Vitamin K antagonists favourably modulate fibrin clot properties in patients with atrial fibrillation as early as after 3days of treatment: Relation to coagulation factors and thrombin generation

Thrombosis and Aging: Fibrin Clot Properties and Oxidative Stress

Significance: Aging is a complex process associated with an increased risk of many diseases, including thrombosis. This review summarizes age-related prothrombotic mechanisms in clinical settings of thromboembolism, focusing on the role of fibrin structure and function modified by oxidative stress. Recent Advances: Aging affects blood coagulation and fibrinolysis via multiple mechanisms, including enhanced oxidative stress, with an imbalance in the oxidant/antioxidant mechanisms, leading to loss of function and accumulation of oxidized proteins, including fibrinogen. Age-related prothrombotic alterations are multifactorial involving enhanced platelet activation, endothelial dysfunction, and changes in coagulation factors and inhibitors. Formation of more compact fibrin clot networks displaying impaired susceptibility to fibrinolysis represents a novel mechanism, which might contribute to atherothrombosis and venous thrombosis. Alterations to fibrin clot structure/function are at least in part modulated by post-translational modifications of fibrinogen and other proteins involved in thrombus formation, with a major impact of carbonylation. Fibrin clot properties are also involved in the efficacy and safety of therapy with oral anticoagulants, statins, and/or aspirin. Critical Issues: Since a prothrombotic state is observed in very elderly individuals free of diseases associated with thromboembolism, the actual role of activated blood coagulation in health remains elusive. It is unclear to what extent oxidative modifications of coagulation and fibrinolytic proteins, in particular fibrinogen, contribute to a prothrombotic state in healthy aging. Future Directions: Ongoing studies will show whether novel therapies that may alter oxidative stress and fibrin characteristics are beneficial to prevent atherosclerosis and thromboembolic events associated with aging.

Reviewing the Rich History of Fibrin Clot Research with a Focus on Clinical Relevance

Fibrin, described on a single-lens microscopy for the first time by Malpighi in 1666 and named by de Fourcroy, has been extensively studied by biochemists, biophysicists, and more recently by clinicians who recognized that fibrin is the major component of most thrombi. Elucidation of key reactions leading to fibrin clot formation in the 1950s and 1960s grew interest in the clinical relevance of altered fibrin characteristics. Implementation of scanning electron microscopy to image fibrin clots in 1947 and clot permeation studies in the 1970s to evaluate an average pore size enabled plasma clot characterization in cohorts of patients. Unfavorably altered fibrin clot structure was demonstrated by Blombäck's group in coronary artery disease in 1992 and in diabetes in 1996. Fifteen years ago, similar plasma fibrin clot alterations were reported in patients following venous thromboembolism. Multiple myeloma was the first malignant disease to be found to lead to abnormal fibrin clot phenotype in the 1970s. Apart from anticoagulant agents, in 1998, aspirin was first shown to increase fibrin clot permeability in cardiovascular patients. The current review presents key data on the rich history of fibrin research, in particular, those that first documented abnormal fibrin clot properties in a variety of human disease states, as well as factors affecting fibrin phenotype.

Effects of dabigatran, rivaroxaban, and apixaban on fibrin network permeability, thrombin generation, and fibrinolysis

INTRODUCTION

There are important pharmacological differences between direct oral anticoagulants (DOAC) and a deeper knowledge of how they influence different aspects of hemostasis in patients on treatment is desirable.

MATERIALS AND METHODS

Blood samples from patients on dabigatran (n = 23), rivaroxaban (n = 26), or apixaban (n = 20) were analyzed with a fibrin network permeability assay, a turbidimetric clotting and lysis assay, the calibrated automated thrombogram (CAT), plasma levels of thrombin-antithrombin complex (TAT) and D-dimer, as well as DOAC concentrations, PT-INR and aPTT. As a comparison, we also analyzed samples from 27 patients on treatment with warfarin.

RESULTS

Patients on dabigatran had a more permeable fibrin network, longer lag time (CAT and turbidimetric assay), and lower levels of D-dimer in plasma, compared with patients on rivaroxaban- and apixaban treatment, and a more permeable fibrin network than patients on warfarin. Clot lysis time was slightly longer in patients on dabigatran than in patients on rivaroxaban. Warfarin patients formed a more permeable fibrin network than patients on apixaban, had longer lag time than patients on rivaroxaban (CAT assay), and lower peak thrombin and ETP compared to patients on treatment with both FXa-inhibitors.

CONCLUSIONS

Results from this study indicate dabigatran treatment is a more potent anticoagulant than apixaban and rivaroxaban. However, as these results are not supported by clinical data, they are probably more related to the assays used and highlight the difficulty of measuring and comparing the effect of anticoagulants.

Initiation of warfarin is associated with decreased mortality in patients with infective endocarditis: A population-based cohort study

IMPORTANCE

The use of warfarin to prevent thromboembolism in patients with infective endocarditis (IE) remains controversial due to potentially increased bleeding risks.

DESIGN

Population-based retrospective cohort study.

