A multicenter, randomized study of argatroban versus heparin as adjunct to tissue plasminogen activator (TPA) in acute myocardial infarction: myocardial infarction with novastan and TPA (MINT) study

Anticoagulation Management during Extracorporeal Membrane Oxygenation-A Mini-Review

Extracorporeal membrane oxygenation (ECMO) has been established as a life-saving technique for patients with the most severe forms of respiratory or cardiac failure. It can, however, be associated with severe complications. Anticoagulation therapy is required to prevent ECMO circuit thrombosis. It is, however, associated with an increased risk of hemocoagulation disorders. Thus, safe anticoagulation is a cornerstone of ECMO therapy. The most frequently used anticoagulant is unfractionated heparin, which can, however, cause significant adverse effects. Novel drugs (e.g., argatroban and bivalirudin) may be superior to heparin in the better predictability of their effects, functioning independently of antithrombin, inhibiting thrombin bound to fibrin, and eliminating heparin-induced thrombocytopenia. It is also necessary to keep in mind that hemocoagulation tests are not specific, and their results, used for setting up the dosage, can be biased by many factors. The knowledge of the advantages and disadvantages of particular drugs, limitations of particular tests, and individualization are cornerstones of prevention against critical events, such as life-threatening bleeding or acute oxygenator failure followed by life-threatening hypoxemia and hemodynamic deterioration. This paper describes the effects of anticoagulant drugs used in ECMO and their monitoring, highlighting specific conditions and factors that might influence coagulation and anticoagulation measurements.

Development of a Carotid Artery Thrombolysis (iCAT) Stroke Model in Mice

Development of a mouse carotid artery thrombolysis model of stroke.

iCAT enables assessment of adjunctive antithrombotic therapies on arterial recanalization, cerebral perfusion, and stroke outcomes.

Recanalization with restored cerebral perfusion is the primary goal of thrombolytic therapy in acute ischemic stroke. The identification of adjunctive therapies that can be safely used to enhance thrombolysis in stroke remains an elusive goal. We report here the development of a mouse in situ carotid artery thrombolysis (iCAT) stroke model involving graded cerebral ischemia to induce unihemispheric infarction after thrombotic occlusion of the common carotid artery (CCA). Electrolytic-induced thrombotic occlusion of the left CCA enabled real-time assessment of recanalization and rethrombosis events after thrombolysis with recombinant tissue-type plasminogen activator (rtPA). Concurrent transient stenosis of the right CCA induced unihemispheric hypoperfusion and infarction in the left middle cerebral artery territory. Real-time assessment of thrombolysis revealed recanalization rates <30% in rtPA-treated animals with high rates of rethrombosis. Addition of the direct thrombin inhibitor argatroban increased recanalization rates to 50% and reduced rethrombosis. Paradoxically, this was associated with increased cerebral ischemia and stroke-related mortality (25%-42%). Serial analysis of carotid and cerebral blood flow showed that coadministration of argatroban with rtPA resulted in a marked increase in carotid artery embolization, leading to distal obstruction of the middle cerebral artery. Real-time imaging of carotid thrombi revealed that adjunctive anticoagulation destabilized platelet-rich thrombi at the vessel wall, leading to dislodgement of large platelet emboli. These studies confirm the benefits of anticoagulants in enhancing thrombolysis and large artery recanalization; however, at high levels of anticoagulation (∼3-fold prolongation of activated partial thromboplastin time), this effect is offset by increased incidence of carotid artery embolization and distal middle cerebral artery occlusion. The iCAT stroke model should provide important new insight into the effects of adjunctive antithrombotic agents on real-time thrombus dynamics during thrombolysis and their correlation with stroke outcomes.

Thromboprophylaxis with argatroban in critically ill patients with sepsis: a review

During sepsis, an initial prothrombotic shift takes place, in which coagulatory acute-phase proteins are increased, while anticoagulatory factors and platelet count decrease. Further on, the fibrinolytic system becomes impaired, which contributes to disease severity. At a later stage in sepsis, coagulation factors may become depleted, and sepsis patients may shift into a hypo-coagulable state with an increased bleeding risk. During the pro-coagulatory shift, critically ill patients have an increased thrombosis risk that ranges from developing micro-thromboses that impair organ function to life-threatening thromboembolic events. Here, thrombin plays a key role in coagulation as well as in inflammation. For thromboprophylaxis, low molecular weight heparins (LMWH) and unfractionated heparins (UFHs) are recommended. Nevertheless, there are conditions such as heparin resistance or heparin-induced thrombocytopenia (HIT), wherein heparin becomes ineffective or even puts the patient at an increased prothrombotic risk. In these cases, argatroban, a direct thrombin inhibitor (DTI), might be a potential alternative anticoagulatory strategy. Yet, caution is advised with regard to dosing of argatroban especially in sepsis. Therefore, the starting dose of argatroban is recommended to be low and should be titrated to the targeted anticoagulation level and be closely monitored in the further course of treatment. The authors of this review recommend using DTIs such as argatroban as an alternative anticoagulant in critically ill patients suffering from sepsis or COVID-19 with suspected or confirmed HIT, HIT-like conditions, impaired fibrinolysis, in patients on extracorporeal circuits and patients with heparin resistance, when closely monitored.

Antithrombin and Its Role in Host Defense and Inflammation

Antithrombin (AT) is a natural anticoagulant that interacts with activated proteases of the coagulation system and with heparan sulfate proteoglycans (HSPG) on the surface of cells. The protein, which is synthesized in the liver, is also essential to confer the effects of therapeutic heparin. However, AT levels drop in systemic inflammatory diseases. The reason for this decline is consumption by the coagulation system but also by immunological processes. Aside from the primarily known anticoagulant effects, AT elicits distinct anti-inflammatory signaling responses. It binds to structures of the glycocalyx (syndecan-4) and further modulates the inflammatory response of endothelial cells and leukocytes by interacting with surface receptors. Additionally, AT exerts direct antimicrobial effects: depending on AT glycosylation it can bind to and perforate bacterial cell walls. Peptide fragments derived from proteolytic degradation of AT exert antibacterial properties. Despite these promising characteristics, therapeutic supplementation in inflammatory conditions has not proven to be effective in randomized control trials. Nevertheless, new insights provided by subgroup analyses and retrospective trials suggest that a recommendation be made to identify the patient population that would benefit most from AT substitution. Recent experiment findings place the role of various AT isoforms in the spotlight. This review provides an overview of new insights into a supposedly well-known molecule.

