General mechanisms of coagulation and targets of anticoagulants (Section I)

Mechanisms of thrombogenesis in polycythemia vera

Thrombotic and cardiovascular events are among the leading causes of death for patients with polycythemia vera (PV), and thrombosis history is a key criterion for patient risk stratification and treatment strategy. Little is known, however, about mechanisms of thrombogenesis in patients with PV. This report provides an overview of thrombogenesis pathophysiology in patients with PV and elucidates the roles of conventional and nonconventional thrombotic risk factors. In addition to several conventional risk factors for thrombosis, clinical data have implicated increased hematocrit and red blood cell adhesiveness, activated platelets, leukocytosis, and elevated JAK2(V617F) allele burden in patients with PV. Furthermore, PV-related inflammation may exacerbate thrombogenesis through varied mechanisms, including endothelial damage, inhibition of natural anticoagulant pathways, and secretion of procoagulant factors. These findings suggest a direct link between myeloproliferation and thrombogenesis in PV, which is likely to provide new opportunities for targeted antithrombotic interventions aimed at decreasing PV-related morbidity and mortality.

Bleeding complications of targeted oral anticoagulants: what is the risk?

The vitamin K antagonists (VKAs) are a widely used class of agent to prevent thromboembolism. In recent years, numerous alternatives to VKAs have been developed, the target-specific oral anticoagulants (TSOACs), which are available in clinical practice. Currently available agents target thrombin and factor Xa. The most significant side effect of these agents, as with VKAs, is the development of bleeding complications. In this review, the risks of major bleeding complications with the TSOACs will be discussed. Data from meta-analyses, randomized controlled trials, and observational studies will be used to highlight bleeding complications associated with TSOACs and warfarin. We highlight the most common causes of major bleeding, GI and intracranial hemorrhage.

Antiplatelet and anticoagulation agents in acute coronary syndromes: what is the current status and what does the future hold?

Mortality and morbidity in acute coronary syndromes (ACSs), caused principally by plaque erosion or rupture leading to thrombus formation and myocardial ischemia, have been reduced by a combination of antithrombotic agents (antiplatelet drugs and anticoagulants) and early revascularization. Aspirin is the foundation antiplatelet agent. New P2Y12 receptor inhibitors (prasugrel and ticagrelor) have clear benefits compared with clopidogrel for dual antiplatelet therapy, and cangrelor or vorapaxar, a thrombin receptor inhibitor, may be of value in specific settings. Anticoagulation uses 1 of 4 choices: bivalirudin, unfractionated heparin, enoxaparin, and fondaparinux. Moreover, some patients (such as those who have chronic atrial fibrillation) require triple therapy with aspirin, clopidogrel, plus an anticoagulant, frequently a vitamin K antagonist. New oral anticoagulants have been shown to be at least as effective as vitamin K antagonists in atrial fibrillation and led to fewer bleeding complications. Finally, the combination of aspirin, clopidogrel, and low-dose rivaroxaban has recently been approved by the European Medicines Agency (but not the Food and Drug Administration) for secondary prevention after ACS. Several strategies have been developed to balance the potential benefit of antithrombotic therapy against the risk of bleeding complications, for example, radial access in coronary angiography or restricted use of combination therapy, and others are under investigation, such as discontinuation of aspirin. This overview summarizes the current status of antithrombotic therapy in ACS and describes strategies currently explored to optimize its benefit/risk ratio.

SAMe-TT2R2 score, time in therapeutic range, and outcomes in anticoagulated patients with atrial fibrillation

BACKGROUND

Oral anticoagulation is highly effective in preventing stroke and mortality in nonvalvular atrial fibrillation patients. However, the efficacy and safety of vitamin K antagonists (the main oral anticoagulation drug used) strongly depends upon the quantity of anticoagulation control, as reflected by the average percentage of the time in therapeutic range of international normalized ratio 2.0-3.0. An easy, simple prediction of which atrial fibrillation patients are likely to do well on vitamin K antagonists (with good average time in therapeutic range) could guide decision-making between using vitamin K antagonists (eg, warfarin) and non-vitamin K antagonist oral anticoagulants.

