Coagulation Assays

Intracardiac ultrasound-guided transseptal puncture in horses: Outcome, follow-up, and perioperative anticoagulant treatment

BACKGROUND

Cardiac catheterizations in horses are mainly performed in the right heart, as access to the left heart traditionally requires an arterial approach. Transseptal puncture (TSP) has been adapted for horses but data on follow-up and closure of the iatrogenic atrial septal defect (iASD) are lacking.

HYPOTHESIS/OBJECTIVES

To perform TSP and assess postoperative complications and iASD closure over a minimum of 4 weeks.

ANIMALS

Eleven healthy adult horses.

METHODS

Transseptal puncture was performed under general anesthesia. Serum cardiac troponin I concentrations were measured before and after puncture. Weekly, iASD closure was monitored using transthoracic and intracardiac echocardiography. Relationship between activated clotting time and anti-factor Xa activity during postoperative enoxaparin treatment was assessed in vitro and in vivo.

RESULTS

Transseptal puncture was successfully achieved in all horses within a median duration of 22 (range, 10-104) minutes. Balloon dilatation of the puncture site for sheath advancement was needed in 4 horses. Atrial arrhythmias occurred in 9/11 horses, including atrial premature depolarizations (N = 1), atrial tachycardia (N = 5), and fibrillation (N = 3). Serum cardiac troponin I concentrations increased after TSP, but remained under the reference value in 10/11 horses. Median time to iASD closure was 14 (1-35) days. Activated clotting time correlated with anti-factor Xa activity in vitro but not in vivo.

CONCLUSIONS AND CLINICAL IMPORTANCE

Transseptal puncture was successfully performed in all horses. The technique was safe and spontaneous iASD closure occurred in all horses. Clinical application of TSP will allow characterization and treatment of left-sided arrhythmias in horses.

Reprograming Clots for In Vivo Chemical Targeting in Traumatic Brain Injury

Traumatic brain injury (TBI) is a critical public health concern, yet there are no therapeutics available to improve long-term outcomes. Drug delivery to TBI remains a challenge due to the blood-brain barrier and increased intracranial pressure. In this work, a chemical targeting approach to improve delivery of materials to the injured brain, is developed. It is hypothesized that the provisional fibrin matrix can be harnessed as an injury-specific scaffold that can be targeted by materials via click chemistry. To accomplish this, the brain clot is engineered in situ by delivering fibrinogen modified with strained cyclooctyne (SCO) moieties, which incorporated into the injury lesion and is retained there for days. Improved intra-injury capture and retention of diverse, clickable azide-materials including a small molecule azide-dye, 40 kDa azide-PEG nanomaterial, and a therapeutic azide-protein in multiple dosing regimens is subsequently observed. To demonstrate therapeutic translation of this approach, a reduction in reactive oxygen species levels in the injured brain after delivery of the antioxidant catalase, is achieved. Further, colocalization between azide and SCO-fibrinogen is specific to the brain over off-target organs. Taken together, a chemical targeting strategy leveraging endogenous clot formation is established which can be applied to improve therapeutic delivery after TBI.

Platelet reactivity and activated clotting time predict hemorrhagic site complications in patients with chronic coronary syndromes undergoing percutaneous coronary interventions

BACKGROUND

Radial access is preferred in patients with chronic coronary syndromes (CCSs) treated with ad hoc percutaneous coronary intervention (PCI). Antithrombotic and antiplatelet treatment before PCI may affect outcomes at vascular access sites. QuikClot Radial is a kaolin-based band that may shorten hemostasis time. Using point-of-care testing, we investigated the effect of antithrombotic and antiplatelet treatment on access-site complications.

METHODS

This prospective observational study included consecutive patients with CCS on chronic aspirin therapy referred for ad hoc PCI. The activated clotting time (ACT), global thrombosis test and VerifyNow P2Y 12 test were done sequentially after unfractionated heparin (UFH) and clopidogrel administration. Patients were monitored for radial artery patency, bleeding and local hematoma until discharge.

RESULTS

We enrolled 40 patients [mean age, 68.8 ± 8.8 years; men, 30 (75%)] who received UFH (median dose, 8000 IU; interquartile range, 7000-9000 IU) and clopidogrel (600 mg). All radial arteries remained patent during follow-up. Local bleeding and hematomas were noted in 11 patients (27.5%) each. Patients with bleeding had lower mean platelet activity at 2 h [122.5 ± 51 platelet reactivity units (PRU) vs. 158.7 ± 43 PRU, P  = 0.04] and higher ACT (216.9 ± 40 s vs. 184.6 ± 28 s, P = 0.006) than patients without bleeding. An ACT >196 s at 2 h predicted bleeding or hematoma (AUC, 0.72; 95% CI, 0.56-0.85, P = 0.008).