A Prospective Pilot Trial to Assess the Efficacy of Argatroban (Argatra®) in Critically Ill Patients with Heparin Resistance

The current study aims to evaluate whether prophylactic anticoagulation using argatroban or an increased dose of unfractionated heparin (UFH) is effective in achieving the targeted activated partial thromboplastin time (aPTT) of more than 45 s in critically ill heparin-resistant (HR) patients. Patients were randomized either to continue receiving an increased dose of UFH, or to be treated with argatroban. The endpoints were defined as achieving an aPTT target of more than 45 s at 7 h and 24 h. This clinical trial was registered on clinicaltrials.gov (NCT01734252) and on EudraCT (2012-000487-23). A total of 42 patients, 20 patients in the heparin and 22 in the argatroban group, were included. Of the patients with continued heparin treatment 55% achieved the target aPTT at 7 h, while only 40% of this group maintained the target aPTT after 24 h. Of the argatroban group 59% reached the target aPTT at 7 h, while at 24 h 86% of these patients maintained the targeted aPTT. Treatment success at 7 h did not differ between the groups (p = 0.1000), whereas at 24 h argatroban showed significantly greater efficacy (p = 0.0021) than did heparin. Argatroban also worked better in maintaining adequate anticoagulation in the further course of the study. There was no significant difference in the occurrence of bleeding or thromboembolic complications between the treatment groups. In the case of heparin-resistant critically ill patients, argatroban showed greater efficacy than did an increased dose of heparin in achieving adequate anticoagulation at 24 h and in maintaining the targeted aPTT goal throughout the treatment phase.

Bivalirudin during thrombolysis with catheter-directed tPA in a heparin-refractory patient: A case report

Venous thromboembolism has increasing significance in hospitalized pediatric patients. Patients who have life-threatening or limb-threatening thrombotic events require thrombolysis in addition to anticoagulation. In patients who show signs of heparin resistance or heparin-induced thrombocytopenia, it is imperative to identify alternative therapeutic options. We present a child in whom bivalirudin was used for systemic anticoagulation during catheter-directed thrombolysis along with tissue plasminogen activator (Alteplase^® ) for the treatment of a near-occlusive organ-threatening thrombus. We also review the currently available literature on the use of combination therapy of an intravenous direct thrombin inhibitor with alteplase.

Update in the Early Management and Reperfusion Strategies of Patients with Acute Ischemic Stroke

Acute ischemic stroke (AIS) remains a leading cause of death and long-term disability. The paradigms on prehospital care, reperfusion therapies, and postreperfusion management of patients with AIS continue to evolve. After the publication of pivotal clinical trials, endovascular thrombectomy has become part of the standard of care in selected cases of AIS since 2015. New stroke guidelines have been recently published, and the time window for mechanical thrombectomy has now been extended up to 24 hours. This review aims to provide a focused up-to-date review for the early management of adult patients with AIS and introduce the new upcoming areas of ongoing research.

Changing Management of Acute Ischaemic Stroke: the New Treatments and Emerging Role of Endovascular Therapy

OPINION STATEMENT

Urgent reperfusion of the ischaemic brain is the aim of stroke treatment, and the last two decades have seen a rapid advancement in the medical and endovascular treatment of acute ischaemic stroke. Intravenous tissue plasminogen activator (tPA) was first introduced as a safe and effective thrombolytic agent followed by the introduction of newer thrombolytic agents as well as anticoagulant and antiplatelet agents, proposed as potentially safer drugs with more favourable interaction profiles. In addition to chemo-thrombolysis, other techniques including transcranial sonothrombolysis and microbubble cavitation have been introduced which are showing promising results, but await large-scale clinical trials. These developments in medical therapies which are undoubtedly of great importance due to their potential widespread and immediate availability are paralleled with gradual but steady improvements in endovascular recanalisation techniques which were initiated by the introduction of the MERCI (Mechanical Embolus Removal in Cerebral Ischemia) and Penumbra systems. The introduction of the Solitaire device was a significant achievement in reliable and safe endovascular recanalisation and was followed by further innovative stent retrievers. Initial trials failed to show a solid benefit in endovascular intervention compared with IV-tPA alone. These counterintuitive results did not last long, however, when a series of very well-designed randomised controlled trials, pioneered by MR-CLEAN, EXTEND-IA and ESCAPE, emerged, confirming the well-believed daily anecdotal evidence. There have now been seven positive trials of endovascular treatment for acute ischaemic stroke. Now that level I evidence regarding the superiority of endovascular recanalisation is abundantly available, the clinical challenge is how to select patients suitable for intervention and to familiarise and educate stroke care providers with this recent development in stroke care. It is important for the interventional services to be provided only in comprehensive stroke centres and endovascular interventions attempted by experienced well-trained operators, at this stage as an adjunct to the established medical treatment of IV-tPA, if there are no contraindications.

Imaging of prehospital stroke therapeutics

Despite significant quality improvement efforts to streamline in-hospital acute stroke care in the conventional model, there remain inherent layers of treatment delays, which could be eliminated with prehospital diagnostics and therapeutics administered in a mobile stroke unit. Early diagnosis using telestroke and neuroimaging while in the ambulance may enable targeted routing to hospitals with specialized care, which will likely improve patient outcomes. Key clinical trials in telestroke, mobile stroke units with prehospital neuroimaging capability, prehospital ultrasound and co-administration of various classes of neuroprotectives, antiplatelets and antithrombin agents with intravenous thrombolysis are discussed in this article.

Advances in medical revascularisation treatments in acute ischemic stroke

Urgent reperfusion of the ischaemic brain is the aim of stroke treatment and there has been ongoing research to find a drug that can promote vessel recanalisation more completely and with less side effects. In this review article, the major studies which have validated the use and safety of tPA are discussed. The safety and efficacy of other thrombolytic and anticoagulative agents such as tenecteplase, desmoteplase, ancrod, tirofiban, abciximab, eptifibatide, and argatroban are also reviewed. Tenecteplase and desmoteplase are both plasminogen activators with higher fibrin affinity and longer half-life compared to alteplase. They have shown greater reperfusion rates and improved functional outcomes in preliminary studies. Argatroban is a direct thrombin inhibitor used as an adjunct to intravenous tPA and showed higher rates of complete recanalisation in the ARTTS study with further studies which are now ongoing. Adjuvant thrombolysis techniques using transcranial ultrasound are also being investigated and have shown higher rates of complete recanalisation, for example, in the CLOTBUST study. Overall, development in medical therapies for stroke is important due to the ease of administration compared to endovascular treatments, and the new treatments such as tenecteplase, desmoteplase, and adjuvant sonothrombolysis are showing promising results and await further large-scale clinical trials.

