Coagulation 2006: a modern view of hemostasis

Fibrinolysis in trauma: a review

Fibrinolytic dysregulation is an important mechanism in traumatic coagulopathy. It is an incompletely understood process that consists of a spectrum ranging from excessive breakdown (hyperfibrinolysis) and the shutdown of fibrinolysis. Both hyperfibrinolysis and shutdown are associated with excess mortality and post-traumatic organ failure. The pathophysiology appears to relate to endothelial injury and hypoperfusion, with several molecular markers identified in playing a role. Although there are no universally accepted diagnostic tests, viscoelastic studies appear to offer the greatest potential for timely identification of patients presenting with fibrinolytic dysregulation. Treatment is multimodal, involving prompt hemorrhage control and resuscitation, with controversy surrounding the use of antifibrinolytic drug therapy. This review presents the current evidence on the pathophysiology, diagnostic challenges, as well as the management of this hemostatic dysfunction.

LEVEL OF EVIDENCE

Level III.

Significant genetic association of a functional TFPI variant with circulating fibrinogen levels and coronary artery disease

The tissue factor pathway inhibitor (TFPI) gene encodes a protease inhibitor with a critical role in regulation of blood coagulation. Some genomic variants in TFPI were previously associated with plasma TFPI levels, however, it remains to be further determined whether TFPI variants are associated with other coagulation factors. In this study, we carried out a large population-based study with 2313 study subjects for blood coagulation data, including fibrinogen levels, prothrombin time (PT), activated partial thromboplastin time (APTT), and thrombin time (TT). We identified significant association of TFPI variant rs10931292 (a functional promoter variant with reduced transactivation) with increased plasma fibrinogen levels (P = 0.017 under a recessive model), but not with PT, APTT or TT (P > 0.05). Using a large case-control association study population with 4479 CAD patients and 3628 controls, we identified significant association between rs10931292 and CAD under a recessive model (OR 1.23, P = 0.005). For the first time, we show that a TFPI variant is significantly associated with fibrinogen levels and risk of CAD. Our finding contributes significantly to the elucidation of the genetic basis and biological pathways responsible for fibrinogen levels and development of CAD.

Targeted Thromboelastographic (TEG) Blood Component and Pharmacologic Hemostatic Therapy in Traumatic and Acquired Coagulopathy

Trauma-induced coagulopathy (TIC) is a recently described condition which traditionally has been diagnosed by the common coagulation tests (CCTs) such as prothrombin time/international normalized ratio (PT/INR), activated partial thromboplastin time (aPTT), platelet count, and fibrinogen levels. The varying sensitivity and specificity of these CCTs have led trauma coagulation researchers and clinicians to use Viscoelastic Tests (VET) such as Thromboelastography (TEG) to provide Targeted Thromboelastographic Hemostatic and Adjunctive Therapy (TTHAT) in a goal directed fashion to those trauma patients in need of hemostatic resuscitation. This review describes the utility of VETs, in particular, TEG, to provide TTHAT in trauma and acquired non-trauma-induced coagulopathy.

Platelet count as a predictor of metastasis and venous thromboembolism in patients with cancer

Platelets are anucleate cells in the blood at concentrations of 150,000 to 400,000 cells/µL and play a key role in hemostasis. Several studies have suggested that platelets contribute to cancer progression and cancer-associated thrombosis. In this review, we provide an overview of the biochemical and biophysical mechanisms by which platelets interact with cancer cells and review the evidence supporting a role for platelet-enhanced metastasis of cancer, and venous thromboembolism (VTE) in patients with cancer. We discuss the potential for and limitations of platelet counts to discriminate cancer disease burden and prognosis. Lastly, we consider more advanced diagnostic approaches to improve studies on the interaction between the hemostatic system and cancer cells.

Anticoagulation in cirrhosis: a new paradigm?

The liver plays a crucial role in coagulation cascade. Global hemostatic process is profoundly influenced by the presence of liver disease and its complications. Patients with cirrhosis have impaired synthesis of most of the factors involved in coagulation and fibrinolysis process due to a reduced liver function and altered platelet count secondary to portal hypertension. Altered routine tests and thrombocytopenia were considered in the past as associated with increased risk of bleeding. These concepts explain both the routine use of plasma and/or platelets transfusion in patients with liver cirrhosis, especially before invasive procedures, and why these patients were considered "auto-anticoagulated". New recent evidences show that patients with liver cirrhosis have a more complex hemostatic alteration. Despite the presence of altered levels of factors involved in primary hemostasis, coagulation and fibrinolysis, patients with stable cirrhosis have a rebalanced hemostatic, which however can easily be altered by decompensation or infection, both in hemorrhagic or thrombotic direction. Patients with cirrhosis have an increased risk of venous thrombotic events (namely portal vein thrombosis) while bleeding seems to be related to the grade of portal hypertension rather than to a hemostatic imbalance. The use of anticoagulants both as treatment or prophylaxis is safe, reduces the rate of portal vein thrombosis and decompensation, and improves survival. Standard laboratory coagulation tests are unable to predict bleeding and are inadequate for the assessment of hemostatic status in these patients, hence more comprehensive tests are required to guide the management of thrombotic and bleeding complications.

The effect of fibrinogen concentrate on perioperative bleeding in transurethral resection of the prostate: a double-blind placebo-controlled and randomized study

Essentials Perioperative bleeding during prostate surgery is still a common morbidity. Anticoagulant and antiplatelet medications contribute to the risk of hemorrhage and prolonged hospital stay. Multiple pharmacological agents have been proposed, but none of them have been widely accepted. It is crucial to find a safe and effective modality to reduce hemorrhage.

SUMMARY

Background Hemorrhage during transurethral resection of the prostate (TUR-P) has always been a concern. Several studies have shown preoperative administration of fibrinogen concentrate to have promising results in reducing hemorrhage in cardiac surgery. Objectives To investigate the hemostatic effect of fibrinogen concentrate administration on reducing the amount of bleeding during TUR-P in patients with benign prostatic hyperplasia. Methods Sixty men with benign prostatic hyperplasia, who were chosen to undergo TUR-P, entered this prospective randomized double-blind placebo-controlled study. The participants were randomly assigned to two groups: treatment (n = 31) and placebo (n = 29). They received an infusion of 2 g of fibrinogen concentrate (treatment group) or normal saline (placebo group) before surgery. Data regarding the amount of bleeding, the operation and complications were recorded and analyzed. Results No difference was observed in bleeding between the fibrinogen and placebo groups during (521 mL versus 557 mL, respectively) and after (291 mL versus 341 mL, respectively) surgery. This lack of difference was also seen in operation time (43 min versus 42 min), irrigating fluid volume used during (17 L versus 19 L) and after (29 L versus 28 L) surgery, and resected adenoma volume (19 g versus 19 g). The mean blood pressure was also similar in both groups as a confounding factor for the amount of bleeding. Conclusion Preoperative administration of fibrinogen concentrate had no significant influence on intraoperative and postoperative bleeding in TUR-P surgery.

