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Competing Interests: J.I.W. has served as a consultant and has received honoraria from Alnylam, Alveron, Anthos, Bayer, Bristol-Myers Squibb, Johnson & Johnson, Regeneron, and VarmX; and holds the Heart and Stroke Foundation J. Fraser Mustard Chair in Cardiovascular Research and the Canada Research Chair (Tier 1) in Thrombosis.

Objective: In this retrospective cohort study of consecutive patients with atrial fibrillation and surgical or transcatheter bioprosthetic valve, we compared the efficacy and safety of direct oral anticoagulants with warfarin., Methods: Using linked health administrative databases housed at the Institute for Clinical Evaluative Sciences, we identified consecutive patients in Ontario (Canada) 65 years of age or older with AF who underwent bioprosthetic valve replacement between 1 April 2012 and 31 March 2017. We created a time-varying Cox model to examine the relationship between the type of anticoagulant and time to thrombotic or bleeding events after adjustment for baseline risk of thrombosis using the CHA 2 DS 2 -VASc score and risk of bleeding using the HAS-BLED scores. We conducted prespecified subgroup analyses according to whether valve implantation was surgical or transcatheter., Results: We identified 2245 eligible patients. The mean age was 79 years, 41% were female, and 39% had transcatheter aortic valve replacement. Risk of death or thrombosis was not different between direct oral anticoagulants and warfarin after adjustment for CHA 2 DS 2 -VASc score (hazard ratio [HR] 1.02, 95% confidence interval [CI], 0.83-1.25). Risk of death or bleeding was not different between direct oral anticoagulants and warfarin after adjustment for HAS-BLED score (HR 0.89, 95% CI 0.75-1.07). Subgroup analyses of surgical or transcatheter valves were consistent with overall results., Conclusions: In a real-world population of patients with atrial fibrillation and bioprosthetic valve replacement, we found no difference between direct oral anticoagulants and warfarin with regard to the risk of thrombosis or bleeding., (© 2022. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

For most patients, direct oral anticoagulants (DOACs) are preferred over vitamin K antagonists for stroke prevention in atrial fibrillation and for venous thromboembolism treatment. However, randomized controlled trials suggest that DOACs may not be as efficacious or as safe as the current standard of care in conditions such as mechanical heart valves, thrombotic antiphospholipid syndrome, and atrial fibrillation associated with rheumatic heart disease. DOACs do not provide a net benefit in conditions such as embolic stroke of undetermined source. Their efficacy is uncertain for conditions such as left ventricular thrombus, catheter-associated deep vein thrombosis, cerebral venous sinus thrombosis, and for patients with atrial fibrillation or venous thrombosis who have end-stage renal disease. This paper provides an evidence-based review of randomized controlled trials on DOACs, detailing when they have demonstrated efficacy and safety, when DOACs should not be the standard of care, where their safety and efficacy are uncertain, and areas requiring further research., Competing Interests: Funding Support and Author Disclosures Dr Piazza has received research support paid to his institution from Bristol Myers Squibb/Pfizer Alliance, Bayer, Janssen, Alexion, Amgen, and Boston Scientific Corporation; and has received consulting fees from Pfizer, Boston Scientific Corporation, Janssen, and Amgen. Dr Fanikos has served as a consultant to AstraZeneca, Mallinckrodt, and Pfizer. Dr Connors has received research funding to her institution from CSL Behring; has received consulting fees from Abbott; has received honoraria for lectures from Bristol Myers Squibb, Roche, and Sanofi; and has participated on the advisory board of Abbott, Alnylam, Anthos, Bristol Myers Squibb, Sanofi, and Takeda, outside of the submitted work. Dr Siegal is supported by a Tier 2 Canada Research Chair in Anticoagulant Management of Cardiovascular Disease; declares that she has received honoraria paid indirectly to her research institute from AstraZeneca, Bristol Myers Squibb-Pfizer, Roche, and Servier. Dr Barnes has served as a consultant for Pfizer, Bristol Myers Squibb, Janssen, Bayer, AstraZeneca, Sanofi, Anthos, Boston Scientific, and Abbott Vascular; and has received grant funding from Boston Scientific. Dr Martin is supported by National Institutes of Health K23HL157758; and has received research support paid to her institution from Janssen Scientific Affairs. Dr Angiolillo has received consulting fees or honoraria from Abbott, Amgen, AstraZeneca, Bayer, Biosensors, Boehringer Ingelheim, Bristol Myers Squibb, Chiesi, CSL Behring, Daiichi-Sankyo, Eli Lilly, Haemonetics, Janssen, Merck, Novartis, PhaseBio, PLx Pharma, Pfizer, Sanofi, and Vectura; and his institution has received research grants from Amgen, AstraZeneca, Bayer, Biosensors, CeloNova, CSL Behring, Daiichi-Sankyo, Eisai, Eli Lilly, Gilead, Idorsia, Janssen, Matsutani Chemical Industry Co, Merck, Novartis, and the Scott R. MacKenzie Foundation. Dr Kleindorfer has received other support from the University of Michigan College of Medicine. Dr Monreal has received unrestricted grants for research from Sanofi, Leo and Rovi; and has participated in advisory meetings sponsored by Sanofi. Dr Jimenez has served as an advisor or consultant for Pfizer and Sanofi; and has served as a speaker or a member of a Speakers Bureau for Bristol Myers Squibb, Pfizer and Sanofi. Dr Middeldorp has received grants and personal fees from Daiichi-Sankyo, Bayer, Pfizer, and Boehringer Ingelheim; and has received personal fees from Portola/Alexion, Abbvie, Pfizer/Bristol Myers Squibb, Norgine, Viatris, and Sanofi, all paid to her institution and outside of the submitted work. Dr Elkind has received study drug in kind from the Bristol Myers Squibb-Pfizer Alliance; has received ancillary research funding from Roche for a National Institutes of Health-funded trial of stroke prevention; and has received royalties from UpToDate for chapters on stroke. Dr Elkind has received study drug in kind from the Bristol Myers Squibb-Pfizer Alliance and ancillary research funding from Roche for a National Institutes of Health-funded trial of stroke prevention, and royalties from UpToDate for chapters on stroke. Dr Ruff is a member of the TIMI Study Group, which has received institutional research grant support through Brigham and Women’s Hospital from Abbott, Amgen, Anthos Therapeutics, ARCA Biopharma, Inc, AstraZeneca, Bayer HealthCare Pharmaceuticals, Inc, Daiichi-Sankyo, Eisai, Intarcia, Ionis Pharmaceuticals, Inc, Janssen Research and Development, LLC, MedImmune, Merck, Novartis, Pfizer, Quark Pharmaceuticals, Regeneron Pharmaceuticals, Inc, Roche, Siemens Healthcare Diagnostics, Inc, Softcell Medical Limited, The Medicines Company, and Zora Biosciences. Dr Goldhaber has received research support from Bayer, Bristol Myers Squibb, Boston Scientific BTG EKOS, Janssen, National Heart, Lung, and Blood Institute, and Pfizer; and has received consulting fees from Agile, Bayer, and Pfizer, outside of the submitted work. In the past 3 years, Dr Krumholz has received expenses and/or personal fees from UnitedHealth, Element Science, Eyedentifeye, and F-Prime; is a co-founder of Refactor Health and HugoHealth; and is associated with contracts, through Yale New Haven Hospital, from the Centers for Medicare and Medicaid Services and through Yale University from Janssen, Google, and Pfizer. Dr Mehran has received institutional research payments from Abbott, Abiomed, Alleviant Medical, Amgen, AM-Pharma, Arena, AstraZeneca, AtriCure Inc, Biosensors, Biotronik, Boston Scientific, Bristol Myers Squibb, CardiaWave, CeloNova, Chiesi, Concept Medical, Cytosorbents, Daiichi-Sankyo, Element Science, Faraday, Humacyte, Idorsia Pharmaceuticals, Janssen, Magenta, MedAlliance, Mediasphere, Medtelligence, Medtronic, MJH Healthcare, Novartis, OrbusNeich, Penumbra, PhaseBio, Philips, Pi-Cardia, PLx Pharma, Protembis, RenalPro, RM Global, Shockwave, Vivasure, Zoll; has received personal fees from Ionis Pharmaceuticals, J-CalC, Novartis, NovoNordisk, Vectura, VoxMedia, WebMD, IQVIA, McVeigh Global, Overcome, Primer Healthcare of New Jersey, Radcliffe, SL Solutions, TARSUS Cardiology, and Esperion Science/Innovative Biopharma; has received honoraria from JAMA Cardiology (Associate Editor) and the ACC (BOT Member, SC Member CTR Program); and has equity <1% in Applied Therapeutics, Elixir Medical, Stel, ControlRad (spouse). Dr Eikelboom has received fees, honoraria and/or research support from Anthos, AstraZeneca, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, DSI, Janssen, Pfizer, Servier, and Takeda. Dr Lip is a consultant and speaker for Bristol Myers Squibb/Pfizer, Boehringer Ingelheim, Daiichi-Sankyo, and Anthos, no fees are received personally; and is coprincipal investigator of the AFFIRMO project on multimorbidity in AF, which has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement #899871. Dr Weitz has served as a consultant and has received honoraria from Alnylam, Anthos, Bayer, Bristol Myers Squibb, Ionis, Janssen, Merck, Pfizer, Regeneron, and Servier. Dr Lopes reports research grants or contracts from Amgen, Bristol Myers Squibb, GlaxoSmithKline, Medtronic, Pfizer, Sanofi; funding for educational activities or lectures from Pfizer, Bristol Myers Squibb, Novo Nordisk, and AstraZeneca; and has received funding for consulting from Bayer, Boehringer Ingelheim, Bristol Myers Squibb, NovoNordisk, and AstraZeneca. Dr Bikdeli is supported by a Career Development Award from the American Heart Association and VIVA Physicians (#938814); was supported by the Scott Schoen and Nancy Adams IGNITE Award; is supported by the Mary Ann Tynan Research Scientist award from the Mary Horrigan Connors Center for Women’s Health and Gender Biology at Brigham and Women’s Hospital, and the Heart and Vascular Center Junior Faculty Award from Brigham and Women’s Hospital; is a consulting expert, on behalf of the plaintiff, for litigation related to 2 specific brand models of IVC filters; has not been involved in the litigation in 2022 or 2023 nor has he received any compensation in 2022 or 2023; is a member of the Medical Advisory Board for the North American Thrombosis Forum; and serves in the Data Safety and Monitory Board of the NAIL-IT trial funded by the National Heart, Lung, and Blood Institute, and Translational Sciences. All other authors have reported that they have no relationships related to the contents of this paper to disclose., (Copyright © 2024 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: Thrombin-activatable fibrinolysis inhibitor (TAFI) levels are positively correlated with the risk of thrombosis. The mechanism of how TAFI affects venous thromboembolism (VTE) remains uncertain. In addition, the role of sex on the risk of VTE has also been studied. However, their association also remains unclear., Objectives: To investigate how TAFI and/or sex affect venous thrombus stability and consequent pulmonary embolism (PE)., Methods: Ferric chloride-induced thrombi were formed within the femoral veins of male and female wild-type (WT) or TAFI-knockout (Cpb2 -/- ) mice. Thrombi were imaged over 2 hours using intravital videomicroscopy to quantify embolization and thrombus size over time. Lungs were examined by immunohistochemistry to quantify (a) emboli and (b) fibrin composition of these emboli., Results: Embolization events in female mice were higher than in males (7.9-fold in WT and 3.1-fold in Cpb2 -/- mice). Although the maximal thrombus sizes were not different across groups, Cpb2 -/- mice had thrombi that were, on average, 24% smaller at the end of the 2-hour experiment than WT mice. Loss of TAFI led to a 4.0- and 2.8-fold increase in PE burden in males and females, respectively, while sex had no influence. Pulmonary emboli in Cpb2 -/- mice had higher fibrin composition compared with WT mice., Conclusion: Female mice had less stable venous thrombi than male mice, suggesting a higher risk of PE in females with deep vein thrombosis. Mice lacking TAFI had more thrombus degradation and higher PE burden than WT mice. These results confirm the role of TAFI in venous thrombosis., Competing Interests: Declaration of competing interests The authors declare no competing financial interests., (Copyright © 2023 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