Catheter-directed thrombolysis with argatroban and tPA for massive iliac and femoropopliteal vein thrombosis

PURPOSE

Catheter-directed thrombolysis (CDT) is a highly effective approach in the treatment of deep venous thrombosis (DVT). There are no data on the primary use of CDT with argatroban and tissue plasminogen activator (tPA) in patients without heparin-induced thrombocytopenia (HIT). The aim of this study was to evaluate the efficacy and safety of the combined administration of argatroban and tPA during CDT for massive DVT in patients without HIT.

METHODS

Thirty-three patients with massive symptomatic iliac and femoropopliteal DVT underwent CDT with tPA and argatroban within 28 ± 6 h of presentation. The dose of tPA was 0.75-1 mg/h through the infusion port and that of argatroban at 0.3-1 μg/kg/min through the side port of the sheath. The patients were evaluated for the efficacy and safety of CDT and recurrent symptomatic venous thromboembolism (VTE) at a mean follow-up of 22 months.

RESULTS

There was no bleeding or iatrogenic pulmonary embolism with the CDT regimen we used. Grade III lysis (complete resolution of thrombus on venography) was achieved in 30 patients (91 %). In 3 patients with additional inferior vena cava filter thrombosis, further thrombectomy of the filter was required. No patient developed recurrent VTE.

CONCLUSION

Concomitant administration of argatroban and tPA is a highly safe and effective regimen for CDT for massive DVT.

Ancillary approaches to plasminogen activators

Acute ischemic stroke develops from an interruption in focal cerebral blood flow. In many cases, it is caused by an acute thromboembolism. Although systemic fibrinolytic therapy for acute ischemic stroke has been a significant breakthrough in the management of this disease, additional agents and methods that could improve or restore cerebral flow are necessary. Similarly to findings in acute myocardial infarction, combination pharmacotherapy has the potential to improve current thrombolytic treatment in acute ischemic stroke. In recent years, research efforts were directed toward various combination therapy with pharmacological and nonpharmacological methods. Several trials tested tissue plasminogen activator (t-PA) in combination with antiplateletes and anticoagulants. Combination of t-PA with nonpharmacological agents included sonothrombolysis (amplifying the thrombolytic effect), laser (neuro-recovery), hypothermia (cytoprotection and decreasing brain swelling), and blood flow augmentation (increasing residual flow and recruitment of collateral vessels). This paper will review ongoing clinical trials and safety of these promising combinatory treatments.

Treatment and prevention of heparin-induced thrombocytopenia: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated adverse drug reaction that can lead to devastating thromboembolic complications, including pulmonary embolism, ischemic limb necrosis necessitating limb amputation, acute myocardial infarction, and stroke.

METHODS

The methods of this guideline follow the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines in this supplement.

RESULTS

Among the key recommendations for this article are the following: For patients receiving heparin in whom clinicians consider the risk of HIT to be > 1%, we suggest that platelet count monitoring be performed every 2 or 3 days from day 4 to day 14 (or until heparin is stopped, whichever occurs first) (Grade 2C). For patients receiving heparin in whom clinicians consider the risk of HIT to be < 1%, we suggest that platelet counts not be monitored (Grade 2C). In patients with HIT with thrombosis (HITT) or isolated HIT who have normal renal function, we suggest the use of argatroban or lepirudin or danaparoid over other nonheparin anticoagulants (Grade 2C). In patients with HITT and renal insufficiency, we suggest the use of argatroban over other nonheparin anticoagulants (Grade 2C). In patients with acute HIT or subacute HIT who require urgent cardiac surgery, we suggest the use of bivalirudin over other nonheparin anticoagulants or heparin plus antiplatelet agents (Grade 2C).

CONCLUSIONS

Further studies evaluating the role of fondaparinux and the new oral anticoagulants in the treatment of HIT are needed.

The argatroban and tissue-type plasminogen activator stroke study: final results of a pilot safety study

BACKGROUND AND PURPOSE

Argatroban is a direct thrombin inhibitor that safely augments recanalization achieved by tissue-type plasminogen activator (tPA) in animal stroke models. The Argatroban tPA Stroke Study was an open-label, pilot safety study of tPA plus Argatroban in patients with ischemic stroke due to proximal intracranial occlusion.

METHODS

During standard-dose intravenous tPA, a 100-μg/kg bolus of Argatroban and infusion for 48 hours was adjusted to a target partial thromboplastin time of 1.75× baseline. The primary outcome was incidence of significant intracerebral hemorrhage defined as either symptomatic intracerebral hemorrhage or Parenchymal Hematoma Type 2. Recanalization was measured at 2 and 24 hours by transcranial Doppler or CT angiography.

RESULTS

Sixty-five patients were enrolled (45% men, mean age 63±14 years, median National Institutes of Health Stroke Scale=13). The median (interquartile range) time tPA to Argatroban bolus was 51 (38-60) minutes. Target anticoagulation was reached at a median (interquartile range) of 3 (2-7) hours. Significant intracerebral hemorrhage occurred in 4 patients (6.2%; 95% CI, 1.7-15.0). Of these, 3 were symptomatic (4.6%; 95% CI, 0.9-12.9). Seven patients (10%) died in the first 7 days. Within the 2-hour monitoring period, transcranial Doppler recanalization (n=47) occurred in 29 (61%) patients: complete in 19 (40%) and partial in another 10 (21%).

CONCLUSIONS

The combination of Argatroban and intravenous tPA is potentially safe in patients with moderate neurological deficits due to proximal intracranial arterial occlusions and may produce more complete recanalization than tPA alone. Continued evaluation of this treatment combination is warranted.

CLINICAL TRIAL REGISTRATION

URL: www.clinicaltrials.gov. Unique identifier: NCT00268762.

