Pharmacologic intervention to prevent graft failure

Comparison of Patients With and Without Anterior Sector Venous Drainage in Right Lobe Liver Transplantation From Live Donors in Terms of Complications, Rejections, and Graft Survival: Single-Center Experience

AIM

The issue of performing an anastomosis of the anterior sector veins to the vena cava in living donor liver transplantation is still controversial. We aimed to research whether there was any difference in terms of complications, rejections, and graft survival between patients with and without anterior sector venous drainage to the vena cava.

PATIENTS AND METHODS

Patients were retrospectively investigated for demographic data and ratio of graft needed to available graft weight. Donors had volumetric calculations and middle hepatic vein anterior sector drainage documented in detail.

RESULTS

Seventy-three donors with middle hepatic vein drainage were included. Thirty-five had anterior sector venous drainage performed and 38 patients did not have drainage procedures performed. The incidence of general complications was higher in the group without anterior sector drainage (78.3% and P = .002). Biloma linked to bile leaks were observed in 8 patients without drainage (72.8%) and 3 patients with drainage (27.2%). Late acute rejection occurring during follow up after transplantation was identified in 28 patients (11.6%). Of these, 1 (14.3%) had anterior sector drainage and 6 (85.7%) were in the patient group without drainage (P = .067).

CONCLUSION

As a result of this study, for patients with grafts at the volume limit (graft weight to receiver weight ratio <0.8) and with congestion observed in the anterior sector after liver implantation and for patients with outflow problems identified on Doppler ultrasonography, anterior sector veins >5 mm should definitely be drained into the vena cava. Hence, both complication and rejection rates will reduce, and we can lengthen the graft, and thus patient, survival.

Preoperative evaluation of the vascular surgery patient

Patients undergoing vascular surgery present a myriad of perioperative challenges due to the complex comorbidities affecting them in conjunction with high-risk surgical procedures. Additionally, advances in endovascular technology have enabled surgical procedures to be performed on patients who would not have been considered surgical candidates in the past. This combination of increasing patient morbidity and evolving surgical technique requires a well-planned preoperative assessment and close communication with surgical and perioperative colleagues. This article outlines an appropriate approach by first considering each organ system, followed by review of considerations unique to various surgical procedures, and then an overall assessment of risk.

Circulating inflammatory cells are associated with vein graft stenosis

OBJECTIVE

Infrainguinal autogenous vein grafts are especially prone to narrowing and failure, and both inflammatory and thrombotic pathways are implicated. Platelets and monocytes are the key thrombo-inflammatory cells that arrive first at sites of vascular injury. These cells have potent interactions that recruit and activate one another, propagating thrombotic and inflammatory responses within the vessel wall. We therefore hypothesized that elevated levels of platelet-monocyte aggregates (PMA) might be associated with stenosis, and could possibly discriminate between patients with or without vein graft stenosis.

METHODS

Thirty-six vascular surgery patients were studied, in a stable quiescent period after infrainguinal autogenous vein graft bypasses for occlusive disease. Eighteen patients had hemodynamically significant graft stenoses confirmed by imaging, and 18 were free from stenosis. The level of PMA in whole blood was quantified after blood draw using two-color flow cytometry. Three measurements were made per sample: the basal, in-vivo level of aggregates (baseline PMA); the predisposition to spontaneously generate PMA (spontaneous PMA); and PMA generation by the addition of exogenous thrombin receptor-activating peptide (stimulated PMA). The baseline, in-vivo level of PMA was estimated by immediate flow analysis. The predisposition to spontaneously generate PMA was measured after in vitro incubation. Responsiveness to thrombin stimulation of the blood was quantified by the in vitro dose response to an exogenous thrombin receptor-activating peptide (sfllrn).