Flavonolignans inhibit ADP induced blood platelets activation and aggregation in whole blood

Flavonolignans are a group of active chemical compounds presented in the silymarin - a standardized extract obtained from fruits and seeds of Milk thistle (Silybum marianum L. Gaernt.). Since the 70s of the last century, flavonolignans have been regarded to the official medicine as a substances having hepatoprotective properties. However many researches performed in recent years have demonstrated that flavonolignans posses many other healthy properties including modulation of variety cell-signaling pathways. The aim of our study was to examine the effects of three major flavonolignans (silybin, silychristin and silydianin) on ADP-induced blood platelet activation using the flow cytometry analysis as well as determine the mechanism of this interaction by bioinformatic ligand docking method. We observed that all tested flavonolignans in dose-dependent manner inhibit formation of blood platelet aggregates and microparticles as well as decrease expression of P-selectin and activation of integrin α_IIbβ₃. Our computer-generated models confirm the flow cytometry analysis. We observed that all tested flavonolignans have conformations which are able to bind to the extracellular domain of P2Y12 receptor and probably block interaction with ADP. Our studies may help in the development of a new potential anti-platelet agent, which might be an alternative to the current using drugs.

Synergy Between Tissue Factor and Exogenous Factor XIa in Initiating Coagulation

OBJECTIVE

Recent evidence suggests involvement of coagulation factor XIa (FXIa) in thrombotic event development. This study was conducted to explore possible synergies between tissue factor (TF) and exogenous FXIa (E-FXIa) in thrombin generation.

APPROACH AND RESULTS

In thrombin generation assays, for increasing concentrations of E-FXIa with low, but not with high TF concentrations, peak thrombin significantly increased whereas lag time and time to peak significantly decreased. Similar dependencies of lag times and rates of thrombin generation were found in mathematical model simulations. In both in vitro and in silico experiments that included E-FXIa, thrombin bursts were seen for TF levels much lower than those required without E-FXIa. For in silico thrombin bursts initiated by the synergistic action of TF and E-FXIa, the mechanisms leading to the burst differed substantially from those for bursts initiated by high TF alone. For the synergistic case, sustained activation of platelet-bound FIX by E-FXIa, along with the feedback-enhanced activation of platelet-bound FVIIIa and FXa, was needed to elicit a thrombin burst. Furthermore, the initiation of thrombin bursts by high TF levels relied on different platelet FIX/FIXa binding sites than those involved in bursts initiated by low TF levels with E-FXIa.

CONCLUSIONS

Low concentrations of TF and exogenous FXIa, each too low to elicit a burst in thrombin production alone, act synergistically when in combination to cause substantial thrombin production. The observation about FIX/FIXa binding sites may have therapeutic implications.

Platelets miRNA as a Prediction Marker of Thrombotic Episodes

The blood platelets are crucial for the coagulation physiology to maintain haemostatic balance and are involved in various pathologies such as atherosclerosis and thrombosis. The studies of recent years have shown that anucleated platelets are able to succeed protein synthesis. Additionally, mRNA translation in blood platelets is regulated by miRNA molecules. Recent works postulate the possibility of using miRNAs as biomarkers of atherosclerosis and ischemic episodes. This review article describes clinical studies that presented blood platelets miRNAs expression profile changes in different thrombotic states, which suggest use of these molecules as predictive biomarkers.

Current Limitations of the Assessment of Haemostasis in Adult Extracorporeal Membrane Oxygenation Patients and the Role of Point-of-Care Testing

Haemostatic perturbations are commonly seen in extracorporeal membrane oxygenation (ECMO) patients and remain a clinical challenge, contributing significantly to morbidity and mortality. The approach to anticoagulation monitoring and the management of bleeding varies considerably across ECMO centres. Routine laboratory tests have their limitations in terms of turnaround time and specificity of information provided. Newer point-of-care testing (POCT) for coagulation may overcome these issues, as it provides information about the entire coagulation pathway from clot initiation to lysis. It is also possible to obtain qualitative information on platelet function from these tests. Furthermore, the ability to incorporate these results into a goal-directed algorithm to manage bleeding with targeted transfusion strategies appears particularly attractive and cost effective. Further studies are required to evaluate the utility of POCT to optimise bleeding and anticoagulation management in these complex patients.

Popular naturally occurring antioxidants as potential anticoagulant drugs

Blood coagulation is a physiological process whose main task is prevention of blood loss from injured vessels. This process consists of a series of zymogens proteolytic activation leading to the generation of the main coagulation enzyme - thrombin. Besides its important role in blood coagulation process, thrombin is involved in many cardiovascular diseases, which are responsible for almost half of fatalities in economically developed countries. The evidence for the increased generation and in vivo activity of thrombin was observed in the plasma of individuals at high risk for clinically significant venous and arterial thromboembolic complications. Antioxidants activity of plants extracts has been well known for many years and was confirmed by many publications. However, during the last decade many research centers presented results suggesting anticoagulant potential of various plant extracts. Many researchers have also provided evidence that polyphenol compounds are able to inhibit the activity of many enzymes, including serine proteases. All research described in this review clearly indicate that polyphenols and polyphenol-rich extracts possess not only antioxidative but also anticoagulant properties and may be useful in creation of new therapeutic agents or dietary supplements. Based on described properties polyphenols would be very helpful with both prevention and treatment of thromboembolic complications associated with multiple failures of haemostasis, because the available therapeutic agents do not offer such double-effects (antioxidant and anticoagulant).