FXI (factor XI) and FXII (factor XII) have emerged as targets for new anticoagulants that have the potential to be both more efficacious and safer than the currently available direct oral anticoagulants for the prevention and treatment of venous thromboembolism. In this review, we discuss the role of FXI and FXII in the pathogenesis of venous thromboembolism, explain why FXI is a better target, and explain why FXI inhibitors have potential advantages over currently available anticoagulants. Finally, we describe the FXI inhibitors under development and discuss their potential to address unmet needs in venous thromboembolism management., Competing Interests: Disclosures J.I. Weitz has served as a consultant and has received honoraria from Alnylam, Alexion, Alveron, Anthos, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, Daiichi Sankyo, Janssen, Merck, PhaseBio, Regeneron, Servier, and VarmX. The other author reports no conflicts.

Factor XII (FXII) knockdown attenuates catheter thrombosis in rabbits. Because histidine-rich glycoprotein (HRG) modulates FXIIa activity, we hypothesized that HRG depletion would promote catheter thrombosis. To test this, rabbits were given either antisense oligonucleotides (ASOs) against HRG or FXII, a control ASO, or saline. The activated partial thromboplastin time (aPTT), prothrombin time (PT), and catheter-induced thrombin generation were determined in blood collected before and after treatment. Compared with the controls, the HRG- and FXII-directed ASOs reduced hepatic messenger RNA and plasma levels of HRG and FXII, respectively, by >90%. Although HRG knockdown shortened the aPTT by 2.5 fold, FXII knockdown prolonged it by fourfold; neither of the ASOs affected the PT. Catheter segments shortened the lag time and increased peak thrombin in the plasma from control rabbits; effects were significantly enhanced and attenuated in the plasma from rabbits given the HRG- and FXII-directed ASOs, respectively. Catheters were then inserted into the right external jugular vein of the rabbits, and the time for catheter occlusion was determined. The catheter occlusion times with the control ASO or saline were 62 ± 8 minutes and 60 ± 11 minutes, respectively. The occlusion time was significantly reduced to 34 ± 9 minutes, with HRG knockdown and significantly prolonged to 128 ± 19 minutes with FXII knockdown. HRG levels are decreased with sepsis or cancer, and such patients are prone to catheter thrombosis. Because HRG modulates catheter thrombosis, our findings suggest that HRG supplementation may prevent this problem., (© 2023 by The American Society of Hematology. Licensed under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0), permitting only noncommercial, nonderivative use with attribution. All other rights reserved.)

