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Changes in blood coagulability as it traverses the ischemic limb
Changes in blood coagulability as it traverses the ischemic limb V. K. Shankar, FRCS(Ed), S. Ray Chaudhury, S FRCS(Eng), M. C. Uthappa, FRCS(Glas), FRCR, A. Handa, FRCS(Eng), FRCS(Ed), and L. J. Hands, MS, FRCS(Eng), Oxford, England Objective: We undertook this study to determine whether changes in blood coagulability associated with peripheral arterial occlusive disease are due to contact with the atherosclerotic arterial wall or passage through distal ischemic tissue. Methods: Thirty patients with peripheral arterial occlusive disease undergoing angiography participated in the study. Ankle-brachial pressure index was recorded before intervention. Blood samples taken from the aorta, common femoral artery, and common femoral vein were analyzed at thromboelastography. Angiograms were scored for stenotic disease by a radiologist blinded to the other results. Results: When femoral artery samples were compared with aortic samples there was a decrease in reaction time (R; P < .05), an increase in maximum amplitude (MA; P < .05), and an increase in coagulation index (CI; P < .002), indicating an increase in coagulability as blood flowed down the iliac segment. These changes also correlated (⌬R, r ⴝ 0.442, P < .05; ⌬MA, r ⴝ 0.379, P < .05; ⌬CI, r ⴝ 0.429, P < .05) with the severity of disease in the ipsilateral iliac segment. Significant differences in R (P < .05), angle (P < .05), MA (P < .005), and CI (P < .001) between common femoral arterial and venous samples confirmed that venous samples were more coagulable in this group of patients. This difference in Thromboelastography parameters across the arteriovenous segment correlated inversely with the degree of ischemia (represented by ankle-brachial pressure index; ⌬CI, r ⴝ ⴚ0.427, P < .05; ⌬MA, r ⴝ ⴚ0.370, P < .05) in the puncture side limb. Conclusion: Passage of blood down an atherosclerotic artery leads to an increase in coagulability proportional to the degree of stenosis in that vessel. Passage of blood through ischemic tissue may also contribute to increased coagulability in peripheral arterial occlusive disease. (J Vasc Surg 2004;39:1033-42.)
Peripheral venous blood samples demonstrate a systemic increase in coagulability in patients with peripheral arterial occlusive disease (PAOD) affecting the legs.1-4 Fibrinogen5 and products of the coagulation cascade, including thrombin-antithrombin complexes, prothrombin F1 and F2,6 and D-dimers,7 indicating increased thrombin synthesis and fibrinolysis, are consistently increased in PAOD. Ischemic heart disease is associated with similar changes.8-10 The mechanism responsible for these changes is not clear. Potential causes of activation of the coagulation cascade include contact between circulating blood and atherosclerosis in the vessel wall, and passage of blood through ischemic tissue. Circulating fibrinogen levels in PAOD correlate inversely with mean ankle-brachial pressure index (ABPI)11 and with angiographic scoring.12 The degree of coagulation activation, indicated by systemic levels of thrombin-antithrombin complex, increases with the severity of disease at angiography or duplex scanning.11 Fibrinolytic activity, reflected in D-dimer levels, also correlates inversely with mean ABPI12 and angiographic scoring.11 From the Nuffield Department of Surgery, John Radcliffe Hospital. Competition of interest: none. Reprint requests: Linda J. Hands, Vascular Unit, Level 6, Nuffield Department of Surgery, John Radcliffe Hospital,Oxford OX39DU, England (e-mail: [email protected]). 0741-5214/$30.00 Copyright © 2004 by The Society for Vascular Surgery. doi:10.1016/j.jvs.2003.12.039
It is therefore clearly established that an ischemic limb has associated increased clotting activity, but although Lassila et al11 and Woodburn et al12 showed a correlation between the level of activation and the extent of atherosclerosis, the extent of atherosclerosis also correlates with the degree of ischemia, and thus it is still not clear which drives the increase in clotting activity. We have used thromboelastography (TEG; Thromboelastograph Hemostasis Analyzer; Hemoscope Corp, Niles, Ill) to measure changes in platelet function and the coagulation cascade across the ischemic limb, then sought to determine whether the changes in coagulability were caused by flow through an atherosclerotic vessel or through ischemic tissue. TEG enables measurement of the viscoelastic properties of a blood clot, and thereby gives information about the combined function of all factors involved in the process of clot formation and its subsequent dissolution (fibrinolysis). This is in contrast to routinely available coagulation tests, which assess only isolated stages of this process. TEG enables identification of functional abnormalities of factors involved in coagulation, even if their concentration is in the normal range, and it is a sensitive, specific, rapid method for assessing coagulation.13 TEG has been used to detect activation of coagulation in patients undergoing general surgical,14 abdominal aortic,15 and neurosurgical procedures,16 and TEG-guided transfusion protocols reduce blood and blood product usage in patients undergoing cardiac bypass procedures.17 TEG has been used in patients undergoing abdominal aortic aneurysm repair, to identify postoperative hypercoagulability, to monitor the adequacy of anticoagulation (heparinization) during peripheral vascular recon1033
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Fig 1. Thromboelastography values (mean) for blood samples obtained during transfemoral angiography. R, Reaction time (time to initial fibrin formation); K, dynamics of clot formation; Angle, acceleration of fibrin buildup and cross-linking (clot strengthening); MA, maximum amplitude (ultimate clot strength); CI, coagulation index (overall coagulation status); ABPI, ankle-brachial pressure index; TFA, transfemoral angiography.
struction procedures,18 and in the assessment of platelet function in vascular disease.19 The goals of this study were to measure changes in coagulability of blood as it circulates from the aorta through an ischemic leg to the common femoral vein, with TEG; to identify any relationship between changes in TEG parameters and angiographic severity of atherosclerotic disease in the intervening vessels; and to identify any relationship between changes in TEG parameters as blood flows from common femoral artery to vein, and the degree of ischemia in the limb. MATERIAL AND METHODS Subjects. Thirty sequential patients older than 40 years who were undergoing transfemoral angiography because of lower limb peripheral vascular disease via retrograde femoral puncture and who agreed to participate in the study were recruited. Demographic data, coexistence of other disease, and smoking habits were recorded. The ABPI in both legs was measured, and that in the symptomatically less affected leg was used as a measure of the severity of ischemia for the purposes of the study.