Challenges and Treatment for Stroke Prophylaxis in Patients with Atrial Fibrillation in Mexico: A Review

Atrial fibrillation (AF) is associated with an increased risk of stroke. AF-related strokes cause greater disability and mortality than those in patients without AF, and are associated with a significant clinical and economic burden in Mexico. Antithrombotic therapy reduces stroke risk in patients with AF and is recommended for all patients except those classified as having a low stroke risk. However, its use is suboptimal all around the world; one study showed that only 4 % of Mexican patients with AF who presented with ischemic stroke were in the therapeutic range for anticoagulation. Vitamin K antagonists (VKAs) such as warfarin or acenocoumarin have long been the only oral anticoagulants for stroke prevention in AF. Although effective, VKAs have disadvantages, including the need for regular coagulation monitoring and dose adjustment. Interactions with numerous common medications and foods contribute to the risk of serious bleeding and thrombotic events in VKA-treated patients. Thus novel oral anticoagulants (NOACs), more properly called direct oral anticoagulants (DOACs), such as dabigatran etexilate, rivaroxaban, apixaban, and edoxaban (not available in Mexico), have been developed. These offer the convenience of fixed-dose treatment without the need for monitoring, and have few drug or food interactions. Pivotal phase III trials have demonstrated that these agents are at least as effective as warfarin in preventing stroke and are associated with a reduced risk of intracranial hemorrhage. With apixaban approved in Mexico in April 2013, clinicians now have the choice of three novel DOACs as alternatives to warfarin. However, it is yet to be established which of these agents should be the first choice, and treatment decisions are likely to depend on the individual patient's characteristics.

The role of complement activation in thrombosis and hemolytic anemias

OBJECTIVE

The objective of this study was to describe complement activation in hemostatic and pathologic states of coagulation and in the acquired and congenital hemolytic anemias.

METHODS AND RESULTS

We review published and emerging data on the involvement of the classic, alternative and lectin-based complement pathways in coagulation and the hemolytic anemias. The alternative pathway in particular is always "on," at low levels, and is particularly sensitive to hyper-activation in a variety of physiologic and pathologic states including infection, autoimmune disorders, thrombosis and pregnancy, requiring tight control predicated on a variety of soluble and membrane bound regulatory proteins. In acquired hemolytic anemias such as paroxysmal nocturnal hemoglobinuria (PNH) and cold agglutinin disease (CAD), the complement system directly induces red blood cell injury, resulting in intravascular and extravascular hemolysis. In congenital hemolytic anemias such as sickle cell disease and β-thalassemia, the complement system may also contribute to thrombosis and vascular disease. Complement activation may also lead to a storage lesion in red blood cells prior to transfusion.

CONCLUSION

Complement pathways are activated in hemolytic anemias and are closely linked with thrombosis. In acquired disorders such as PNH and possibly CAD, inhibition of the alternative complement pathway improves clinical outcomes and reduces thrombosis risk. Whether complement inhibition has a similar role in congenital hemolytic anemias apart from the atypical hemolytic-uremic (aHUS)-type thrombotic microangiopathies remains to be determined.

Retrospective Study of 122 Dogs That Were Treated with the Antifibrinolytic Drug Aminocaproic Acid: 2010-2012

Antifibrinolytic drugs are used to promote hemostasis and decrease the need for red blood cell transfusion. Medical records of 122 dogs that were prescribed either oral or intravenous aminocaproic acid between 2010 and 2012 were evaluated retrospectively. Of the 122 dogs, three experienced possible drug-related adverse effects. No significant differences were identified between dogs that experienced adverse effects and those that did not and the possible adverse effects noted were all minor. All dogs that received packed red blood cell transfusions were evaluated for correlations between baseline packed cell volume or dose of red blood cells and aminocaproic acid dose and no correlation was identified. Dogs that received aminocaproic acid as a treatment for active bleeding were divided by cause of hemorrhage into the following groups: neoplastic, non-neoplastic, and unknown. No significant differences in aminocaproic acid dose or the percentage of patients requiring a blood transfusion were identified between groups.

Increased tissue factor and thrombomodulin expression and histopathological changes in placentas of pregnancies with preeclampsia

INTRODUCTION

Preeclampsia has a global frequency of 2-8% and a frequency of 10% in developing countries. In Colombia, preeclampsia causes 42% of maternal mortality. Alterations in placental homeostasis have been proposed to be involved in its pathophysiology. The aim of this study was to compare mRNA and protein levels of tissue factor (F3) and thrombomodulin (THBD) and the histopathological findings of placentas.

MATERIALS AND METHODS

We studied 16 placentas from patients with preeclampsia and 19 term placentas with uncomplicated pregnancy. An expert pathologist, who was masked to the group assignment, conducted an evaluation to determine specific histological changes. Assessments of mRNA and protein levels of F3 and THBD were performed using real-time PCR and ELISA, respectively.

RESULTS

Cases and controls differed in the frequency of decidual arteriopathy (p = 0.027), acute infarction (p = 0.001) and hyperplasia of the syncytiotrophoblast (p = 0.0017). Cases had increased levels of F3 mRNA (p = 0.0124) and protein (p <  0.0001) and THBD mRNA (p <  0.0001) and protein (p <  0.0001).

CONCLUSION

In placenta of patients with preeclampsia, we detected abnormal expression of F3 and THBD with increased protein and mRNA levels. The role of these molecules in the pathogenesis of this disease and in alterations of hemostatic and histopathological aspects of placentas need further studying.

Rivaroxaban transfer across the dually perfused isolated human placental cotyledon

OBJECTIVE

The purpose of this study was to determine the rate and extent of rivaroxaban transfer across the term human placenta and determine whether passive diffusion was the primary mechanism involved in this transfer.

STUDY DESIGN

The transplacental pharmacokinetics of rivaroxaban was determined with the ex-vivo placenta perfusion model. Rivaroxaban was added to the maternal or fetal circulation only (250 ng/mL). Additional experiments were conducted under equilibrative conditions with the addition of rivaroxaban to both the maternal and fetal circulations (250 ng/mL). Rivaroxaban concentrations were measured with the use of liquid chromatography-tandem mass spectrometry.

RESULTS

There was rapid transfer of rivaroxaban across the human placenta in both the maternal-to-fetal and fetal-to-maternal directions, as evidenced by transfer ratios of 0.69 (interquartile range, 0.58-0.73; n = 5) and 0.69 (interquartile range, 0.67-0.71; n = 2), respectively, after 3 hours. Under equilibrative conditions (n = 2), rivaroxaban concentrations remained relatively constant, which suggests that rivaroxaban crosses the placenta down a concentration gradient.

CONCLUSION

This is the first direct evidence of rivaroxaban transfer across the term human placenta from both the mother-to-fetus and fetus-to-mother directions. Our results document that unbound rivaroxaban rapidly crosses the placental barrier via passive diffusion. However, because rivaroxaban is highly bound to plasma proteins (up to 95%), this suggests that the amount of unbound drug that may reach the fetus is likely much lower. Additional studies will need to explore its safety before administering rivaroxaban to a pregnant woman.