CONCLUSION

Lower platelet activity and higher ACT after PCI were associated with higher bleeding risk at a vascular access site. Point-of-care testing of ACT after the procedure may help identify patients with CCS undergoing PCI who are at higher risk of access-site bleeding.

Safety and Effectiveness of an Anti-Xa-based Unfractionated Heparin Protocol for Impella Percutaneous Ventricular Assist Devices

Background: Impella devices are used for mechanical circulatory support in patients with cardiogenic shock or those undergoing high-risk percutaneous coronary intervention (PCI). Anticoagulation protocols in this population are not well established and are complicated by concomitant use of purge solutions containing unfractionated heparin (UFH) and intravenous UFH continuous infusion (CI) for systemic anticoagulation. Objectives: To evaluate thrombotic and bleeding complications when using a novel UFH protocol with a reduced initial UFH CI dose of 6 units/kg/hour targeting an anti-Xa goal of 0.3 to 0.5 units/mL in patients receiving Impella support. Methods: This single-center, retrospective study included 41 patients on Impella support who received an UFH purge solution and/or an IV UFH infusion. The primary outcome was overall composite bleeding. Secondary outcomes included thrombotic events and systemic UFH exposure. An exploratory analysis was performed to identify risk factors for bleeding. Results: Anti-Xa values were in therapeutic range 46% of the time while on support (interquartile range 16.6%-75%), with a median IV UFH dose of 6 units/kg/hour. The overall bleeding rate was 29.2%, with 6 minor bleeds and 2 major bleeds with no fatal bleeding or intracranial hemorrhage. Rate of overall thrombosis was 4.9%, including 1 ischemic stroke and 1 occurrence of limb ischemia. Conclusion: Use of a modified UFH protocol to target an anti-Xa goal of 0.3 to 0.5 units/mL resulted in bleeding and thrombotic event rates similar to previous literature. This protocol utilizing an initial rate of 6 units/kg/hour may be a useful approach to achieve therapeutic anticoagulation while accounting for UFH exposure from the purge solution and minimizing need for frequent calculations.

Coagulation Disorders, Testing, and Treatment in Exotic Animal Critical Care

Despite poor recognition in the literature, exotic companion animals are affected by many diseases that can result in disordered coagulation and fibrinolysis. This article outlines current knowledge of hemostasis, common diagnostic tests and reviews reported diseases associated with coagulopathy in small mammals, bird and reptiles. A range of conditions affect platelets and thrombocytes, endothelium and blood vessels, and plasma clotting factors. Improved recognition and monitoring of hemostatic disorders will enable targeted therapy and improved case outcomes.

Comparison of anticoagulation monitoring strategies for adults supported on extracorporeal membrane oxygenation: A systematic review

BACKGROUND

Anticoagulation is critical in patients supported on extracorporeal membrane oxygenation (ECMO). The appropriate monitoring strategies for heparin remain unclear.

OBJECTIVES

This systematic review aimed to compare the accuracy and safety of various monitoring strategies for patients supported on ECMO.

METHODS

The PubMed and Web of Science databases were searched for articles in March 2023 without restrictions on publication date. Anticoagulation monitoring strategies for adults supported on ECMO were compared across all included studies. The incidence of bleeding, thrombosis, mortality, blood transfusion, correlation between tests and heparin dose, and the discordance between different tests were discussed in the included studies. The risk of bias was assessed using the Newcastle-Ottawa Scale and Cochrane Collaboration's tool.

RESULTS

Twenty-six studies, including a total of 1,684 patients, met the inclusion criteria. The monitoring of anticoagulation by activated partial thromboplastin time (aPTT) resulted in less blood product transfusion than that by activated clotting time (ACT). Moreover, the monitoring of anticoagulation by anti-factor Xa (Anti-Xa) resulted in a more stable anticoagulation than that by aPTT. Anti-Xa and aPTT correlated with heparin dose better than ACT, and the discordance between different monitoring tests was common. Finally, combined monitoring showed some advantages in reducing mortality and blood product transfusion.

CONCLUSION

Anti-Xa and aPTT are more suitable for anticoagulation monitoring for patients supported on ECMO than ACT. Thromboelastography and combination strategies are less applied. Most of the studies were retrospective, and their sample sizes were relatively small; thus, more appropriate monitoring strategies and higher quality research are needed.