PARTICIPANTS

Patients aged 18 or older and diagnosed with IE in Hong Kong between January 1st, 1997 and August 31st, 2020 were included. Patients with use of any anticoagulant 30 days before IE diagnosis were excluded. Patients initiated on warfarin within 14 days of IE diagnosis and patients without warfarin use were matched for baseline characteristics using 1:1 propensity score matching.

EXPOSURE

Warfarin use within 14 days of IE diagnosis.

MAIN OUTCOMES AND MEASURES

Patients were followed up to 90 days for the outcomes of ischemic stroke, all-cause mortality, intracranial hemorrhage, and gastrointestinal bleeding. Cox regression was used to determine hazard ratios (HRs) [95 % confidence intervals (CIs)] between treatment groups. Fine-Gray competing risk regression with all-cause mortality as the competing event was performed as a sensitivity analysis. In addition to 90-day analyses, landmark analyses were performed at 30 days of follow-up.

RESULTS

The matched cohort consisted of 675 warfarin users (57.0 % male, age 59 ± 16 years) and 675 warfarin non-users (53.5 % male, age 61 ± 19 years). Warfarin users had a 50 % decreased 90-day risk in all-cause mortality (HR:0.50 [0.39-0.65]), without significantly different 90-day risks of ischemic stroke (HR:1.04 [0.70-1.53]), intracranial hemorrhage (HR:1.25 [0.77-2.04]), and gastrointestinal bleeding (HR:1.04 [0.60-1.78]). Thirty-day landmark analysis showed similar results. Competing risk regression showed significantly higher 30-day cumulative incidence of intracranial hemorrhage in warfarin users (sub-HR:3.34 [1.34-8.31]), but not at 90-day (sub-HR:1.63 [0.95-2.81]). Results from Fine-Gray regression were otherwise congruent with those from Cox regression.

CONCLUSIONS AND RELEVANCE

Warfarin initiated within 14 days of IE diagnosis was associated with significantly decreased risks of mortality but higher risks of intracranial hemorrhage, with similar risks of ischemic stroke and gastrointestinal bleeding, compared with non-use of warfarin with 14 days of IE diagnosis.

KEY POINTS

Question: Is warfarin, initiated within 14 days of a diagnosis of infective endocarditis (IE), efficacious and safe?

FINDINGS

In this propensity score-matched, population-based, prospective cohort study from Hong Kong, warfarin use within 14 days of IE diagnosis was associated with a 50 % decrease in the risk of all-cause mortality, albeit with higher risk of intracranial hemorrhage, and without significant differences in the risk of ischaemic stroke and gastrointestinal bleeding. Meaning: In patients with IE, warfarin use within 14 days of diagnosis may have mortality benefits, despite increased risks of intracranial hemorrhage.

Fibrin clot properties in cardiovascular disease: from basic mechanisms to clinical practice

Fibrinogen conversion into insoluble fibrin and the formation of a stable clot is the final step of the coagulation cascade. Fibrin clot porosity and its susceptibility to plasmin-mediated lysis are the key fibrin measures, describing the properties of clots prepared ex vivo from citrated plasma. Cardiovascular disease (CVD), referring to coronary heart disease, heart failure, stroke, and hypertension, has been shown to be associated with the formation of dense fibrin networks that are relatively resistant to lysis. Denser fibrin mesh characterized acute patients at the onset of myocardial infarction or ischaemic stroke, while hypofibrinolysis has been identified as a persistent fibrin feature in patients following thrombotic events or in those with stable coronary artery disease. Traditional cardiovascular risk factors, such as smoking, diabetes mellitus, hyperlipidaemia, obesity, and hypertension, have also been linked with unfavourably altered fibrin clot properties, while some lifestyle modifications and pharmacological treatment, in particular statins and anticoagulants, may improve fibrin structure and function. Prospective studies have suggested that prothrombotic fibrin clot phenotype can predict cardiovascular events in short- and long-term follow-ups. Mutations and splice variants of the fibrinogen molecule that have been proved to be associated with thrombophilia or increased cardiovascular risk, along with fibrinogen post-translational modifications, prothrombotic state, inflammation, platelet activation, and neutrophil extracellular traps formation, contribute also to prothrombotic fibrin clot phenotype. Moreover, about 500 clot-bound proteins have been identified within plasma fibrin clots, including fibronectin, α2-antiplasmin, factor XIII, complement component C3, and histidine-rich glycoprotein. This review summarizes the current knowledge on the mechanisms underlying unfavourable fibrin clot properties and their implications in CVD and its thrombo-embolic manifestations.