Thrombin Generating Capacity and Phenotypic Association in ABO Blood Groups

Individuals with blood group O have a higher bleeding risk than non-O blood groups. This could be explained by the lower levels of FVIII and von Willebrand Factor (VWF) levels in O individuals. We investigated the relationship between blood groups, thrombin generation (TG), prothrombin activation and thrombin inactivation. Plasma levels of VWF, FVIII, antithrombin, fibrinogen, prothrombin and α₂Macroglobulin (α₂M) levels were determined. TG was measured in platelet rich (PRP) and platelet poor plasma (PPP) of 217 healthy donors and prothrombin conversion and thrombin inactivation were calculated. VWF and FVIII levels were lower (75% and 78%) and α₂M levels were higher (125%) in the O group. TG is 10% lower in the O group in PPP and PRP. Less prothrombin was converted in the O group (86%) and the thrombin decay capacity was lower as well. In the O group, α₂M plays a significantly larger role in the inhibition of thrombin (126%). In conclusion, TG is lower in the O group due to lower prothrombin conversion, and a larger contribution of α₂M to thrombin inactivation. The former is unrelated to platelet function because it is similar in PRP and PPP, but can be explained by the lower levels of FVIII.

The simultaneous occurrence of both hypercoagulability and hypofibrinolysis in blood and serum during systemic inflammation, and the roles of iron and fibrin(ogen)

Although the two phenomena are usually studied separately, we summarise a considerable body of literature to the effect that a great many diseases involve (or are accompanied by) both an increased tendency for blood to clot (hypercoagulability) and the resistance of the clots so formed (hypofibrinolysis) to the typical, 'healthy' or physiological lysis. We concentrate here on the terminal stages of fibrin formation from fibrinogen, as catalysed by thrombin. Hypercoagulability goes hand in hand with inflammation, and is strongly influenced by the fibrinogen concentration (and vice versa); this can be mediated via interleukin-6. Poorly liganded iron is a significant feature of inflammatory diseases, and hypofibrinolysis may change as a result of changes in the structure and morphology of the clot, which may be mimicked in vitro, and may be caused in vivo, by the presence of unliganded iron interacting with fibrin(ogen) during clot formation. Many of these phenomena are probably caused by electrostatic changes in the iron-fibrinogen system, though hydroxyl radical (OH˙) formation can also contribute under both acute and (more especially) chronic conditions. Many substances are known to affect the nature of fibrin polymerised from fibrinogen, such that this might be seen as a kind of bellwether for human or plasma health. Overall, our analysis demonstrates the commonalities underpinning a variety of pathologies as seen in both hypercoagulability and hypofibrinolysis, and offers opportunities for both diagnostics and therapies.

Viscoelasticity and Ultrastructure in Coagulation and Inflammation: Two Diverse Techniques, One Conclusion

The process of blood clotting has been studied for centuries. A synopsis of current knowledge pertaining to haemostasis and the blood components, including platelets and fibrin networks which are closely involved in coagulation, are discussed. Special emphasis is placed on tissue factor (TF), calcium and thrombin since these components have been implicated in both the coagulation process and inflammation. Analysis of platelets and fibrin morphology indicate that calcium, tissue factor and thrombin at concentrations used during viscoelastic analysis (with thromboelastography or TEG) bring about alterations in platelet and fibrin network ultrastructure, which is similar to that seen in inflammation. Scanning electron microscopy indicated that, when investigating platelet structure in disease, addition of TF, calcium or thrombin will mask disease-induced alterations associated with platelet activation. Therefore, washed platelets without any additives is preferred for morphological analysis. Furthermore, morphological and viscoelastic analysis confirmed that thrombin activation is the preferred method of fibrin activation when investigating fibrin network ultrastructure.

Plasma and Plasma Protein Product Transfusion: A Canadian Blood Services Centre for Innovation Symposium

Plasma obtained via whole blood donation processing or via apheresis technology can either be transfused directly to patients or pooled and fractionated into plasma protein products that are concentrates of 1 or more purified plasma protein. The evidence base supporting clinical efficacy in most of the indications for which plasma is transfused is weak, whereas high-quality evidence supports the efficacy of plasma protein products in at least some of the clinical settings in which they are used. Transfusable plasma utilization remains composed in part of applications that fall outside of clinical practice guidelines. Plasma contains all of the soluble coagulation factors and is frequently transfused in efforts to restore or reinforce patient hemostasis. The biochemical complexities of coagulation have in recent years been rationalized in newer cell-based models that supplement the cascade hypothesis. Efforts to normalize widely used clinical hemostasis screening test values by plasma transfusion are thought to be misplaced, but superior rapid tests have been slow to emerge. The advent of non-vitamin K-dependent oral anticoagulants has brought new challenges to clinical laboratories in plasma testing and to clinicians needing to reverse non-vitamin K-dependent oral anticoagulants urgently. Current plasma-related controversies include prophylactic plasma transfusion before invasive procedures, plasma vs prothrombin complex concentrates for urgent warfarin reversal, and the utility of increased ratios of plasma to red blood cell units transfused in massive transfusion protocols. The first recombinant plasma protein products to reach the clinic were recombinant hemophilia treatment products, and these donor-free equivalents to factors VIII and IX are now being supplemented with novel products whose circulatory half-lives have been increased by chemical modification or genetic fusion. Achieving optimal plasma utilization is an ongoing challenge in the interconnected worlds of transfusable plasma, plasma protein products, and recombinant and engineered replacements.

Laboratory assessment of the anticoagulant activity of dabigatran

BACKGROUND

Our aim was to identify laboratory assays in order to assess the anticoagulant effects of dabigatran etexilate (DE).

METHODS

Twenty patients with nonvalvular atrial fibrillation treated on DE (110 mg per os twice daily) and 20 on acenocoumarol were studied. Conventional coagulation tests, endogenous thrombin potential (ETP), thromboelastometry (ROTEM), epinephrine-induced light transmission aggregometry (LTA), and Hemoclot Thrombin Inhibitors (HTI) were performed in all patients.

RESULTS

In ROTEM analysis, the lysis index at 60 minutes was significantly lower in patients receiving DE (P = .011). In LTA, patients on DE showed decreased aggregation compared to those on acenocoumarol, marginally insignificant (P = .068). Regarding ETP, acenocoumarol affected thrombin generation more than dabigatran (area under the curve [AUC], P < .001), while statistically significant associations were detected between dabigatran levels, as determined by the HTI assay, and almost all parameters of ETP assay (AUC, P < .001).

CONCLUSION

The role of ETP in estimating anticoagulant activity of dabigatran possibly requires further research.