All patients underwent duplex scanning of the lower limb veins bilaterally, to rule out deep vein thrombosis (DVT) before angiography. Exclusion criteria for participation in the study included presence of DVT, liver impairment, known hypercoagulable state (excluding PAOD, ischemic heart disease, and cerebrovascular disease), and any malignancy. Those patients who were receiving warfarin because of cardiac valve replacement stopped it 3 days before angiography and were given heparin infusion until 4 hours before the intervention. Patients receiving subcutaneous low-dose heparin for DVT prophylaxis did not stop it before angiography. Activated partial thromboplastin time (aPTT) and prothrombin time (PT) were confirmed to be in the normal range before angiography in all patients, but heparinase cups were used in the TEG analysis in those who had received heparin, because heparin can still affect this assay even when aPTT and PT are normal.20 Patients receiving warfarin because of atrial fibrillation discontinued it 3 days before angiography, and were not given heparin. These patients also had PT and aPTT in the normal range before angiography was performed, and heparinase cups were not
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Fig 2. Coagulation state of each blood sample. R, Reaction time (time to initial fibrin formation); K, dynamics of clot formation; Angle, acceleration of fibrin buildup and cross-linking (clot strengthening); MA, maximum amplitude (ultimate clot strength); CI, coagulation index (overall coagulation status); LY30, percent lysis at 30 minutes after MA; LY60, percent lysis at 60 minutes after MA; G, clot firmness as shear elastic modulus; EPL, estimated percent lysis; A, current amplitude.
used. We have validated the use of heparinase cups with TEG analysis of blood samples from 15 patients undergoing aortic aneurysm repair or peripheral vascular reconstruction procedures. The samples were taken from a radial artery line before and 2 minutes after heparin (5000 IU) administration via a central vein. We found no significant differences (Mann-Whitney U test) in TEG parameters between samples analyzed before and after heparin administration with heparinase21-coated cups, confirming complete reversal of exogenous heparin. Blood sampling and analysis. Blood samples were obtained from the common femoral vein (sample V) on the same side as the intended arterial puncture, via separate percutaneous puncture, after infiltration of the subcutaneous tissue with local anesthetic (lignocaine 1%). The radiology protocol dictated that this puncture be on the side of the less symptomatic leg. A sample was then taken from the ipsilateral common femoral artery (sample A) via separate arterial puncture with a size 19 needle, before insertion of a guide wire, followed by angiography sheath insertion (Seldinger method22) and collection of aortic blood samples from the abdominal aorta (sample Ao) via the catheter before injection of contrast material (Fig 1). Citrated tubes were used for storage of blood samples before analysis.23,24 TEG was used to analyze the coagulation state of each blood sample (Fig 2), and this yielded five parameters: R, K, angle (&alpha), MA, and CI (Fig 2).
R is the latent period between placing the sample in the analyzer and the initial fibrin formation, and it correlates with platelet activity. K time is a measure of the period from the beginning of clot formation until the amplitude of the TEG trace reaches 20 mm, and represents the dynamics of clot formation. Angle, or alpha (␣) is the angle between the horizontal line through the center of the TEG tracing and the line tangential to the developing “body” of the TEG tracing. The alpha angle represents the acceleration of fibrin buildup and cross-linking (clot strengthening). MA, or maximum amplitude, is a direct function of the maximum dynamic properties of fibrin and platelet bonding via glycoprotein IIb and IIIa receptors; it represents the ultimate strength of the fibrin clot, and depends on the number and function of platelets and their interaction with fibrin. CI, or coagulation index,25 describes the patient’s overall coagulation status, and is derived from R, K, MA, and angle (␣) of blood tracings: CI ⫽ ⫺ 0.245R ⫹ 0.0184K ⫹ 0.1655MA-0.0241␣ ⫺ 5.0220 TEG analyses of samples were carried out after storage in citrate for 1 to 8 hours. In a previous study of TEG assay variability, 15 citrated peripheral venous blood samples collected from patients with vascular disease were analyzed after 1 hour of storage. Each sample was analyzed, divided
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Table I. Clinical and angiographic data for study group Parameter Risk factors Antihypertensive therapy Diabetes Smoking (current) Hyperlipidemia Previous acute myocardial infarction Previous cerebrovascular accident Previous deep venous thrombosis Previous peripheral vascular surgery Aortic aneurysmal disease Antiplatelet therapy Anticoagulation therapy (warfarin stopped 3 days before angiography) Symptoms Short-distance claudication Rest pain Tissue loss Ankle-brachial pressure index Puncture side limb (mean ⫾ SD) Opposite, more symptomatic, limb (mean ⫾ SD) Angiographic severity of Iliac disease in puncture side limb (%) Stenosis ⱖ70% (severe) Stenosis 50%-70% (moderate) Stenosis ⬍50% (minimal) Total angiographic score for infralinguinal disease Median Range
No. of patients (N ⫽ 30) 26 11 16 19 7 4 2 13 4 12 4
7 9 14 0.74 ⫾ 0.15 0.50 ⫾ 0.15
8 10 12 2.00 3.00
into three parts, and each one was assayed separately. The intra-assay variability was excellent (P ⫽ NS), and the reliability coefficients (␣) were greater than 0.9 for all parameters studied (R, K, angle, MA, CI). Samples from any patient receiving heparin before angiography were analyzed with a heparinase21-coated cup. Assessment of disease severity. Arteriographic findings were interpreted by a vascular radiologist blinded to the TEG results. Atherosclerotic disease in the aortoiliac segment on the same side as the arterial puncture was reported as maximum percentage (%) diameter stenosis and graded as less than 50% (minimal), 50% to 70% (moderate), and greater than 70% (severe). Infrainguinal disease was graded in four segments (superficial femoral artery, popliteal artery, trifurcation, crural vessels) as less than 50% or 50% or greater stenosis at any point. A score of 0 for less than 50% and 1 for 50% or greater was given, and the total score for infrainguinal disease was calculated for the puncture side limb in each patient. Statistical analysis. TEG and patient group data were analyzed with the Wilcoxon signed rank test, Spearman correlation, and descriptive analyses (SPSS version 11.00; SPSS, Chicago, Ill), including mean and standard deviation values for the TEG parameters and frequency of distribu-
tion of vascular risk factors. The Mann-Whitney U test was used for comparison of TEG parameters between groups. The Ethics Committee of Oxford Radcliffe Hospitals NHS Trust approved the study. RESULTS The 30 study patients (21 men, nine women; median age, 72 ⫾ 9.6 years) underwent transfemoral angiography for a range of ischemic symptoms, including intermittent claudication (n ⫽ 8), rest pain (n ⫽ 9), and ischemic tissue loss (n ⫽ 13). Two patients were receiving warfarin because of heart valve replacement, and three were receiving lowdose subcutaneous heparin for DVT prophylaxis. Another two patients receiving warfarin because of atrial fibrillation stopped it before angiography. Further details are given in Table I. Fifty-five percent of common femoral arterial punctures were on the left side. Angiographic scoring for disease severity is given in Table I. When comparing common femoral artery samples with aortic samples (Table II), there was a decrease in R (time to onset of clotting, reflecting platelet activity; P ⬍ .05; Fig 3), an increase in MA (clot strength; P ⬍ .05; Fig 4), and an increase in CI (coagulation index; P ⬍ .002; Fig 5), consistent with an increase in coagulability due to both platelet activation and increased thrombin generation as blood flowed down the iliac arteries. These changes in TEG parameters also correlated with the severity of atherosclerotic disease in the ipsilateral aortoiliac segment (⌬R, r ⫽ 0.442, P ⬍ .05; ⌬MA, r ⫽ 0.379, P ⬍ .05; ⌬CI, r ⫽ 0.429, P ⬍ .05). TEG parameters showed significant differences in R (P ⬍ .05), angle (measure of clot development; P ⬍ .05), MA (P ⬍ .005), and CI (P ⬍ .001) between common femoral arterial and venous samples, confirming that venous samples were more coagulable in this group of patients, again due to increased platelet activation and thrombin production (Table III). This difference in coagulation between the arterial and venous ends of the circulation in the puncture side limb correlated inversely with degree of ischemia (ABPI) on that side (⌬CI vs ABPI, r ⫽ ⫺0.427, P ⬍ .05; ⌬MA vs ABPI, r ⫽ ⫺0.370, P ⬍ .05; Figs 6 and 7). The change in MA across the limb circulation also correlated with the angiographic score for infrainguinal disease (⌬MA, r ⫽ 0.459, P ⬍ .05; Fig 8), but none of the other TEG parameters did so. Twelve patients were taking regular aspirin, and had prolongation of R time in samples taken from the aorta (Ao R; P ⬍ .05) and prolongation of K values in samples taken from the common femoral artery (P ⬍ .05), compared with the 18 patients not taking aspirin. Neither gender nor hyperlipidemia were associated with significant differences in TEG parameters. We found a significant decrease in K value in venous samples taken from the common femoral vein (P ⬍ .05), but no other changes in TEG parameters in those who were smokers compared with nonsmokers and ex-smokers.