Relationship between Renal Function, Fibrin Clot Properties and Lipoproteins in Anticoagulated Patients with Atrial Fibrillation

Background: Mechanisms by which chronic kidney disease (CKD) influences fibrin clot properties in atrial fibrillation (AF) remain ill-defined. We aimed to investigate the effects of AF and CKD on fibrin clot properties and lipoproteins, and determine the relationship between these factors. Methods: Prospective cross-sectional study of patients recruited from cardiology services in Liverpool between September 2019 and October 2021. Primary groups consisted of anticoagulated AF patients with and without CKD in a 1:1 ratio. Control group comprised anticoagulated patients without AF or CKD. Fibrin clot properties were analysed using turbidity and permeation assays. Detailed lipoprotein characteristics, including total cholesterol, low-density lipoprotein cholesterol (LDL-C), small dense LDL and oxidised LDL, were measured. Results: Fifty-six anticoagulated patients were enrolled (median age 72.5; 34% female); 46 with AF (23 with CKD and 23 without CKD) and 10 controls. AF was associated with changes in three indices of fibrin clot properties using PTT (Tlag 314 vs. 358 s, p = 0.047; Abspeak 0.153 vs. 0.111 units, p = 0.031; Tlysis50% 884 vs. 280 s, p = 0.047) and thrombin reagents (Tlag 170 vs. 132 s, p = 0.031; Tmax 590 vs. 462 s, p = 0.047; Tpeak50% 406 vs. 220 s, p = 0.005) while the concomitant presence of CKD led to changes in fibrin clot properties using kaolin (Tlag 1072 vs. 1640 s, p = 0.003; Tmax 1458 vs. 1962 s, p = 0.005; Tpeak50% 1294 vs. 2046, p = 0.008) and PPP reagents (Tlag 566 vs. 748 s, p = 0.044). Neither of these conditions were associated with changes in fibrin clot permeability. Deteriorating eGFR was significantly correlated to the speed of clot formation, and CKD was independently associated with unfavourable clot properties (Tlag −778, p = 0.002; Tmax −867, p = 0.004; Tpeak50% −853, p = 0.004 with kaolin reagent). AF alone was not associated with changes in lipoprotein distribution while AF patients with CKD had lower total cholesterol, LDL-C and small dense LDL due to the presence of other risk factors. No significant relationship was observed between fibrin clot properties and lipoprotein distribution. Conclusions: There are important changes that occur in fibrin clot properties with AF and CKD that may account for the increased risk of thromboembolic complications. However, these changes in fibrin clot properties were not attributable to alterations in lipoprotein distribution.

Perioperative Considerations for Antithrombotic Therapy in Oculofacial Surgery: A Review of Current Evidence and Practice Guidelines

PURPOSE

Recent survey studies have demonstrated wide variability in practice patterns regarding the management of antithrombotic medications in oculofacial plastic surgery. Current evidence and consensus guidelines are reviewed to guide perioperative management of antithrombotic medications.

METHODS

Comprehensive literature review of PubMed database on perioperative use of antithrombotic medication.

RESULTS/CONCLUSIONS

Perioperative antithrombotic management is largely guided by retrospective studies, consensus recommendations, and trials in other surgical fields due to the limited number of studies in oculoplastic surgery. This review summarizes evidence-based recommendations from related medical specialties and provides context for surgeons to tailor antithrombotic medication management based on patient's individual risk. The decision to continue or cease antithrombotic medications prior to surgery requires a careful understanding of risk: risk of intraoperative or postoperative bleeding versus risk of a perioperative thromboembolic event. Cessation and resumption of antithrombotic medications after surgery should always be individualized based on the patient's thrombotic risk, surgical and postoperative risk of bleeding, and the particular drugs involved, in conjunction with the prescribing doctors. In general, we recommend that high thromboembolic risk patients undergoing high bleeding risk procedures (orbital or lacrimal surgery) may stop antiplatelet agents, direct oral anticoagulants, and warfarin including bridging warfarin with low-molecular weight heparin. Low-risk patients, regardless of type of procedure performed, may stop all agents. Decision on perioperative management of antithrombotic medications should be made in conjunction with patient's internist, cardiologist, hematologist, or other involved physicians which may limit the role of guidelines depending on patient risk and should be used on a case-by-case basis. Further studies are needed to provide oculofacial-specific evidence-based guidelines.

Ischemic Stroke of Suspected Cardioembolic Origin Despite Anticoagulation: Does Thrombus Analysis Help to Clarify Etiology?

Introduction

Despite sufficient oral anticoagulation (OAC) to prevent cardioembolism, some patients suffer from cerebral ischemic strokes of suspected cardioembolic origin. Reasons for that are not clarified yet. In certain cases, the suspected cardioembolic origin of stroke is questioned. This study aimed to understand the thrombi origin and pathophysiology in patients suffering from stroke despite OAC by the analysis of histologic thrombus composition and imaging characteristics.

Materials and Methods

On two distinct cohorts, we retrospectively analyzed histologic (n = 92) and imaging features (n = 64), i.e., thrombus perviousness in admission CT imaging, of cerebral thrombi retrieved by the endovascular treatment for a large vessel occlusion of the anterior circulation. In each group, patients with non-cardioembolic strokes and suspected cardioembolic strokes with or without anticoagulation were compared.

