Whole blood coagulation assays ROTEM and T-TAS to monitor dabigatran treatment

The impact of direct oral anticoagulants on viscoelastic testing - A systematic review

BACKGROUND

In case of bleeding patients and in acute care, the assessment of residual direct oral anticoagulant (DOAC) activity is essential for evaluating the potential impact on hemostasis, especially when a timely decision on urgent surgery or intervention is required. Viscoelastic tests are crucial in a modern goal-directed coagulation management to assess patients' coagulation status. However, the role of viscoelastic test to detect and quantify residual DOAC plasma levels is controversially discussed. The aim of this review was to systematically summarize the evidence of viscoelastic tests for the assessment of residual DOAC activity.

METHOD

PubMed, Embase, Scopus, and the Cochrane Library were searched for original articles investigating the effect of rivaroxaban, apixaban, edoxaban, or dabigatran plasma levels on different viscoelastic tests of the adult population from database inception to December 31, 2021.

RESULTS

We included 53 studies from which 31 assessed rivaroxaban, 22 apixaban, six edoxaban, and 29 dabigatran. The performance of viscoelastic tests varied across DOACs and assays. DOAC specific assays are more sensitive than unspecific assays. The plasma concentration of rivaroxaban and dabigatran correlates strongly with the ROTEM EXTEM, ClotPro RVV-test or ECA-test clotting time (CT) and TEG 6s anti-factor Xa (AFXa) or direct thrombin inhibitor (DTI) channel reaction time (R). Results of clotting time (CT) and reaction time (R) within the normal range do not reliable exclude relevant residual DOAC plasma levels limiting the clinical utility of viscoelastic assays in this context.

CONCLUSION

Viscoelastic test assays can provide fast and essential point-of-care information regarding DOAC activity, especially DOAC specific assays. The identification and quantification of residual DOAC plasma concentration with DOAC unspecific viscoelastic assays are not sensitive enough, compared to recommended anti-Xa activity laboratory measurements.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=320629], identifier [CRD42022320629].

Rapid Detection of Apixaban by a ROTEM-Based Approach and Reversibility with Andexanet Alfa or DOAC-Stop

Background  A rapid test to detect apixaban treatment would be useful in acute situations such as major bleeding, urgent surgery, or in acute thrombosis.

Objective  This article aims to study if the viscoelastic test rotational thromboelastometry (ROTEM) can rapidly detect apixaban in whole blood using modified triggers based on factor Xa (FXa) or Russell viper venom (RVV).

Method  ROTEM clotting time (CT) was measured in samples from 40 patients on apixaban treatment, and in vitro in samples spiked with apixaban (20–500 ng/mL). Commercially available trigger Ex-tem was compared with modified triggers based on FXa or RVV. Reversibility of apixaban in the samples was studied; CT was measured with and without addition of DOAC-Stop or andexanet alfa, respectively, and the difference in CT was calculated (CT _diff ).

Results  Using FXa as trigger, we detected apixaban concentrations at 20 ng/mL and above with 100% sensitivity and 100% specificity in patient samples and in vitro. Corresponding data for Ex-tem were 92% sensitivity and 100% specificity in patients, and 94% sensitivity and 100% specificity in vitro, and for RVV 97% sensitivity and 94% specificity in patients, and 97% sensitivity and 100% specificity in vitro, respectively. CT _diff data were similar. Patient sample data were obtained within 20 minutes from sampling.

Conclusion  Apixaban at low therapeutic concentrations was detected within 20 minutes, and with high sensitivity and specificity. A trigger based on FXa outperformed the commercial trigger Ex-tem and a trigger based on RVV. ROTEM with a FXa-based trigger is a promising method to detect apixaban bedside in acute settings.

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.

"In Less than No Time": Feasibility of Rotational Thromboelastometry to Detect Anticoagulant Drugs Activity and to Guide Reversal Therapy

Anticoagulant drugs (i.e., unfractionated heparin, low-molecular-weight heparins, vitamin K antagonists, and direct oral anticoagulants) are widely employed in preventing and treating venous thromboembolism (VTE), in preventing arterial thromboembolism in nonvalvular atrial fibrillation (NVAF), and in treating acute coronary diseases early. In certain situations, such as bleeding, urgent invasive procedures, and surgical settings, the evaluation of anticoagulant levels and the monitoring of reversal therapy appear essential. Standard coagulation tests (i.e., activated partial thromboplastin time (aPTT) and prothrombin time (PT)) can be normal, and the turnaround time can be long. While the role of viscoelastic hemostatic assays (VHAs), such as rotational thromboelastometry (ROTEM), has successfully increased over the years in the management of bleeding and thrombotic complications, its usefulness in detecting anticoagulants and their reversal still appears unclear.