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Fig 3. Severity of iliac disease and change in reaction (R) time.
Fig 4. Severity of iliac disease and change in maximum amplitude (MA).
Patients with diabetes demonstrated significantly reduced K time (rapidity of clot strengthening; P ⬍ .05), increased angle (acceleration of fibrin buildup; P ⬍ .05), and MA (ultimate clot strength; P ⬍ .05).
We also found a significant decrease in R (P ⬍ .05) and K (P ⬍ .05) and increase in angle (P ⬍ .05) and CI (P ⬍ .05) in blood samples taken from the common femoral vein in patients with a history of DVT (n ⫽ 2), compared with
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Fig 5. Severity of iliac disease and change in coagulation index (CI).
Table II. Correlation between changes in thromboelastographic parameters between aorta and common femoral artery and extent of iliac stenosis Mean difference between aortic and femoral samples (Mean/CI) Parameter R K Angle MA CI
Correlation with Iliac disease
Mean ⫾ SD
95% confidence interval
r
P
⫺0.44 ⫾ 3.1 0.08 ⫾ 1.67 2.08 ⫾ 12.3 3.1 ⫾ 9.97 0.75 ⫾ 1.42
⫺1.6, 0.72 ⫺0.54, 0.7 ⫺2.5, 6.6 ⫺0.62, 6.8 0.22, 1.2
0.443 0.151 0.218 0.379 0.429
.014 .151 .248 .039 .018
R, Reaction time (time to initial fibrin formation); K, dynamics of clot formation; Angle, acceleration of fibrin buildup and cross-linking (clot strengthening); MA, maximum amplitude (ultimate clot strength); CI, coagulation index (overall coagulation status).
those with no such history, but the results in patients with a history of acute myocardial infarction, cerebrovascular accident, and peripheral vascular surgery did not differ from those in patients without such history. DISCUSSION Our study confirms that blood becomes more coagulable as it traverses the ischemic limb. Platelet activation, as well as increased thrombin production, takes place within the limb. Blood coagulability increases as it flows down an atherosclerotic iliac artery, and the magnitude of that change is related to the severity of stenosis. Ischemia is unlikely to have a role here, and it is probable that the changes in blood coagulability are caused by the presence
of atherosclerotic disease. This may be due to interaction with atherosclerotic plaque, but in the carotid and coronary arteries, where this has been extensively studied, enhanced coagulation is usually associated with “unstable plaque” and ulceration. We recorded no details of plaque ulceration or measures of plaque stability, but unstable plaque is usually associated with acute symptoms rather than the relatively stable chronic ischemia seen in our patients. Another possible cause of coagulation activation in the iliac arteries might be the increased shear stress26 associated with localized stenosis. This induces platelet aggregation in both acute coronary syndromes27 and chronic coronary artery disease.28 It is possible that other steps in coagulation are also activated under such circumstances. The third
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Fig 6. Correlation between change in coagulation index (CI) and ankle-brachial pressure index (ABPI).
Table III. Correlation between changes in thromboelastographic parameters between common femoral artery and vein, and ABPI Mean difference across A-V segment
Parameter R K Angle MA CI
Mean ⫾ SD
95% Confidence interval
⫺0.91 ⫾ 0.43 ⫺0.30 ⫾ 0.15 3.53 ⫾ 1.49 3.81 ⫾ 1.04 0.76 ⫾ 0.19
⫺1.7, 0.02 ⫺.62, 0.01 0.47, 6.5 1.6, 5.9 0.36, 1.16
Correlation with ABPI
r
P
⫺0.370 0.129 ⫺0.209 ⫺0.370 ⫺0.427
.074 .496 .268 .044 .018
ABPI, Ankle-brachial pressure index; A-V, arteriovenous; R, reaction time (time to initial fibrin formation); K, dynamics of clot formation; Angle, acceleration of fibrin buildup and cross-linking (clot strengthening); MA, maximum amplitude (ultimate clot strength); CI, coagulation index (overall coagulation status).
possibility is that turbulence in blood flow over irregular plaque promotes coagulation, although there is no direct evidence for this in the literature. Changes recorded as blood flows through the ischemic limb are more complex. It is presumed that the same mechanisms that induce a change in coagulability in the iliac segment also have a role in changes within the limb. Sobel et al29 demonstrated increased thrombin generation within the ischemic limb by measuring fibrinopeptide A levels, which were consistently higher in venous samples than in the arterial inflow to an ischemic limb. These same authors found no increase in -thromboglobulin, and concluded that there was no activation of platelets across the ischemic leg, although other studies have found systemic evidence of platelet activation in such limbs.30 We attempted to measure the extent of atherosclerotic disease in the infrainguinal vessels with a crude angio-
graphic score, but arteries that are heavily diseased are likely to cause diversion of flow into disease-free collateral vessels; indeed, blood will never be exposed to the most heavily diseased (occluded) arteries. We did show a correlation between the increase in coagulability across a limb and the extent of ischemia, as measured with ABPI on that side. Thus flow through ischemic tissue may promote coagulation, but we cannot exclude the possibility that this relationship arises through the close association between the severity of ischemia and the extent of atherosclerotic disease past which the blood must flow to the distal limb. The changes in coagulability could all be due to exposure to atherosclerotic disease. We have shown that arterial blood entering the ischemic leg is significantly less coagulable than that leaving it. Somehow the degree of coagulation activation is reduced before blood returns to the leg. The blood supply to even
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Fig 7. Correlation between change in maximum amplitude (MA) and ankle-brachial pressure index (ABPI) across ischemic limb.