Results

Fibrin/platelet content of suspected cardioembolic thrombi (mean/SD 57.2% ± 13) is higher than in non-cardioembolic thrombi (48.9% ± 17; p = 0.01). In suspected cardioembolic thrombi, the fibrin/platelet content does not differ in the subgroups of patients with (57.3% ± 13) and without prior OAC treatment (56.6% ±13; p = 0.8), both with higher values than non-cardioembolic thrombi. Thrombus perviousness (ε) of suspected cardioembolic OAC thrombi (mean/SD: 0.09 ± 0.06) differs significantly from non-cardioembolic thrombi (0.02 ± 0.02; p < 0.001). Further, ε is higher in suspected cardioembolic thrombi with OAC than in cardioembolic thrombi without OAC (0.06 ± 0.03; p = 0.04) and with insufficient OAC (0.04 ± 0.02; p = 0.07).

Conclusion

Thrombi of the suspected cardioembolic origin of patients with prior OAC do not differ in their histologic composition from those without prior OAC, but both differ from non-cardioembolic thrombi. These histologic results make a non-cardioembolic etiology for strokes despite prior OAC rather unlikely but favor other reasons for these ischemic events. Perviousness assessment reinforces the histologic findings, with additional information about the OAC thrombi, which present with higher perviousness. This suggests that OAC would not affect the relative histologic thrombus composition but may alter the microstructure, as reflected by perviousness.

The effects of cardiovascular and orthopaedic surgery on vitamin concentrations: a narrative review of the literature and mechanisms of action

Given the rise in worldwide chronic diseases, supplemented by an aging population, the volume of global major surgeries, encompassing cardiac and orthopedic procedures is anticipated to surge significantly. Surgical trauma can be accompanied by numerous postoperative complications and metabolic changes. The present review summarized the results from studies assessing the effects of orthopedic and cardiovascular surgery on vitamin concentrations, in addition to exploring the possible mechanisms associated with changes in concentrations. Studies have revealed a potentially severe depletion in plasma/serum concentrations of numerous vitamins following these surgeries acutely. Vitamins C, D and B1 appear particularly vulnerable to significant depletions, with vitamin C and D depletions consistently transpiring into inadequate and deficient concentrations, respectively. The possible multifactorial mechanisms impacting postoperative vitamin concentrations include changes in hemodilution and vitamin utilization, redistribution, circulatory transport and absorption. For a majority of vitamins, there has been a lack of investigation into the effects of both, cardiac and orthopedic surgery. Additionally, studies were predominantly restricted to short-term postoperative investigations, primarily performed within the first postoperative week of surgery. Overall, results indicated that further examination is necessary to determine the severity and clinical significance of the possible depletions in vitamin concentrations that ensue cardiovascular and orthopedic surgery.

Altered fibrin clot properties and fibrinolysis in patients with atrial fibrillation: practical implications

Compelling evidence indicates that a hypercoagulable state occurs in patients with atrial fibrillation (AF) including those in sinus rhythm following paroxysmal and persistent AF. Activation of blood coagulation in AF reflects heightened thrombin generation with the subsequent increased formation of fibrin as evidenced by elevated soluble fibrin monomers and D-dimer. Formation of denser fibrin meshworks, relatively resistant to plasmin-mediated lysis has been demonstrated in patients with AF. The presence of stroke risk factors in AF, such as diabetes, heart failure, hypertension, previous myocardial infarction, or stroke, advanced age have been shown to be linked to the prothrombotic clot characteristics, including reduced clot permeability and lysability. Importantly, biomarkers, including cardiac troponins and N-terminal pro-brain natriuretic peptide, are associated with thrombin generation and fibrin-related markers in AF patients. Recently, increased fibrin clot density (low clot permeability measured in plasma-based assays) and impaired fibrinolysis measured off anticoagulation have been demonstrated to predict ischaemic cerebrovascular events in patients with AF receiving vitamin K antagonists and those on rivaroxaban. The current review summarizes evidence for a role of altered fibrin clot properties and hypofibrinolysis in AF and their prognostic value in terms of adverse events.

Fibrinolysis in Venous Thromboembolism

Fibrinolysis is of paramount importance in maintaining or regaining the patency of veins and pulmonary arteries obstructed by thrombi. Growing experimental and clinical evidence indicates that impaired fibrinolysis mediated by multiple complex mechanisms is involved in venous thromboembolism (VTE). Global plasma fibrin clot lysis markers, especially clot lysis time, have been reported to predict recurrent deep-vein thrombosis and pulmonary embolism. The current overview summarizes available data linking fibrinolysis to VTE and its long-term sequelae.