Rotational Thromboelastometry in High-Risk Patients on Dual Antithrombotic Therapy After Percutaneous Coronary Intervention

Aims: Patients using antithrombotic drugs after percutaneous coronary intervention (PCI) are at risk for bleeding and recurrent ischemia. We aimed to explore routine and tissue plasminogen activated (tPA) ROTEM results in a post-PCI population on dual antithrombotic treatment.

Methods and Results: In this prospective cohort, 440 patients treated with double antithrombotic therapy after recent PCI and with ≥3 risk factors for either ischemic or bleeding complications were included and compared with a control group (n = 95) consisting of perioperative patients not using antithrombotic medication. Laboratory assessment, including (tPA) ROTEM, was performed one month post-PCI and bleeding/ischemic complications were collected over a five-month follow-up. Patients were stratified by antithrombotic regimen consisting of a P2Y12 inhibitor with either aspirin (dual antiplatelet therapy; DAPT, n = 323), a vitamin K antagonist (VKA, n = 69) or a direct oral anticoagulant (DOAC, n = 48). All post-PCI patients had elevated ROTEM clot stiffness values, but only the DAPT group additionally presented with a decreased fibrinolytic potential as measured with tPA ROTEM. Patients receiving anticoagulants had prolonged clotting times (CT) when compared to the control and DAPT group; EXTEM and FIBTEM CT could best discriminate between patients (not) using anticoagulants (AUC > 0.97). Furthermore, EXTEM CT was significantly prolonged in DAPT patients with bleeding complications during follow-up (68 [62–70] vs. 62 [57–68], p = 0.030).

Conclusion: ROTEM CT has high potential for identifying anticoagulants and tPA ROTEM could detect a diminished fibrinolytic potential in patients using DAPT. Furthermore, the ability of EXTEM CT to identify patients at risk for bleeding may be promising and warrants further research.

Point-of-care detection and differentiation of anticoagulant therapy - development of thromboelastometry-guided decision-making support algorithms

Background

DOAC detection is challenging in emergency situations. Here, we demonstrated recently, that modified thromboelastometric tests can reliably detect and differentiate dabigatran and rivaroxaban. However, whether all DOACs can be detected and differentiated to other coagulopathies is unclear. Therefore, we now tested the hypothesis that a decision tree-based thromboelastometry algorithm enables detection and differentiation of all direct Xa-inhibitors (DXaIs), the direct thrombin inhibitor (DTI) dabigatran, as well as vitamin K antagonists (VKA) and dilutional coagulopathy (DIL) with high accuracy.

Methods

Following ethics committee approval (No 17–525-4), and registration by the German clinical trials database we conducted a prospective observational trial including 50 anticoagulated patients (n = 10 of either DOAC/VKA) and 20 healthy volunteers. Blood was drawn independent of last intake of coagulation inhibitor. Healthy volunteers served as controls and their blood was diluted to simulate a 50% dilution in vitro. Standard (extrinsic coagulation assay, fibrinogen assay, etc.) and modified thromboelastometric tests (ecarin assay and extrinsic coagulation assay with low tissue factor) were performed. Statistical analyzes included a decision tree analyzes, with depiction of accuracy, sensitivity and specificity, as well as receiver-operating-characteristics (ROC) curve analysis including optimal cut-off values (Youden-Index).

Results

First, standard thromboelastometric tests allow a good differentiation between DOACs and VKA, DIL and controls, however they fail to differentiate DXaIs, DTIs and VKAs reliably resulting in an overall accuracy of 78%. Second, adding modified thromboelastometric tests, 9/10 DTI and 28/30 DXaI patients were detected, resulting in an overall accuracy of 94%. Complex decision trees even increased overall accuracy to 98%. ROC curve analyses confirm the decision-tree-based results showing high sensitivity and specificity for detection and differentiation of DTI, DXaIs, VKA, DIL, and controls.