Fig 8. Correlation between change in maximum amplitude (MA) across ischemic limb and angiographic severity of infrainguinal atherosclerotic disease. A-V, arteriovenous.
an ischemic limb is about 400 mL/min.31 This represents less than 10% of cardiac output, and thus is subject to dilution by blood returning to the heart from elsewhere in the body. In addition, activated clotting factors are removed by the reticuloendotheial system, in particular the
liver.32 Thus blood returning to the ischemic limb has much lower coagulation activity than blood that left it. We used ABPI as a measure of ischemia rather than as a measure of atherosclerotic disease in the limb, because it reflects the perfusion pressure at ankle level and thus relates
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to the level of ischemia. It depends on flow through collateral vessels as well as through stenosed arteries, and is therefore not a measure simply of atherosclerotic disease. We could have used symptoms as a measure of ischemia (eg, asymptomatic vs claudication vs rest pain), but because we were investigating the less symptomatic leg, any symptoms of claudication could have been masked by more severe disability in the other leg. We used TEG to assess coagulation, because its sensitivity and specificity compare well with routine coagulation tests33,34 and it provides a measure of the overall coagulation status of a given blood sample rather than of individual clotting factors in isolation.35 TEG analysis of citrated samples is more sensitive in the detection of procoagulant alterations than other coagulation tests are,14 and is therefore ideal for assessment of coagulation in patients with PAOD. Patients with peripheral vascular disease exhibit increased aggregation of platelets in baseline measurements when studied with aggregometry,36 and this has been shown to increase further during and immediately after peripheral vascular surgery despite preprocedure ingestion of aspirin and administration of heparin during the procedure. The TEG method has the potential to unmask hypercoagulability in these patients, and can enable identification of those patients at risk for thrombotic events after vascular surgery. Aspirin ingestion in our patients (n ⫽ 12) was reflected in prolongation of R time in samples taken from the aorta, and K values of samples taken from the common femoral artery. Previous studies in subjects taking aspirin have failed to detect an effect of aspirin. These studies were performed in healthy control subjects, with blood samples taken from a peripheral vein after ingestion of aspirin in doses up to 650 mg/d over 10 days. Our study involved subjects in whom platelet activation already exists,1,37 and it is perhaps not surprising that the results differ. Patients with PAOD have relatively high mortality from cardiovascular and cerebrovascular disease. A significant part of that mortality relates to thrombosis in critical vessels, which may be promoted by hypercoagulability of the systemic circulation. We have shown that atherosclerotic disease in the leg is a potential promoter of coagulation. We do not know whether the presence of ischemic tissue in the leg also contributes. Our current approach to treatment of the ischemic leg is to reverse ischemic changes or ablate ischemic tissue; we do not remove the atherosclerotic disease. On the other hand, advances in drug therapy, in particular cholesterol-lowering drugs, have the potential to reduce the size of atherosclerotic plaque. We have shown that the mere presence of such disease is sufficient to enhance coagulation, but we do not yet know whether the persistence of ischemic tissue is likely to prejudice patient survival as a result of its systemic effect. CONCLUSION We have found that blood increases in platelet and coagulation factor activity as it flows down the iliac vessel in
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proportion to the extent of iliac atherosclerotic disease. We have also shown that blood circulating through an ischemic limb increases in coagulability. Part of the change is probably due to contact with atherosclerotic arteries, but some of the change may be due to flow through ischemic tissue. We thank Dr R. Weatherall, Medical Statistician, at ICRF/NHS Centre for Statistics in Medicine, Institute of Health Sciences, Oxford, for valuable advice regarding the statistical methods used in this study. REFERENCES 1. Cassar K, Bachoo P, Ford I, Greaves M, Brittenden J. Platelet activation is increased in peripheral arterial disease. J Vasc Surg 2003;38:99-103. 2. Reininger CB, Graf J, Reininger AJ, Spannagl M, Steckmeier B, Schweiberer L. Increased platelet and coagulatory activity indicate ongoing thrombogenesis in peripheral arterial disease. Thromb Res 1996;82: 523-32. 3. Boneu B, Leger P, Arnaud C. Haemostatic system activation and prediction of vascular events in patients presenting with stable peripheral arterial disease of moderate severity. Blood Coagulation Fibrinolysis 1998;9:129-35. 4. Speiser W, Speiser P, Minar E, Korninger C, Neissner H, Huber K, et al. Activation of coagulation and fibrinolysis in patients with arteriosclerosis: relation to localization of vessel disease and risk factors. Thromb Res 1990;59:77-88. 5. Banerjee AK, Pearson J, Gilliland D, Lewis JD, Stirling Y, Meade TW. A six-year prospective study of fibrinogen and other risk factors associated with mortality in stable claudicants. Thromb Haemost 1992;68:261-3. 6. Cortellaro M, Boschetti C, Cofranesco E, Zanbussi C, Catalano M, Gaetano G, et al, and the PLAT Study Group. The PLAT study. Hemostatic function in relation to atherothrombotic ischemic events in vascular disease patients: principal results. Arterioscler Thromb 1992; 12:1063-70. 7. Lee AJ, Fowkes FG, Lowe GD, Rumley A. Fibrin D-dimer, haemostatic factors and peripheral vascular disease. Thromb Haemost 1995;74:82832. 8. Van der Bom JG, Bots ML, Haverkate F, Meijer P, Hofman A, Kluft C, et al. Activation products of the haemostatic system in coronary, cerebrovascular and peripheral arterial disease. Thromb Haemost 2001;85: 233-9. 9. Meade TW, Ruddock V, Stirling Y, Chakrabarti R, Miller GJ. Fibrinolytic activity, clotting factors, and long-term incidence of ischaemic heart disease in the Northwick Park Heart Study. Lancet 1993;342: 1076-9. 10. Thompson SG, Kienast J, Pyke SDM, Haverkate F, van de Loo CJW, for the European Concerted Action on Thrombosis and Disabilities Angina Pectoris Study Group. Hemostatic factors and the risk of myocardial infarction or sudden death in patients with angina pectoris. N Engl J Med 1995;332:635-41. 11. Lassila R, Peltonen S, Lepatalo M, Saarien O, Kauhanen P, Manninen V. Severity of peripheral atherosclerosis is associated with fibrinogen and degradation of cross-linked fibrin. Atheroscler Thromb 1993;13: 1412-7. 12. Woodburn KR, Lowe GD, Rumley A, Love J, Pollock JG. Relation of hemostatic, fibrinolytic and rheological variables to the angiographic extent of peripheral arterial occlusive disease. Int Angiol 1995;14:34652. 13. Mallett SV, Platt M. Role of thromboelastography in bleeding diatheses and regional anaesthesia. Lancet 1991;338:765-7. 14. Mahla E, Long T, Vicenzi MN, Werkgartner G, Maier R, Probst C, et al. Thromboelastography for monitoring prolonged hypercoagulability after major abdominal surgery. Anesth Analg 2001;92:572-7. 15. Gibbs NM, Crawford GPM, Michalopoulos N. Thromboelastographic patterns following abdominal aortic surgery. Anaesth Intens Care 1994; 22:534-8. 16. Abrahams JM, Torchia MB, McGarvey M, Putt M, Baranov D, Sinson GP. Perioperative assessment of coagulability in neurosurgical patients
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patients with acute coronary syndromes. Arteriscler Throm Vasc Biol 1999;19:877-82. Kawano K, Yoshino H, Aoki N, Udagawa H, Watanuki A, Hioki Y, et al. Shear-induced platelet aggregation increases in patients with proximal and severe coronary artery stenosis. Clin Cardiol 2002;25:154-60. Sobel M, Gervin CA, Qureshi DG, Greenfield LJ. Coagulation responses to heparin in the ischaemic limb: assessment of thrombin and platelet activation during vascular surgery. Circulation 1987;76(3 Pt 2):III8-13. Magruder C, Donaldson MD, Matthews ET, Hadjimichael J, Rickles FR. Markers of thrombotic activity in arterial disease. Arch Surg 1987; 122:897-900. Pentecost BL. The effect of exercise on the external iliac vein blood flow and local oxygen consumption in normal subjects and in those with occlusive arterial disease. Clin Sci 1964;27:437-45. Harmening DM. Clinical haematology and fundamentals of haemostasis. 4th edition. Part IV. Philadelphia: F.A. Davis Co; 2002. p 526. Nielson VG. The detection of changes in heparin activity in the rabbit: a comparison of anti-Xa activity, thromboelastography, activated partial thromboplastin time, and activated coagulation time. Anaesth Analg 2002;95:1503-6. Essell JH, Martin TJ, Salinas J, Thompson JM, Smith VC. Comparison of thromboelastography to bleeding time and standard coagulation tests in patients after cardiopulmonary bypass. J Cardiothor Vasc Anaesth 1993;7:410-5. Zuckerman L, Cohen E, Vagher JP, Woodward E, Caprini JA. Comparison of thromboelasrography with common coagulation tests. Thromb Haemost 1981;46:752-6. Reininger CB, Reininger AJ, Steckmeier B, Lasser R, Schweiberer L. Increased pre- and postoperative thrombocyte activity in vascular surgery patients. Vasa 1994;23:217-27. Reininger CB, Graf J, Reininger AJ, Spannagl M, Steckmeier B, Schweiberer L. Increased platelet and coagulatory activity indicate ongoing thrombogenesis in peripheral arterial disease. Thromb Res 1996;82: 523-32.