Immobility-associated thromboprotection is conserved across mammalian species from bear to human

Venous thromboembolism (VTE) comprising deep venous thrombosis and pulmonary embolism is a major cause of morbidity and mortality. Short-term immobility-related conditions are a major risk factor for the development of VTE. Paradoxically, long-term immobilized free-ranging hibernating brown bears and paralyzed spinal cord injury (SCI) patients are protected from VTE. We aimed to identify mechanisms of immobility-associated VTE protection in a cross-species approach. Mass spectrometry-based proteomics revealed an antithrombotic signature in platelets of hibernating brown bears with heat shock protein 47 (HSP47) as the most substantially reduced protein. HSP47 down-regulation or ablation attenuated immune cell activation and neutrophil extracellular trap formation, contributing to thromboprotection in bears, SCI patients, and mice. This cross-species conserved platelet signature may give rise to antithrombotic therapeutics and prognostic markers beyond immobility-associated VTE.

Evaluation of a Multimodal Heparin Laboratory Monitoring Protocol in Adult Extracorporeal Membrane Oxygenation Patients

BACKGROUND

Anticoagulation monitoring practices vary during extracorporeal membrane oxygenation (ECMO). The Extracorporeal Life Support Organization describes that a multimodal approach is needed to overcome assay limitations and minimize complications.

OBJECTIVE

Compare activated clotting time (ACT) versus multimodal approach (activated partial thromboplastin time (aPTT)/anti-factor Xa) for unfractionated heparin (UFH) monitoring in adult ECMO patients.

METHODS

We conducted a single-center retrospective pre- (ACT) versus post-implementation (multimodal approach) study. The incidence of major bleeding and thrombosis, blood product and antithrombin III (ATIII) administration, and UFH infusion rates were compared.

RESULTS

Incidence of major bleeding (69.2% versus 62.2%, p = 0.345) and thrombosis (23% versus 14.9%, p = 0.369) was similar between groups. Median number of ATIII doses was reduced in the multimodal group (1.0 [IQR 0.0-2.0] versus 0.0 [0.0 -1.0], p = 0.007). The median UFH infusion rate was higher in the ACT group, but not significant (16.9 [IQR 9.6-22.4] versus 13 [IQR 9.6-15.4] units/kg/hr, p = 0.063). Fewer UFH infusion rate changes occurred prior to steady state in the multimodal group (0.9 [IQR 0.3 -1.7] versus 0.1 [IQR 0.0-0.2], p < 0.001).

CONCLUSION

The incidence of major bleeding and thrombosis was similar between groups. Our multimodal monitoring protocol standardized UFH infusion administration and reduced ATIII administration.

Application of anti-Xa assay in monitoring unfractionated heparin therapy in contemporary antithrombotic management

INTRODUCTION

Unfractionated heparin remains the most widely used agent in the prevention and acute treatment of thrombosis. Pharmacological complexities of this intriguing agent mandate frequent monitoring of its anticoagulant properties to maintain safe and effective hematological outcomes. Although activated partial thromboplastin time has been the standard test to monitor unfractionated heparin therapy for many decades, the anti-Xa assay has emerged as a substitute or adjunct in many institutions.

AREAS COVERED

This brief report outlines the key features of anti-Xa assay in monitoring unfractionated heparin in acute management of thrombosis in various contemporary settings, with emphasis on evidence for clinical outcomes. PubMed.gov database was utilized to obtain the pertinent literature.

EXPERT OPINION

The anti-Xa activity is primarily a reflection of UFH concentration and does not account for other hematological variables frequently present in contemporary anticoagulation management. The advantage of the anti-Xa assay in monitoring UFH therapy is predicated upon its limitations to account for global physiological hemostasis. There are significant disease and drug interactions that may potentially result in false in-vitro analysis of anti-Xa activity. Routine application of the anti-Xa assay is not evidence-based at this time.

Nanoclays in medicine: a new frontier of an ancient medical practice

Clays have been used as early as 2500 BC in human civilization for medicinal purposes. The ease of availability, biocompatibility, and versatility of these unique charged 2D structures abundantly available in nature have enabled the extensive applications of clays in human history. Recent advances in the use of clays in nanostructures and as components of polymer clay nanocomposites have exponentially expanded the use of clays in medicine. This review covers the details of structures and biomedical applications of several common clays, including montmorillonite, LAPONITE®, kaolinite, and halloysite. Here we describe the applications of these clays in wound dressings as hemostatic agents in drug delivery of drugs for cancer and other diseases and tissue engineering. Also reviewed are recent experimental and modeling studies that elucidate the impact of clay structures on cellular processes and cell adhesion processes. Various mechanisms of clay-mediated bioactivity, including protein localization, modulation of cell adhesion, biomineralization, and the potential of clay nanoparticles to impact cell differentiation, are presented. We also review the current developments in understanding the impact of clays on cellular responses. This review also elucidates new emerging areas of use of nanoclays in osteogenesis and the development of in vitro models of bone metastasis of cancer.