Relationship between lipoproteins, thrombosis and atrial fibrillation

The prothrombotic state in atrial fibrillation (AF) occurs as a result of multifaceted interactions, known as Virchow’s triad of hypercoagulability, structural abnormalities, and blood stasis. More recently, there is emerging evidence that lipoproteins are implicated in this process, beyond their traditional role in atherosclerosis. In this review, we provide an overview of the various lipoproteins and explore the association between lipoproteins and AF, the effects of lipoproteins on haemostasis, and the potential contribution of lipoproteins to thrombogenesis in AF. There are several types of lipoproteins based on size, lipid composition, and apolipoprotein category, namely: chylomicrons, very low-density lipoprotein, low-density lipoprotein (LDL), intermediate-density lipoprotein, and high-density lipoprotein. Each of these lipoproteins may contain numerous lipid species and proteins with a variety of different functions. Furthermore, the lipoprotein particles may be oxidized causing an alteration in their structure and content. Of note, there is a paradoxical inverse relationship between total cholesterol and LDL cholesterol (LDL-C) levels, and incident AF. The mechanism by which this occurs may be related to the stabilizing effect of cholesterol on myocardial membranes, along with its role in inflammation. Overall, specific lipoproteins may interact with haemostatic pathways to promote excess platelet activation and thrombin generation, as well as inhibiting fibrinolysis. In this regard, LDL-C has been shown to be an independent risk factor for thromboembolic events in AF. The complex relationship between lipoproteins, thrombosis and AF warrants further research with an aim to improve our knowledge base and contribute to our overall understanding of lipoprotein-mediated thrombosis.

Impaired Fibrinolysis in Patients with Isolated Aortic Stenosis is Associated with Enhanced Oxidative Stress

Aortic stenosis (AS) has been associated with impaired fibrinolysis and increased oxidative stress. This study aimed to investigate whether oxidative stress could alter fibrin clot properties in AS. We studied 173 non-diabetic patients, aged 51–79 years, with isolated AS. We measured plasma protein carbonylation (PC) and thiobarbituric acid reactive substances (TBARS), along with plasma clot permeability (K_s), thrombin generation, and fibrinolytic efficiency, which were evaluated by two assays: clot lysis time (CLT) and lysis time (Lys50). Coagulation factors and fibrinolytic proteins were also determined. Plasma PC showed an association with AS severity, reflected by the aortic valve area and the mean and maximum aortic gradients. Plasma PC was positively correlated with CLT, Lys50, plasminogen activator inhibitor-1 (PAI-1), and tissue factor (TF) antigens. TBARS were positively correlated with maximum aortic gradient, Lys50, and TF antigen. Regression analysis showed that PC predicted prolonged CLT (>104 min; odds ratio (OR) 6.41, 95% confidence interval (CI) 2.58–17.83, p < 0.001) and Lys50 (>565 s; OR 5.83, 95% CI 2.23–15.21, p < 0.001). Multivariate regression analysis showed that mean aortic gradient, PC, α2-antiplasmin, PAI-1, and triglycerides were predictors of prolonged CLT, while PC, α2-antiplasmin, and fibrinogen were predictors of Lys50. Our findings suggest that elevated oxidative stress contributes to impaired fibrinolysis in AS and is associated with AS severity.

Clot Lysis Time Predicts Stroke During Anticoagulant Therapy in Patients with Atrial Fibrillation

BACKGROUND

Formation of dense fibrin clots has been reported in both atrial fibrillation (AF) and ischemic stroke. We have previously demonstrated that such clot properties can predict thromboembolism and major bleeding in AF patients treated with vitamin K antagonists (VKAs). In this longitudinal cohort study, we evaluated whether impaired fibrinolysis is associated with clinical outcomes in AF.

METHODS

In 236 patients with AF receiving VKAs, we measured ex vivo plasma clot lysis time (CLT), a measure of global fibrinolysis along, with von Willebrand factor antigen (vWF), plasminogen activator inhibitor 1 antigen (PAI-1), and other fibrinolysis modulators. The primary outcome were ischemic cerebrovascular events. Secondary end points were death and major bleeding.

RESULTS

During a median follow-up time of 4.3 (interquartile range 3.7-4.8) years, annual rates of death, ischemic cerebrovascular events, and major bleeding were 1.48%, 2.96%, and 3.45%, respectively. Patients with CLT in the fourth quartile (> 115 min) had 8-fold higher stroke or transient ischemic attack (TIA) rates compared with the other patients (8.67% vs 1.1%; P < 0.0001). CLT correlated with PAI-1 and vWF (r = 0.59; P < 0.0001 for both). In the multivariate Cox regression analysis adjusted for potential confounders, the independent predictors of stroke or TIA were CLT > 115 minutes (hazard ratio [HR] 7.67, 95% confidence interval [CI] 2.78-21.17; P < 0.0001), PAI-1 (HR 1.16, 95% 1.05-1.28; P = 0.003), and CHA₂DS₂-VASc score ≥3 (HR 5.18, 95% 1.76-15.29; P = 0.003). CLT was not associated with death or major and minor bleeding events.

CONCLUSIONS

Impaired fibrinolysis may predict thromboembolic events in AF patients receiving VKA.