Conclusions

Decision tree-based machine-learning algorithms using standard and modified thromboelastometric tests allow reliable detection of DTI and DXaIs, and differentiation to VKA, DIL and controls.

Trial registration

Clinical trial number: German clinical trials database ID: DRKS00015704.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12959-021-00313-7.

Strategies for the prevention and treatment of bleeding in patients treated with dabigatran: an update

INTRODUCTION

Although dabigatran is safer than vitamin K antagonists, bleeding still occurs. Bleeding is an important cause of short-term morbidity and rarely mortality and can also have long-term consequences that are often under-appreciated. After bleeding, patients often do not restart treatment or are poorly adherent, which is associated with increased thromboembolism and mortality. Consequently, we need strategies to prevent and treat bleeding in patients with atrial fibrillation treated with dabigatran.

AREAS COVERED

We review a) relevant dabigatran pharmacology, b) the burden and consequences of bleeding, c) how to identify patients at high risk of bleeding; and d) existing and novel approaches to prevent and treat bleeding in dabigatran-treated patients.

EXPERT OPINION

Concerns about the risk of bleeding associated with anticoagulant therapy and emerging evidence of increased risk of thromboembolism and mortality after bleeding highlight the need for improved approaches to prevention and treatment of bleeding. Future research priorities should focus on improving our ability to prevent bleeding by identifying modifiable risk factors and the development of safer agents. The current front runners include drugs that selectively target the contact pathway of coagulation (e.g. factor XI). Targeting upstream drivers of thrombosis (e.g. inflammation) could help to further reduce the risk of thromboembolism.

The Use of Total Thrombus Formation Analysis System as a Tool to Assess Platelet Function in Bleeding and Thrombosis Risk-A Systematic Review

BACKGROUND

Today there are many devices that can be used to study blood clotting disorders by identifying abnormalities in blood platelets. The Total Thrombus Formation Analysis System is an automated microchip flow chamber system that is used for the quantitative analysis of clot formation under blood flow conditions. For several years, researchers have been using a tool to analyse various clinical situations of patients to identify the properties and biochemical processes occurring within platelets and their microenvironment.

METHODS

An investigation of recent published literature was conducted based on PRISMA. This review includes 52 science papers directly related to the use of the Total Clot Formation Analysis System in relation to bleeding, surgery, platelet function assessment, anticoagulation monitoring, von Willebrand factor and others.

CONCLUSION

Most available studies indicate that The Total Thrombus Formation Analysis System may be useful in diagnostic issues, with devices used to monitor therapy or as a significant tool for predicting bleeding events. However, T-TAS not that has the potential for diagnostic indications, but allows the direct observation of the flow and the interactions between blood cells, including the intensity and dynamics of clot formation. The device is expected to be of significant value for basic research to observe the interactions and changes within platelets and their microenvironment.

ROTEM Testing for Direct Oral Anticoagulants

Direct oral anticoagulants (DOACs) are increasingly used worldwide for the prevention of stroke in patients with atrial fibrillation and to prevent or treat venous thromboembolism. In situations such as serious bleeding, the need for urgent surgery/intervention or the management of a thromboembolic event, the laboratory measurement of DOACs levels or anticoagulant activity may be required. Rotational thromboelastometry (ROTEM) is a viscoelastic hemostatic assay (VHA) which has been used in emergencies (trauma and obstetrics), and surgical procedures (cardiac surgery and liver transplants), but experience with this assay in DOACs-treated patients is still limited. This article reviews the use of ROTEM in the setting of DOACs therapy, focusing on DOACs-associated bleeding and the use of this VHA for the management of reversal strategies for DOACs-associated anticoagulation.