METHODS AND RESULTS

In a consecutive cohort of nonvalvular atrial fibrillation patients attending our anticoagulation clinic, we tested the hypothesis that the new Sex, Race, Medical history, Tobacco use, Race (SAMe-TT2R2) score was a predictor for good average time in therapeutic range, and second, this would translate into adverse events in a "real world" cohort of patients with nonvalvular atrial fibrillation. The incidence of bleeding, adverse cardiovascular events (including stroke/thromboembolism), and mortality during the follow-up was higher with increasing SAMe-TT2R2 score. The SAMe-TT2R2 score was predictive for the composite of all adverse events (hazard ratio 1.32 [95% Confidence Interval 1.17-1.50]; P <.001), adverse cardiovascular events (1.52 [1.28-1.83]; P <.001), and all-cause mortality (1.41 [1.16-1.67]; P = .001). A trend was also observed for major bleeding events (1.23 [0.99-1.53]; P = .059).

CONCLUSION

In a "real world" cohort of consecutive patients with nonvalvular atrial fibrillation, a high SAMe-TT2R2 score (reflecting poor anticoagulation control with poor time in therapeutic range) was associated with more bleeding, adverse cardiovascular events, and mortality during follow-up.

Non-vitamin K oral anticoagulants in atrial fibrillation: Where are we now?

Atrial fibrillation (AF) confers increased risk of stroke and other thromboembolic events, and oral anticoagulation therefore is the essential part of AF management to reduce the risk of these complications. Until recently, the vitamin K antagonists (VKAs, e.g., warfarin) were the only oral anticoagulants available, acting by decreased synthesis of vitamin K-dependent coagulation factors (II, VI, IX, and X). The VKAs had many limitations: delayed onset and prolonged offset of action, variability of anticoagulant effect among patients, multiple food and drug interactions affecting pharmacological properties of warfarin, narrow therapeutic window, and obligatory regular laboratory control, which all made warfarin "inconvenient" both for patients and clinicians. The limitations of VKAs led to development of a new class of drugs collectively defined as non-VKA oral anticoagulants (NOACs), which included direct thrombin inhibitors (dabigatran) and factor Xa inhibitors (rivaroxaban, apixaban, and edoxaban). The NOACs avoid many of the VKA drawbacks. In this review, we will focus on the current evidence justifying the use of NOACs in non-valvular AF.

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

INTRODUCTION

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

AREAS COVERED

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

EXPERT OPINION

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

Non-vitamin K antagonist oral anticoagulants in atrial fibrillation and venous thromboembolism: where are we now?

Four non-vitamin-K antagonist oral anticoagulants (NOACs) are now available and are variously approved for stroke prevention in atrial fibrillation and the management of venous thromboembolism. On the whole, these drugs offer clear benefits over warfarin, overcoming problems with unpredictable individual responses and avoiding the need for frequent and resource-intensive monitoring. Sufficient data are now available to recommend the use of particular NOACs in defined settings. As a group these drugs offer a real alternative to warfarin; their more widespread use for stroke prevention in atrial fibrillation, in the management of venous thromboembolism, and perhaps in other settings promises to bring real clinical gains for at-risk populations worldwide. This review highlights the growing importance of effective anticoagulation therapy at a time when cardiovascular risk profiles are evolving, discusses the relative merits of the NOACs over warfarin, and describes the use of specific agents in specific patient populations.

Endovascular Treatment of Deep Vein Thrombosis

Venous thromboembolism (VTE) is associated with substantial morbidity and mortality. Conventional treatment with anticoagulation therapy may undertreat the condition. Patients with VTE are at risk for recurrence with increasing time passage. Endovascular approaches exist for treating VTE, including deep vein thrombosis, but it is unclear which patients are appropriate candidates for endovascular versus medical approaches. Many new endovascular technologies are in development, and new oral anticoagulants are also on the market. Clinicians must be mindful of these new products and use them appropriately to better manage VTE.

Non-vitamin K antagonist oral anticoagulants (NOACs): clinical evidence and therapeutic considerations

Warfarin, a vitamin K antagonist, is the most widely used oral anticoagulant in the world. It is cheap and effective, but its use is limited in many patients by unpredictable levels of anticoagulation, which increases the risk of thromboembolic or haemorrhagic complications. It also requires regular blood monitoring and dose adjustment. New classes of drugs, non-vitamin K antagonist oral anticoagulants (NOACs), are now supported as alternatives to warfarin. Three NOACs are licensed: dabigatran, a direct thrombin inhibitor, and rivaroxaban and apixaban, antagonists of factor Xa. NOACs do not require routine blood monitoring or dose adjustment. They have a rapid onset and offset of action and fewer food and drug interactions. Current indications include treatment and prophylaxis of venous thromboembolism and prevention of cardioembolic disease in non-valvular atrial fibrillation. Effective antidotes are lacking and some caution must be used in severe renal impairment, but favourable trial evidence has led to their widespread adoption. Research is ongoing, and an increase in their use and indications is expected in the coming years.