Cancer-associated thrombosis, with the incidence rising over the years, is associated with significant morbidity and mortality in patients with cancer. Recent advances in the treatment of cancer-associated venous thromboembolism (VTE) include the introduction of direct oral anticoagulants (DOACs), which provide a more convenient and effective option than low-molecular-weight heparin (LMWH). Nonetheless, important unmet needs remain including an increased risk of bleeding in certain patient subgroups such as those with gastroesophageal cancer, concerns about drug-drug interactions, and management of patients with severe renal impairment. Although DOACs are more convenient than LMWH, persistence can decline over time. Factor XI inhibitors have potential safety advantages over DOACs because factor XI appears to be essential for thrombosis but not hemostasis. In phase II trials, some factor XI inhibitors were superior to enoxaparin for the prevention of VTE after knee replacement surgery without increasing the risk of bleeding. Ongoing trials are assessing the efficacy and safety of factor XI inhibitors for the treatment of cancer-associated VTE., (© The Author(s) 2023. Published by Oxford University Press.)

Oral anticoagulation therapy has evolved beyond vitamin K antagonists to include oral direct thrombin inhibitors and factor Xa inhibitors. Collectively known as "direct oral anticoagulants," this class of medications represents the current standard of care for the prevention and treatment of common thrombotic disorders, including atrial fibrillation and venous thromboembolism. Medications that target factors XI/XIa and XII/XIIa are currently under investigation for several thrombotic and nonthrombotic conditions. Given that these emerging medications will likely have distinct risk-benefit profiles to the current direct oral anticoagulants, may have different routes of administration, and could be used for unique clinical conditions (e.g., hereditary angioedema), the International Society on Thrombosis and Haemostasis Subcommittee on Control of Anticoagulation assembled a writing group to make recommendations on the nomenclature of anticoagulant medications. With input from the broader thrombosis community, the writing group recommends that anticoagulant medications be described by the route of administration and specific targets (e.g., oral factor XIa inhibitor)., (Crown Copyright © 2023. Published by Elsevier Inc. All rights reserved.)

Background: Central venous catheters are prone to clotting, particularly in patients with cancer. Although low-molecular-weight heparin and direct oral anticoagulants, such as apixaban and rivaroxaban, have been evaluated for the prevention of catheter thrombosis, their efficacy remains uncertain., Objectives: Compare apixaban and rivaroxaban with enoxaparin for the prevention of catheter-induced clotting in vitro., Methods: To address this uncertainty, we used a well-established microplate-based assay to compare the effects of enoxaparin, apixaban, and rivaroxaban on catheter-induced thrombosis and thrombin generation in human plasma., Results: Consistent with our previous findings, catheter segments shortened the clotting time and promoted thrombin generation. When compared at concentrations with similar anti-factor Xa activity as enoxaparin, apixaban and rivaroxaban were >20-fold less potent than enoxaparin for the prevention of catheter-induced clotting and thrombin generation., Conclusion: The prevention of catheter thrombosis in patients with cancer is challenging. Clinical trials are needed to compare the efficacy of low-molecular-weight heparin with that of direct oral anticoagulants both for the prevention and treatment of catheter thrombosis., Competing Interests: Declaration of competing interest J.I.W. has received research support from the Canadian Institutes of Health Research, Heart and Stroke Foundation of Canada, and the Canadian Fund for Innovation, and honoraria from Anthos, Bayer, Boehringer-Ingelheim, Bristol Myers Squibb, Daiichi-Sankyo, Ionis, Janssen, Merck, Pfizer, and Servier. The other authors declare no competing financial conflicts of interest., (Copyright © 2022 International Society on Thrombosis and Haemostasis. Published by Elsevier Inc. All rights reserved.)

Venous thromboembolism (VTE) and arterial thromboembolism (ATE) are linked by the common mechanism of thrombin generation. Historically these entities have been treated as separate pathophysiologic processes requiring different treatments: VTE, as the formation of fibrin-/coagulation-factor-derived thrombus in low-flow vasculature, requiring anticoagulants; versus ATE, as largely platelet-derived thrombus in high-flow vasculature, requiring antiplatelet agents. Observational studies have elucidated shared risk factors and comorbidities predisposing individuals with VTE to ATE, and vice versa, and have bolstered the strategy of dual-pathway inhibition (DPI)-the combination of low-dose anticoagulants with antiplatelet agents-to reduce thrombotic outcomes on both sides of the vasculature. Randomized clinical trials have evaluated the efficacy and safety of such regimens-mostly rivaroxaban and aspirin-in high-risk groups of patients, including those with recent acute or chronic coronary syndrome, as well as those with peripheral artery disease with or without revascularization. Studies of extended VTE prophylaxis in acutely ill medical patients have also contributed to the evidence evaluating DPI. The totality of available data supports the concept that DPI can reduce major and fatal thromboembolic outcomes, including stroke, myocardial infarction, VTE, and cardiovascular death in key patient cohorts, with acceptable risk of bleeding. Further data are needed to refine which patients derive the best net clinical benefit from such an approach. At the same time, other novel agents such as contact pathway inhibitors that reduce thrombin generation without affecting hemostasis-and thus maximize safety-should be assessed in appropriate populations., Competing Interests: J.I.W. has served as a consultant and has received honoraria from Alnylam, Anthos, Bayer, BMS, Boehringer Ingelheim, Ionis, Janssen, and Merck. A.C.S. has received research grants from Boehringer Ingelheim and consultation fees from Janssen, Bristol Meyers Squibb, Portola, Boehringer Ingelheim, Bayer, and the ATLAS group. M.G. has received research grant support and honoraria from Janssen. I.K. has no conflict of interest to declare., (Thieme. All rights reserved.)

The surface fouling of biomedical devices has been an ongoing issue in healthcare. Bacterial and blood adhesion in particular, severely impede the performance of such tools, leading to poor patient outcomes. Various structural and chemical modifications have been shown to reduce fouling, but all existing strategies lack the combination of physical, chemical, and economic traits necessary for widespread use. Herein, a lubricant infused, hierarchically micro- and nanostructured polydimethylsiloxane surface is presented. The surface is easy to produce and exhibits the high flexibility and optical transparency necessary for incorporation into various biomedical tools. Tests involving two clinically relevant, priority pathogens show up to a 98.5% reduction in the biofilm formation of methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa. With blood, the surface reduces staining by 95% and suppresses thrombin generation to background levels. Furthermore, the surface shows applicability within applications such as catheters, extracorporeal circuits, and microfluidic devices, through its effectiveness in dynamic conditions. The perfusion of bacterial media shows up to 96.5% reduction in bacterial adhesion. Similarly, a 95.8% reduction in fibrin networks is observed following whole blood perfusion. This substrate stands to hold high applicability within biomedical systems as a means to prevent fouling, thus improving performance., (© 2022 Wiley-VCH GmbH.)

Histidine-rich glycoprotein (HRG) is an abundant plasma protein that binds factor XIIa (FXIIa) and inhibits factor XII (FXII) autoactivation and FXIIa-mediated activation of FXI. Polyphosphate (polyP), a potent procoagulant released from activated platelets, may serve as a physiological activator of the contact system. Previously, we showed that HRG binds DNA and neutralizes its procoagulant activity. Consequently, our goal was to determine whether the capacity of HRG to bind polyanions enables it to regulate polyP-induced thrombosis. In a plate-based assay, immobilized polyP bound HRG, FXII, and FXIIa in a zinc-dependent manner. Basal and polyP-induced thrombin generation was greater in plasma from HRG-deficient mice than in plasma from wild-type mice. Intraperitoneal injection of polyP shortened the activated partial thromboplastin time, enhanced thrombin generation, increased thrombin-antithrombin levels, reduced lung perfusion, and promoted pulmonary fibrin deposition to a greater extent in HRG-deficient mice than in wild-type mice, effects that were abrogated with FXII knockdown. HRG thus attenuates the procoagulant and prothrombotic effects of polyP in an FXII-dependent manner by modulating the contact system., (© 2021 by The American Society of Hematology.)