RESULTS

Baseline PMA levels were similar in patients with vein graft stenosis vs nonstenosis (14.8% ± 3.2 vs 10.1% ± 1.5, respectively, mean ± SEM). However, patients with stenosis showed higher spontaneous PMA levels (58.5% ± 4.5 vs 28.3% ± 4.3; P < .001) and higher stimulated PMA levels (P < .001; analysis of variance). Covariables of smoking, diabetes, statin, or antithrombotic therapy could not account for these differences.

CONCLUSIONS

Platelet-monocyte reactivity may play a role in the development of vein graft stenoses. Those with/without stenosis differed primarily in their threshold, or predisposition to form aggregates (spontaneous PMA), while their basal circulating levels of PMA (baseline PMA) were similar. These measurements may unmask pathologic differences in thrombo-inflammatory responsiveness that are not apparent in basal measurements. Understanding the causes and mechanisms leading to abnormal platelet-monocyte responses may improve approaches to predicting or preventing vein graft stenosis.

Antithrombotic agents for preventing thrombosis after infrainguinal arterial bypass surgery

BACKGROUND

Peripheral arterial disease (PAD) is frequently treated by either an infrainguinal autologous (using the patient's own veins) or synthetic graft bypass. The rate of occlusion of the graft after one year is between 12% and 60%. To prevent occlusion, patients are treated with an antiplatelet or antithrombotic drug, or a combination of both. Little is known about which drug is optimal to prevent infrainguinal graft occlusion. This is an update of a Cochrane review first published in 2003.

OBJECTIVES

To evaluate whether antithrombotic treatment improves graft patency, limb salvage and survival in patients with chronic PAD undergoing infrainguinal bypass surgery.

SEARCH STRATEGY

The Cochrane Peripheral Vascular Diseases Group searched their Specialised Register (last searched August 2010) and the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2010, Issue 3).

SELECTION CRITERIA

Randomised, controlled trials; two review authors independently assessed the methodological quality of each trial using a standardised checklist.

DATA COLLECTION AND ANALYSIS

Data collected included patient details, inclusion and exclusion criteria, type of graft, antithrombotic therapy, outcomes, and side effects.

MAIN RESULTS

A total of 14 trials were included in this review; 4970 patient results were analysed. Four trials evaluating vitamin K antagonists (VKA) versus no VKA suggested that oral anticoagulation may favour autologous venous, but not artificial, graft patency as well as limb salvage and survival. Two other studies comparing VKA with aspirin (ASA) or aspirin and dipyridamole provided evidence to support a positive effect of VKA on the patency of venous but not artificial grafts. Three trials comparing low molecular weight heparin (LMWH) to unfractionated heparin (UFH) failed to demonstrate a significant difference on patency. One trial comparing LMWH with placebo found no significant improvement in graft patency over the first postoperative year in a population receiving aspirin. One trial showed an advantage for LMWH versus aspirin and dipyridamol at one year for patients undergoing limb salvage procedures. Perioperative administration of ancrod showed no greater benefit when compared to unfractionated heparin. Dextran 70 showed similar graft patency rates to LMWH but a significantly higher proportion of patients developed heart failure with dextran.

AUTHORS' CONCLUSIONS

Patients undergoing infrainguinal venous graft are more likely to benefit from treatment with VKA than platelet inhibitors. Patients receiving an artificial graft benefit from platelet inhibitors (aspirin). However, the evidence is not conclusive. Randomised controlled trials with larger patient numbers are needed in the future to compare antithrombotic therapies with either placebo or antiplatelet therapies.