Point-of-Care Blood Coagulation Assay Based on Dynamic Monitoring of Blood Viscosity Using Droplet Microfluidics

Monitoring of the coagulation function has applications in many clinical settings. Routine coagulation assays in the clinic are sample-consuming and slow in turnaround. Microfluidics provides the opportunity to develop coagulation assays that are applicable in point-of-care settings, but reported works required bulky sample pumping units or costly data acquisition instruments. In this work, we developed a microfluidic coagulation assay with a simple setup and easy operation. The device continuously generated droplets of blood sample and buffer mixture and reported the temporal development of blood viscosity during coagulation based on the color appearance of the resultant droplets. We characterized the relationship between blood viscosity and color appearance of the droplets and performed experiments to validate the assay results. In addition, we developed a prototype analyzer equipped with simple fluid pumping and economical imaging module and obtained similar assay measurements. This assay showed great potential to be developed into a point-of-care coagulation test with practical impact.

Hemocompatibility Evaluation of Thai Bombyx mori Silk Fibroin and Its Improvement with Low Molecular Weight Heparin Immobilization

Bombyx mori silk fibroin (SF), from Nangnoi Srisaket 1 Thai strain, has shown potential for various biomedical applications such as wound dressing, a vascular patch, bone substitutes, and controlled release systems. The hemocompatibility of this SF is one of the important characteristics that have impacts on such applications. In this study, the hemocompatibility of Thai SF was investigated and its improvement by low molecular weight heparin (LMWH) immobilization was demonstrated. Endothelial cell proliferation on the SF and LMWH immobilized SF (Hep/SF) samples with or without fibroblast growth factor-2 (FGF-2) was also evaluated. According to hemocompatibility evaluation, Thai SF did not accelerate clotting time, excess stimulate complement and leukocyte activation, and was considered a non-hemolysis material compared to the negative control PTFE sheet. Platelet adhesion of SF film was comparable to that of the PTFE sheet. For hemocompatibility enhancement, LMWH was immobilized successfully and could improve the surface hydrophilicity of SF films. The Hep/SF films demonstrated prolonged clotting time and slightly lower complement and leukocyte activation. However, the Hep/SF films could not suppress platelet adhesion. The Hep/SF films demonstrated endothelial cell proliferation enhancement, particularly with FGF-2 addition. This study provides fundamental information for the further development of Thai SF as a hemocompatible biomaterial.

Meriandra dianthera Aqueous Extract and Its Fraction Prevents Blood Coagulation by Specifically Inhibiting the Intrinsic Coagulation Pathway: An in vitro Study

Background

Currently, cardiovascular disorders are the primary cause of mortality in the world and constitute a serious medical problem. Blood coagulation is an essential process to prevent excessive blood loss through injured blood vessels; however, abnormal blood clotting in the blood vessels can result in fatal cardiovascular disorders. This study investigated the in vitro anticoagulant activity of Meriandra dianthera crude extract and its fractions and their erythrocyte membrane stabilizing activity.

Methods

The plant leaves were extracted by a decoction method and were further fractionated by a liquid–liquid partition with a solvent of crescent polarity. The in vitro anticoagulant activity of the plant extract and its fractions was assessed by PT and APTT assays, while the membrane stabilizing activity was determined through hypotonic induced hemolysis.

Results

The crude aqueous leaf extract of Meriandra dianthera significantly (P < 0.001) prolonged the intrinsic clotting pathway measured by APTT by specifically acting on the intrinsic coagulation pathway. By using liquid–liquid fractionation, the residual aqueous fraction was identified as the fraction responsible for the anticoagulant activity of the crude extract as it significantly (P<0.001) prolonged APTT while the other fractions failed. Both the crude extract and its aqueous residue fraction did not affect the extrinsic coagulation pathway measured by PT. In the membrane stabilizing assay, crude extract and aqueous residue fraction showed the highest membrane stabilizing activity.

Conclusion

The crude extract and its aqueous residue fraction showed a potent in vitro anticoagulant and membrane stabilizing activity, which shows the potential of the plant’s leaves as a new source of bioactive molecules for coagulation-related disorders.