Warfarin versus dabigatran etexilate: an assessment of efficacy and safety in patients with atrial fibrillation

INTRODUCTION

Oral anticoagulation is the mainstay for stroke and thromboembolic event prevention in patients with atrial fibrillation (AF). Given limitations of warfarin therapy, non-vitamin K oral anticoagulants have been developed including direct thrombin inhibitors (i.e., dabigatran etexilate). Dabigatran etexilate has been tested thoroughly in terms of efficacy and safety in clinical trials and studies, involving 'real-world' cohorts. In this review, currently available evidence in patients with non-valvular AF is discussed.

AREAS COVERED

The pharmacology, efficacy and safety, and current aspects of use of dabigatran etexilate in patients with non-valvular AF are reviewed in a comparative manner to warfarin both for chronic anticoagulation and in different clinical settings.

EXPERT OPINION

Dabigatran etexilate appeared to have several pharmacokinetic and pharmacodynamic advantages over warfarin, as well as a favorable efficacy and safety profile being at least noninferior and often superior to warfarin in patients with non-valvular AF. The latter was shown in the clinical trials, meta-analyses and studies with 'real-world' data. Currently ongoing trials will expand the body of evidence on warfarin and will aid decision making in currently controversial areas. Important limitations of dabigatran etexilate include contraindications for its use in patients with prosthetic heart valves and end-stage chronic kidney disease.

Kinetic model facilitates analysis of fibrin generation and its modulation by clotting factors: implications for hemostasis-enhancing therapies

Current mechanistic knowledge of protein interactions driving blood coagulation has come largely from experiments with simple synthetic systems, which only partially represent the molecular composition of human blood plasma. Here, we investigate the ability of the suggested molecular mechanisms to account for fibrin generation and degradation kinetics in diverse, physiologically relevant in vitro systems. We represented the protein interaction network responsible for thrombin generation, fibrin formation, and fibrinolysis as a computational kinetic model and benchmarked it against published and newly generated data reflecting diverse experimental conditions. We then applied the model to investigate the ability of fibrinogen and a recently proposed prothrombin complex concentrate composition, PCC-AT (a combination of the clotting factors II, IX, X, and antithrombin), to restore normal thrombin and fibrin generation in diluted plasma. The kinetic model captured essential features of empirically detected effects of prothrombin, fibrinogen, and thrombin-activatable fibrinolysis inhibitor titrations on fibrin formation and degradation kinetics. Moreover, the model qualitatively predicted the impact of tissue factor and tPA/tenecteplase level variations on the fibrin output. In the majority of considered cases, PCC-AT combined with fibrinogen accurately approximated both normal thrombin and fibrin generation in diluted plasma, which could not be accomplished by fibrinogen or PCC-AT acting alone. We conclude that a common network of protein interactions can account for key kinetic features characterizing fibrin accumulation and degradation in human blood plasma under diverse experimental conditions. Combined PCC-AT/fibrinogen supplementation is a promising strategy to reverse the deleterious effects of dilution-induced coagulopathy associated with traumatic bleeding.

Coagulopathy in liver diseases: complication or therapy?

Coagulopathy in cirrhosis is a composite condition where liver synthetic deficit rebalances coagulation to a parallel reduction of both pro- and anticoagulant factors. Cirrhosis is therefore no longer considered a hypocoagulable state but rather a more unstable hemostatic balance with a lower threshold for tipping toward thrombosis or bleeding. Tendency to bleeding in cirrhosis is due to the reduction in the synthesis of procoagulants and a low platelet count as well as hyperfibrinolysis. Variceal hemorrhage is a frequent bleeding complication in decompensated cirrhosis. However, the possible contribution of coagulopathy as a precipitant or an aggravating factor is poorly documented and further data are required to clarify its real contributing role. Moreover, apart from the gastrointestinal tract, the occurrence of spontaneous and procedure-related bleeding elsewhere in the body, whilst not uncommon, is less than would be expected. By contrast, a large-scale population-based study has shown the propensity towards venous thrombosis in patients with liver diseases. Portal vein thrombosis (PVT) is a critical but frequent event occurring in up to 40% of patients with liver cirrhosis. PVT causes deterioration of the clinical course, the complications of portal hypertension and an increase in post-transplant mortality. The pathogenesis of PVT includes both local alterations, like blood flow reduction and endothelial activation, and systemic derangement. Systemic prohemostatic alterations include high von Willebrand factor, low ADAMTS-13, low levels of anticoagulants (antithrombin, proteins C and S) and increases in procoagulants like factor VIII. Low-molecular-weight heparin such as enoxaparin has proven to be safe and effective in both the treatment and prevention of PVT. In addition, patients in prophylaxis with enoxaparin showed a lower rate of decompensation and a better survival without bleeding complications. In such patients, circulating bacterial DNA, endotoxemia and markers of inflammation were attenuated compared to controls. These results therefore suggest a possible connection between enoxaparin, decrease of endotoxemia and reduction of portal hypertension. The approach to the coagulopathy in patients with liver diseases is changing: while the main goal for clinicians so far has been to reduce the risk of bleeding, the results of these new studies highlight the importance of preventing or treating thrombophilic disorders like PVT to avoid microcirculatory damage and eventually liver decompensation.

Trauma hemostasis and oxygenation research position paper on remote damage control resuscitation: definitions, current practice, and knowledge gaps

The Trauma Hemostasis and Oxygenation Research Network held its third annual Remote Damage Control Resuscitation Symposium in June 2013 in Bergen, Norway. The Trauma Hemostasis and Oxygenation Research Network is a multidisciplinary group of investigators with a common interest in improving outcomes and safety in patients with severe traumatic injury. The network's mission is to reduce the risk of morbidity and mortality from traumatic hemorrhagic shock, in the prehospital phase of resuscitation through research, education, and training. The concept of remote damage control resuscitation is in its infancy, and there is a significant amount of work that needs to be done to improve outcomes for patients with life-threatening bleeding secondary to injury. The prehospital phase of resuscitation is critical in these patients. If shock and coagulopathy can be rapidly identified and minimized before hospital admission, this will very likely reduce morbidity and mortality. This position statement begins to standardize the terms used, provides an acceptable range of therapeutic options, and identifies the major knowledge gaps in the field.