Adjunctive and alternative approaches to current reperfusion therapy

BACKGROUND AND PURPOSE

Current ischemic stroke reperfusion therapy consists of intravenous thrombolysis given in eligible patients after review of a noncontrast CT scan and a time-based window of opportunity. Rapid clot lysis has a strong association with clinical improvement but remains incomplete in many patients. This review appraises novel adjunctive or alternative approaches to current reperfusion strategies being tested in all trial phases. Summary of Review- Alternative approaches to current reperfusion therapy can be separated into 4 main categories: (1) combinatory approaches with other drugs or devices; (2) novel systemic thrombolytic agents; (3) endovascular medical or mechanical reperfusion treatments; and (4) noninvasive or minimally invasive methods to augment cerebral blood flow and alleviate intracranial blood flow steal.

CONCLUSIONS

Reperfusion treatments must be provided as fast as possible in patients most likely to benefit. Patients who fail to rapidly reperfuse may benefit from other strategies that maintain collateral flow or protect tissue at risk.

The thrombin hypothesis in ACS: a disappointing disconnect between bench data and bedside clinical trials

Studies have demonstrated the efficacy and safety of unfractionated heparin and low-molecular-weight heparin in the management of patients with acute coronary syndrome. However, a common limitation of unfractionated heparin and low-molecular-weight heparin is that neither can neutralize clot-bound thrombin. To overcome this limitation of the broad heparin-based anticoagulants, novel anticoagulants targeted for both the free and clot-bound forms of thrombin (direct thrombin inhibitors), or other individual components of the coagulation cascade (eg, direct and indirect factor Xa inhibitors), were developed. These targeted anticoagulation agents showed promising results in preclinical testing and have been evaluated in large-scale clinical acute coronary syndrome trials. This review discusses the disconnect between the excellent preclinical findings obtained with these novel, targeted agents and the efficacy and safety data observed in patients with acute coronary syndrome, compared with the broader-range heparin-based anticoagulants.

Anticoagulants in coronary artery disease

Anticoagulant therapy for acute coronary syndromes is becoming more complex as newer agents are added to unfractionated heparin and warfarin. The anticoagulants used in current clinical practice are low molecular weight heparins, direct thrombin inhibitors, and heparinoids. Properties of and recent clinical trial data regarding these newer anticoagulants are reviewed in reference to current American College of Cardiology/American Heart Association guidelines.

Argatroban enhances fibrinolysis by differential inhibition of thrombin-mediated activation of thrombin activatable fibrinolysis inhibitor and factor XIII

Direct thrombin inhibitors enhance fibrinolysis more efficiently than heparin. Direct thrombin inhibitors and heparin enhance fibrinolysis by inhibition of activation of thrombin activatable fibrinolysis inhibitor (TAFI); however, the role played by other thrombin-activated proteins [e.g., factor XIII (FXIII)] in fibrinolysis remained to be elucidated. Our goal was thus to define the roles of TAFI and FXIII in direct thrombin inhibitor-mediated fibrinolysis enhancement. Plasma was exposed to argatroban or heparin, with coagulation initiated with kaolin/tissue factor and fibrinolysis initiated with tissue plasminogen activator. Additional experiments utilized TAFI and FXIII-deficient plasmas. Coagulation/fibrinolysis kinetics were monitored with thrombelastography. Argatroban (1.25, 2.5 microg/ml) significantly decreased clot lysis time and increased the maximum rate of lysis compared with unexposed plasma, whereas heparin exposure only diminished clot lysis time. When changes in maximum rate of lysis were related to changes in the maximum rate of thrombus generation, argatroban was associated with a greater increase in maximum rate of lysis per decrease in maximum rate of thrombus generation compared with heparin. Experiments with TAFI-deficient and FXIII-deficient plasma demonstrated a sparing of thrombin-mediated FXIII activation with concurrent inhibition of TAFI activation. The mechanism by which argatroban more efficiently enhanced fibrinolysis was via a differential inhibition of thrombin-mediated activation of TAFI and FXIII.

Combination pharmacotherapy for achievement and maintenance of vascular patency

Acute ischemic stroke results from an abrupt interruption of focal cerebral blood flow. In the majority of cases, this interruption is caused by an acute thromboembolism. Arising from the clinical trials in acute myocardial infarction, combination pharmacotherapy is gaining significant interest as a potential method to improve current thrombolytic treatment in acute ischemic stroke. This article reviews the scientific rationale and available evidence for the potential options to improve current pharmacologic therapy for achieving and maintaining vascular patency in acute ischemic stroke.

Efficacy and safety of argatroban in patients with heparin induced thrombocytopenia undergoing endovascular intervention for peripheral arterial disease

OBJECTIVES

This study aimed to evaluate the efficacy and safety of argatroban during percutaneous interventions for peripheral arterial disease (PAD).

BACKGROUND

Endovascular interventions are commonly used in patients with peripheral arterial disease. Heparin is routinely administered during these procedures, but cannot be used in patients with a history of heparin-induced thrombocytopenia (HIT). Argatroban is an approved direct thrombin inhibitor for treatment of patients with HIT. There are currently few data on the efficacy and safety of argatroban during endovascular interventions for PAD.

METHODS

Patients who underwent endovascular interventions for PAD on argatroban between 2002 and 2005 were identified from out database. Efficacy was evaluated using a composite of death, urgent revascularization, and amputation, while safety was assessed by TIMI major bleeding during the index hospitalization.

RESULTS

A total of 48 patients undergoing lower extremity revascularization on argatroban were identified. Thirty two of these patients (67%) had antibody-confirmed HIT and the other 16 (33%) had suspected HIT. A mean dose of argatroban was 173.5 +/- 143 microg/kg bolus, followed by a 10.7 +/- 9.64 microg/kg/min infusion during the procedure. Twelve patients (25%) met the composite end point (two deaths, one urgent revascularization, nine amputations because of progressive peripheral arterial disease). TIMI major bleeding occurred in three (6%) patients.

CONCLUSION

In patients with confirmed or suspected HIT undergoing endovascular intervention for PAD, argatroban appears to be effective and safe. A larger study is warranted to confirm these findings from a single center.