Novel Technologies in Chronic Wound Care

In Israel, 20% of wounds do not progress to full healing under treatment with conservative technologies of which 1 to 2% are eventually defined as chronic wounds. Chronic wounds are a complex health burden for patients and pose considerable therapeutic and budgetary burden on health systems. The causes of chronic wounds include systemic and local factors. Initial treatment involves the usual therapeutic means, but as healing does not progress, more advanced therapeutic technologies are used. Undoubtedly, advanced means, such as negative pressure systems, and advanced technologies, such as oxygen systems and micrografts, have vastly improved the treatment of chronic wounds. Our service specializes in treating ulcers and difficult-to-heal wounds while providing a multiprofessional medical response. Herein, we present our experience and protocols in treating chronic wounds using a variety of advanced dressings and technologies.

Passive high-frequency microrheology of blood

Indicative of various pathologies, blood properties are under intense scrutiny. The hemorheological characteristics are traditionally gauged by bulk, low-frequency indicators that average out critical information about the complex, multi-scale, and multi-component structure. In particular, one cannot discriminate between the erythrocytes contribution to global rheology and the impact of plasma. Nevertheless, in their fast stochastic movement, before they encounter each other, the erythrocytes probe the subtle viscoelasticity of their protein-rich environment. Thus, if these short time scales can be resolved experimentally, the plasma properties could be determined without having to separate the blood components; the blood is practically testing itself. This microrheological description of blood plasma provides a direct link between the composition of whole blood and its coagulability status. We present a parametric model for the viscoelasticity of plasma, which is probed by the erythrocytes over frequency ranges of kilohertz in a picoliter-sized volume. The model is validated both in vitro, using artificial hemo-systems where the composition is controlled, as well as on whole blood where continuous measurements provide real-time information. We also discuss the possibility of using this passive microrheology as an in vivo assay for clinically relevant situations where the blood clotting condition must be observed and managed continuously for diagnosis or during therapeutic procedures at different stages of hemostatic and thrombotic processes.

Point-of-care blood coagulation assay enabled by printed circuit board-based digital microfluidics

The monitoring of coagulation function has great implications in many clinical settings. However, existing coagulation assays are simplex, sample-consuming, and slow in turnaround, making them less suitable for point-of-care testing. In this work, we developed a novel blood coagulation assay that simultaneously assesses both the tendency of clotting and the stiffness of the resultant clot using printed circuit board (PCB)-based digital microfluidics. A drop of blood was actuated to move back and forth on the PCB electrode array, until the motion winded down as the blood coagulated and became thicker. The velocity tracing and the deformation of the clot were calculated via image analysis to reflect the coagulation progression and the clot stiffness, respectively. We investigated the effect of different hardware and biochemical settings on the assay results. To validate the assay, we performed assays on blood samples with hypo- and hyper-coagulability, and the results confirmed the assay's capability in distinguishing different blood samples. We then examined the correlation between the measured metrics in our assays and standard coagulation assays, namely prothrombin time and fibrinogen level, and the high correlation supported the clinical relevance of our assay. We envision that this method would serve as a powerful point-of-care coagulation testing method.

Anticoagulation Monitoring for Perioperative Physicians

From preoperative medications to intraoperative needs to postoperative thromboprophylaxis, anticoagulants are encountered throughout the perioperative period. This review focuses on coagulation testing clinicians utilize to monitor the effects of these medications.

Efficacy of Early Prophylaxis Against Catheter-Associated Thrombosis in Critically Ill Children: A Bayesian Phase 2b Randomized Clinical Trial

OBJECTIVES

We obtained preliminary evidence on the efficacy of early prophylaxis on the risk of central venous catheter-associated deep venous thrombosis and its effect on thrombin generation in critically ill children.

DESIGN

Bayesian phase 2b randomized clinical trial.

SETTING

Seven PICUs.

PATIENTS

Children less than 18 years old with a newly inserted central venous catheter and at low risk of bleeding.

INTERVENTION

Enoxaparin adjusted to anti-Xa level of 0.2-0.5 international units/mL started at less than 24 hours after insertion of central venous catheter (enoxaparin arm) versus usual care without placebo (usual care arm).

MEASUREMENTS AND MAIN RESULTS

At the interim analysis, the proportion of central venous catheter-associated deep venous thrombosis on ultrasonography in the usual care arm, which was 54.2% of 24 children, was significantly higher than that previously reported. This resulted in misspecification of the preapproved Bayesian analysis, reversal of direction of treatment effect, and early termination of the randomized clinical trial. Nevertheless, with 30.4% of 23 children with central venous catheter-associated deep venous thrombosis on ultrasonography in the enoxaparin arm, risk ratio of central venous catheter-associated deep venous thrombosis was 0.55 (95% credible interval, 0.24-1.11). Including children without ultrasonography, clinically relevant central venous catheter-associated deep venous thrombosis developed in one of 27 children (3.7%) in the enoxaparin arm and seven of 24 (29.2%) in the usual care arm (p = 0.02). Clinically relevant bleeding developed in one child randomized to the enoxaparin arm. Response profile of endogenous thrombin potential, a measure of thrombin generation, was not statistically different between trial arms.

