and 1985 were reviewed to evaluate the effects of 20 factors possibly affecting outcome. The amputation rate was 79%. Of the 20 factors studied, only the presence of overt limb sepsis was associated with the need for amputation, with 100% of patients having limb sepsis requiring amputation vs. 72% of patients without limb sepsis (p = 0.03). The in-hospital mortality rate was 22%. Eighty-six percent of the deaths were due to ongoing sepsis. Again, a single factor was associated with death. Five of the 12 patients (42%) in whom preservation of axial flow was attempted died in contrast to only 2 of 20 patients (10%) who did not have attempted arterial reconstruction (p = 0.04). Limb salvage did not occur in any of the patients in whom preservation of axial flow was attempted and nine required above-knee amputation. Thirteen of the remaining 20 patients had occluded femoral vessels either because of operative ligation (nine) or previous thrombosis (four). Above-knee amputations healed in all but one of these 13 patients. Determined attempts at increasing limb preservation were associated with no improvement in amputation rate or level and were accompanied by an unacceptably high mortality rate. Aggressive control of sepsis through the early amputation of septic limbs after graft removal may improve survival without further detriment to limb preservation.     

Experience with heparin-bonded collagen-coated grafts for infrainguinal bypass.

The perfect conduit for infrainguinal reconstructive surgery does not exist. When autologous vein is not available, then a prosthetic graft must be used. The use of a heparin-bonded graft has the theoretical advantage of reducing smooth muscle cell proliferation and thrombus formation, thereby reducing occlusion rates. The application of a collagen layer to the external surface of the graft serves to reduce transfabric haemorrhage. Forty-six patients underwent 47 infrainguinal reconstructions using heparin-bonded collagen-coated Dacron grafts over a 4-year period. Twenty grafts were for disabling claudication and 27 for critical ischaemia. Twenty-two grafts were to the above knee popliteal artery (47%), 10 to the below knee popliteal (21%) and 15 to one of the crural vessels (32%). There was a cumulative patency at 4 years of 69% for the above knee grafts, and 30-month patency of 58% and 45% for the below knee and crural grafts, respectively. There were three deaths over the study period and eight patients required major amputations.