Differential effects of direct thrombin inhibitors and antithrombin-dependent anticoagulants on the dynamics of clot formation

New anticoagulants, including the direct thrombin inhibitors (DTIs) and fondaparinux, are increasingly replacing unfractionated heparin and enoxaparin. We examined the effects of argatroban (n = 60), bivalirudin (n = 44), heparin (n = 14), enoxaparin (n = 22), and fondaparinux (n = 24) on clot formation utilizing thromboelastography. Blood samples containing anticoagulants at clinically relevant concentrations were prepared ex vivo and analyzed using kaolin or tissue factor activation. Thromboelastography parameters of clot initiation (R), clot propagation (K and angle), clot rigidity (maximum amplitude) and clot elasticity (G) were compared between anticoagulants. Thromboelastography was also performed on blood from eight patients receiving anticoagulants. Each anticoagulant exerted significant concentration-dependent effects on R, K and angle. Only heparin, enoxaparin, and fondaparinux significantly affected maximum amplitude and G. Significant differences existed for all parameters between heparin and each anticoagulant and between fondaparinux and each DTI (P < 0.001), and for angle, maximum amplitude, and G between enoxaparin and each DTI (P < 0.008). Thromboelastography responses in ex-vivo samples and patient samples were comparable. In conclusion, whereas argatroban, bivalirudin, heparin, enoxaparin and fondaparinux each delay clot formation, the DTIs do not alter clot rigidity or elasticity. The reduced bleeding reported with DTIs versus heparin may relate to the fact that clots form with normal rigidity and elasticity.

Strategies for the management of suspected heparin-induced thrombocytopenia: a cost-effectiveness analysis

BACKGROUND

Heparin-induced thrombocytopenia (HIT) is a rare but serious complication of heparin therapy. The diagnosis of HIT is difficult because its signs are non-specific and the heparin-platelet factor 4 (PF4) antibody test used to confirm the diagnosis is imprecise. Drugs used to treat HIT are costly and may carry an increased risk of bleeding.

OBJECTIVE

To evaluate the cost effectiveness, from a societal perspective, of four treatment approaches for patients with suspected HIT within a US critical care setting.

METHODS

A decision-tree was constructed for the management of a hypothetical cohort of critical care patients with possible evidence of HIT. The management strategies were: (i) no antibody testing, continue heparin (No Test and Wait); (ii) antibody testing, continue heparin while test results pending (Test and Wait); (iii) antibody testing and switch to a direct thrombin inhibitor (DTI) while test results pending (Test and Switch); and (iv) no antibody testing but switch to a DTI (No Test and Switch). We used argatroban as the DTI in our analysis. The outcomes were direct medical costs ($US; 2004 values), QALYs and incremental cost-effectiveness ratios (ICERs).

RESULTS

Assuming an HIT prevalence of 3%, relative to less costly strategies, ordering an antibody test and switching patients to argatroban if the result was positive (Test and Wait) had an ICER of $US163 396/QALY. Pre-emptive switching to argatroban without antibody testing (No Test and Switch) was the most effective strategy but had an ICER of >$US1 million/QALY relative to the Test and Switch option. These results were highly sensitive to HIT prevalence among patients presenting with thrombocytopenia. Assuming a willingness to pay of $US50 000 per QALY, the Test and Wait strategy became cost effective when the prior probability of HIT was 8%. At a prior probability of 12%, Test and Switch was cost effective, and at probabilities of HIT in the 60-75% range, No Test and Switch was cost effective. In two-way analysis, the probability of developing a thrombotic event was a key driver of treatment choice at specific HIT probabilities.

CONCLUSIONS

Testing for HIT in all typical critical care patients with thrombocytopenia is unlikely to represent a cost-effective management strategy. With increasing probability of HIT, strategies that include testing and a more rapid switch to a DTI appear more desirable. Accurate clinical judgment of the prior probability of HIT has a critical influence on the cost-effective management of HIT.

Direct antithrombins: mechanisms, trials, and role in contemporary interventional medicine

Direct thrombin inhibitors have several potential advantages over indirect thrombin inhibitors such as heparin. Bivalirudin, a bivalent direct thrombin inhibitor, is most commonly used in clinical practice and has a proven role in contemporary interventional medicine with elective percutaneous coronary intervention (PCI) as well as in patients with non-ST-elevation acute coronary syndrome (NSTEACS). Results from well-controlled clinical trials have shown that bivalirudin is associated with an approximate 50% reduction in major bleeding while having similar effects on incidence of death and myocardial infarction (MI) compared with herapin or enoxaparin and glycoprotein IIb/IIIa inhibitors. Bivalirudin has been successfully used in off- and on-pump cardiac surgery. Argatroban is the most evaluated among the univalent direct thrombin inhibitors inhibiting only the catalytic site of thrombin. It has been associated with similar rates of major bleeding compared with heparin in patients with acute MI receiving either streptokinase or alteplase with no effects on clinical endpoints. In a meta-analysis of 11 randomised trials where direct thrombin inhibitors (hirudin, bivalirudin, argatroban, efegatan or inogatran) were compared with unfractionated heparin in >35,000 patients with ST-elevation MI (STEMI) or NSTEACS there was no mortality difference between treatment groups but the incidence of MI at 30 days was significantly reduced in patients treated with direct thrombin inhibitors compared with heparin (4.7% vs 5.3%; p < 0.004). The role of direct thrombin inhibitors in both primary angioplasty for STEMI and angioplasty after fibrinolytic therapy needs to be established. Overall, the efficacy and improved safety profile make bivalirudin an attractive first-line anticoagulant for elective PCI and in patients with NSTEACS undergoing an invasive strategy.

Platelet activity, coagulation, and fibrinolysis during exercise in healthy males: effects of thrombin inhibition by argatroban and enoxaparin

BACKGROUND

Relationships between exercise-induced activation of platelets, blood coagulation, and fibrinolysis, and the importance of thrombin for responses to exercise are not clear.