Hemostasis and thrombosis are believed to be so intricately linked that any strategies that reduce thrombosis will have an inevitable impact on hemostasis. Consequently, bleeding is viewed as an unavoidable side effect of anticoagulant therapy. Emerging evidence suggests that factor XI is important for thrombosis but has a minor role in hemostasis. This information raises the possibility that anticoagulants that target factor XI will be safer than currently available agents. The authors provide a visual representation of the coagulation pathways that distinguishes between the steps involved in thrombosis and hemostasis to explain why factor XI inhibitors may serve as hemostasis-sparing anticoagulants. A safer class of anticoagulants would provide opportunities for treatment of a wider range of patients, including those at high risk for bleeding. Ongoing clinical studies will determine the extent to which factor XI inhibitors attenuate thrombosis without disruption of hemostasis., Competing Interests: Funding Support and Author Disclosures The development of this paper was funded by Anthos Therapeutics. Drs Gailani and Weitz had complete editorial control of the manuscript with Anthos providing project management support. Dr Hsu was a contractor to Anthos Therapeutics during the development of this paper. Dr Hutt has received consulting fees from Anthos Therapeutics. Dr Bloomfield is an employee of Anthos Therapeutics. Drs Gailani and Weitz have received consulting fees and honoraria from Anthos Therapeutics, Bayer, Bristol Myers Squibb, Ionis, and Janssen. Dr. Weitz holds the Canada Research Chair (Tier I) in Thrombosis and the Heart and Stroke Foundation J. F. Mustard Chair in Cardiovascular Research at McMaster University., (Copyright © 2021 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Despite advances in anticoagulant therapy, thrombosis remains the leading cause of morbidity and mortality worldwide. Heparin and vitamin K antagonists (VKAs), the first anticoagulants to be used successfully for the prevention and treatment of thrombosis, are associated with a risk of bleeding. These agents target multiple coagulation factors. Thus, by activating antithrombin, heparin mainly inhibits factor Xa and thrombin, whereas VKAs lower the levels of the vitamin K-dependent clotting factors. Direct oral anticoagulants, which have replaced VKAs for many indications, inhibit only factor Xa or thrombin. Although the direct oral anticoagulants are associated with less bleeding than VKAs, bleeding remains their major side effect. Epidemiological and animal studies have identified factor XI as a target for potentially safer anticoagulant drugs because factor XI deficiency or inhibition protects against thrombosis and is associated with little or no bleeding. Several factor XI-directed strategies are currently under investigation. This article (1) reviews the rationale for the development of factor XI inhibitors, (2) identifies the agents in most advanced stages of development, (3) describes the results of completed clinical trials and provides a summary of those underway, and (4) highlights the opportunities and challenges for this next generation of anticoagulants., Competing Interests: J.I.W. reports personal fees from Anthos, Bayer, Boehringer Ingelheim, Bristol-Myers Squibb, Daiichi-Sankyo, Ionis, Janssen, Novartis, Pfizer, PhaseBio, and Servier, outside the submitted work. J.C.F. reports no conflict of interest., (Thieme. All rights reserved.)

Like all biofluid-contacting medical devices, intranasal splints are highly prone to bacterial adhesion and clot formation. Despite their widespread use and the numerous complications associated with infected splints, limited success has been achieved in advancing their safety and surface biocompatibility, and, to date, no surface-coating strategy has been proposed to simultaneously enhance the antithrombogenicity and bacterial repellency of intranasal splints. Herein, we report an efficient, highly stable lubricant-infused coating for intranasal splints to render their surfaces antithrombogenic and repellent toward bacterial cells. Lubricant-infused intranasal splints were prepared by creating superhydrophobic polysiloxane nanofilament (PSnF) coatings using surface-initiated polymerization of n -propyltrichlorosilane ( n -PTCS) and further infiltrating them with a silicone oil lubricant. Compared with commercially available intranasal splints, lubricant-infused, PSnF-coated splints significantly attenuated plasma and blood clot formation and prevented bacterial adhesion and biofilm formation for up to 7 days, the typical duration for which intranasal splints are kept. We further demonstrated that the performance of our engineered biointerface is independent of the underlying substrate and could be used to enhance the hemocompatibility and repellency properties of other medical implants such as medical-grade catheters.

Low-molecular-weight heparin (LMWH) therapy is recommended over vitamin K antagonists (VKAs) for the treatment of cancer-associated thrombosis (CAT) and extended therapy is recommended in those with active cancer to prevent recurrent thrombosis. However, the inconvenience of daily subcutaneous injections and the cost of LMWH therapy hinder long-term use. Observational data demonstrate that persistence with LMWH therapy is low in clinical practice and that many patients are switched to oral alternatives - namely VKAs and direct oral anticoagulants (DOACs). Recently, the efficacy and safety of apixaban, edoxaban, and rivaroxaban versus LMWH therapy for the treatment of CAT have been demonstrated in randomized trials. This review provides a critical evaluation of studies with DOACs in this setting and an update on the guidance regarding anticoagulant use for the treatment of CAT. In recognition of the heterogeneity of patients with cancer and the challenges of CAT, patient cases with expert clinical perspectives are presented., (Copyright © 2020. Published by Elsevier B.V.)

Although anticoagulants have been in use for more than 80 years, heparin and vitamin K antagonists were the sole available options until recently. Although these agents revolutionized the prevention and treatment of thrombotic diseases, their use has been hampered by the necessity for coagulation monitoring and by bleeding complications resulting in part from their multiple sites of action. Owing to advances in basic science, animal models, and epidemiology, the arsenal of available anticoagulants has expanded in the past two decades. This evolution has yielded many novel compounds that target single coagulation enzymes. Initially, thrombin and factor Xa were targeted because of their critical roles in coagulation. However, attention has now shifted to compounds that target upstream reactions, particularly those catalyzed by factors XIIa and XIa, which are part of the contact system. This shift is predicated on epidemiological and experimental evidence suggesting that these factors are more important for thrombosis than for hemostasis. With the goal of developing a new class of anticoagulants associated with a lower risk of bleeding than currently available agents, dozens of drugs targeting the contact system are now in development. This article focuses on the rationale, development, and testing of these new agents with a concentration on those that have reached or completed phase 2 evaluation for at least one indication., (© 2020 International Society on Thrombosis and Haemostasis.)