CONCLUSIONS

These findings suggest the efficacy and safety of early prophylaxis that should be validated in a pivotal randomized clinical trial.

The Interlaboratory Performance in Measurement of Dabigatran and Rivaroxaban: Results of the College of American Pathologists External Quality Assessment Program

CONTEXT.—

Assessing direct oral anticoagulant (DOAC) drug levels by reliable laboratory assays is necessary in a number of clinical scenarios.

OBJECTIVE.—

To evaluate the performance of DOAC-specific assays for various concentrations of dabigatran and rivaroxaban, assess the interlaboratory variability in measurement of these DOACs, and investigate the responsiveness of the routine clotting assays to various concentrations of these oral anticoagulants.

DESIGN.—

College of American Pathologists proficiency testing survey data from 2013 to 2016 were summarized and analyzed.

RESULTS.—

For dabigatran, the interlaboratory coefficient of variation (CV) of ecarin chromogenic assay was broad (ranging from 7.5% to 29.1%, 6.3% to 15.5%, and 6.8% to 9.0% for 100-ng/mL, 200-ng/mL, and 400-ng/mL targeted drug concentrations, respectively). The CV for diluted thrombin time for dabigatran was better overall (ranging from 11.6% to 17.2%, 9.3% to 12.3, and 7.1% to 11.2% for 100 ng/mL, 200 ng/mL, and 400 ng/mL, respectively). The rivaroxaban-calibrated anti-Xa assay CVs also showed variability (ranging from 11.5% to 22.2%, 7.2% to 10.9%, and 6.4% to 8.1% for 50-ng/mL, 200-ng/mL, and 400-ng/mL targeted drug concentrations, respectively). The prothrombin time (PT) and activated partial thromboplastin time (aPTT) showed variable dose and reagent-dependent responsiveness to DOACs: PT was more responsive to rivaroxaban and aPTT to dabigatran. The undiluted thrombin time showed maximum prolongation across all 3 dabigatran concentrations, making it too sensitive for drug-level monitoring, but supporting its use as a qualitative screening assay.

CONCLUSIONS.—

DOAC-specific assays performed reasonably well. While PT and aPTT cannot be used safely to determine DOAC degree of anticoagulation, a normal thrombin time excludes the presence of dabigatran.

Variability of Activated Clotting Time by Site of Sample Draw During Percutaneous Coronary Intervention: A Prospective Single-Center Study

The activated clotting time (ACT) assay is used to monitor and titrate anticoagulation therapy with unfractionated heparin during percutaneous coronary intervention (PCI). Observations at our institution suggested a considerable difference between ACT values drawn from varying arterial sites, prompting the current study. Patients undergoing PCI with unfractionated heparin therapy were prospectively enrolled. Simultaneous arterial blood samples were drawn from the access sheath and the coronary guide catheter. Differences between Hemochron ACT values were determined, and potential interactions with clinical variables were analyzed. Immediately postprocedure, the simultaneous mean guide and sheath ACTs were 327 ± 62 seconds and 257 ± 44 seconds, respectively, with a mean difference of 70 ± 60 seconds (P < .001). Nearly all (90%) ACT values obtained via the guide catheter were higher than the concurrent ACT drawn from the sheath. Logistic regression analysis demonstrated that lower weight-adjusted heparin doses and absence of diabetes were associated with a greater difference between the ACT values. We conclude that the ACT value is substantially greater when assessed via the guide catheter versus the access sheath. Although the biological mechanisms require further study, this difference should be considered when managing anticoagulation during PCI and when reporting ACT as part of research protocols.

Prolonged Activated Partial Thromboplastin Time after Successful Resuscitation from Cardiac Arrest is Associated with Unfavorable Neurologic Outcome