METHODS AND RESULTS

Effects of thrombin inhibition on hemostatic parameters were examined in a double-blind crossover study comparing the direct thrombin inhibitor argatroban (350 microg/kg intravenous bolus followed by 25 microg/kg per minute of infusion), the indirect thrombin inhibitor enoxaparin (0.75 mg/kg, intravenous bolus), or placebo (saline) in 21 healthy males. Measurements were made at rest, before and during/after thrombin inhibitor treatment, and immediately after exhaustive exercise. At rest argatroban abolished, and enoxaparin attenuated platelet activation by thrombin, but not by adenosine diphosphate. Argatroban and, even more so, enoxaparin decreased thrombin generation (prothrombin F1+2) and the coagulation potential, and increased the fibrinolytic potential. Exercise increased circulating activated platelets (from 5.5+/-0.3 to 9.4+/-0.9x10(9)/L; P<0.001), circulating platelet-platelet microaggregates, the platelet responsiveness to in vitro stimulation, leukocyte activation (leukocyte CD11b expression and plasma elastase), and platelet-leukocyte aggregation (P<0.01 for all). Exercise increased coagulation (F1+2; P<0.01) and fibrinolysis, but did not alter the balance between them; fibrin gel permeability increased (P<0.01), probably because of release of endogenous tissue plasminogen activator from the vessel wall. Neither argatroban nor enoxaparin counteracted exercise-induced platelet or leukocyte activation. Both thrombin inhibitors augmented exercise effects on fibrinolysis.

CONCLUSIONS

Strenuous exercise enhances platelet and leukocyte activation independently of thrombin. Exercise augments both coagulation and fibrinolysis, but the balance between them appears to be maintained. At therapeutic dosages argatroban counteracted thrombin-induced platelet activation most efficiently, whereas enoxaparin had somewhat stronger anticoagulant and profibrinolytic effects.

Argatroban: update

Unfractionated heparin has historically been used as the anticoagulant of choice in the management of a number of thrombotic diseases. Recognition of the limitations of heparin has led to the development of a newer class of anticoagulants, the direct thrombin inhibitors. Argatroban is a synthetic small molecule that selectively inhibits thrombin at its active site. In preclinical studies, argatroban has been shown to be more effective than heparin in preventing arterial thrombosis and in promoting vessel patency in conjunction with thrombolysis in a number of animal models. In clinical trials, argatroban has been shown to be as effective as heparin in the management of ST-segment elevation myocardial infarction in conjunction with thrombolysis. It has been shown to be an effective anticoagulant in patients undergoing percutaneous coronary interventions. In patients with heparin-induced thrombocytopenia and heparin-induced thrombocytopenia complicated by thrombosis, argatroban significantly decreases the risk of thrombotic events. Small studies have demonstrated a potential role for its use in ischemic stroke and hemodialysis. Additional studies are warranted to confirm argatroban's efficacy in a wide variety of clinical settings.

Treatment of heparin-induced thrombocytopenia in cardiovascular patients

Heparin-induced thrombocytopenia (HIT) is an antibody-mediated syndrome associated with heparin exposure, a falling platelet count and a high risk of thrombosis. Cardiovascular patients are at increased risk of HIT due to wide use of heparin in this population. Should HIT be suspected, heparin must be avoided in most situations, and anticoagulation with an alternative anticoagulant should be instituted. Preferred agents include the direct thrombin inhibitors argatroban and lepirudin, whilst bivalirudin or desirudin (other direct thrombin inhibitors) can be used in some situations. The indirect thrombin inhibitors, danaparoid and fondaparinux, can also be considered at times. These agents and their use in cardiac patients, including patients with acute coronary syndrome, percutaneous coronary interventions, acute ST elevation myocardial infarction or cardiac surgery, will be reviewed.

Argatroban, a direct thrombin inhibitor for heparin-induced thrombocytopaenia: present and future perspectives

Heparin remains the most commonly used anticoagulant in the treatment of patients with acute vascular syndromes, including myocardial infarction, unstable angina and ischaemic stroke. However, heparin therapy is not always associated with a significant improvement of clinical outcomes, is linked with enhanced bleeding risk and can occasionally provoke the development of heparin-induced thrombocytopaenia, the most devastating complication of conventional therapy with unfractioned heparin. Understanding the key role of thrombin in clot formation and platelet activation has stimulated the development of a new class of drugs - direct thrombin inhibitors. The direct thrombin inhibitor argatroban has been known for decades. Similar to the unfractioned heparin, argatroban requires intravenous administration and activated partial prothrombin time-dependent dose adjustment; however, this pharmacological agent has a relatively short half-life that broadens its safety margins, as well as its low antigenic potential due to the small molecular weight of the compound. The efficacy of argatroban has been demonstrated among patients with acute coronary syndromes and stroke. However, this drug is currently approved by the FDA only for the treatment of patients with heparin-induced thrombocytopaenia. Indeed, in such patients, argatroban significantly improves clinical outcomes, and is associated with reduced mortality. Further clinical studies are needed to present more clinical evidence necessary to broad the indication spectrum of this agent.

Effect of argatroban on the activated partial thromboplastin time: a comparison of 21 commercial reagents

Argatroban is a direct thrombin inhibitor used for the treatment of heparin-induced thrombocytopenia. The drug is administered by continuous infusion, at a recommended initial dose of 2 microg/kg per min, to achieve activated partial thromboplastin times (aPTTs) 1.5-3.0 times baseline. We evaluated the effect of argatroban, at clinically relevant concentrations, on aPTTs using 21 commercially available reagents. The aPTTs of plasma containing argatroban at 0.125-8.0 microg/ml (final concentration) were assessed using each reagent and an ACL 3000+ coagulation analyzer. Argatroban increased aPTTs (and aPTT ratios relative to control) in a broadly comparable fashion among reagents. Concentration-aPTT ratio profiles linearized well using logarithmic-logarithmic transformation (r > 0.98), with the regression slope taken as the reagent's sensitivity to argatroban. Sensitivity ranged from 0.304 +/- 0.006 to 0.364 +/- 0.007. Only the least and two most sensitive reagents (all now unavailable in the United States) differed significantly in sensitivity from the other reagents (P < 0.05). aPTT ratios of 2.25 occurred for all reagents at 0.41-0.92 mug/ml argatroban, and for 14 (67%) reagents at 0.53-0.67 microg/ml. This corresponds to a approximately 0.5 microg/kg per min dose difference in healthy subjects. We conclude that most aPTT reagents are similarly sensitive to argatroban, and reagent choice is unlikely to significantly affect argatroban monitoring in patients with heparin-induced thrombocytopenia.