Oral anticoagulant use in addition to antiplatelet therapy for secondary prevention in acute coronary syndrome: current perspectives

Patients with acute coronary syndrome (ACS) are typically managed with long-term dual antiplatelet therapy of acetylsalicylic acid plus a P2Y12 platelet receptor antagonist; however, although effective, the risk of another vascular event within 12 months remains at approximately 10%. Considerable efforts have been made to find improved therapeutic approaches to secondary prevention in ACS. The ATLAS ACS 2-TIMI 51 trial demonstrated that rivaroxaban (2.5 mg twice daily) significantly reduced recurrent vascular events, increased the risk of major bleeding but not the risk of fatal bleeding, and resulted in reduced rates of death from cardiovascular causes. These results formed the basis for approval in Europe of rivaroxaban (2.5 mg twice daily) in conjunction with standard antiplatelet therapy for the secondary prevention of ACS.

A prospective validation of the SAME-TT2R 2 score: how to identify atrial fibrillation patients who will have good anticoagulation control on warfarin

Stroke prevention, achieved with oral anticoagulation therapy (OAT), is central to the management of patients with atrial fibrillation (AF). Well-managed OAT, as reflected by a long time in therapeutic range (TTR), is associated with good clinical outcomes. The SAME-TT2R2 score has been proposed to identify patients who will maintain a high average TTR on vitamin K antagonists (VKA) treatment. The objective of the study was to validate this score in a cohort of AF patients followed by an anticoagulation clinic. We applied the SAME-TT2R2 score to 1,089 patients with AF on VKAs followed by two anticoagulation clinics. The median TTR overall for the whole cohort was 73.0 %. There was a significant decline in mean (or median) TTR in relation to the SAME-TT2R2 score (p = 0.042). When the SAME-TT2R2 scores were categorized we find a TTR 74.0 % for score ≤2 and 68.0 % for score >2 (p = 0.006). The rate of major bleeding events and stroke/TIA was 1.78 × 100 patient-years (pt-yrs) and 1.26 × 100 pt-yrs, respectively. No relationship exists between the SAME-TT2R2 score and adverse events. We describe the first validation of the SAME-TT2R2 score in AF patients where, despite an overall good quality of anticoagulation, the SAME-TT2R2 score is able to identify the patients who are less likely to do well on VKA therapy if this is the chosen OAT.

Rivaroxaban in patients with a recent acute coronary syndrome event: integration of trial findings into clinical practice

Despite significant advances in the management of acute coronary syndrome (ACS) and long-term antiplatelet therapy after an ACS event, patients continue to be at risk of further cardiovascular events. There is evidence that recurrent events are at least partly attributed to the persistent activation of the coagulation system after ACS. Various anticoagulants, including vitamin K antagonists (VKAs) and non-VKA oral anticoagulants, have been evaluated in patients post-ACS, in combination with antiplatelet therapy. The desired outcome would be a further reduction of recurrent cardiovascular events with low or acceptable levels of bleeding complications. Here, we provide an overview of the current clinical trial data of non-VKA oral anticoagulants, focusing on rivaroxaban in particular, for secondary prevention in patients with a recent ACS event.

Management of anticoagulant-related intracranial hemorrhage: an evidence-based review

The increased use of anticoagulants for the prevention and treatment of thromboembolic diseases has led to a rising incidence of anticoagulant-related intracranial hemorrhage (AICH) in the aging western population. High mortality accompanies this form of hemorrhagic stroke, and significant and debilitating long-term consequences plague survivors. Although management guidelines for such hemorrhages are available for the older generation anticoagulants, they are still lacking for newer agents, which are becoming popular among physicians. Supportive care, including blood pressure control, and reversal of anticoagulation remain the cornerstone of acute management of AICH. Prothrombin complex concentrates are gaining popularity over fresh frozen plasma, and reversal agents for newer anticoagulation agents are being developed. Surgical interventions are options fraught with complications, and are decided on a case-by-case basis. Our current state of understanding of this condition and its management is insufficient. This deficit calls for more population-based studies and therapeutic trials to better evaluate risk factors for, and to prevent and treat AICH.