Improving fibrinolysis in venous thromboembolism: impact of fibrin structure

Introduction. Fibrinolysis is of key importance in maintaining vessel patency. Impaired fibrinolysis associated with more compact fibrin structure has been shown in patients with venous thromboembolism (VTE), including deep-vein thrombosis and pulmonary embolism (PE). Currently, recombinant or modified plasminogen activators are the only commonly available thrombolytic agents. However, they are fraught with side effects and suboptimal effectiveness. Areas covered. Based on the available literature, the current evidence linking fibrinolysis with VTE and potential therapeutic targets among fibrinolysis proteins are presented. Expert opinion. Prolonged clot lysis time has been reported as a new predictor of first-time and recurrent VTE, including PE. Anticoagulant therapy, including non-vitamin K antagonist oral anticoagulants, has a favorable impact on fibrinolysis in VTE patients. Several VTE risk factors are also related to lower efficiency of fibrinolysis and their treatment improve fibrinolysis, in part by alterations to fibrin properties. There is an increasing number of studies aiming at developing novel profibrinolytic therapeutic agents for treatment of VTE patients, mostly targeting the antifibrinolytic proteins, i.e. antiplasmin, plasminogen activator inhibitor-1 and thrombin-activatable fibrinolysis inhibitor.

Atherothrombosis and Thromboembolism: Position Paper from the Second Maastricht Consensus Conference on Thrombosis

Atherothrombosis is a leading cause of cardiovascular mortality and long-term morbidity. Platelets and coagulation proteases, interacting with circulating cells and in different vascular beds, modify several complex pathologies including atherosclerosis. In the second Maastricht Consensus Conference on Thrombosis, this theme was addressed by diverse scientists from bench to bedside. All presentations were discussed with audience members and the results of these discussions were incorporated in the final document that presents a state-of-the-art reflection of expert opinions and consensus recommendations regarding the following five topics: 1. Risk factors, biomarkers and plaque instability: In atherothrombosis research, more focus on the contribution of specific risk factors like ectopic fat needs to be considered; definitions of atherothrombosis are important distinguishing different phases of disease, including plaque (in)stability; proteomic and metabolomics data are to be added to genetic information. 2. Circulating cells including platelets and atherothrombosis: Mechanisms of leukocyte and macrophage plasticity, migration, and transformation in murine atherosclerosis need to be considered; disease mechanism-based biomarkers need to be identified; experimental systems are needed that incorporate whole-blood flow to understand how red blood cells influence thrombus formation and stability; knowledge on platelet heterogeneity and priming conditions needs to be translated toward the in vivo situation. 3. Coagulation proteases, fibrin(ogen) and thrombus formation: The role of factor (F) XI in thrombosis including the lower margins of this factor related to safe and effective antithrombotic therapy needs to be established; FXI is a key regulator in linking platelets, thrombin generation, and inflammatory mechanisms in a renin-angiotensin dependent manner; however, the impact on thrombin-dependent PAR signaling needs further study; the fundamental mechanisms in FXIII biology and biochemistry and its impact on thrombus biophysical characteristics need to be explored; the interactions of red cells and fibrin formation and its consequences for thrombus formation and lysis need to be addressed. Platelet-fibrin interactions are pivotal determinants of clot formation and stability with potential therapeutic consequences. 4. Preventive and acute treatment of atherothrombosis and arterial embolism; novel ways and tailoring? The role of protease-activated receptor (PAR)-4 vis à vis PAR-1 as target for antithrombotic therapy merits study; ongoing trials on platelet function test-based antiplatelet therapy adjustment support development of practically feasible tests; risk scores for patients with atrial fibrillation need refinement, taking new biomarkers including coagulation into account; risk scores that consider organ system differences in bleeding may have added value; all forms of oral anticoagulant treatment require better organization, including education and emergency access; laboratory testing still needs rapidly available sensitive tests with short turnaround time. 5. Pleiotropy of coagulation proteases, thrombus resolution and ischaemia-reperfusion: Biobanks specifically for thrombus storage and analysis are needed; further studies on novel modified activated protein C-based agents are required including its cytoprotective properties; new avenues for optimizing treatment of patients with ischaemic stroke are needed, also including novel agents that modify fibrinolytic activity (aimed at plasminogen activator inhibitor-1 and thrombin activatable fibrinolysis inhibitor.

Plasma fibrin clot properties in the G20210A prothrombin mutation carriers following venous thromboembolism: the effect of rivaroxaban

We sought to investigate whether the G20210A prothrombin mutation modifies plasma fibrin clot properties in patients after venous thromboembolism (VTE) and how rivaroxaban treatment affects these alterations. We studied 34 prothrombin mutation heterozygous carriers and sex- and age-matched 34 non-carriers, all at least three months since the first VTE episode, before and during treatment with rivaroxaban. Clot permeability (Ks) and clot lysis time (CLT) with or without elimination of thrombin activatable fibrinolysis inhibitor (TAFI) were assessed at baseline, 2–6 hours (h) after and 20–25 h after intake of rivaroxaban (20 mg/day). At baseline, the prothrombin mutation group formed denser clots (Ks −12 %, p=0.0006) and had impaired fibrinolysis (CLT +14 %, p=0.004, and CLT-TAFI +13 %, p=0.03) compared with the no mutation group and were similar to those observed in 15 healthy unrelated prothrombin mutation carriers. The G20210A prothrombin mutation was the independent predictor for Ks and CLT before rivaroxaban intake. At 2–6 h after rivaroxaban intake, clot properties improved in both G20210A carriers and non-carriers (Ks +38 %, and +37 %, CLT −25 % and −25 %, CLT-TAFI −20 % and −24 %, respectively, all p<0.001), but those parameters were worse in the prothrombin mutation group (Ks −12.8 %, CLT +17 %, CLT-TAFI +13 %, all p<0.001). Rivaroxaban concentration correlated with fibrin clot properties. After 20–25 h since rivaroxaban intake most clot properties returned to baseline. Rivaroxaban-related differences in clot structure were confirmed by scanning electron microscopy images. In conclusion, rivaroxaban treatment, though improves fibrin clot properties, cannot abolish more prothrombotic fibrin clot phenotype observed in prothrombin mutation carriers following VTE.

