Macrovascular Thrombosis Research Articles

Macrovascular thrombosis is driven by tissue factor derived primarily from the blood vessel wall

AbstractLeukocytes and leukocyte-derived microparticles contain low levels of tissue factor (TF) and incorporate into forming thrombi. Although this circulating pool of TF has been proposed to play a key role in thrombosis, its functional significance relative to that of vascular wall TF is poorly defined. We tested the hypothesis that leukocyte-derived TF contributes to thrombus formation in vivo. Compared to wild-type mice, mice with severe TF deficiency (ie, TF–/–, hTF-Tg+, or “low-TF”) demonstrated markedly impaired thrombus formation after carotid artery injury or inferior vena cava ligation. A bone marrow transplantation strategy was used to modulate levels of leukocyte-derived TF. Transplantation of low-TF marrow into wild-type mice did not suppress arterial or venous thrombus formation. Similarly, transplantation of wild-type marrow into low-TF mice did not accelerate thrombosis. In vitro analyses revealed that TF activity in the blood was very low and was markedly exceeded by that present in the vessel wall. Therefore, our results suggest that thrombus formation in the arterial and venous macrovasculature is driven primarily by TF derived from the blood vessel wall as opposed to leukocytes.

Platelet-endothelial interactions: sepsis, HIT, and antiphospholipid syndrome.

Acquired abnormalities in platelets, endothelium, and their interaction occur in sepsis, immune heparin-induced thrombocytopenia (HIT), and the antiphospholipid syndrome. Although of distinct pathogeneses, these three disorders have several clinical features in common, including thrombocytopenia and the potential for life- and limb-threatening thrombotic events, ranging from microvascular (sepsis > antiphospholipid > HIT) to macrovascular (HIT > antiphospholipid > sepsis) thrombosis, both venous and arterial. In Section I, Dr. William Aird reviews basic aspects of endothelial-platelet interactions as a springboard to considering the common problem of thrombocytopenia (and its mechanism) in sepsis. The relationship between thrombocytopenia and other aspects of the host response in sepsis, including activation of coagulation/inflammation pathways and the development of organ dysfunction, is discussed. Practical issues of platelet count triggers and targeted use of activated protein C concentrates are reviewed. In Section II, Dr. Theodore Warkentin describes HIT as a clinicopathologic syndrome, i.e., the diagnosis should be based on the concurrence of an appropriate clinical picture together with detection of platelet-activating and/or platelet factor 4-dependent antibodies (usually in high levels). HIT is a profound prothrombotic state (odds ratio for thrombosis, 20-40), and the risk for thrombosis persists for a time even when heparin is stopped. Thus, pharmacologic control of thrombin (or its generation), and postponing oral anticoagulation pending substantial resolution of thrombocytopenia, is appropriate. Indeed, coumarin-associated protein C depletion during uncontrolled thrombin generation of HIT can explain limb loss (coumarin-associated venous limb gangrene) or skin necrosis syndromes in some patients. In Section III, Dr. Jacob Rand presents the most recent concepts on the mechanisms of thrombosis in the antiphospholipid syndrome, and focuses on the role of beta(2)-glycoprotein I as a major antigenic target in this condition. Diagnosis of the syndrome is often complicated because the clinical laboratory tests to identify this condition have been empirically derived. Dr. Rand addresses the practical aspects of current testing for the syndrome and current recommendations for treating patients with thrombosis and with spontaneous pregnancy losses.

Coagulation and fibrinolysis in patients undergoing operation for ruptured and nonruptured infrarenal abdominal aortic aneurysms