Background: Patients with mechanical heart valves (MHVs) require warfarin to prevent thromboembolism. Dabigatran was less effective than warfarin in patients with MHVs, which prompted a black box warning against the use of direct oral anticoagulants for this indication. However, rivaroxaban and apixaban, which inhibit factor Xa, have not been evaluated in patients with MHVs. To determine whether rivaroxaban and apixaban would be effective, we used MHV-induced thrombin generation assays to compare them with warfarin either alone or in combination with dabigatran., Methods: Thrombin generation in the absence or presence of MHV leaflets or sewing ring segments (SRSs) was quantified. Studies were done in control plasma; plasma from patients on warfarin; plasma containing varying concentrations of rivaroxaban, apixaban, or dabigatran alone; or plasma containing rivaroxaban plus dabigatran., Results: Mean endogenous thrombin potential (ETP) increased 1.2-fold, 1.5-fold, and 1.8-fold in the presence of leaflets, Teflon (Terumo Aortic (Sunrise, FL)) SRSs, or Dacron (Terumo Aortic (Sunrise, FL)) SRSs, respectively. Rivaroxaban and apixaban reduced ETP at concentrations above 50 ng/mL but were less effective than warfarin. When rivaroxaban and dabigatran were combined, they suppressed ETP in a more than additive manner., Conclusions: Whereas warfarin suppresses MHV-induced thrombin generation, MHVs induce the generation of factor Xa in concentrations that overwhelm clinically relevant concentrations of rivaroxaban or apixaban. When used in combination, rivaroxaban and dabigatran are more effective than either agent is alone, suggesting that concomitant inhibition of factor Xa and thrombin is better than inhibition of either clotting enzyme alone., (Copyright © 2020 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Coronavirus disease 2019 (COVID-19), currently a worldwide pandemic, is a viral illness caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The suspected contribution of thrombotic events to morbidity and mortality in COVID-19 patients has prompted a search for novel potential options for preventing COVID-19-associated thrombotic disease. In this article by the Global COVID-19 Thrombosis Collaborative Group, we describe novel dosing approaches for commonly used antithrombotic agents (especially heparin-based regimens) and the potential use of less widely used antithrombotic drugs in the absence of confirmed thrombosis. Although these therapies may have direct antithrombotic effects, other mechanisms of action, including anti-inflammatory or antiviral effects, have been postulated. Based on survey results from this group of authors, we suggest research priorities for specific agents and subgroups of patients with COVID-19. Further, we review other agents, including immunomodulators, that may have antithrombotic properties. It is our hope that the present document will encourage and stimulate future prospective studies and randomized trials to study the safety, efficacy, and optimal use of these agents for prevention or management of thrombosis in COVID-19., Competing Interests: No specific funding was sought or received for this manuscript. A list of Disclosures for co-authors is available online in the Supplementary Material (available in the online version)., (Georg Thieme Verlag KG Stuttgart · New York.)

Antiplatelet agents and anticoagulants are a mainstay for the prevention and treatment of thrombosis. However, despite advances in antithrombotic therapy, a fundamental challenge is the side effect of bleeding. Improved understanding of the mechanisms of haemostasis and thrombosis has revealed new targets for attenuating thrombosis with the potential for less bleeding, including glycoprotein VI on platelets and factor XIa of the coagulation system. The efficacy and safety of new agents are currently being evaluated in phase III trials. This Review provides an overview of haemostasis and thrombosis, details the current landscape of antithrombotic agents, addresses challenges with preventing thromboembolic events in patients at high risk and describes the emerging therapeutic strategies that may break the inexorable link between antithrombotic therapy and bleeding risk.

Advances in antiplatelet therapies for patients with cardiovascular disease have improved patient outcomes over time, but the challenge of balancing the risks of ischaemia and bleeding remains substantial. Moreover, many patients with cardiovascular disease have a residual risk of ischaemic events despite receiving antiplatelet therapy. Therefore, novel strategies are needed to prevent clinical events through mechanisms beyond platelet inhibition and with an acceptable associated risk of bleeding. The advent of non-vitamin K antagonist oral anticoagulants, which attenuate fibrin formation by selective inhibition of factor Xa or thrombin, has renewed the interest in dual-pathway inhibition strategies that combine an antiplatelet agent with an anticoagulant drug. In this Review, we highlight the emerging pharmacological rationale and clinical development of dual-pathway inhibition strategies for the prevention of atherothrombotic events in patients with different manifestations of cardiovascular disease, such as coronary artery disease, cerebrovascular disease and peripheral artery disease.

Patients with renal impairment are at higher risk of thrombosis and bleeding than those with normal renal function. The optimal rivaroxaban dose for thromboprophylaxis in acutely ill medical patients with renal impairment is unknown. MARINER and MAGELLAN were multicenter, randomized clinical trials of rivaroxaban in acutely ill medical patients. Efficacy and safety outcomes in patients with renal impairment in MARINER (7.5 mg once daily) were compared with those in patients with normal renal function in MARINER (10 mg once daily) and in a subpopulation of MAGELLAN that excluded patients at high risk for bleeding at baseline (10 mg once daily). Compared with enoxaparin/placebo in the MAGELLAN subpopulation, the relative risk (RR) of symptomatic venous thromboembolism (VTE) and VTE-related death with rivaroxaban 10 mg in patients with renal impairment (RR = 0.62; 95% confidence interval [CI] 0.27-1.44) was similar to that in those with normal renal function (RR = 0.78; 95% CI 0.44-1.40), while in MARINER, the 7.5 mg dose did not reduce the risk in patients with renal impairment (hazard ratio = 1.00; 95% CI 0.52-1.92). Major bleeding with rivaroxaban 10 mg once daily was higher in patients with renal impairment than in those with normal renal function in MAGELLAN (1.54% vs. 0.98%) and in the MAGELLAN subpopulation (0.94% vs. 0.61%). At a dose of 10 mg once daily, rivaroxaban is effective for thromboprophylaxis in acutely ill medical patients with impaired or normal renal function. The safety of this regimen is enhanced without loss of efficacy by excluding patients at high risk for bleeding, but not by using a reduced-dose strategy. TRIAL REGISTRATION:  ClinicalTrials.gov identifiers: NCT00571649 for the MAGELLAN trial, NCT02111564 for the MARINER trial., Competing Interests: J.I.W.: Bayer, Boehringer Ingelheim, Bristol-Meyers Squibb, Daiichi Sankyo, Ionis, Janssen, Merck, Novartis, Pfizer, Portola; A.C.S.: Janssen Research & Development LLC, Bayer, Portola, Boehringer Ingelheim, ATLAS group: Research Grants and Consulting; C.L., J.X., W.L., E.S., J.A., D.A., E.S.B.: Janssen Research & Development LLC: Employee/Stock; Y.D.S., T.E.S.: Bayer U.S. LLC: Employee; G.E.R.: Janssen Research & Development LLC & Bayer U.S. LLC, Daiichi Sankyo, Portola, Boehringer Ingelheim, PHRI Mc Master, Tetherex, Eli Lilly: Research Grants and Consulting., (Georg Thieme Verlag KG Stuttgart · New York.)

Antiplatelet therapy is the mainstay for the treatment of acute and chronic arterial disease involving the coronary and peripheral beds. However, questions remain about optimal antithrombotic therapy for long-term treatment of chronic vascular disease. The observation that dual antiplatelet therapy with acetylsalicylic acid and clopidogrel was associated with lower thrombotic event rates than acetylsalicylic acid monotherapy in patients with acute coronary syndromes and those undergoing percutaneous coronary intervention changed the treatment paradigm. Moreover, the demonstration that more pharmacodynamically potent P2Y 12 inhibitors than clopidogrel were associated with fewer thrombotic event occurrences further solidified the dual antiplatelet therapy approach. However, recurrent thrombotic events occur in ≈1 in 10 patients in the first year following an acute coronary syndrome event, despite treatment with the most potent P2Y 12 inhibitors, a limitation that has stimulated interest in exploring the efficacy and safety of approaches using anticoagulants on top of antiplatelet therapy. These investigations have included treatment with very-low-dose oral anticoagulation, and even its replacement of acetylsalicylic acid in the presence of a P2Y 12 inhibitor, in patients stabilized after an acute coronary syndrome event. Recent basic and translational studies have suggested noncanonical effects of coagulation factor inhibition that may further modulate clinical benefits. This in-depth review will discuss developments in our understanding of the roles that platelets and coagulation factors play in atherothrombosis and review the rationale and clinical evidence for combining antiplatelet and oral anticoagulant therapy in patients with coronary and peripheral artery disease.