Thrombin inhibitory activity of some polyphenolic compounds

Thrombin, also known as an active plasma coagulation factor II, belongs to the family of serine proteases and plays a crucial role in blood coagulation process. The process of thrombin generation is the central event of the hemostatic process and regulates blood coagulant activity. For this reason, thrombin inhibition is key to successful novel antithrombotic pharmacotherapy. The aim of our present study was to examine the effects of the well-known polyphenolic compounds on the activity of thrombin, by characterization of its interaction with selected polyphenols using different biochemical methods and biosensor BIAcore analyses. Only six compounds, cyanidin, quercetin, silybin, cyanin, (+)-catechin and (-)-epicatechin, of all examined in this study polyphenols caused the inhibition of thrombin amidolytic activity. But only three of the six compounds (cyanidin, quercetin and silybin) changed thrombin proteolytic activity. BIAcore analyses demonstrated that cyanidin and quercetin caused a strong response in the interaction with immobilized thrombin, while cyanin and (-)-epicatechin induced a low response. Lineweaver-Burk curves show that used polyphenol aglycones act as competitive thrombin inhibitors. Our results suggest that polyphenolic compounds might be potential structural bases and source to find and project nature-based, safe, orally bioavailable direct thrombin inhibitors.

Monitoring target specific anticoagulants

New, target specific, oral anticoagulants have been shown to be safe and effective in prevention and treatment of thromboembolism without laboratory monitoring. However, clinical use of the drugs dabigatran, rivaroxaban, and apixaban requires laboratory measurement of their anticoagulant effect in specific clinical situations. This paper reviews the data available on use of screening and specialized testing to measure the anticoagulant effect and drug levels in patients prescribed these medications. Their effect on other coagulation assays is also reviewed.

Uncontrolled hemorrhagic shock results in a hypercoagulable state modulated by initial fluid resuscitation regimens

BACKGROUND

Previous studies have shown large-volume resuscitation modulates coagulopathy and inflammation. Our objective was to analyze the effects of initial bolus fluids used in military and civilian settings on coagulation and inflammation in a prospective, randomized, blinded trial of resuscitation of uncontrolled hemorrhage.

METHODS

Fifty swine were anesthetized, intubated, and ventilated and had monitoring lines placed. A Grade V liver injury was performed followed by 30 minutes of hemorrhage. After 30 minutes, the liver was packed, and randomized fluid resuscitation was initiated during a 12-minute period with 2 L of normal saline, 2 L of lactated Ringer's solution, 250 mL of 7.5% saline with 3% Dextran, 500 mL of Hextend, or no fluid (NF). Animals were monitored for 2 hours after injury. Thrombelastograms (TEGs), prothrombin time (PT), partial thromboplastin time, fibrinogen as well as serum interleukin 6, interleukin 8, and tumor necrosis factor α levels were drawn at baseline and after 1 hour and 2 hours.

RESULTS

The NF group had less posttreatment blood loss compared with other groups (p < 0.01). Blood loss was similar in the other groups. TEG R values in each group decreased from baseline at 1 and 2 hours (p < 0.02). The groups receiving 2 L of normal saline, 250 mL of 7.5% saline with 3% Dextran, or 500 mL of Hextend had lower TEG maximum amplitude values compared with NF group (p < 0.02). All fluids except lactated Ringer's solution resulted in significant increases in PT compared with NF, whereas all fluids resulted in significant decreases in fibrinogen compared with NF (p < 0.02). Fluid resuscitation groups as well as NF group demonstrated significant increases in inflammatory cytokines from baseline to 1 hour and baseline to 2 hours. There were no significant differences in inflammatory cytokines between groups at 2 hours.

CONCLUSION

Withholding fluid resulted in the least significant change in PT, fibrinogen, and maximum amplitude and in the lowest posttreatment blood loss. Resuscitation with different initial fluid resuscitation strategies did not result in increased proinflammatory mediators compared with animals that did not receive fluid.

Computational analysis of the effects of reduced temperature on thrombin generation: the contributions of hypothermia to coagulopathy

BACKGROUND

Hypothermia, which can result from tissue hypoperfusion, body exposure, and transfusion of cold resuscitation fluids, is a major factor contributing to coagulopathy of trauma and surgery. Despite considerable efforts, the mechanisms of hypothermia-induced blood coagulation impairment have not been fully understood. We introduce a kinetic modeling approach to investigate the effects of hypothermia on thrombin generation.

METHODS

We extended a validated computational model to predict and analyze the impact of low temperatures (with or without concomitant blood dilution) on thrombin generation and its quantitative parameters. The computational model reflects the existing knowledge about the mechanistic details of thrombin generation biochemistry. We performed the analysis for an "average" subject, as well as for 472 subjects in the control group of the Leiden Thrombophilia Study.

RESULTS

We computed and analyzed thousands of kinetic curves characterizing the generation of thrombin and the formation of the thrombin-antithrombin complex (TAT). In all simulations, hypothermia in the temperature interval 31°C to 36°C progressively slowed down thrombin generation, as reflected by clotting time, thrombin peak time, and prothrombin time, which increased in all subjects (P < 10(-5)). Maximum slope of the thrombin curve was progressively decreased, and the area under the thrombin curve was increased in hypothermia (P < 10(-5)); thrombin peak height remained practically unaffected. TAT formation was noticeably delayed (P < 10(-5)), but the final TAT levels were not significantly affected. Hypothermia-induced fold changes in the affected thrombin generation parameters were larger for lower temperatures, but were practically independent of the parameter itself and of the subjects' clotting factor composition, despite substantial variability in the subject group. Hypothermia and blood dilution acted additively on the thrombin generation parameters.

CONCLUSIONS

We developed a general computational strategy that can be used to simulate the effects of changing temperature on the kinetics of biochemical systems and applied this strategy to analyze the effects of hypothermia on thrombin generation. We found that thrombin generation can be noticeably impaired in subjects with different blood plasma composition even in moderate hypothermia. Our work provides mechanistic support to the notion that thrombin generation impairment may be a key factor in coagulopathy induced by hypothermia and complicated by blood plasma dilution.

Rivaroxaban and other novel oral anticoagulants: pharmacokinetics in healthy subjects, specific patient populations and relevance of coagulation monitoring

Unlike traditional anticoagulants, the more recently developed agents rivaroxaban, dabigatran and apixaban target specific factors in the coagulation cascade to attenuate thrombosis. Rivaroxaban and apixaban directly inhibit Factor Xa, whereas dabigatran directly inhibits thrombin. All three drugs exhibit predictable pharmacokinetic and pharmacodynamic characteristics that allow for fixed oral doses in a variety of settings. The population pharmacokinetics of rivaroxaban, and also dabigatran, have been evaluated in a series of models using patient data from phase II and III clinical studies. These models point towards a consistent pharmacokinetic and pharmacodynamic profile, even when extreme demographic factors are taken into account, meaning that doses rarely need to be adjusted. The exception is in certain patients with renal impairment, for whom pharmacokinetic modelling provided the rationale for reduced doses as part of some regimens. Although not routinely required, the ability to measure plasma concentrations of these agents could be advantageous in emergency situations, such as overdose. Specific pharmacokinetic and pharmacodynamic characteristics must be taken into account when selecting an appropriate assay for monitoring. The anti-Factor Xa chromogenic assays now available are likely to provide the most appropriate means of determining plasma concentrations of rivaroxaban and apixaban, and specific assays for dabigatran are in development.