The Potential Role of Edoxaban in Stroke Prevention Guidelines

With the emergence of edoxaban, the oral factor Xa inhibitors now appear consolidated as the dominant class of novel oral anticoagulants (NOACs) for stroke prevention in non-valvular atrial fibrillation (AF). The oral factor Xa inhibitors do not require an adequate time in therapeutic range to be effective, presenting a potential advantage over the vitamin K antagonists (VKAs). Guidelines are changing to reflect the increased choice of anticoagulants and as clinicians move away from the VKAs towards the relative safety and efficacy of NOACs, they must consider which one offers the best therapy for their patient. The ENGAGE-AF study was the latest phase III trial to report on the safety and efficacy of a new factor Xa inhibitor relative to warfarin. Both edoxaban 60mg once daily, and edoxaban 30mg once daily were found to be non-inferior compared to warfarin for the prevention of ischaemic stroke and systemic embolism, being associated with significantly lower rates of major bleeding, intracranial haemorrhage and cardiovascular death. A two-tiered dosing option may present clinicians with a further element of choice for the individual patient.

Non-vitamin K antagonist oral anticoagulants (NOACs): No longer new or novel

Note: The editorial process for this paper was fully handled by Prof Christian Weber, Editor in Chief.

Efficacy and safety of apixaban compared with warfarin regarding time within the therapeutic range

Prevention of thromboembolism by lifelong anticoagulation is an important therapeutic goal in patients with atrial fibrillation according to recent guidelines. Major drawback of vitamin K antagonists are their narrow therapeutic range and interactions with other drugs and food. These have significant impact on the pharmacokinetics and pharmacodynamics requiring regular measurements of the international normalized ratio. Efficiency of the anticoagulant therapy depends considerably on time within the therapeutic range of prothrombin international normalized ratio. Time within the therapeutic range represents the percentage of time within the required range of prothrombin international normalized ratio. Prothrombin international normalized ratio outside the therapeutic range increases the risk of thromboembolism or bleeding according to whether it falls below or above the range. New oral anticoagulants do not require routine monitoring of anticoagulation. Their efficacy and safety are shown to be at least as good as or better than those of warfarin. In patients with nonvalvular atrial fibrillation ARISTOTLE study revealed that antithrombotic effect of apixaban compared with warfarin is better and with lower bleeding risk irrespective of the quality of prothrombin international normalized ratio control. Orv. Hetil., 2014, 155(5), 177–181.

Patient's values and preferences for stroke prevention in atrial fibrillation: balancing stroke and bleeding risk with oral anticoagulation

Note: The review process for this editorial was handled by Christian Weber, Editor in Chief.

Assessment of anticoagulation intensity and management of bleeding with old and new oral anticoagulants

Warfarin is effective for the prevention and treatment of thromboembolism but produces variable anticoagulant effects and requires routine monitoring of the international normalized ratio (INR) to optimize the balance between efficacy and safety. The new oral anticoagulants (NOACs) have a more predictable anticoagulant effect and were recently demonstrated to be at least as efficacious and safe as warfarin despite being administered in fixed doses without routine coagulation monitoring. Specific laboratory tests have been developed to measure the anticoagulant effect of the NOACs but are not yet widely available, and the relation between drug levels and both coagulation test results and outcomes is uncertain. It remains to be demonstrated whether adjustment of the dose of NOACs, according to the results of laboratory testing, may lead to even greater efficacy and safety. The principles of bleeding management in patients treated with NOACs compared with patients receiving warfarin are similar. Most patients can be safely managed by interrupting drug treatment, performing local measures to stem the bleeding, and providing transfusion support as required. In patients with major or life-threatening bleeding and those requiring surgery, the anticoagulant effects of warfarin can be reversed using oral or intravenous vitamin K, fresh frozen plasma (FFP), and prothrombin complex concentrates (PCCs). Specific antidotes are under development for the NOACs but are not yet approved for clinical use. PCCs and recombinant factor VIIa may improve hemostasis in patients in whom bleeding develops during treatment with a NOAC, but their efficacy is unproven.

Exercise perspective on common cardiac medications

Medicinal tablets have been used for a long time to treat cardiovascular disease. However, mortality rate is steadily increasing partly because of the patients’ sedentary lifestyle and unhealthy diet. By contrast, exercise has been systematically shown to have multiple benefits. Regular exercise training can prevent various diseases in healthy individuals. Combined exercise and cardiac medications may lead to the improvement of heart disease. Numerous exercise training pathways still need further investigations. How exercise can prevent, treat, or attenuate diseases remains somewhat elusive. Thus, this review will discuss cardiac medications in parallel with the mechanism of action of exercise.