Overview of contemporary reperfusion strategies in acute ST-elevation myocardial infarction

The rupture of an atherosclerotic plaque in an epicardial coronary artery with subsequent occlusive coronary thrombosis has been established as the decisive event in the pathogenesis of an acute coronary syndrome, which encompasses the clinical entities of unstable angina, non-ST- and ST-elevation myocardial infarction. This article focuses on contemporary treatment strategies for patients with acute ST-elevation myocardial infarction and reviews the role of pharmacologic thrombolysis and mechanical reperfusion by percutaneous transluminal approaches. Statements of the latest guidelines for the treatment of ST-elevation myocardial infarction are included, as well as some recently distributed information not covered by the guideline publications. Finally, some future perspectives for the treatment of acute ST-elevation myocardial infarction are outlined.

Alternative parenteral anticoagulation with argatroban, a direct thrombin inhibitor

Argatroban, a direct thrombin inhibitor, effectively inhibits free and clot-bound thrombin without the need of a cofactor and exerts dose-dependent anticoagulant effects that are rapidly active and rapidly reversible (elimination half-life: 39-51 min). Argatroban provides predictable parenteral anticoagulation and is well tolerated with an acceptably low bleeding risk in a variety of clinical settings, including heparin-induced thrombocytopenia, acute ischemic stroke, percutaneous coronary intervention and hemodialysis. This review will discuss the clinical pharmacology and utility of argatroban; in particular, clinical trial experiences will be discussed in patients with, or at risk of, heparin-induced thrombocytopenia (where heparins must be avoided) including those requiring hemodialysis or percutaneous coronary intervention, and in patients with acute ischemic stroke (where heparins are not generally recommended).

Late ventricular potentials in risk assessment of the occurrence of complex ventricular arrhythmia in patients with myocardial infarction and heart failure

AIM

To determine the prognostic significance of late ventricular potentials on signal-averaged electrocardiogram and left ventricular ejection fraction for the occurrence of complex ventricular arrhythmia in patients treated with accelerated tissue-type plasminogen activator, using the rapid protocol, within six months of acute myocardial infarction.

METHODS

In this analytic observational prospective study patients were divided into four groups: patients with left ventricular ejection fraction bellow 40% and late ventricular potentials, patients with left ventricular ejection fraction bellow 40% and without late ventricular potentials, patients with left ventricular ejection fraction over 40% and late ventricular potentials, and patients with left ventricular ejection fraction over 40% and without late ventricular potentials. Complex ventricular arrhythmias (Lown grade IVa, IVb, and V) were recorded using standard electrocardiography and 24-hour Holter monitoring 21, 60, and 90 days after acute myocardial infarction, respectively. Serial recordings of signal-averaged electrocardiogram were obtained 30, 90, and 180 days after acute myocardial infarction. Left ventricular ejection fraction was determined by echocardiography between 15 and 21 days after acute myocardial infarction. Multivariant logistic regression analysis was used to evaluate the relation between late ventricular potentials and left ventricular ejection fraction with the occurrence of complex ventricular arrhythmias. Sensitivity, specificity, positive and negative predictive values of late ventricular potentials and left ventricular ejection fraction for the occurrence of complex ventricular arrhythmias were determined.

RESULTS

The prospective study included 80 patients (73% men), mean age 64 +/- 3.5 years. Complex ventricular arrhythmias were recorded in 34 (42.5%) of patients, all 17 (50%) of which were from the first group (p < 0.01). Complex ventricular arrhythmias were recorded in 25 (73.5%) patients with late ventricular potentials, and in 23 (67.6%) patients with left ventricular ejection fraction bellow 40%. Left ventricular ejection fraction bellow 40% and late ventricular potentials represented independent predictors for the occurrence of complex ventricular arrhythmias (RR = 14.33, p < 0.01). When combined with left ventricular ejection fraction bellow 40%, late ventricular potentials had sensitivity (0.50), specificity (0.93), and positive predictive accuracy (0.85) higher than late ventricular potentials alone (0.44, 0.67, and 0.37, respectively) for the occurrence of complex ventricular arrhythmias following acute myocardial infarction.

CONCLUSION

In this study, late ventricular potentials in patients with left ventricular ejection fraction bellow 40% represented the independent predictor for the occurrence of complex ventricular arrhythmias in the first six months after the first myocardial infarction treated with accelerated tissue-type plasminogen activator, using the rapid protocol.

The Direct Thrombin Inhibitors: Their Role and Use for Rational Anticoagulation

Major clinical advantages are achieved when direct thrombin inhibitors are used in venous thromboembolism. These agents provide more reliable anticoagulant response patterns because they are not significantly bound to plasma proteins and few, if any, drug-drug interactions are seen. The studies to date confirm that not all direct thrombin inhibitors are the same. The new reversible, short-acting catalytic site-specific drugs provide an excellent safety profile and high degree of efficacy for the prophylaxis and treatment of venous thromboembolism and pulmonary embolic states. The availability of the oral prodrug ximelagatran allows reproducible, effective, and safe direct thrombin inhibition without the requirement for coagulation laboratory monitoring; it appears destined to be the oral anticoagulant of the future.

Direct thrombin inhibitors are not equally effective in vivo against arterial thrombosis

BACKGROUND

Qualitative differences in antithrombotic efficacy between thrombin inhibitors may be explained by the affinity for which they bind thrombin. This affinity is inversely proportional to the inhibitory constant for the agent (Ki). Thrombin inhibitors, DuP714 (Ki=10(-11)) and argatroban (Ki=10(-8)), were compared to our previous studies with r-hirudin (Ki=10(-13)).

METHODS AND RESULTS

Prior to balloon angioplasty, thirty pigs randomly received DuP714 (0.1 mg/kg bolus and 0.6 mg/kg/h infusion; n=8), argatroban (0.2 mg/kg/min. continuous infusion; n=9), or saline (n=17). Injured arterial segments were measured for (111)In-platelet and 125I-fibrin(ogen) deposition and the incidence of macroscopic thrombus. In DuP714-treated animals, platelet and fibrin(ogen) deposition were significantly lower than controls in both carotid (10+/-2 vs. 62+/-18 and 20+/-4 vs. 74+/-6) and coronary (10+/-4 vs. 160+/-63 and 17+/-3 vs. 86+/-22) arteries (p<0.005). In contrast, platelet and fibrin(ogen) deposition were similar when comparing argatroban to saline in carotid (41+/-20 vs. 40+/-9 and 71+/-5 vs. 49+/-7) and coronary (92+/-33 vs. 151+/-45 and 114+/-37 vs. 89+/-38) arteries (p=0.82 and 0.38, respectively). Compared to argatroban, fibrin(ogen) (p<0.001) and coronary platelet deposition (p<0.05) were significantly reduced in animals treated with DuP714 with no significant difference in carotid platelet deposition (p=0.10). Neither inhibitor prevented macroscopic thrombosis. In previous studies with r-hirudin in this model, platelet deposition was limited to a monolayer with complete inhibition of macroscopic thrombus.