Admission rapid thrombelastography delivers real-time "actionable" data in pediatric trauma

PURPOSE

Admission rapid thrombelastography (rTEG) is a "real-time" clinical tool used to evaluate trauma-induced coagulopathy and direct hemostatic resuscitation. The relationship of rTEG to conventional coagulation tests (CCT) and early lifesaving interventions (LSI) in pediatric trauma is unknown.

METHODS

Severely injured patients (age ≤ 14 years) with an rTEG were retrospectively reviewed (8/1/2009-8/31/2011). Demographic and clinical information was collected. Spearman's correlation and regression models were used to evaluate rTEG with respect to CCT, early transfusion, LSI, and mortality.

RESULTS

Eighty-six patients were identified. The median age was 8 years, and the median injury severity score (ISS) was 21. Activated clotting time (r=0.68), k-time (r=0.77), and α-angle (r=-0.75) showed strong correlation to PTT, and maximum amplitude (MA) (r=0.46) showed good correlation to platelet count (all p<0.001). When controlling for age, gender, and ISS, regression analysis showed that ACT, r-value, k-time, α-angle, and MA predicted red blood cell and plasma transfusion within 6h. MA (OR 0.82, 95% CI 0.70-0.96; p=0.018) was predictive of LSI. All rTEG values, except for LY30, predicted mortality.

CONCLUSION

Admission rTEG correlates with CCT and predicts early transfusion, early LSI, and outcome in pediatric trauma. rTEG provides valuable data for goal-directed hemostatic resuscitation of critically injured children.

β2 -Glycoprotein I binds to thrombin and selectively inhibits the enzyme procoagulant functions

BACKGROUND

This work was aimed at characterizing the interaction of β(2)-glycoprotein I (β(2)GPI), an abundant plasma protein of unknown function, with human thrombin, the final effector protease in the coagulation cascade.

METHODS

The β(2)GPI-thrombin interaction was studied by surface plasmon resonance (SPR), fluorescence, and molecular modeling. The effect of β(2)GPI on the procoagulant (fibrin generation and platelet aggregation) and anticoagulant (protein C activation) functions of thrombin were investigated with turbidimetric, immunocytofluorimetric and enzymatic assays.

RESULTS

SPR and fluorescence data indicated that β(2)GPI tightly bound thrombin (K(d) = 34 nM) by interacting with both protease exosites, while leaving the active site accessible. This picture is fully consistent with the theoretical model of the β(2)GPI-thrombin complex. In particular, blockage of thrombin exosites with binders specific for exosite-1 (hirugen and HD1 aptamer) or exosite-2 (fibrinogen γ'-peptide and HD22 aptamer) impaired the β2 GPI-thrombin interaction. Identical results were obtained with thrombin mutants having one of the two exosites selectively compromised by mutation (Arg73Ala and Arg101Ala). Fluorescence measurements indicated that β(2)GPI did not affect the affinity of the enzyme for active site inhibitors, such as p-aminobenzamidine and the hirudin(1-47) domain, in agreement with the structural model. β(2)GPI dose-dependently prolonged the thrombin clotting time and ecarin clotting time in β(2)GPI-deficient plasma. β(2)GPI inhibited thrombin-induced platelet aggregation (IC50 = 0.36 μM) by impairing thrombin cleavage of protease-activated receptor 1 (PAR1) (IC50 = 0.32 μM), both on gel-filtered platelets and in whole blood. Strikingly, β(2) GPI did not affect thrombin-mediated generation of the anticoagulant protein C.

CONCLUSIONS

β(2) GPI functions as a physiologic anticoagulant by inhibiting the key procoagulant activities of thrombin without affecting its unique anticoagulant function.

Bleeding diatheses and preoperative screening

Bleeding disorders pose a significant perioperative risk. Surgeons and surgical consultants should have a working knowledge of the cell-based coagulation model. Careful screening for bleeding diatheses begins with a careful history and physical examination. It is paramount to ascertain what medications and nonprescribed supplements and herbal preparations a patient is taking, as these medications can have significant effects on perioperative bleeding tendencies. Finally, screening laboratory-based coagulation assays are available. These must be used judiciously with regard to a patient's history and the clinical circumstances surrounding the surgical stressor.

Oral direct factor Xa inhibitors

Vitamin K antagonists, such as warfarin, have been the mainstay of oral anticoagulation for many decades. Although effective, warfarin has numerous limitations, including a variable dose requirement from patient to patient because of differences in dietary vitamin K intake, common genetic polymorphisms, and multiple drug interactions that affect its pharmacodynamics and metabolism. Consequently, warfarin requires frequent monitoring to ensure that a therapeutic anticoagulant effect has been achieved because excessive anticoagulation can lead to bleeding, and because insufficient anticoagulation can result in thrombosis. Such monitoring is burdensome for patients and physicians and is costly for the health care system. These limitations have prompted the development of new oral anticoagulants that target either factor Xa or thrombin. Although the path to the development of these drugs has been long, the new drugs are at least as effective and safe as warfarin, but they streamline clinical care because they can be administered in fixed doses without routine coagulation monitoring. This article focuses on rivaroxaban, apixaban, and edoxaban, the oral factor Xa inhibitors in the most advanced stages of development. After 20 years of discovery research, these agents are already licensed for several indications. Thus, the long path to finding replacements for warfarin has finally reached fruition. Therefore, development of the oral factor Xa inhibitors represents a translational science success story.

Bleeding and Thrombotic Emergencies in Pediatric Cardiac Intensive Care

Children in the cardiac intensive care unit (CICU) with congenital or acquired heart disease are at risk for hematologic complications, both hemorrhage and thrombosis. The overall incidence of hematologic complications in the CICU is unknown, but risk factors and target groups have been identified where the essential physiologic balance between bleeding and clotting has been disrupted. Although the best management of life-threatening bleeding and clotting is prevention, the cardiac intensivist is often faced with managing life-threatening hematologic events involving patients from within the unit or those who present from outside. Part I of this review deals with the propensity of children with congenital and acquired heart disease to complications of both bleeding and clotting, and includes discussions of perioperative bleeding, thromboses in single-ventricle patients, clotting of Blalock-Taussig shunts and thrombotic complications of mechanical valves. Part II deals with the subject of stroke in children with heart disease. Part III reviews monitoring the effectiveness of anticoagulation and thrombolysis in the CICU. Currently available diagnostics modalities, medications and management strategies are reviewed and future directions discussed.