Coagulation abnormalities after successful resuscitation from cardiac arrest may be associated with unfavorable neurologic outcome. We investigated a potential association of activated partial thromboplastin time (aPTT) with neurologic outcome in adult cardiac arrest survivors. Therefore, we included all adults ≥18 years of age who suffered a nontraumatic cardiac arrest and had achieved return of spontaneous circulation between January 2013 and December 2018. Patients receiving anticoagulants or thrombolytic therapy and those subjected to extracorporeal membrane oxygenation support were excluded. Routine blood sampling was performed on admission as soon as a vascular access was available. The primary outcome was 30-day neurologic function, assessed by the Cerebral Performance Category scale (3-5 = unfavorable neurologic function). Multivariable regression was used to assess associations between normal (≤41 seconds) and prolonged (>41 seconds) aPTT on admission (exposure) and the primary outcome. Results are given as odds ratio (OR) with 95% confidence intervals (95% CIs). Out of 1,591 cardiac arrest patients treated between 2013 and 2018, 360 patients (32% female; median age: 60 years [interquartile range: 48-70]) were eligible for analysis. A total of 263 patients (73%) had unfavorable neurologic function at day 30. aPTT prolongation >41 seconds was associated with a 190% increase in crude OR of unfavorable neurologic function (crude OR: 2.89; 95% CI: 1.78-4.68, p < 0.001) and with more than double the odds after adjustment for traditional risk factors (adjusted OR: 2.01; 95% CI: 1.13-3.60, p = 0.018). In conclusion, aPTT prolongation on admission is associated with unfavorable neurologic outcome after successful resuscitation from cardiac arrest.

Monitoring standard and extended half-life products in hemophilia: Assay discrepancies for factor VIII and IX in pre- and postinfusion samples

BACKGROUND

Monitoring hemophilia treatment with extended half-life products is challenging for coagulation laboratories since factor assays may show substantial differences between results obtained with the one-stage assay (OSA) and the chromogenic substrate assay (CSA).

OBJECTIVES

The aim of this study was to evaluate and compare different factor assays and global coagulation methods.

METHODS

Factor VIII (FVIII) and IX (FIX) activities and global assay parameters were analyzed in pre- and postinfusion samples (5 patients 2 samples/product/method).

RESULTS

Samples containing FVIII products (NovoEight, Elocta, and Nuwiq) gave higher levels when measured with CSA compared to OSA. The correlation was excellent (r 2 ≥ .97) while biases of 42%-72% of mean (CSA-OSA) were obtained. With FVIII (OSA) as independent variable, the correlations to kaolin clot time (CT) and thrombin generation assay (TGA) peak were modest (r2  = .71-.72 and .64-.65, respectively), except for Nuwiq for which there was a poor correlation to TGA peak (r 2 = .08). Samples containing Alprolix, a FIX product, gave a smaller difference between activity levels (CSA-OSA), and the correlation was excellent (r 2 = .96). With FIX (CSA) as independent variable for both Alprolix and Refixia, the correlations to Innovin CT and TGA peaks were weak (r 2 = .33-.45 and .44-.76, respectively).

CONCLUSIONS

Our data show that factor activity assays differ between methods used and agents. These discrepancies indicate the value of having more than one type of assay available in the coagulation laboratory when monitoring hemophilia treatment with extended half-life products. Global assays gave complementary information indicated by the modest correlations to factor activities.

Performance Assessment of a Multifaceted Unfractionated Heparin Dosing Protocol in Adult Patients on Extracorporeal Membrane Oxygenator

BACKGROUND

The use of extracorporeal membrane oxygenator (ECMO) support devices are associated with complications, including bleeding and thrombosis. Unfractionated heparin (UFH) is the gold standard anticoagulant in ECMO patients. Clinically, UFH is monitored through activated clotting time (ACT), activated partial thromboplastin time (aPTT), and anti-factor Xa assay. It is unknown which assay best predicts anticoagulation effects in adults.

OBJECTIVE

To assess the correlation of UFH dosing and monitoring using an established protocol.

METHODS

A pilot, prospective cohort, historically controlled study was conducted at a tertiary care hospital. Patients ≥18 years-old who received ECMO on the multifaceted anticoagulation protocol were included and compared with those on the conventional method of anticoagulation. The primary end point was to assess the correlation between UFH dose and different monitoring methods throughout 72 hours using the new protocol guided by ACT and anti-factor Xa assay.

RESULTS

In each arm, 20 patients were enrolled. The study revealed that anti-factor Xa assay had the largest number of "strong" correlations 11/20 (55%), followed by both aPTT and aPTT ratio 10/20 (50%), and, finally, ACT 2/20 (10%). Concordance between anti-factor Xa assay and the other monitoring parameters in the prospective arm was generally low: 31% with aPTT ratio, 26% with ACT, and 23% with aPTT.

CONCLUSION AND RELEVANCE

The adaption of a multifaceted anticoagulation protocol using anti-factor Xa assay may provide a better prediction of heparin dosing in adults ECMO patients compared with the conventional ACT-based protocol. Further studies are needed to assess the safety and different monitoring modalities.