Recent advances in our understanding of the contribution of thrombin generation to arterial thrombosis and the role of platelets in venous thrombosis have prompted new treatment paradigms. Nonetheless, bleeding remains the major side effect of such treatments spurring the quest for new antithrombotic regimens with better benefit-risk profiles and for safer anticoagulants for existing and new indications. The aims of this article are to review the results of recent trials aimed at enhancing the benefit-risk profile of antithrombotic therapy and explain how these findings are changing our approach to the management of arterial and venous thrombosis. Focusing on these 2 aspects of thrombosis management, this article discusses 4 advances: (1) the observation that in some indications, lowering the dose of some direct oral anticoagulants reduces the risk of bleeding without compromising efficacy, (2) the recognition that aspirin is not only effective for secondary prevention of atherothrombosis but also for prevention of venous thromboembolism, (3) the finding that dual pathway inhibition with the combination of low-dose rivaroxaban to attenuate thrombin generation plus aspirin to reduce thromboxane A2-mediated platelet activation is superior to aspirin or rivaroxaban alone for prevention of atherothrombosis in patients with coronary or peripheral artery disease, and (4) the development of inhibitors of factor XI or XII as potentially safer anticoagulants.

Thrombosis remains a major cause of morbidity and mortality. Consequently, advances in antithrombotic therapy are needed to reduce the disease burden. This article focuses on 2 such advances. First, the prevention of atherothrombosis in patients with coronary or peripheral artery disease, which has been enhanced by the finding that the combination of low-dose rivaroxaban plus aspirin is superior to aspirin alone for prevention of recurrent ischemic events. However, this benefit comes at the cost of increased bleeding albeit not fatal bleeding. To overcome this problem, the second advance is the identification of factor XI as a target for new anticoagulants that are potentially safer than those currently available.

Objective- Dual-antiplatelet therapy with acetylsalicylic acid and a P2Y 12 antagonist, such as clopidogrel, is the standard of care for acute coronary syndromes. However, the drugs have divergent effects on the formation of cAMP, an inhibitory second messenger. Thus, by inhibiting the synthesis of prostacyclin, acetylsalicylic acid reduces cAMP formation, whereas clopidogrel potentiates it. Therefore, with higher doses of acetylsalicylic acid, the potentiation of cAMP production by clopidogrel may be attenuated, which could limit the antithrombotic potential of the drug combination. The purpose of this study was to examine this possibility in vivo. Approach and Results- Mice were given oral acetylsalicylic acid at varying doses, oral clopidogrel (5 mg/kg body weight), or both. At doses of 0.15 and 0.6 mg/kg, acetylsalicylic acid inhibited arachidonic acid-induced platelet aggregation, but only 0.6 mg/kg acetylsalicylic acid, or higher, decreased the plasma levels of 6-keto-prostaglandin-F 1α , the stable metabolite of prostacyclin. When given with clopidogrel, laser injury-induced arterial thrombi were significantly larger with the 0.6 mg/kg dose of acetylsalicylic acid than with the 0.15 mg/kg dose. Thrombi in mice treated with clopidogrel and the 0.15 mg/kg dose of acetylsalicylic acid were smaller than in mice treated with clopidogrel alone, suggesting that acetylsalicylic acid can add to the antithrombotic effect of clopidogrel but that higher doses of acetylsalicylic acid blunt the antithrombotic effect of clopidogrel. Conclusions- These findings support the use of lower, prostacyclin-preserving, doses of acetylsalicylic acid in conjunction with clopidogrel.

Competing Interests: Conflict-of-interest disclosure: N.C.C. receives personal fees from Bayer outside the submitted work. J.I.W. receives personal fees from Bristol-Myers Squibb, Bayer, Boehringer Ingelheim, Daiichi-Sankyo, Merck, Novartis, Pfizer, Ionis Pharmaceuticals, Janssen, and Portola outside the submitted work.

Background: Superficial-vein thrombosis can lead to deep-vein thrombosis and pulmonary embolism. Rivaroxaban, an oral factor Xa inhibitor, might simplify treatment compared with fondaparinux because it does not require daily subcutaneous injection and is cheaper. We compared efficacy outcomes in patients with superficial-vein thrombosis and additional risk factors given either rivaroxaban or fondaparinux to assess whether rivaroxaban is non-inferior to fondaparinux in the prevention of thromboembolic complications., Methods: In this open-label, masked endpoint, randomised, non-inferiority phase 3b trial, we recruited patients aged 18 years or older with symptomatic superficial-vein thrombosis from 27 sites (academic, community hospitals, and specialist practices) in Germany. We randomly assigned patients (1:1) to receive 10 mg oral rivaroxaban or 2·5 mg subcutaneous fondaparinux once a day for 45 days. Patients were eligible if they had symptomatic thrombosis (at least 5 cm in a supragenual superficial-vein segment) and at least one additional risk factor (older than 65 years, male sex, previous venous thromboembolism, cancer, autoimmune disease, thrombosis of non-varicose veins). Main exclusion criteria were: symptoms for longer than 3 weeks, thrombus within 3 cm of the sapheno-femoral junction, indication for full-dose anticoagulation therapy, and substantial hepatic or renal impairment. Randomisation was done with a central block randomisation process. The primary efficacy outcome was a composite of symptomatic deep-vein thrombosis or pulmonary embolism, progression or recurrence of superficial vein-thrombosis, and all-cause mortality at 45 days in the per-protocol population (all randomly assigned patients without major protocol violations). We used a non-inferiority margin of 4·5% (absolute difference between rivaroxaban and fondaparinux). The main safety outcome was major bleeding. This study is registered with ClinicalTrials.gov, number NCT01499953., Findings: Between April 25, 2012, and Feb 18, 2016, 485 patients were enrolled in the study and 472 were randomly assigned to the rivaroxaban group (n=236) or the fondaparinux group (n=236). In the 435 patients included in the per-protocol analysis set, the primary efficacy outcome occurred in seven (3%) of 211 patients (95% CI 1·6-6·7) in the rivaroxaban group and in four (2%) of 224 patients (0·7-4·5) in the fondaparinux group (hazard ratio [HR] 1·9, 95% CI 0·6-6·4; p=0·0025 for non-inferiority) at day 45. There were no major bleeds in either group. There was one death in the rivaroxaban group; this patient died from cardiogenic shock on day 50 after a type A aortic dissection, not related to treatment., Interpretation: Rivaroxaban was non-inferior to fondaparinux for treatment of superficial-vein thrombosis in terms of symptomatic deep-vein thrombosis or pulmonary embolism, progression or recurrence of superficial vein-thrombosis, and all-cause mortality, and was not associated with more major bleeding. Therefore, rivaroxaban could offer patients with symptomatic superficial-vein thrombosis a less burdensome and less expensive oral treatment option instead of a more expensive subcutaneous injection., Funding: GWT-TUD and Bayer Vital., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Despite the introduction of direct oral anticoagulants (DOACs), the search for more effective and safer antithrombotic strategies continues. Better understanding of the pathogenesis of thrombosis has fostered 2 new approaches to achieving this goal. First, evidence that thrombin may be as important as platelets to thrombosis at sites of arterial injury and that platelets contribute to venous thrombosis has prompted trials comparing anticoagulants with aspirin for secondary prevention in arterial thrombosis and aspirin with anticoagulants for primary and secondary prevention of venous thrombosis. These studies will help identify novel treatment strategies. Second, emerging data that naturally occurring polyphosphates activate the contact system and that this system is critical for thrombus stabilization and growth have identified factor XII (FXII) and FXI as targets for new anticoagulants that may be even safer than the DOACs. Studies are needed to determine whether FXI or FXII is the better target and to compare the efficacy and safety of these new strategies with current standards of care for the prevention or treatment of thrombosis. Focusing on these advances, this article outlines how treatment strategies for thrombosis are evolving and describes the rationale and approaches to targeting FXII and FXI. These emerging anticoagulant strategies should address unmet needs and reduce the systemic underuse of anticoagulation because of the fear of bleeding., (© 2017 by The American Society of Hematology.)