Therapeutic correction of thrombin generation in dilution-induced coagulopathy: computational analysis based on a data set of healthy subjects

BACKGROUND

Prothrombin complex concentrates (PCCs), which contain different coagulation proteins, are attractive alternatives to the standard methods to treat dilution-induced (and, generally, traumatic) coagulopathy. We investigated the ability of a novel PCC composition to restore normal thrombin generation in diluted blood. The performance of the proposed PCC composition (coagulation factors [F] II, IX, and X and the anticoagulant antithrombin), designated PCC-AT, was compared with that of FVIIa and PCC-FVII, which is the PCC composition containing FII, FVII, FIX, and FX (main components of most PCCs).

METHODS

We used a thoroughly validated computational model to simulate thrombin generation in normal and diluted blood for 472 healthy subjects in the control group of the Leiden Thrombophilia Study. For every simulated thrombin curve, we calculated and analyzed five standard thrombin generation parameters.

RESULTS

The three therapeutic agents (FVIIa, PCC-FVII, and PCC-AT) caused statistically significant changes in each of the five thrombin generation parameters in diluted blood. Factor VIIa tended to primarily impact clotting time, thrombin peak time, and maximum slope of the thrombin curve, whereas in the case of PCC-FVII, thrombin peak height and the area under the thrombin curve were affected particularly strongly. As a result, these two therapeutics tended to push those respective parameters outside their normal ranges. PCC-AT significantly outperformed both FVIIa and PCC-FVII in its ability to normalize individual thrombin generation parameters in diluted blood. Furthermore, PCC-AT could simultaneously restore all five thrombin generation parameters to their normal levels in every subject in the study group.

CONCLUSIONS

Our computational results suggest that PCC-AT may demonstrate a superior ability to restore normal thrombin generation compared with FVIIa and PCC-FVII.

Relationship between ABO blood groups and von Willebrand factor, ADAMTS13 and factor VIII in patients undergoing hemodialysis

Several studies have demonstrated that non-O blood groups subjects present an increased VTE risk as compared to those carrying O blood group. The aim of this study was to investigate the ABO blood groups influence on factor VIII (FVIII) activity, von Willebrand factor (VWF), and ADAMTS13 plasma levels in patients undergoing hemodialysis (HD). Patients undergoing HD (N=195) and 80 healthy subjects (control group) were eligible for this cross-sectional study. The ABO blood group phenotyping was performed by the reverse technique. FVIII activity was measured through coagulometric method, and VWF and ADAMTS13 antigens were assessed by ELISA. FVIII activity and VWF levels were significantly higher and ADAMTS13 levels was decreased in HD patients, as compared to healthy subjects (P < 0.001, in three cases). HD patients carrying non-O blood groups showed a significant increase in FVIII activity (P = 0.001) and VWF levels (P < 0.001) when compared to carriers of O blood group. However, no significant difference was observed in ADAMTS13 levels (P = 0.767). In the control group, increased in FVIII activity (P = 0.001) and VWF levels (P = 0.002) and decreased in ADAMTS13 levels (P = 0.005) were observed in subjects carrying non-O blood groups as compared to carriers of O blood group.Our data confirmed that ABO blood group is an important risk factor for increased procoagulant factors in plasma, as FVIII and VWF. Admitting the possible role of kidneys in ADAMTS13 synthesis or on its metabolism, HD patients were not able to increase ADAMTS13 levels in order to compensate the increase of VWF levels mediated by ABO blood groups. Considering that non-O blood groups constitute a risk factor for thrombosis, it is reasonable to admit that A, B and AB HD patients need a careful and continuous follow-up in order to minimize thrombotic events.

Mechanisms and monitoring of bypassing agent therapy

Understanding the mechanism of action of normal hemostasis and how the bypassing agents recombinant activated factor VII (rFVIIa; NovoSeven) and plasma-derived activated prothrombin complex concentrate (Factor Eight Inhibitor Bypassing Agent [FEIBA]) control abnormal bleeding is imperative for healthcare professionals who treat patients with hemophilia and other bleeding disorders. A cell-based model has improved our understanding of in vivo mechanisms of hemostasis and the basis of the bleeding tendency in hemophilia. Bypassing agents do not restore the normal pathways of hemostasis in hemophilia, but rather boost thrombin generation in spite of a lack of platelet surface FVIIIa-FIXa ('tenase') activity. Thus, the common clinical laboratory coagulation assays do not reflect the clinically relevant hemostatic activity of bypassing agents, and no validated assay is available with which to measure the in vivo efficacy of these agents or predict individual patient responses to treatment. Global hemostasis assays measuring overall coagulation capacity have potential for assessment of the effects of bypassing agents. This review will focus on the mechanisms of clotting and their relationship to understanding the mechanisms of action of the bypassing agents in vivo and the methodologies that are emerging to monitor the clinical efficacy of bypassing agent therapy.

An integrated fluid-chemical model toward modeling the formation of intra-luminal thrombus in abdominal aortic aneurysms

Abdominal Aortic Aneurysms (AAAs) are frequently characterized by the presence of an Intra-Luminal Thrombus (ILT) known to influence their evolution biochemically and biomechanically. The ILT progression mechanism is still unclear and little is known regarding the impact of the chemical species transported by blood flow on this mechanism. Chemical agonists and antagonists of platelets activation, aggregation, and adhesion and the proteins involved in the coagulation cascade (CC) may play an important role in ILT development. Starting from this assumption, the evolution of chemical species involved in the CC, their relation to coherent vortical structures (VSs) and their possible effect on ILT evolution have been studied. To this end a fluid-chemical model that simulates the CC through a series of convection-diffusion-reaction (CDR) equations has been developed. The model involves plasma-phase and surface-bound enzymes and zymogens, and includes both plasma-phase and membrane-phase reactions. Blood is modeled as a non-Newtonian incompressible fluid. VSs convect thrombin in the domain and lead to the high concentration observed in the distal portion of the AAA. This finding is in line with the clinical observations showing that the thickest ILT is usually seen in the distal AAA region. The proposed model, due to its ability to couple the fluid and chemical domains, provides an integrated mechanochemical picture that potentially could help unveil mechanisms of ILT formation and development.