Comparison between allogenic and autologous vascular conduits in the drainage of anterior sector in right living donor liver transplantation

Congestion of the anterior sector may lead to graft failure in right lobe grafts. Selective drainage of the prominent segment 5 and/or 8 veins is proposed to overcome this problem. Different vascular conduits may be used during drainage of the anterior sector. In this study, we evaluated the efficiency of the vascular conduits. Between June 1999 and December 2005, 190 patients underwent living donor right lobe liver transplantation and reconstruction of segment 5 and/or 8 veins was performed in 48 patients (25.2%). Two groups were formed according to the types of vascular conduits. Cryopreserved cadaveric iliac artery (n = 28) and cryopreserved cadaveric iliac vein (n = 8) were used in group A. In group B, recipient saphenous vein (n = 6), recipient umbilical vein (n = 5) and recipient collateral omental vein (n = 1) were used for reconstruction. The graft-recipient weight ratio, mean duration of anhepatic phase and MELD scores between two groups were not significantly different. All of the conduits were found to be patent just after reperfusion and in the early postoperative period by Doppler ultrasonography. In follow-up period of 1 year, four (11%) patients died in group A, two patients (16%) in group B. One of these patients died because of sepsis started from the saphenous vein incision site. None of the patients dying in the two groups were lost due to venous outflow problems. This study proves the efficacy of drainage of segment 5 and/or 8 veins using cryopreserved cadaveric vascular conduits. Every effort should be employed to store cadaveric iliac vessels, otherwise, whole other additive surgical intervention to ensure vascular conduit may lead uninvited serious complication.

Antithrombotic agents for preventing thrombosis after infrainguinal arterial bypass surgery

BACKGROUND

Chronic peripheral arterial disease (PAD) is frequently treated by implantation of either an infrainguinal autologous venous or artificial graft. One-year occlusion rates for infrainguinal bypasses vary between 15 and 75%, depending on the site of distal anastomosis, length, quality, and material of the graft, but also on other factors such as proximal inflow and distal outflow conditions. To prevent graft occlusion, patients are usually treated with either an antiplatelet or antithrombotic drug, or a combination of both. Little is known about which drug is optimal to prevent infrainguinal graft occlusion.

OBJECTIVES

To evaluate whether antithrombotic treatment in patients with chronic PAD undergoing infrainguinal bypass surgery improves graft patency, limb salvage and survival by performing a meta-analysis of performed RCTs.

SEARCH STRATEGY

The search strategy was that adopted by the Cochrane Review Group on Peripheral Vascular Diseases. Additional data bases were reviewed (Reference lists of papers resulting from this search, MEDLINE from 1966-onwards and EMBASE from 1980-onwards using the terms 'anticoagulant' and 'arterial surgery'.

SELECTION CRITERIA

The methodological quality of each trial was assessed independently by at least two reviewers using the checklist provided by the Peripheral Vascular Diseases Collaborative Review Group, with emphasis on concealment of randomisation. Each trial was given an allocation score of A (clearly concealed), B (unclear if concealed), or C (clearly not concealed) and a summary score of A (low risk of bias), B (moderate risk), or C (high risk). Trials scoring A were included and those scoring C were excluded. For a trial scoring B, an attempt was made to obtain more information by contacting the author.

DATA COLLECTION AND ANALYSIS

For each trial, the number of patients originally allocated to each treatment group was extracted from the data and an 'intention to treat' analysis performed. Data collection on each trial included inclusion and exclusion criteria, patient details, type of graft, type and dose of antithrombotic therapy used, outcome, and side effects. The treatment and control groups were compared for important prognostic factors and differences described. If any of the above data was not available, further information was sought from the author. However, the heterogeneity between trials could not be tested due to inaccessible data. Data were synthesized by comparing group results.

MAIN RESULTS

The analysis including four trials which evaluated vitamin K antagonists (VKA) versus no VKA indicate, that oral anticoagulation tendentially favours venous but not artificial graft patency as well as limb salvage and survival. Two other studies comparing VKA with aspirin or aspirin/dipyridamole supported evidence for a positive effect of VKA on the patency of venous but not artificial grafts. Subgroup analysis for artificial grafts as performed in one trial showed a favourable effect of antiplatelet agents on synthetic bypasses. In two trials with a relatively small number of patients low molecular weight heparin treatment was associated with a lower incidence of early postoperative graft thrombosis compared to treatment with unfractionated heparin. In one trial infusion of antithrombin concentrate was reported to have a negative effect on intraoperative graft thrombosis necessitating the study to be stopped before termination. Perioperative administration of ancrod was compared to unfractionated heparin showing no benefit of one drug compared to the other.