Impact of Dabigatran Treatment on Rotation Thromboelastometry

A rapid and reliable assessment of the dabigatran effect is desirable in dabigatran treated patients with uncontrolled bleeding or before acute surgery. The aim of this study was to study the anticoagulant effects of dabigatran in patients with atrial fibrillation (AF) as assessed by the whole blood assays ROTEM, and how data from these methods correlate to plasma dabigatran concentrations measured by Hemoclot. ROTEM was performed with ROTEM Gamma (Pentapharm GmbH, Munich, Germany). The assays used in our study were Ex-tem and In-tem assay. Plasma dabigatran concentrations were determined by hemoclot thrombin inhibitor assay (Hyphen BioMed, France) at trough and post-dose in 27 patients on dabigatran 150 mg BID. Median plasma dabigatran concentrations at trough were 74 ng/mL (11.2–250) and post-dose (2 h after ingestion) 120 ng/mL (31–282). The ROTEM clotting time (CT) and maximum clot firmnes (MCF) correlated strongly with dabigatran concentrations when activated with the reagents Ex-tem (p < 0.0001) and In-tem (p < 0.0001). In summary, in our study, we have found that the ROTEM variable CT and MCF, when activated with triggers Ex-tem and In-tem, has a strong and highly significant correlation with the plasma dabigatran concentration in a real-life population of AF-patients and could thereby be an alternative to estimate dabigatran concentration in emergency situations. However, additional studies are needed to further validate these findings.

The Clotting Trigger Is an Important Determinant for the Coagulation Pathway In Vivo or In Vitro-Inference from Data Review

Blood coagulation comprises a series of enzymatic reactions leading to thrombin generation and fibrin formation. This process is commonly illustrated in a waterfall-like manner, referred to as the coagulation cascade. In vivo, this "cascade" is initiated through the tissue factor (TF) pathway, once subendothelial TF is exposed and bound to coagulation factor VII (FVII) in blood. In vitro, a diminutive concentration of recombinant TF (rTF) is used as a clotting trigger in various global hemostasis assays such as the calibrated automated thrombogram, methods that assess fibrin turbidity and fibrin viscoelasticity tests such as rotational thromboelastometry. These assays aim to mimic in vivo global coagulation, and are useful in assessing hyper-/hypocoagulable disorders or monitoring therapies with hemostatic agents. An excess of rTF, a sufficient amount of negatively charged surfaces, various concentrations of exogenous thrombin, recombinant activated FVII, or recombinant activated FIXa are also used to initiate activation of specific sub-processes of the coagulation cascade in vitro. These approaches offer important information on certain specific coagulation pathways, while alterations in pro-/anticoagulants not participating in these pathways remain undetectable by these methods. Reviewing available data, we sought to enhance our knowledge of how choice of clotting trigger affects the outcome of hemostasis assays, and address the call for further investigations on this topic.

Real-time detection and differentiation of direct oral anticoagulants (rivaroxaban and dabigatran) using modified thromboelastometric reagents

INTRODUCTION

Timely measurement of direct oral anticoagulants (DOACs) is challenging, though clinically important. We tested the hypotheses, that thromboelastometry is able to detect dabigatran and rivaroxaban and discriminates between dabigatran and rivaroxaban as representatives of the two groups of DOACs.

METHODS AND MATERIALS

We conducted a prospective-observational study: In-vitro dose-effect-curves for rivaroxaban and dabigatran were performed (n = 10). Ex-vivo: Patients with indication of DOAC treatment (stroke; dabigatran/rivaroxaban) were included (n = 21). Blood samples were analyzed before first intake, at first estimated peak level and at 24 h after first but before following intake and 3 h after 24 h-intake. Standard and modified thromboelastometric-assays, using low tissue factor concentrations (TFTEM) or ecarin (ECATEM) were used. Receiver-operating-characteristics-curve-analysis (ROC), regression-analysis and two-way-ANOVA were performed.

RESULTS

In-vitro: TFTEM detected dabigatran and rivaroxaban (ROC_AUC: 0.99; sensitivity/specificity: 100%/98%) but could not discriminate. Dabigatran prolongs CT_ECATEM whereas rivaroxaban did not. Clotting Time (CT)-ratio TFTEM/ECATEM discriminated highly sensitive (100%) and specific (100%) between dabigatran and rivaroxaban even at very low concentrations (ROC_AUC:1.0). CT_ECATEM correlated with dabigatran spiked concentrations (r = 0.9985; p < 0.001) and CT_TFTEM (r = 0.9363; p = 0.006) with rivaroxaban. Similarly results could be demonstrated with patient data: We confirmed the performance for the differentiation of CT-ratio TFTEM/ECATEM (sensitivity 100%/specificity 100%) at any time after first intake of either DOAC.

CONCLUSION

The thromboelastometric tests TFTEM and ECATEM detect and differentiate rivaroxaban and dabigatran. Further investigations evaluate the other DOACs and the differentiation to phenprocoumon. However, results need to be confirmed in a larger study, and especially cut off values for differentiation need to be calculated from a larger sample size.