Submitted Sep 10, 2003; accepted Dec 9, 2003. Available online Mar 8, 2004.
Peripheral venous blood samples demonstrate a systemic increase in coagulability in patients with peripheral arterial occlusive disease (PAOD) affecting the legs.1-4 Fibrinogen5 and products of the coagulation cascade, including thrombin-antithrombin complexes, prothrombin F1 and F2,6 and D-dimers,7 indicating increased thrombin synthesis and fibrinolysis, are consistently increased in PAOD. Ischemic heart disease is associated with similar changes.8-10 The mechanism responsible for these changes is not clear. Potential causes of activation of the coagulation cascade include contact between circulating blood and atherosclerosis in the vessel wall, and passage of blood through ischemic tissue. Circulating fibrinogen levels in PAOD correlate inversely with mean ankle-brachial pressure index (ABPI)11 and with angiographic scoring.12 The degree of coagulation activation, indicated by systemic levels of thrombin-antithrombin complex, increases with the severity of disease at angiography or duplex scanning.11 Fibrinolytic activity, reflected in D-dimer levels, also correlates inversely with mean ABPI12 and angiographic scoring.11 From the Nuffield Department of Surgery, John Radcliffe Hospital. Competition of interest: none. Reprint requests: Linda J. Hands, Vascular Unit, Level 6, Nuffield Department of Surgery, John Radcliffe Hospital,Oxford OX39DU, England (e-mail: [email protected]). 0741-5214/$30.00 Copyright © 2004 by The Society for Vascular Surgery. doi:10.1016/j.jvs.2003.12.039
It is therefore clearly established that an ischemic limb has associated increased clotting activity, but although Lassila et al11 and Woodburn et al12 showed a correlation between the level of activation and the extent of atherosclerosis, the extent of atherosclerosis also correlates with the degree of ischemia, and thus it is still not clear which drives the increase in clotting activity. We have used thromboelastography (TEG; Thromboelastograph Hemostasis Analyzer; Hemoscope Corp, Niles, Ill) to measure changes in platelet function and the coagulation cascade across the ischemic limb, then sought to determine whether the changes in coagulability were caused by flow through an atherosclerotic vessel or through ischemic tissue. TEG enables measurement of the viscoelastic properties of a blood clot, and thereby gives information about the combined function of all factors involved in the process of clot formation and its subsequent dissolution (fibrinolysis). This is in contrast to routinely available coagulation tests, which assess only isolated stages of this process. TEG enables identification of functional abnormalities of factors involved in coagulation, even if their concentration is in the normal range, and it is a sensitive, specific, rapid method for assessing coagulation.13 TEG has been used to detect activation of coagulation in patients undergoing general surgical,14 abdominal aortic,15 and neurosurgical procedures,16 and TEG-guided transfusion protocols reduce blood and blood product usage in patients undergoing cardiac bypass procedures.17 TEG has been used in patients undergoing abdominal aortic aneurysm repair, to identify postoperative hypercoagulability, to monitor the adequacy of anticoagulation (heparinization) during peripheral vascular recon1033
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Fig 1. Thromboelastography values (mean) for blood samples obtained during transfemoral angiography. R, Reaction time (time to initial fibrin formation); K, dynamics of clot formation; Angle, acceleration of fibrin buildup and cross-linking (clot strengthening); MA, maximum amplitude (ultimate clot strength); CI, coagulation index (overall coagulation status); ABPI, ankle-brachial pressure index; TFA, transfemoral angiography.
struction procedures,18 and in the assessment of platelet function in vascular disease.19 The goals of this study were to measure changes in coagulability of blood as it circulates from the aorta through an ischemic leg to the common femoral vein, with TEG; to identify any relationship between changes in TEG parameters and angiographic severity of atherosclerotic disease in the intervening vessels; and to identify any relationship between changes in TEG parameters as blood flows from common femoral artery to vein, and the degree of ischemia in the limb. MATERIAL AND METHODS Subjects. Thirty sequential patients older than 40 years who were undergoing transfemoral angiography because of lower limb peripheral vascular disease via retrograde femoral puncture and who agreed to participate in the study were recruited. Demographic data, coexistence of other disease, and smoking habits were recorded. The ABPI in both legs was measured, and that in the symptomatically less affected leg was used as a measure of the severity of ischemia for the purposes of the study.