Although surgery was the mainstay of treatment for valvular heart disease, transcatheter valve therapies have grown exponentially over the past decade. Two types of artificial heart valve exist: mechanical heart valves (MHV), which are implanted surgically, and bioprosthetic heart valves (BHV), which can be implanted via a surgical or transcatheter approach. Whereas long-term anticoagulation is required to prevent thromboembolism after MHV replacement, its value in patients receiving BHVs is uncertain. Patients undergoing transcatheter BHV replacement are at risk for thromboembolism in the first few months, and recent data suggest that the risk continues thereafter. BHV thrombosis provides a substrate for subsequent thromboembolism and may identify a reversible cause of prosthesis dysfunction. Hereafter, the authors: 1) review the data on prosthetic valve thrombosis; 2) discuss the pathophysiological mechanisms that may lead to valve thrombus formation; and 3) provide perspective on the implications of these findings in the era of transcatheter valve replacement., (Copyright © 2016 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Although the non-vitamin antagonist oral anticoagulants produce less intracranial bleeding than warfarin, serious bleeding still occurs. Therefore, the search for safer anticoagulants continues. Factor XII and factor XI have emerged as promising targets whose inhibition has the potential to prevent thrombosis with little or no disruption of hemostasis. Thus, thrombosis is attenuated in mice deficient in factor XII or factor XI and patients with congenital factor XII deficiency do not bleed and those with factor XI deficiency rarely have spontaneous bleeding. Strategies targeting factor XII and XI include antisense oligonucleotides to decrease their synthesis, inhibitory antibodies or aptamers, and small molecule inhibitors. These strategies attenuate thrombosis in various animal models and factor XI knockdown with an antisense oligonucleotide in patients undergoing knee replacement surgery reduced postoperative venous thromboembolism to a greater extent than enoxaparin without increasing bleeding. Therefore, current efforts are focused on evaluating the efficacy and safety of factor XII and factor XI directed anticoagulant strategies., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Blood-contacting medical devices, such as vascular grafts, stents, heart valves, and catheters, are often used to treat cardiovascular diseases. Thrombus formation is a common cause of failure of these devices. This study (i) examines the interface between devices and blood, (ii) reviews the pathogenesis of clotting on blood-contacting medical devices, (iii) describes contemporary methods to prevent thrombosis on blood-contacting medical devices, (iv) explains why some anticoagulants are better than others for prevention of thrombosis on medical devices, and (v) identifies future directions in biomaterial research for prevention of thrombosis on blood-contacting medical devices., (© 2015 International Society on Thrombosis and Haemostasis.)

Factor (F) XII, a key component of the contact system, triggers clotting via the intrinsic pathway, and is implicated in propagating thrombosis. Although nucleic acids are potent activators, it is unclear how the contact system is regulated to prevent uncontrolled clotting. Previously, we showed that histidine-rich glycoprotein (HRG) binds FXIIa and attenuates its capacity to trigger coagulation. To investigate the role of HRG as a regulator of the intrinsic pathway, we compared RNA- and DNA-induced thrombin generation in plasma from HRG-deficient and wild-type mice. Thrombin generation was enhanced in plasma from HRG-deficient mice, and accelerated clotting was restored to normal with HRG reconstitution. Although blood loss after tail tip amputation was similar in HRG-deficient and wild-type mice, carotid artery occlusion after FeCl3 injury was accelerated in HRG-deficient mice, and HRG administration abrogated this effect. To confirm that HRG modulates the contact system, we used DNase, RNase, and antisense oligonucleotides to characterize the FeCl3 model. Whereas DNase or FVII knockdown had no effect, carotid occlusion was abrogated with RNase or FXII knockdown, confirming that FeCl3-induced thrombosis is triggered by RNA in a FXII-dependent fashion. Therefore, in a nucleic acid-driven model, HRG inhibits thrombosis by modulating the intrinsic pathway of coagulation., (© 2015 by The American Society of Hematology.)

Plasma fibronectin (pFn) has long been suspected to be involved in hemostasis; however, direct evidence has been lacking. Here, we demonstrated that pFn is vital to control bleeding in fibrinogen-deficient mice and in WT mice given anticoagulants. At the site of vessel injury, pFn was rapidly deposited and initiated hemostasis, even before platelet accumulation, which is considered the first wave of hemostasis. This pFn deposition was independent of fibrinogen, von Willebrand factor, β3 integrin, and platelets. Confocal and scanning electron microscopy revealed pFn integration into fibrin, which increased fibrin fiber diameter and enhanced the mechanical strength of clots, as determined by thromboelastography. Interestingly, pFn promoted platelet aggregation when linked with fibrin but inhibited this process when fibrin was absent. Therefore, pFn may gradually switch from supporting hemostasis to inhibiting thrombosis and vessel occlusion following the fibrin gradient that decreases farther from the injured endothelium. Our data indicate that pFn is a supportive factor in hemostasis, which is vital under both genetic and therapeutic conditions of coagulation deficiency. By interacting with fibrin and platelet β3 integrin, pFn plays a self-limiting regulatory role in thrombosis, suggesting pFn transfusion may be a potential therapy for bleeding disorders, particularly in association with anticoagulant therapy.

In patients with mechanical heart valves, thromboembolic events were more frequent with dabigatran, an oral thrombin inhibitor, than with warfarin. This observation raises the possibility that dabigatran may be less effective than conventional anticoagulants in patients with other blood-contacting devices, such as catheters. To address this, we compared the capacity of dabigatran and/or heparin to inhibit catheter-induced thrombin generation in vitro and to attenuate catheter occlusion in rabbits. Using a catheter-induced thrombin generation assay, concentrations of dabigatran over 100 ng/ml prolonged the lag time and time to peak thrombin, and reduced the peak thrombin concentration and endogenous thrombin potential in a concentration-dependent fashion. Compared with saline in a rabbit model of catheter thrombosis, dabigatran prolonged the mean time to catheter occlusion by 2.9- and 1.9-fold when plasma levels were 173 and 140 ng/ml, respectively; values comparable to median peak levels in humans given dabigatran 150 mg twice daily. In contrast, low-dose dabigatran, which produced a level of 60 ng/ml; a value comparable to the trough level of dabigatran in humans, did not prolong the time to occlusion. Whereas a 70 U/kg bolus of heparin prolonged the mean time to occlusion by 3.4-fold, a 15 U/kg bolus had no effect. When low-dose dabigatran was given in combination with 15 U/kg heparin, the mean time to occlusion was prolonged by 2.7-fold. These findings suggest that only peak levels of dabigatran are sufficient to prevent catheter-induced clotting unless supplemented heparin is given.

Central venous catheter thrombosis can cause venous obstruction and pulmonary embolism. To determine the extent to which catheter thrombosis is triggered by the contact or extrinsic pathway of coagulation, we used antisense oligonucleotides (ASOs) to selectively knock down factor (f)XII, fXI, or high-molecular-weight kininogen (HK), key components of the contact pathway, or fVII, which is essential for the extrinsic pathway. Knockdown of contact pathway components prolonged the activated partial thromboplastin time and decreased target protein activity levels by over 90%, whereas fVII knockdown prolonged the prothrombin time and reduced fVII activity to a similar extent. Using a rabbit model of catheter thrombosis, catheters implanted in the jugular vein were assessed daily until they occluded, up to a maximum of 35 days. Compared with control, fXII and fXI ASO treatment prolonged the time to catheter occlusion by 2.2- and 2.3-fold, respectively. In contrast, both HK and fVII knockdown did not significantly prolong the time to occlusion, and dual treatment with fVII- and fXI-directed ASOs produced a time to occlusion similar to that with the fXI ASO alone. These findings suggest that catheter thrombosis is triggered via the contact pathway and identify fXII and fXI as potential targets to attenuate this complication.