Fibrin Clot Permeability as a Predictor of Stroke and Bleeding in Anticoagulated Patients With Atrial Fibrillation

BACKGROUND AND PURPOSE

Formation of denser fiber networks has been reported in atrial fibrillation and ischemic stroke. In this longitudinal cohort study, we evaluated whether fibrin clot density may predict thromboembolic and bleeding risk in patients with atrial fibrillation on vitamin K antagonists.

METHODS

In 236 patients with atrial fibrillation receiving vitamin K antagonists treatment, we measured ex vivo plasma clot permeability (K_s), a measure of the pore size in fibrin networks.

RESULTS

During a median follow-up of 4.3 (interquartile range, 3.7-4.8) years, annual rates of ischemic stroke or transient ischemic attack and major bleeds were 2.96% and 3.45%, respectively. In multivariate Cox regression analysis, patients with lower K_s (<6.8 cm²×10^-9, median) had increased risk of ischemic stroke or transient ischemic attack (hazard ratio [HR], 6.55; 95% confidence interval [CI], 2.17-19.82) and major bleeds (HR, 10.65; 95% CI, 3.52-32.22). Patients with elevated K_s (≥6.8 cm²×10^-9) had an increased rate of minor bleeding compared with the remainder (11.63% per year versus 3.55% per year; P<0.0001). The independent predictors of stroke or transient ischemic attack were low K_s (<6.8 cm²×10^-9; HR, 7.24; 95% CI, 2.53-20.76), age (HR, 1.05; 95% CI, 1.01-1.10), and treatment with angiotensin-converting enzyme inhibitors (HR, 2.27; 95% CI, 1.08-4.77). Major bleeds were predicted by low K_s (<6.8 cm²×10^-9; HR, 8.48; 95% CI, 2.99-24.1) and HAS-BLED score ≥3 (HR, 2.22; 95% CI, 1.12-4.38).

CONCLUSIONS

This study is the first to show that unfavorable fibrin properties reflected by formation of denser fibrin networks determine, in part, the efficacy and safety of anticoagulation with vitamin K antagonists in patients with atrial fibrillation.

Elevated NT-proBNP is associated with unfavorably altered plasma fibrin clot properties in atrial fibrillation

BACKGROUND

Dense fibrin clot formation and hypofibrinolysis have been reported in atrial fibrillation (AF). It is unclear which factors affect fibrin clot properties in AF.

METHODS AND RESULTS

We investigated plasma fibrin clot permeability (K_s), clot lysis time (CLT), endogenous thrombin potential (ETP) as well as other coagulation and fibrinolysis parameters along with N-terminal pro-B-type natriuretic peptide (NT-proBNP) in 160 AF patients (median age, 70.5years). Previous stroke (n=15; 9.4%) was associated with decreased K_s (P=0.04) and longer CLT (P=0.005), together with higher antiplasmin (P=0.03) and lower tissue-type plasminogen activator (P=0.01). Lower K_s (P=0.04) and tendency towards longer CLT (P=0.10) were observed in patients with a left atrium diameter>40mm. Patients with a CHA₂DS₂-VASc score of 3 or more (82.5%) were characterized by higher thrombin-activatable fibrinolysis inhibitor antigen (P=0.009). K_s was inversely correlated with log NT-proBNP (r=-0.34, P<0.0001), plasminogen activator inhibitor-1 (PAI-1) antigen (r=-0.24, P=0.002) and C-reactive protein (r=-0.18, P=0.02), while CLT was positively correlated with log NT-proBNP (R=0.61, P<0.0001) and ETP (r=0.37, P<0.0001), which were interrelated (r=0.59, P<0.0001). After adjustment for potential confounders, PAI-1 (odds ratio [OR]: 1.14; 95% confidence interval [CI]: 1.02-1.26) was the only independent predictor of low K_s (the lowest quartile,≤6×10^-9cm²), while NT-proBNP (OR: 1.21; 95% CI: 1.12-1.31) and PAI-1 (OR: 1.30; 95% CI: 1.12-1.51) both predicted prolonged CLT (the top quartile,≥109min).

CONCLUSION

In AF patients prothrombotic fibrin clot properties assessed ex vivo are determined by PAI-1 and NT-proBNP and this phenotype is associated with prior ischemic stroke.