REVIEWER'S CONCLUSIONS

Patients operated for an infrainguinal venous graft might benefit from treatment with VKA, whereas patients receiving an artificial graft might profit more from platelet inhibitors (aspirin). However, the evidence is not conclusive. Randomised controlled trials with larger patient numbers comparing antithrombotic therapies with either placebo or antiplatelet therapies are called for in the future.

Comparison of the use of enoxaparin versus unfractionated heparin in patients undergoing lower extremity revascularization

Present available studies suggest that heparin prevents early vessel thrombosis in the immediate postoperative (POP) period after lower extremity bypass. Long-term anticoagulation with warfarin has also been used in these patients, based on its beneficial effect in preventing long-term graft failure. To compare the effectiveness between unfractionated heparin (UH) and low-molecular-weight heparin (enoxaparin) when used as transitional therapeutic POP anticoagulant therapy, a prospective study was performed. Seventy consecutive patients undergoing lower extremity bypass were studied. The initial 35 patients were started on a drip of UH 6 hours POP. The next 35 consecutive patients were treated with enoxaparin, the first dose starting 6 hours POP. All patients underwent subsequent anticoagulation with oral warfarin. There were no statistically significant differences between the two groups with regard to demographics, percentage of above/below the knee bypasses, type of conduit used, emergency operations, and overall complications. There was a significant difference in the length of stay (p = 0.05) in favor of the enoxaparin group, which also reflected a decreased overall cost in this group. In conclusion, POP anticoagulation with enoxaparin is as safe end effective as UH in patients undergoing lower extremity revascularization. Enoxaparin was associated with a decreased overall length of stay and hospital costs.

Recent strategies to reduce vein graft occlusion: a need to limit the effect of vascular damage

Despite early identification and aggressive modification of atherosclerotic risk factors, many patients still require surgical revascularisation for established atherosclerotic vascular disease. However, bypass surgery is hampered by a high incidence of vein graft failure. New strategies are being introduced to improve these results, with early data suggesting that improved patency rates are possible. These vary from the use of adjuvant pharmacological agents and local gene transfer strategies to the modification of vein harvesting techniques in order to reduce vascular damage to all layers of the graft. Advances in vascular biology have resulted in new insights into the role of the endothelium and adventitia in vein graft remodelling. Although recent pharmacological adjuvant therapy and molecular techniques have been described that may be used to reduce the incidence of vein graft occlusion a more desirable approach for improved graft patency rates may be achieved simply by using atraumatic surgical techniques aimed at minimising vascular damage during vessel harvesting and subsequent anastamoses during bypass surgery.

Pretreatment of a Dacron graft with tissue factor pathway inhibitor decreases thrombogenicity and neointimal thickness: a preliminary animal study

The purpose of this study was to evaluate the effects of locally applied TFPI on the reduction of neointimal thickness in Dacron grafts. Seven millimeter internal diameter 5 cm lengths of albumin coated knitted Dacron grafts were interposed in the infrarenal aorta in 14 mongrel dogs. Before implantation, the grafts were immersed in saline solution containing 200 microg/ml of TFPI (TFPI group, n = 7) or 100 IU/ml of heparin (control group, n = 7) for 15 minutes at room temperature. Three months after implantation, neointimal thickness and percentage of graft stenosis were measured by computerized planimetry. All grafts were patent 3 months after implantation. Thrombus was found in one graft in the TFPI group, but observed in three of seven control grafts. Neointimal thickness in the TFPI group was significantly smaller than that in the control group (mean +/- SD, 0.26 +/- 0.1 mm vs. 0.57 +/- 0.15 mm, p < 0.001). Percentage of graft stenosis was significantly lower in the TFPI group than in the control group (13.4 +/- 5.3% vs. 26.9 +/- 7.0%, p < 0.001). Scanning electron micrographs showed that the neointima of TFPI treated grafts were completely covered by endothelial cells. The present results indicate that locally applied TFPI reduces thrombogenicity and neointimal thickness in albumin coated knitted Dacron grafts.