Influence of Direct Thrombin Inhibitor and Low Molecular Weight Heparin on Platelet Function in Patients with Coronary Artery Disease: A Prospective Interventional Trial

INTRODUCTION

The interaction between anticoagulants and platelet function is complex. Previous publications showed mixed results regarding the role of heparins in platelet aggregation. On the other hand, the direct thrombin inhibitor (DTI) dabigatran might enhance the risk of myocardial infarction in patients with atrial fibrillation, which could be related to increased platelet aggregability.

METHODS

This was a prospective, interventional study of patients with chronic coronary artery disease (CAD) taking low-dose aspirin. The objective of the current study was to compare the effects of dabigatran versus enoxaparin on platelet aggregability. Subjects initially were on orally administered dabigatran for 5 days followed by subcutaneously administered enoxaparin after a 30-day washout period. Platelet function was assessed at baseline and after each intervention by multiple electrode aggregometry (MEA-ASPI) (primary endpoint), serum thromboxane B2 (TXB2), VerifyNow Aspirin™, and coagulation tests (secondary endpoints).

RESULTS

Compared to baseline MEA-ASPI values, dabigatran increased platelet aggregation while enoxaparin decreased platelet aggregation (+ 5 U ± 24.1 vs - 6 U ± 22.2, respectively, p = 0.012). The TXB2 assay showed the same pattern (+ 2 pg/ml for dabigatran vs - 13 pg/ml for enoxaparin, p = 0.011). None of the additional tests showed significant differences between the groups. Individually, compared to baseline TXB2 results, enoxaparin significantly decreased platelet activation [33 (16.5-95) pg/mL vs 20 (10-52) pg/mL, respectively, p = 0.026], but no significant differences were observed with dabigatran.

CONCLUSIONS

DTI and anti-Xa drugs exert opposite effects on platelet function. A significant decrease in platelet activation through COX1 (also known as prostaglandin G/H synthase 1) was observed with enoxaparin, but no significant differences in platelet function were observed with dabigatran.

TRIAL REGISTRATION

ClinicalTrials.gov identifier, NCT02389582.

Exploring the effect of factor Xa inhibitors on rotational thromboelastometry: a case series of bleeding patients

Direct oral anticoagulants (DOACs) have become the standard for thromboembolic risk management. In cases of major bleeding, trauma, or urgent surgery, accurate monitoring of DOAC activity is desirable; however, there is often no rapid, readily available test. We therefore explored the degree to which DOAC activity correlated with two coagulation assays: rotational thromboelastometry (ROTEM) and a standard coagulation assay in bleeding patients. We conducted a retrospective review of patients who experienced bleeding while on DOAC therapy from 2015 to 2017 at a Level 1 trauma center. ROTEM (EXTEM-clotting time {CT} in seconds), activated partial thromboplastin time (aPTT) (in seconds), prothrombin time (PT) (in seconds), DOAC specific drug test (anti-Xa and Hemoclot in ng/mL), and relevant clinical parameters were recorded. Descriptive statistics (median, range) and Spearman correlation coefficients were estimated. Differences between correlations were tested using Williams' t test. Twelve cases were reviewed (13 separate bleeding episodes). Sixteen measurements of DOAC activity, EXTEM-CT, and PT were obtained. The correlations with rivaroxaban activity were 0.96 and 0.86 (p = 0.2062) for PT and EXTEM-CT, respectively. The correlations with apixaban activity were 0.63 and 0.56 (p = 0.7175) for PT and EXTEM-CT, respectively. Analyses were not conducted for dabigatran due to limited data. Although not statistically significant, PT appears to have a higher correlation with direct Xa inhibitor activity than EXTEM-CT. Further research with larger samples is necessary to clarify the differences between ROTEM and standard assays in detecting DOAC activity.

Recent advances in microfluidic platelet function assays: Moving microfluidics into clinical applications

The analysis of platelet aggregation and thrombosis kinetics has significantly advanced with progress in microfluidic technology. However, the results of platelet aggregation tests do not fully reflect the observed clinical outcomes. To address the present unmet clinical needs, the basic but essential biology of platelets should be reconsidered in relation to the characteristics of microfluidic systems employed for platelet tests. To this end, the present article provides an overview of commercially available point of care devices and focuses on recent microfluidic studies, describing their measurement principles. We critically discuss the characteristics of the microfluidics systems used to evaluate the complex processes underlying platelet aggregation, and that are specifically designed to mimic the pathophysiological environment of blood vessels, including hemodynamic factors as well as blood vessel injury. To this end, we summarize unsolved issues related to the application of platelet function tests based on microfluidics. Overall, we confirm that platelet function tests based on microfluidics provide a versatile platform that encompasses a variety of basic research, as well as clinical diagnostic applications.