Oral anticoagulants are a mainstay of cardiovascular therapy, and for over 60 years vitamin K antagonists (VKAs) were the only available agents for long-term use. VKAs interfere with the cyclic inter-conversion of vitamin K and its 2,3 epoxide, thus inhibiting γ-carboxylation of glutamate residues at the amino-termini of vitamin K-dependent proteins, including the coagulation factors (F) II (prothrombin), VII, IX and X, as well as of the anticoagulant proteins C, S and Z. The overall effect of such interference is a dose-dependent anticoagulant effect, which has been therapeutically exploited in heart disease since the early 1950s. In this position paper, we review the mechanisms of action, pharmacological properties and side effects of VKAs, which are used in the management of cardiovascular diseases, including coronary heart disease (where their use is limited), stroke prevention in atrial fibrillation, heart valves and/or chronic heart failure. Using an evidence-based approach, we describe the results of completed clinical trials, highlight areas of uncertainty, and recommend therapeutic options for specific disorders. Although VKAs are being increasingly replaced in most patients with non-valvular atrial fibrillation by the new oral anticoagulants, which target either thrombin or FXa, the VKAs remain the agents of choice for patients with atrial fibrillation in the setting of rheumatic valvular disease and for those with mechanical heart valves.

There is mounting evidence that zinc, the second most abundant transition metal in blood, is an important mediator of haemostasis and thrombosis. Prompted by the observation that zinc deficiency is associated with bleeding and clotting abnormalities, there now is evidence that zinc serves as an effector of coagulation, anticoagulation and fibrinolysis. Zinc binds numerous plasma proteins and modulates their structure and function. Because activated platelets secrete zinc into the local microenvironment, the concentration of zinc increases in the vicinity of a thrombus. Consequently, the role of zinc varies depending on the microenvironment; a feature that endows zinc with the capacity to spatially and temporally regulate haemostasis and thrombosis. This paper reviews the mechanisms by which zinc regulates coagulation, platelet aggregation, anticoagulation and fibrinolysis and outlines how zinc serves as a ubiquitous modulator of haemostasis and thrombosis.

Hemostasis maintains the blood in a fluid state under physiological conditions, yet enables rapid clot formation at sites of vascular injury to prevent excessive bleeding. Disruption of hemostasis can lead to thrombosis, which can occur in arteries, veins, or in the chambers of the heart. Factors contributing to thrombosis in these sites include endothelial injury, reduced blood flow, and hypercoagulability of the blood. Vessel wall injury and stasis are particularly important in the pathogenesis of arterial thrombosis, whereas hypercoagulability and stasis are the key contributors to venous thrombosis. Hereditary and acquired risk factors combine to establish the intrinsic risk for thrombosis in each individual and superimposed environmental factors can add to this risk. Although hereditable risk factors for venous thrombosis are well defined, much less is known about the genetic risk factors for arterial thrombosis. This article reviews our current knowledge of hereditable risk factors for arterial and venous thrombosis from the cardiology perspective., (Copyright © 2013 Canadian Cardiovascular Society. Published by Elsevier Inc. All rights reserved.)

Catheters initiate coagulation by activating factor (f) XII, which can lead to catheter thrombosis. Fondaparinux, which only targets activated fX (fXa), is associated with more catheter thrombosis than heparin, which targets fXa and thrombin. To render catheters less thrombogenic and fondaparinux more effective, we examined whether coating catheters with corn trypsin inhibitor (CTI), which blocks fXIIa, attenuates catheter-induced clotting and promotes fondaparinux activity. Compared with unmodified catheters, CTI-coated catheters demonstrated (a) decreased adsorption of fibrinogen and fXII, (b) greater inhibition of fXIIa generated by catheter-induced autoactivation, (c) attenuated fXIIa-mediated activation of fXI and (d) longer plasma clotting times in the absence or presence of fondaparinux. In an accelerated catheter thrombosis model in rabbits, (a) the time to catheter occlusion was longer with CTI-coated catheters than with unmodified catheters and (b) an intravenous dose of fondaparinux that had no effect on the time to occlusion of unmodified catheters extended the time to occlusion of CTI-coated catheters. These findings support the concept that the prothrombotic activity of catheters reflects their capacity to activate fXII and identify CTI immobilization as a novel approach for rendering catheters and other blood-contacting medical devices less thrombogenic., (Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.)

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.

Anticoagulants are the cornerstone of therapy for conditions associated with arterial and venous thrombosis. Direct thrombin inhibitors (DTIs) are anticoagulants that bind to thrombin and block its enzymatic activity. The bivalent parenteral DTIs hirudin and bivalirudin were based on the observation that the salivary extracts of medicinal leeches prevented blood from clotting. Key events that facilitated the subsequent development of small molecule active site inhibitors, such as argatroban, were the observation that fibrinopeptide A had antithrombotic properties and determination of the crystal structure of thrombin. Hirudin and argatroban have found their niche for the treatment of patients with heparin-induced thrombocytopenia, whereas bivalirudin is approved as an alternative to heparin for patients undergoing percutaneous coronary intervention. The development of orally active direct thrombin inhibitors was challenging because of the need to convert water-soluble, poorly absorbable, active site inhibitors into fat-soluble prodrugs that were then transformed back to the active drug after intestinal absorption. Dabigatran etexilate was the first new oral anticoagulant to be approved for long-term anticoagulant treatment in 6 decades. This Review highlights the development of DTIs as a translational success story; an example in which the combination of scientific ingenuity, structure-based design, and rigorous clinical trials has created a new class of anticoagulants that has improved patient care.

Background: Shielding of procoagulant phosphatidylserine (PS) with annexin A5 attenuates thrombosis, but annexin A5 (35.7 kDa) is rapidly cleared from the circulation. In contrast, Diannexin, a 73.1 kDa homodimer of annexin A5, has an extended half-life., Objectives: To quantify the affinity of Diannexin for PS, examine its interaction with activated platelets and determine its effects on platelet-mediated events during thrombus formation., Methods: The affinities of Diannexin and annexin A5 for PS-containing lipid bilayers were compared using surface plasmon resonance, and binding to activated platelets was assessed by flow cytometry. Calibrated automated thrombography and thromboelastography were employed to study the effects of Diannexin on thrombin generation and platelet-fibrin clot formation, respectively, whereas intravital videomicroscopy was used to examine its effect on platelet accumulation and activation after laser-induced injury to murine cremaster arterioles, and a tail tip bleeding model was used to explore its effects on hemostasis., Results: Diannexin and annexin A5 bind PS with K(D) values of 0.6 and 5 nm, respectively, and both bind to the same subpopulation of PS-exposing platelets. Diannexin inhibited thrombin generation and platelet-fibrin clot formation in vitro at 10 nm (P<0.05-0.001 compared with control), and reduced platelet accumulation at 1 μg g(-1) (P<0.05) and activation at 0.25 μg g(-1) (P<0.001) in experimentally induced arterial thrombi in mice while increasing blood loss at 1 μg g(-1) (P<0.01)., Conclusions: Diannexin binds to PS with high affinity and is a potent inhibitor of platelet-mediated events during thrombus formation., (© 2012 International Society on Thrombosis and Haemostasis.)