Purpose : Hemorrhage and thrombosis predisposing to myocardial infarction, multiple organ failure, and thromboembolism account for the majority of the morbidity and mortality associated with repair of ruptured and nonruptured abdominal aortic aneurysms (AAAs). The aim of this study was to examine coagulation and fibrinolysis in patients operated on for ruptured and nonruptured infrarenal AAAs. Methods : Ten patients operated on for ruptured and 9 patients operated on for nonruptured AAAs were studied. Tissue plasminogen activator (t-PA) antigen, thrombin-antithrombin (TAT), and D-dimer were measured before induction of anesthesia. Plasminogen activator inhibitor (PAI) activity, t-PA activity, and prothrombin fragment (PF) 1+2 were measured before induction of anesthesia, immediately before aortic clamp release, and 5 minutes and 24 hours after aortic clamp release. Results : Preoperatively, ruptured AAA was associated with significantly elevated t-PA antigen (median 15.7 ng/mL, range 9.0 to 22.1 ng/mL versus nonrupture: median 6.6 ng/mL, range 4.7 to 16.4 ng/mL; P < .01, Mann-Whitney test), increased PAI activity (median 36.5 arbitrary units/mL, range 20.6 to 38.8 arbitrary units/mL versus nonrupture: median 8.2 arbitrary units/mL, range 3.2 to 21.7 arbitrary units/mL; P < .001), reduced t-PA activity (median 0.12 IU/mL, range 0.06 to 0.4 IU/mL versus nonrupture: median 0.49 IU/mL, range 0.14 to 3.2 IU/mL; P < .01), elevated TAT (median 135.5 μg/L, range 61.2 to 209.4 μg/L versus nonrupture: median 21.6 μg/L, range 6.6 to 180.4 μg/L; P < .02) and elevated PF 1+2 (median 9.0 nmol/L, range 5.4 to 11.6 nmol/L versus nonrupture: median 2.2 nmol/L, range 0.7 to 7.1 nmol/L, P < .001). There was no significant difference in preoperative D-dimer levels (median 3460 ng/mL, range 1236 to 7860 ng/mL versus nonrupture: median 1642 ng/mL, range 728 to 5334 ng/mL; P = .07). The differences in PAI activity, t-PA activity, and PF 1+2 persisted throughout the course of surgery, but there was no significant difference between the groups at 24 hours. Conclusion: These novel data demonstrate that ruptured AAA repair is associated with inhibition of systemic fibrinolysis and intense thrombin generation. Similar changes are seen in nonruptured AAA but are of a lesser magnitude. This procoagulant state may contribute to the microvascular and macrovascular thrombosis that leads to myocardial infarction, multiple organ failure, and thromboembolism. (J Vasc Surg 1999;30:641-50.)

Vascular surgical society of great britain and ireland: inhibition of systemic fibrinolysis is associated with myocardial injury in patients operated on for ruptured abdominal aortic aneurysm

BACKGROUND: Previous work has demonstrated that ruptured abdominal aortic aneurysm (AAA) is associated with systemic thrombin generation and inhibition of systemic fibrinolysis. The procoagulant and hypofibrinolytic state associated with ruptured AAA predisposes to microvascular and macrovascular thrombosis and subsequent myocardial injury. The aim of this study was to determine the relationship between haemostatic derangement and biochemical evidence of myocardial injury in patients operated on for ruptured AAA. METHODS: Ten patients undergoing repair of ruptured AAA were studied. Tissue plasminogen activator (tPA) activity, plasminogen activator inhibitor (PAI) activity, prothrombin fragment (PF) 1 + 2, D-dimer and fibrinogen levels were measured before operation, and immediately before and 5 min after aortic clamp release. Plasma levels of cardiac troponin (cTn) I were measured before operation, and 6 and 24 h after aortic clamp release. RESULTS: There was no relationship between tPA activity, PF 1 + 2, D-dimer or fibrinogen and cTn-I levels at any sampling point. There was, however, a significant positive correlation (Spearman rank test) between PAI activity immediately before (median 38.6 (range 13.0-39.4) units ml-1) and 5 min after (37.2 (10.6-39.4) units ml-1) aortic clamp release, and cTn-I at 6 h (median 3.17 (range less than 0.5 to 71.1) ng ml-1) and 24 h (5.55 (range less than 0.5 to 110) ng ml-1) after aortic clamp release. CONCLUSION: These data strongly support the hypothesis that the inhibition of systemic fibrinolysis which occurs in response to ischaemia and reperfusion during ruptured AAA repair contributes to the development of subsequent myocardial injury.

State-of-the-Art Review : Role of Antithrombin and Tissue Factor Pathway Inhibitor in the Control of Thrombosis and Mediation of Heparin Action

Deficiency of any of the two coagulation in hibitors antithrombin (AT) and tissue factor pathway in hibitor (TFPI) lowers the resistance to thrombosis. He reditary deficiency of AT leads to a high risk of throm bosis, which occasionally responds poorly to heparin therapy. Experimental deficiency of TFPI lowers the re sistance to infusion of both tissue factor and endotoxin, both regarding microvascular thrombosis and fatality. Administration of either AT or TFPI protects against mi cro- and macrovascular thrombosis. Injection of heparin and some other glycosaminoglycans releases intima bound TFPI to the blood. Heparin accelerates the inhib itory effects of both inhibitors, in particular the effect of AT. The influence of the two inhibitors on the various anticoagulant reactions have been studied using blocking antibodies. It is suggested that the anticoagulant and an tithrombotic effects of heparin are mainly mediated by the accelerated inactivation of thrombin, factor IXa and factor X by AT, and augmented inactivation of tissue factor-factor VIIa by TFPI released to the blood.