Rapid determination of anticoagulating effects of dabigatran in whole blood with rotational thromboelastometry and a thrombin-based trigger

Essentials A rapid test to detect thrombin inhibition by dabigatran would be valuable in acute situations. A thrombin-based trigger was applied in whole blood using rotation thromboelastometry. Effects of dabigatran were assessed in vitro and in samples from patients on dabigatran. The test produced data rapidly and was sensitive to dabigatran concentrations from 20 to 500 ng mL-1 . SUMMARY: Background Rapid determination of the anticoagulant effect of dabigatran is essential in emergency situations. Objective To study a viscoelastic test (rotational thromboelastometry [ROTEM]) for rapid determination of dabigatran effects in whole blood samples. Method ROTEM measurements were performed with comparison of two triggers (thrombin-based versus the commercial tissue factor-based trigger Ex-tem) in samples from 10 healthy donors spiked with dabigatran (20-500 ng mL-1 ) and in samples from 35 patients receiving dabigatran treatment; 10 healthy subjects served as controls. Clotting time (CT) and the difference in CT without versus with addition of the dabigatran antidote idarucizumab (CTdiff ) were measured. Addition of idarucizumab reveals the contribution of dabigatran to ROTEM measurements and its potential reversibility. Results In vitro studies showed that thrombin CT and thrombin CTdiff were more sensitive than Ex-tem CT and Ex-tem CTdiff in detecting dabigatran in whole blood samples. In patient samples, when thrombin CT and thrombin CTdiff were used, it was possible to detect dabigatran with a cut-off of dabigatran at 20 ng mL-1 , whereas, when Ex-tem CT and Ex-tem CTdiff were used, the method was less sensitive. Data from patient samples were obtained within 15 min of blood sampling. Conclusions ROTEM CT with a thrombin-based trigger is more sensitive to dabigatran effects than Ex-tem CT, and detects anticoagulant effects of drug concentrations in the low-very low therapeutic range. Analysis with idarucizumab (CTdiff ) reveals dabigatran-specific effects. As data are rapidly obtained, this method could, with further development and validation of its performance, be suitable for detecting clinically significant dabigatran effects in emergency situations.

Microfluidics contrasted to thrombelastography: perplexities in defining hypercoagulability

BACKGROUND

Elevated clot strength (maximum amplitude [MA]) measured by thrombelastography (TEG) is associated with thrombotic complications. However, it remains unclear how MA translates to thrombotic risks, as this measurement is independent of time, blood flow, and clot degradation. We hypothesize that under flow conditions, increased clot strength correlates to time-dependent measurements of coagulation and resistance to fibrinolysis.

MATERIALS AND METHODS

Surgical patients at high risk of thrombotic complications were analyzed with TEG and total thrombus-formation analysis system (T-TAS). TEG hypercoagulability was defined as an r <10.2 min, angle >59, MA >66 or LY30 <0.2% (based off of healthy control data, n = 141). The T-TAS AR and PL chips were used to measure clotting at arterial shear rates. T-TAS measurements include occlusion start time, occlusion time (OT), occlusion speed (OSp), and total clot generation (area under the curve). These measurements were correlated to TEG indices (R time, angle, MA, and LY30). Both T-TAS and TEG assays were challenged with tissue plasminogen activator (t-PA) to assess clot resistance to fibrinolysis.

RESULTS

Thirty subjects were analyzed, including five controls. TEG-defined hypercoagulability by MA was detected in 52% of the inflammatory bowel disease/cancer patients; 0% was detected in the controls. There were no TEG measurements that significantly correlated with T-TAS AR and PL chip. However, in the presence of t-PA, T-TAS AR determined OSp to have an inverse relationship with TEG angle (-0.477, P = 0.012) and LY30 (-0.449, P = 0.019), and a positive correlation with R time (0.441 P = 0.021). In hypercoagulability determined by TEG MA, T-TAS PL had a significantly reduced OT (4:07 versus 6:27 min, P = 0.043). In hypercoagulability defined by TEG LY30, T-TAS PL had discordant findings, with a significantly prolonged OT (6:36 versus 4:30 min, P = 0.044) and a slower OSp (10.5 versus 19.0 kPa/min, P = 0.030).