Low Molecular Weight Heparin (Enoxaparin) versus Dextran in the Prevention of Early Occlusion Following Arterial Bypass Surgery Distal to the Groin

AIM

to compare the effect of perioperative dextran and low molecular weight heparin on early graft patency after femorodistal bypass surgery.

DESIGN

prospective randomised multicentre study.

PATIENTS AND METHODS

three hundred and fourteen patients were randomised to dextran 70 or the low molecular weight heparin enoxaparin during and after femorodistal bypass surgery. Patency was evaluated at days 1, 5-7, 30 and 90.

RESULTS

there was no difference in patency at any time point between the two regimens, the crude 90 days patency being 88 and 83%, respectively. There were significantly more patients with heart failure in the dextran group (12.8 vs 0.7%), with other side effects being evenly distributed.

CONCLUSION

dextran 70 and the low molecular weight heparin enoxaparin have the same effect on 90 days femorodistal graft patency, but care must be taken using the dextran to patients with a potential heart insufficiency.

Warfarin improves the outcome of infrainguinal vein bypass grafting at high risk for failure

OBJECTIVE

Patients with marginal venous conduit, poor arterial runoff, and prior failed bypass grafts are at high risk for infrainguinal graft occlusion and limb loss. We sought to evaluate the effects of anticoagulation therapy after autogenous vein infrainguinal revascularization on duration of patency, limb salvage rates, and complication rates in this subset of patients.

METHODS

This randomized prospective trial was performed in a university tertiary care hospital and in a Veterans Affairs Hospital. Fifty-six patients who were at high risk for graft failure were randomized to receive aspirin (24 patients, 27 bypass grafts) or aspirin and warfarin (WAR; 32 patients, 37 bypass grafts). All patients received 325 mg of aspirin each day, and the patients who were randomized to warfarin underwent anticoagulation therapy with heparin immediately after surgery and then were started on warfarin therapy to maintain an international normalized ratio between 2 and 3. Perioperative blood transfusions and complications were compared with the Student t test or with the chi2 test. Graft patency rates, limb salvage rates, and survival rates were compared with the Kaplan-Meier method and the log-rank test.

RESULTS

Sixty-one of the 64 bypass grafts were performed for rest pain or tissue loss, and 3 were performed for short-distance claudication. There were no differences between the groups in ages, indications, bypass graft types, risk classifications (ie, conduit, runoff, or graft failure), or comorbid conditions (except diabetes mellitus). The cumulative 5-year survival rate was similar between the groups. The incidence rate of postoperative hematoma (32% vs 3.7%; P = .004) was greater in the WAR group, but no differences were seen between the WAR group and the aspirin group in the number of packed red blood cells transfused, in the incidence rate of overall nonhemorrhagic wound complications, or in the overall complication rate (62% vs 52%). The immediate postoperative primary graft patency rates (97.3% vs 85.2%) and limb salvage rates (100% vs 88.9%) were higher in the WAR group as compared with the aspirin group. Furthermore, the cumulative 3-year primary, primary assisted, and secondary patency rates were significantly greater in the WAR group versus the aspirin group (74% vs 51%, P = .04; 77% vs 56%, P = .05; 81% vs 56%, P = .02) and cumulative limb salvage rates were higher in the WAR group (81% vs 31%, P = .01).

CONCLUSIONS

Perioperative anticoagulation therapy with heparin increases the incidence rate of wound hematomas, but long-term anticoagulation therapy with warfarin improves the patency rate of autogenous vein infrainguinal bypass grafts and the limb salvage rate for patients at high risk for graft failure.