All patients underwent duplex scanning of the lower limb veins bilaterally, to rule out deep vein thrombosis (DVT) before angiography. Exclusion criteria for participation in the study included presence of DVT, liver impairment, known hypercoagulable state (excluding PAOD, ischemic heart disease, and cerebrovascular disease), and any malignancy. Those patients who were receiving warfarin because of cardiac valve replacement stopped it 3 days before angiography and were given heparin infusion until 4 hours before the intervention. Patients receiving subcutaneous low-dose heparin for DVT prophylaxis did not stop it before angiography. Activated partial thromboplastin time (aPTT) and prothrombin time (PT) were confirmed to be in the normal range before angiography in all patients, but heparinase cups were used in the TEG analysis in those who had received heparin, because heparin can still affect this assay even when aPTT and PT are normal.20 Patients receiving warfarin because of atrial fibrillation discontinued it 3 days before angiography, and were not given heparin. These patients also had PT and aPTT in the normal range before angiography was performed, and heparinase cups were not
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Fig 2. Coagulation state of each blood sample. R, Reaction time (time to initial fibrin formation); K, dynamics of clot formation; Angle, acceleration of fibrin buildup and cross-linking (clot strengthening); MA, maximum amplitude (ultimate clot strength); CI, coagulation index (overall coagulation status); LY30, percent lysis at 30 minutes after MA; LY60, percent lysis at 60 minutes after MA; G, clot firmness as shear elastic modulus; EPL, estimated percent lysis; A, current amplitude.
used. We have validated the use of heparinase cups with TEG analysis of blood samples from 15 patients undergoing aortic aneurysm repair or peripheral vascular reconstruction procedures. The samples were taken from a radial artery line before and 2 minutes after heparin (5000 IU) administration via a central vein. We found no significant differences (Mann-Whitney U test) in TEG parameters between samples analyzed before and after heparin administration with heparinase21-coated cups, confirming complete reversal of exogenous heparin. Blood sampling and analysis. Blood samples were obtained from the common femoral vein (sample V) on the same side as the intended arterial puncture, via separate percutaneous puncture, after infiltration of the subcutaneous tissue with local anesthetic (lignocaine 1%). The radiology protocol dictated that this puncture be on the side of the less symptomatic leg. A sample was then taken from the ipsilateral common femoral artery (sample A) via separate arterial puncture with a size 19 needle, before insertion of a guide wire, followed by angiography sheath insertion (Seldinger method22) and collection of aortic blood samples from the abdominal aorta (sample Ao) via the catheter before injection of contrast material (Fig 1). Citrated tubes were used for storage of blood samples before analysis.23,24 TEG was used to analyze the coagulation state of each blood sample (Fig 2), and this yielded five parameters: R, K, angle (&alpha), MA, and CI (Fig 2).
R is the latent period between placing the sample in the analyzer and the initial fibrin formation, and it correlates with platelet activity. K time is a measure of the period from the beginning of clot formation until the amplitude of the TEG trace reaches 20 mm, and represents the dynamics of clot formation. Angle, or alpha (␣) is the angle between the horizontal line through the center of the TEG tracing and the line tangential to the developing “body” of the TEG tracing. The alpha angle represents the acceleration of fibrin buildup and cross-linking (clot strengthening). MA, or maximum amplitude, is a direct function of the maximum dynamic properties of fibrin and platelet bonding via glycoprotein IIb and IIIa receptors; it represents the ultimate strength of the fibrin clot, and depends on the number and function of platelets and their interaction with fibrin. CI, or coagulation index,25 describes the patient’s overall coagulation status, and is derived from R, K, MA, and angle (␣) of blood tracings: CI ⫽ ⫺ 0.245R ⫹ 0.0184K ⫹ 0.1655MA-0.0241␣ ⫺ 5.0220 TEG analyses of samples were carried out after storage in citrate for 1 to 8 hours. In a previous study of TEG assay variability, 15 citrated peripheral venous blood samples collected from patients with vascular disease were analyzed after 1 hour of storage. Each sample was analyzed, divided
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Table I. Clinical and angiographic data for study group Parameter Risk factors Antihypertensive therapy Diabetes Smoking (current) Hyperlipidemia Previous acute myocardial infarction Previous cerebrovascular accident Previous deep venous thrombosis Previous peripheral vascular surgery Aortic aneurysmal disease Antiplatelet therapy Anticoagulation therapy (warfarin stopped 3 days before angiography) Symptoms Short-distance claudication Rest pain Tissue loss Ankle-brachial pressure index Puncture side limb (mean ⫾ SD) Opposite, more symptomatic, limb (mean ⫾ SD) Angiographic severity of Iliac disease in puncture side limb (%) Stenosis ⱖ70% (severe) Stenosis 50%-70% (moderate) Stenosis ⬍50% (minimal) Total angiographic score for infralinguinal disease Median Range
No. of patients (N ⫽ 30) 26 11 16 19 7 4 2 13 4 12 4
7 9 14 0.74 ⫾ 0.15 0.50 ⫾ 0.15
8 10 12 2.00 3.00
into three parts, and each one was assayed separately. The intra-assay variability was excellent (P ⫽ NS), and the reliability coefficients (␣) were greater than 0.9 for all parameters studied (R, K, angle, MA, CI). Samples from any patient receiving heparin before angiography were analyzed with a heparinase21-coated cup. Assessment of disease severity. Arteriographic findings were interpreted by a vascular radiologist blinded to the TEG results. Atherosclerotic disease in the aortoiliac segment on the same side as the arterial puncture was reported as maximum percentage (%) diameter stenosis and graded as less than 50% (minimal), 50% to 70% (moderate), and greater than 70% (severe). Infrainguinal disease was graded in four segments (superficial femoral artery, popliteal artery, trifurcation, crural vessels) as less than 50% or 50% or greater stenosis at any point. A score of 0 for less than 50% and 1 for 50% or greater was given, and the total score for infrainguinal disease was calculated for the puncture side limb in each patient. Statistical analysis. TEG and patient group data were analyzed with the Wilcoxon signed rank test, Spearman correlation, and descriptive analyses (SPSS version 11.00; SPSS, Chicago, Ill), including mean and standard deviation values for the TEG parameters and frequency of distribu-
tion of vascular risk factors. The Mann-Whitney U test was used for comparison of TEG parameters between groups. The Ethics Committee of Oxford Radcliffe Hospitals NHS Trust approved the study. RESULTS The 30 study patients (21 men, nine women; median age, 72 ⫾ 9.6 years) underwent transfemoral angiography for a range of ischemic symptoms, including intermittent claudication (n ⫽ 8), rest pain (n ⫽ 9), and ischemic tissue loss (n ⫽ 13). Two patients were receiving warfarin because of heart valve replacement, and three were receiving lowdose subcutaneous heparin for DVT prophylaxis. Another two patients receiving warfarin because of atrial fibrillation stopped it before angiography. Further details are given in Table I. Fifty-five percent of common femoral arterial punctures were on the left side. Angiographic scoring for disease severity is given in Table I. When comparing common femoral artery samples with aortic samples (Table II), there was a decrease in R (time to onset of clotting, reflecting platelet activity; P ⬍ .05; Fig 3), an increase in MA (clot strength; P ⬍ .05; Fig 4), and an increase in CI (coagulation index; P ⬍ .002; Fig 5), consistent with an increase in coagulability due to both platelet activation and increased thrombin generation as blood flowed down the iliac arteries. These changes in TEG parameters also correlated with the severity of atherosclerotic disease in the ipsilateral aortoiliac segment (⌬R, r ⫽ 0.442, P ⬍ .05; ⌬MA, r ⫽ 0.379, P ⬍ .05; ⌬CI, r ⫽ 0.429, P ⬍ .05). TEG parameters showed significant differences in R (P ⬍ .05), angle (measure of clot development; P ⬍ .05), MA (P ⬍ .005), and CI (P ⬍ .001) between common femoral arterial and venous samples, confirming that venous samples were more coagulable in this group of patients, again due to increased platelet activation and thrombin production (Table III). This difference in coagulation between the arterial and venous ends of the circulation in the puncture side limb correlated inversely with degree of ischemia (ABPI) on that side (⌬CI vs ABPI, r ⫽ ⫺0.427, P ⬍ .05; ⌬MA vs ABPI, r ⫽ ⫺0.370, P ⬍ .05; Figs 6 and 7). The change in MA across the limb circulation also correlated with the angiographic score for infrainguinal disease (⌬MA, r ⫽ 0.459, P ⬍ .05; Fig 8), but none of the other TEG parameters did so. Twelve patients were taking regular aspirin, and had prolongation of R time in samples taken from the aorta (Ao R; P ⬍ .05) and prolongation of K values in samples taken from the common femoral artery (P ⬍ .05), compared with the 18 patients not taking aspirin. Neither gender nor hyperlipidemia were associated with significant differences in TEG parameters. We found a significant decrease in K value in venous samples taken from the common femoral vein (P ⬍ .05), but no other changes in TEG parameters in those who were smokers compared with nonsmokers and ex-smokers.