CONCLUSIONS

Microfluidic coagulation assessment with T-TAS has an overall poor correlation with most TEG measurements in a predominantly hypercoagulable patient population, except in the presence of t-PA. The one anticipated finding was an elevated MA having a shorter time to platelet-mediated microfluidic occlusion, supporting the role of platelets and hypercoagulability. However, hypercoagulability defined by LY30 had opposing results in which a low LY30 was associated with a longer PL time to occlusion and slower OSp. These discordant findings warrant ongoing investigation into the relationship between clot strength and fibrinolysis under different flow conditions.

Role of Thromboelastography and Rotational Thromboelastometry in the Management of Cardiovascular Diseases

The monitoring of coagulation by viscoelastometric methods—thromboelastography and rotational thromboelastometry—may detect the contributions of cellular and plasma components of hemostasis. These methods might overcome some of the serious limitations of conventional laboratory tests. Viscoelastic testing can be repeatedly performed during and after surgery and thus provides a dynamic picture of the coagulation process during these periods. Several experiences with the use of these methods in cardiovascular surgery have been reported, but there is perspective for more frequent use of these assays in the assessment of platelet response to antiplatelet therapy and in the assessment of coagulation in patients on long-term dabigatran therapy. This article reviews the current role and future perspectives of thromboelastography and thromboelastometry in the management of cardiovascular diseases.

Comprehensive characteristics of the anticoagulant activity of dabigatran in relation to its plasma concentration

BACKGROUND

Issues with laboratory measurement of dabigatran include: 1. Do coagulation assays reflect dabigatran plasma concentrations? 2. Do samples from patients treated with dabigatran have the same coagulability as dabigatran-spiked samples from healthy volunteers? 3. What is the long-term stability of dabigatran after storage at -80 °C? This study aims to evaluate these questions.

MATERIALS AND METHODS

Ecarin chromogenic assay (ECA), a laboratory-developed diluted thrombin time (LD-dTT), prothrombin time (PT) and activated partial thromboplastin time (APTT) and ROTEM® were used to measure dabigatran anticoagulant activity and liquid chromatography-tandem mass spectrometry (LC-MS/MS) to measure dabigatran plasma concentrations. ROTEM® (EXTEM, INTEM, FIBTEM) was performed in whole blood and the other assays in platelet poor plasma (PPP), both in samples spiked with dabigatran (0, 25, 50, 100, 250, 500 and 1000 ng/mL) from healthy donors and in ex vivo samples from patients treated with dabigatran etexilate. Citrated PPP samples were frozen and stored at -80 °C, 1, 3, 6 and 12 months until analysis.

RESULTS

EXTEM and FIBTEM clotting time (CT), ECA and LD-dTT correlate well with dabigatran plasma concentrations. With the exception of few ROTEM® parameters, there were no differences between spiked and patient samples. Samples were stable for at least 12 months at -80 °C.

CONCLUSIONS

EXTEM and FIBTEM CT, ECA and LD-dTT are suitable for measuring the effect of dabigatran in treated patients. In general, results from spiked plasma samples are similar to those of patient samples. Storage of dabigatran plasma samples for up to 12 months does not influence measured levels.

Emergency care of patients receiving non-vitamin K antagonist oral anticoagulants

Non-vitamin K antagonist oral anticoagulants (NOACs), which inhibit thrombin (dabigatran) and factor Xa (rivaroxaban, apixaban, edoxaban) have been introduced in several clinical indications. Although NOACs have a favourable benefit-risk profile and can be used without routine laboratory monitoring, they are associated-as any anticoagulant-with a risk of bleeding. In addition, treatment may need to be interrupted in patients who need surgery or other procedures. The objective of this article, developed by a multidisciplinary panel of experts in thrombosis and haemostasis, is to provide an update on the management of NOAC-treated patients who experience a bleeding episode or require an urgent procedure. Recent advances in the development of targeted reversal agents are expected to help streamline the management of NOAC-treated patients in whom rapid reversal of anticoagulation is required.