CONCLUSIONS

Direct thrombin inhibitors do not equally prevent arterial thrombosis. Qualitative differences may be explained in part by the affinity for which they bind thrombin.

Anticoagulant use in patients with chronic renal impairment

Patients with renal failure have an increased risk of both thrombotic and bleeding complications. A number of antithrombotic drugs undergo renal clearance. Therefore, estimation of renal function is necessary when prescribing these drugs to patients with renal dysfunction. Pharmacokinetic and clinical data in patients with chronic renal impairment are limited for several anticoagulants, and adequate administration information is often absent. Dose adjustment of anticoagulants may be indicated when the creatinine clearance falls below 30 mL/min. Unfractionated heparin, argatroban, and vitamin K antagonists generally do not require dose adjustment with renal dysfunction. However, smaller doses of warfarin may be required to achieve a particular target international normalized ratio. Close monitoring of anticoagulation is recommended when argatroban or high doses of unfractionated heparin are administered in patients with severe chronic renal impairment. Low-molecular weight heparins, danaparoid sodium, hirudins, and bivalirudin all undergo renal clearance. Lower doses and closer anticoagulation monitoring may be advisable when these agents are used in patients with chronic renal failure. We recommend that fondaparinux sodium and ximelagatran (not yet licensed) be avoided in the presence of severe renal impairment and be used with caution in patients with moderate renal dysfunction. While acknowledging the lack of pharmacokinetic data, this review provides specific recommendations for the use of anticoagulants in patients with chronic renal impairment.

Clinician update: direct thrombin inhibitors in acute coronary syndromes

Antithrombotic therapy has become the cornerstone of the treatment for atherosclerotic cardiovascular disease. Unfractionated heparin (UFH) has been the thrombin inhibitor of choice for decades. UFH, however, has its deficiencies. To overcome these problems several direct thrombin inhibitors (DTIs) have been developed. These agents are capable of inactivating clot-bound thrombin more efficiently, and provide more predictable and safer anticoagulation in patients with of acute coronary syndromes (ACS). The initial studies of hirudin and bivalirudin in the clinical settings of acute myocardial infarction (AMI), unstable angina (UA) and percutaneous coronary interventions (PCI) conducted in the early 1990s proved to be disappointing. As the knowledge of more appropriate use of these drugs progressed, there is a renewed interest in DTIs. Herein we will review the clinical studies assessing hirudin, bivalirudin and argatroban in the settings of AMI, UA and PCI.

Direct thrombin inhibitors for anticoagulation

OBJECTIVE

To review the progress in developing direct thrombin inhibitors (DTIs) for anticoagulation within the context of existing anticoagulation therapies.

DATA SOURCES

Searches of MEDLINE (1993-June 2003) were conducted.

STUDY SELECTION AND DATA EXTRACTION

We examined English-language articles, human studies, and relevant animal studies, and obtained additional citations from the references of these articles.

DATA SYNTHESIS

Because of its pivotal role in hemostasis, thrombin is a key therapeutic target in the treatment and prevention of thromboembolic disorders. Conventional anticoagulant therapies, such as warfarin, unfractionated heparin, and low-molecular-weight heparin, exert their pharmacologic action by indirect thrombin inhibition. Although these agents are effective, each has limitations, prompting a search for more effective, specific, better-tolerated, and convenient anticoagulants. The efficacy and safety of factor Xa inhibitors are being investigated. Furthermore, the development of DTIs such as recombinant hirudin (lepirudin), bivalirudin, and argatroban continues. Challenges in the development of DTIs include establishing a binding affinity for thrombin that is not associated with excessive bleeding, attaining high thrombin specificity, achieving inhibition of both unbound and clot-bound thrombin, and producing an effective, fixed-dose oral anticoagulant to improve the practicality of anticoagulation therapy. Ximelagatran, an oral DTI designed to meet these standards, is currently in Phase III clinical trials.

CONCLUSIONS

Significant progress has been made in developing DTIs. The recent emergence of orally administered DTIs may simplify the prevention and treatment of thrombosis.

Prevention of Venous Thromboembolism Following Orthopaedic Surgery

Patients undergoing total hip or total knee replacement are at high risk of venous thromboembolism (VTE), and are therefore considered to be populations well suited for the evaluation and dose optimisation of new anticoagulants. Deep vein thrombosis may lead to life-threatening pulmonary embolism, disabling morbidity in the form of the post-thrombotic syndrome, and risk of recurrent thrombotic events. There is increasing evidence that anticoagulant treatment for the prevention of VTE should be extended from 1 to at least 4 weeks after surgery. Anticoagulation with vitamin K antagonists (such as warfarin), low molecular weight heparin or unfractionated heparin effectively lowers the risk of VTE, but these anticoagulants have limitations such as the need for coagulation monitoring and subsequent dose adjustment (vitamin K antagonists), difficulty of continuing prophylaxis out of hospital because of the requirement for parenteral administration, and risk of heparin-induced thrombocytopenia. The development of new anticoagulants has been pursued with the aim of finding more effective, safer and/or more convenient therapies. Thrombin is a central regulator in the coagulation and inflammation process and several direct thrombin inhibitors (DTIs) with distinct pharmacological profiles, as well as pharmacological differences from the conventional anticoagulants, are currently in clinical use for certain indications or are under development. Clinical experience with parenterally administered DTIs has accumulated since the mid 1990s, although only desirudin (a recombinant hirudin) is currently approved for use in patients undergoing orthopaedic surgery. Two oral DTIs, ximelagatran and dabigatran etexilate, are in clinical development. Dabigatran etexilate has recently been evaluated in phase II clinical trials in patients undergoing total hip replacement. Several large phase III trials have now demonstrated the efficacy and safety of ximelagatran in the prevention of VTE following total hip or knee replacement. Ximelagatran can be used with an oral fixed dose without the need for coagulation monitoring or dose adjustment. Hence, it offers significant potential to facilitate the management of anticoagulation in or out of hospital.