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Fig 3. Severity of iliac disease and change in reaction (R) time.
Fig 4. Severity of iliac disease and change in maximum amplitude (MA).
Patients with diabetes demonstrated significantly reduced K time (rapidity of clot strengthening; P ⬍ .05), increased angle (acceleration of fibrin buildup; P ⬍ .05), and MA (ultimate clot strength; P ⬍ .05).
We also found a significant decrease in R (P ⬍ .05) and K (P ⬍ .05) and increase in angle (P ⬍ .05) and CI (P ⬍ .05) in blood samples taken from the common femoral vein in patients with a history of DVT (n ⫽ 2), compared with
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Fig 5. Severity of iliac disease and change in coagulation index (CI).
Table II. Correlation between changes in thromboelastographic parameters between aorta and common femoral artery and extent of iliac stenosis Mean difference between aortic and femoral samples (Mean/CI) Parameter R K Angle MA CI
Correlation with Iliac disease
Mean ⫾ SD
95% confidence interval
r
P
⫺0.44 ⫾ 3.1 0.08 ⫾ 1.67 2.08 ⫾ 12.3 3.1 ⫾ 9.97 0.75 ⫾ 1.42
⫺1.6, 0.72 ⫺0.54, 0.7 ⫺2.5, 6.6 ⫺0.62, 6.8 0.22, 1.2
0.443 0.151 0.218 0.379 0.429
.014 .151 .248 .039 .018
R, Reaction time (time to initial fibrin formation); K, dynamics of clot formation; Angle, acceleration of fibrin buildup and cross-linking (clot strengthening); MA, maximum amplitude (ultimate clot strength); CI, coagulation index (overall coagulation status).
those with no such history, but the results in patients with a history of acute myocardial infarction, cerebrovascular accident, and peripheral vascular surgery did not differ from those in patients without such history. DISCUSSION Our study confirms that blood becomes more coagulable as it traverses the ischemic limb. Platelet activation, as well as increased thrombin production, takes place within the limb. Blood coagulability increases as it flows down an atherosclerotic iliac artery, and the magnitude of that change is related to the severity of stenosis. Ischemia is unlikely to have a role here, and it is probable that the changes in blood coagulability are caused by the presence
of atherosclerotic disease. This may be due to interaction with atherosclerotic plaque, but in the carotid and coronary arteries, where this has been extensively studied, enhanced coagulation is usually associated with “unstable plaque” and ulceration. We recorded no details of plaque ulceration or measures of plaque stability, but unstable plaque is usually associated with acute symptoms rather than the relatively stable chronic ischemia seen in our patients. Another possible cause of coagulation activation in the iliac arteries might be the increased shear stress26 associated with localized stenosis. This induces platelet aggregation in both acute coronary syndromes27 and chronic coronary artery disease.28 It is possible that other steps in coagulation are also activated under such circumstances. The third
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Fig 6. Correlation between change in coagulation index (CI) and ankle-brachial pressure index (ABPI).
Table III. Correlation between changes in thromboelastographic parameters between common femoral artery and vein, and ABPI Mean difference across A-V segment
Parameter R K Angle MA CI
Mean ⫾ SD
95% Confidence interval
⫺0.91 ⫾ 0.43 ⫺0.30 ⫾ 0.15 3.53 ⫾ 1.49 3.81 ⫾ 1.04 0.76 ⫾ 0.19
⫺1.7, 0.02 ⫺.62, 0.01 0.47, 6.5 1.6, 5.9 0.36, 1.16
Correlation with ABPI
r
P
⫺0.370 0.129 ⫺0.209 ⫺0.370 ⫺0.427
.074 .496 .268 .044 .018
ABPI, Ankle-brachial pressure index; A-V, arteriovenous; R, reaction time (time to initial fibrin formation); K, dynamics of clot formation; Angle, acceleration of fibrin buildup and cross-linking (clot strengthening); MA, maximum amplitude (ultimate clot strength); CI, coagulation index (overall coagulation status).
possibility is that turbulence in blood flow over irregular plaque promotes coagulation, although there is no direct evidence for this in the literature. Changes recorded as blood flows through the ischemic limb are more complex. It is presumed that the same mechanisms that induce a change in coagulability in the iliac segment also have a role in changes within the limb. Sobel et al29 demonstrated increased thrombin generation within the ischemic limb by measuring fibrinopeptide A levels, which were consistently higher in venous samples than in the arterial inflow to an ischemic limb. These same authors found no increase in -thromboglobulin, and concluded that there was no activation of platelets across the ischemic leg, although other studies have found systemic evidence of platelet activation in such limbs.30 We attempted to measure the extent of atherosclerotic disease in the infrainguinal vessels with a crude angio-
graphic score, but arteries that are heavily diseased are likely to cause diversion of flow into disease-free collateral vessels; indeed, blood will never be exposed to the most heavily diseased (occluded) arteries. We did show a correlation between the increase in coagulability across a limb and the extent of ischemia, as measured with ABPI on that side. Thus flow through ischemic tissue may promote coagulation, but we cannot exclude the possibility that this relationship arises through the close association between the severity of ischemia and the extent of atherosclerotic disease past which the blood must flow to the distal limb. The changes in coagulability could all be due to exposure to atherosclerotic disease. We have shown that arterial blood entering the ischemic leg is significantly less coagulable than that leaving it. Somehow the degree of coagulation activation is reduced before blood returns to the leg. The blood supply to even
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Fig 7. Correlation between change in maximum amplitude (MA) and ankle-brachial pressure index (ABPI) across ischemic limb.