Thrombin generation assays for global evaluation of the hemostatic system: perspectives and limitations

The existing techniques to evaluate hemostasis in clinical laboratories are not sensitive enough to detect hypercoagulable and mild hypocoagulable states. Under different experimental conditions, the thrombin generation test may meet these requirements. This technique evaluates the overall balance between procoagulant and anticoagulant forces and has provided new insights in our understanding of the coagulation cascade, as well as of the diagnosis of hypocoagulability and hypercoagulability conditions. Thrombin generated in the thrombin generation test can be quantified as platelet-rich or platelet-poor plasma using the calibrated automated thrombogram method, which monitors the cleavage of a fluorogenic substrate that is simultaneously compared to the known thrombin activity in a non-clotting plasma sample. The calibrated automated thrombogram method is an open system, in which different antibodies, proteins, enzymes and peptides can be introduced to answer specific questions regarding hemostatic processes. The thrombin generation test has great clinical potential, such as in monitoring patients taking anticoagulants and antiplatelet drugs, screening for genetic or acquired thrombotic disorders, and evaluating bleeding risk control in patients with hemophilia using bypass agents or replacement therapy. Different to conventional coagulation tests, the thrombin generation test can be used for an overall evaluation of hemostasis, the results of which can then be used to evaluate specific characteristics of hemostasis, such as prothrombin time, activated partial thromboplastin time, and levels of fibrinogen and other coagulation factors. The introduction of this method will contribute to a better understanding and evaluation of overall hemostatic processes; however, this method still requires standardization and clinical validation.

Laboratory assessment of anti-thrombotic therapy in heart failure, atrial fibrillation and coronary artery disease: insights using thrombelastography and a micro-titre plate assay of thrombogenesis and fibrinolysis

As heart failure, coronary artery disease and atrial fibrillation all bring a risk of thrombosis, anti-thrombotic therapy is recommended. Despite such treatment, major cardiovascular events such as myocardial infarction and stroke still occur, implying inadequate suppression of thrombus formation. Accordingly, identification of patients whose haemostasis remains unimpaired by treatment is valuable. We compared indices for assessing thrombogenesis and fibrinolysis by two different techniques in patients on different anti-thrombotic agents, i.e. aspirin or warfarin. We determined fibrin clot formation and fibrinolysis by a microplate assay and thromboelastography, and platelet marker soluble P selectin in 181 patients with acute or chronic heart failure, coronary artery disease who were taking either aspirin or warfarin. Five thromboelastograph indices and four microplate assay indices were different on aspirin versus warfarin (p < 0.05). In multivariate regression analysis, only microplate assay indices rate of clot formation and rate of clot dissolution were independently related to aspirin or warfarin use (p ≤ 0.001). Five microplate assay indices, but no thrombelastograph index, were different (p < 0.001) in aspirin users. Three microplate assay indices were different (p ≤ 0.002) in warfarin users. The microplate assay indices of lag time and rate of clot formation were abnormal in chronic heart failure patients on aspirin, suggesting increased risk of thrombosis despite anti-platelet use. Soluble P selectin was lower in patients on aspirin (p = 0.0175) but failed to correlate with any other index of haemostasis. The microplate assay shows promise as a tool for dissecting thrombogenesis and fibrinolysis in cardiovascular disease, and the impact of antithrombotic therapy. Prospective studies are required to determine a role in predicting thrombotic risk.

Effect of renal function on whole blood and fibrin clot formation in atrial fibrillation patients on warfarin

OBJECTIVE

Atrial fibrillation (AF) brings a risk of thrombosis, requiring oral coagulation, and is associated with renal impairment. The two processes may be linked, as altered fibrin clot structure is present in end-stage renal failure. We hypothesised that progressively deteriorating renal function is linked to altered whole blood and fibrin clot properties and fibrinolysis.

METHODS

Thrombogenesis and fibrinolysis in 200 warfarinised AF patients was assessed by thromboelastography (TEG), a micro-plate assay (MPA) and the international normalized ratio (INR). Renal function was determined by creatinine clearance and two versions of the estimated glomerular filtration rate (eGFR).

RESULTS

Two TEG indices independently reflecting thrombogenesis were linked to creatinine clearance (p < 0.01), whilst a third, reflecting clot strength, was linked to the eGFR (p < 0.001). MPA indices of thrombogenesis and clot density (p < 0.001), and an index of fibrinolysis (p < 0.001) were linked to the eGFR. The time for 50% of the fibrin clot to lyse was linked to creatinine clearance (p = 0.001). The INR was unrelated to any renal function index, and the CHA2DS2VASc score was unrelated to any index.

CONCLUSION

In warfarinised AF patients, renal function is linked to whole blood clot and fibrin clot formation, structure and dissolution, but has no effect on the INR. Key messages Despite oral anticoagulation, patients with atrial fibrillation (AF) still suffer from stroke and venous thromboembolism. The effect of renal function in warfarinised patients with AF is unknown and may account for excess thrombosis and/or haemorrhage. Using two different laboratory methods, our data point to an effect of renal function on clot structure and function that is independent of an effect of warfarin.