Fig 8. Correlation between change in maximum amplitude (MA) across ischemic limb and angiographic severity of infrainguinal atherosclerotic disease. A-V, arteriovenous.
an ischemic limb is about 400 mL/min.31 This represents less than 10% of cardiac output, and thus is subject to dilution by blood returning to the heart from elsewhere in the body. In addition, activated clotting factors are removed by the reticuloendotheial system, in particular the
liver.32 Thus blood returning to the ischemic limb has much lower coagulation activity than blood that left it. We used ABPI as a measure of ischemia rather than as a measure of atherosclerotic disease in the limb, because it reflects the perfusion pressure at ankle level and thus relates
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to the level of ischemia. It depends on flow through collateral vessels as well as through stenosed arteries, and is therefore not a measure simply of atherosclerotic disease. We could have used symptoms as a measure of ischemia (eg, asymptomatic vs claudication vs rest pain), but because we were investigating the less symptomatic leg, any symptoms of claudication could have been masked by more severe disability in the other leg. We used TEG to assess coagulation, because its sensitivity and specificity compare well with routine coagulation tests33,34 and it provides a measure of the overall coagulation status of a given blood sample rather than of individual clotting factors in isolation.35 TEG analysis of citrated samples is more sensitive in the detection of procoagulant alterations than other coagulation tests are,14 and is therefore ideal for assessment of coagulation in patients with PAOD. Patients with peripheral vascular disease exhibit increased aggregation of platelets in baseline measurements when studied with aggregometry,36 and this has been shown to increase further during and immediately after peripheral vascular surgery despite preprocedure ingestion of aspirin and administration of heparin during the procedure. The TEG method has the potential to unmask hypercoagulability in these patients, and can enable identification of those patients at risk for thrombotic events after vascular surgery. Aspirin ingestion in our patients (n ⫽ 12) was reflected in prolongation of R time in samples taken from the aorta, and K values of samples taken from the common femoral artery. Previous studies in subjects taking aspirin have failed to detect an effect of aspirin. These studies were performed in healthy control subjects, with blood samples taken from a peripheral vein after ingestion of aspirin in doses up to 650 mg/d over 10 days. Our study involved subjects in whom platelet activation already exists,1,37 and it is perhaps not surprising that the results differ. Patients with PAOD have relatively high mortality from cardiovascular and cerebrovascular disease. A significant part of that mortality relates to thrombosis in critical vessels, which may be promoted by hypercoagulability of the systemic circulation. We have shown that atherosclerotic disease in the leg is a potential promoter of coagulation. We do not know whether the presence of ischemic tissue in the leg also contributes. Our current approach to treatment of the ischemic leg is to reverse ischemic changes or ablate ischemic tissue; we do not remove the atherosclerotic disease. On the other hand, advances in drug therapy, in particular cholesterol-lowering drugs, have the potential to reduce the size of atherosclerotic plaque. We have shown that the mere presence of such disease is sufficient to enhance coagulation, but we do not yet know whether the persistence of ischemic tissue is likely to prejudice patient survival as a result of its systemic effect. CONCLUSION We have found that blood increases in platelet and coagulation factor activity as it flows down the iliac vessel in
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proportion to the extent of iliac atherosclerotic disease. We have also shown that blood circulating through an ischemic limb increases in coagulability. Part of the change is probably due to contact with atherosclerotic arteries, but some of the change may be due to flow through ischemic tissue. We thank Dr R. Weatherall, Medical Statistician, at ICRF/NHS Centre for Statistics in Medicine, Institute of Health Sciences, Oxford, for valuable advice regarding the statistical methods used in this study. REFERENCES 1. Cassar K, Bachoo P, Ford I, Greaves M, Brittenden J. Platelet activation is increased in peripheral arterial disease. J Vasc Surg 2003;38:99-103. 2. Reininger CB, Graf J, Reininger AJ, Spannagl M, Steckmeier B, Schweiberer L. Increased platelet and coagulatory activity indicate ongoing thrombogenesis in peripheral arterial disease. Thromb Res 1996;82: 523-32. 3. Boneu B, Leger P, Arnaud C. Haemostatic system activation and prediction of vascular events in patients presenting with stable peripheral arterial disease of moderate severity. Blood Coagulation Fibrinolysis 1998;9:129-35. 4. Speiser W, Speiser P, Minar E, Korninger C, Neissner H, Huber K, et al. Activation of coagulation and fibrinolysis in patients with arteriosclerosis: relation to localization of vessel disease and risk factors. Thromb Res 1990;59:77-88. 5. Banerjee AK, Pearson J, Gilliland D, Lewis JD, Stirling Y, Meade TW. A six-year prospective study of fibrinogen and other risk factors associated with mortality in stable claudicants. Thromb Haemost 1992;68:261-3. 6. Cortellaro M, Boschetti C, Cofranesco E, Zanbussi C, Catalano M, Gaetano G, et al, and the PLAT Study Group. The PLAT study. Hemostatic function in relation to atherothrombotic ischemic events in vascular disease patients: principal results. Arterioscler Thromb 1992; 12:1063-70. 7. Lee AJ, Fowkes FG, Lowe GD, Rumley A. Fibrin D-dimer, haemostatic factors and peripheral vascular disease. Thromb Haemost 1995;74:82832. 8. Van der Bom JG, Bots ML, Haverkate F, Meijer P, Hofman A, Kluft C, et al. Activation products of the haemostatic system in coronary, cerebrovascular and peripheral arterial disease. Thromb Haemost 2001;85: 233-9. 9. Meade TW, Ruddock V, Stirling Y, Chakrabarti R, Miller GJ. Fibrinolytic activity, clotting factors, and long-term incidence of ischaemic heart disease in the Northwick Park Heart Study. Lancet 1993;342: 1076-9. 10. Thompson SG, Kienast J, Pyke SDM, Haverkate F, van de Loo CJW, for the European Concerted Action on Thrombosis and Disabilities Angina Pectoris Study Group. Hemostatic factors and the risk of myocardial infarction or sudden death in patients with angina pectoris. N Engl J Med 1995;332:635-41. 11. Lassila R, Peltonen S, Lepatalo M, Saarien O, Kauhanen P, Manninen V. Severity of peripheral atherosclerosis is associated with fibrinogen and degradation of cross-linked fibrin. Atheroscler Thromb 1993;13: 1412-7. 12. Woodburn KR, Lowe GD, Rumley A, Love J, Pollock JG. Relation of hemostatic, fibrinolytic and rheological variables to the angiographic extent of peripheral arterial occlusive disease. Int Angiol 1995;14:34652. 13. Mallett SV, Platt M. Role of thromboelastography in bleeding diatheses and regional anaesthesia. Lancet 1991;338:765-7. 14. Mahla E, Long T, Vicenzi MN, Werkgartner G, Maier R, Probst C, et al. Thromboelastography for monitoring prolonged hypercoagulability after major abdominal surgery. Anesth Analg 2001;92:572-7. 15. Gibbs NM, Crawford GPM, Michalopoulos N. Thromboelastographic patterns following abdominal aortic surgery. Anaesth Intens Care 1994; 22:534-8. 16. Abrahams JM, Torchia MB, McGarvey M, Putt M, Baranov D, Sinson GP. Perioperative assessment of coagulability in neurosurgical patients
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Submitted Sep 10, 2003; accepted Dec 9, 2003. Available online Mar 8, 2004.