Successful intraosseous factor VIII application in a haemophilic emergency

WHAT IS KNOWN AND OBJECTIVES

Intravenous (IV) replacement therapy with plasma derived or recombinant factor VIII (FVIII) and factor IX concentrates is the mainstay for treatment of patients with haemophilia A and B. Therefore, the current therapy is particularly dependent on the presence of a secure IV access especially in case of emergency.

CASE DESCRIPTION

A life-threatening bleeding event in an 8-month-old boy is managed by intraosseous (IO) infusion of recombinant FVIII concentrate. No adverse events have been observed 6 months after the application, and complete heeling has been reported.

WHAT IS NEW AND CONCLUSION

Venous application of factor concentrate remains inevitable in any haemophilic emergency. In case IV access is lacking, an IO institution of factor might be considered. To our knowledge, this represents the first reported case of IO application of recombinant FVIII concentrate in a patient with haemophilia.

Population Pharmacokinetic Analysis of Dalteparin in Pediatric Patients With Venous Thromboembolism

This article describes the population pharmacokinetics (PK) of dalteparin in pediatric patients with venous thromboembolism (VTE). A prospective multicenter open‐label study was conducted in children who required anticoagulation for the treatment of VTE. The study population included children with and without cancer. The goal was to describe the pharmacokinetics of dalteparin using anti‐Xa as a surrogate marker and to determine the dose required to achieve therapeutic anti‐Xa levels (0.5‐1.0 IU/mL). The anti‐Xa data were supplemented with 2 published studies and analyzed using population pharmacokinetic approaches. The pharmacokinetics of dalteparin following subcutaneous injection in pediatric patients was described by a 1‐compartment model with linear absorption and elimination. Body weight was added as a covariate on both CL/F and Vd/F as a power function with fixed exponents of 0.75 and 1.0, respectively. The estimates of CL/F and Vd/F in the full model were 929 mL/h and 7180 mL, respectively, for a reference female patient aged 12 years with body weight of 43 kg. Body weight‐normalized CL/F decreased with age. Cancer status and sex did not have significant effects on CL/F and Vd/F. Simulations were conducted to select starting doses of dalteparin that would rapidly achieve therapeutic anti‐Xa levels. These simulations suggested that the recommended starting doses of dalteparin administered subcutaneously in pediatric patients of different age cohort groups for treatment of VTE were 150 IU/kg every 12 hours (1 month to <2 years), 125 IU/kg every 12 hours (≥2 to <8 years), and 100 IU/kg every 12 hours (≥8 to <19 years).

Microfluidic devices for studying coagulation biology

The ability to study the behavior of cells, proteins, and cell-cell or cell-protein interactions under dynamic forces such as shear stress under fluid flow, provides a more accurate understanding of the physiopathology of hemostasis. This review touches upon the traditional methods for studying blood coagulation and platelet aggregation and provides an overview on cellular and protein response to shear stress. We also elaborate on the biological aspects of how cells recognize mechanical forces and convert them into biochemical signals that can drive various signaling pathways. We give a detailed description of the various types of microfluidic devices that are employed to study the complex processes of platelet aggregation and blood coagulation under flow conditions as well as to investigate endothelial shear-response. We also highlight works mimicking artificial vessels as platforms to study the mechanisms of coagulation, and finish our review by describing anticipated clinical uses of microfluidics devices and their standardization.

Microfluidics in Haemostasis: A Review

Haemostatic disorders are both complex and costly in relation to both their treatment and subsequent management. As leading causes of mortality worldwide, there is an ever-increasing drive to improve the diagnosis and prevention of haemostatic disorders. The field of microfluidic and Lab on a Chip (LOC) technologies is rapidly advancing and the important role of miniaturised diagnostics is becoming more evident in the healthcare system, with particular importance in near patient testing (NPT) and point of care (POC) settings. Microfluidic technologies present innovative solutions to diagnostic and clinical challenges which have the knock-on effect of improving health care and quality of life. In this review, both advanced microfluidic devices (R&D) and commercially available devices for the diagnosis and monitoring of haemostasis-related disorders and antithrombotic therapies, respectively, are discussed. Innovative design specifications, fabrication techniques, and modes of detection in addition to the materials used in developing micro-channels are reviewed in the context of application to the field of haemostasis.

Global coagulation assays in hemophilia A: A comparison to conventional assays

BACKGROUND

Global assays measure the interactions of coagulants, anticoagulants, and platelets on thrombin generation and may reflect the comprehensive coagulation potential in patients with hemophilia better than conventional assays.

OBJECTIVES

The objectives of the current study were to investigate the value of global assays for measuring and monitoring the coagulation potential of patients with hemophilia A (HA).

PATIENTS/METHODS

Rotational thromboelastometry, thrombin generation assay (TGA), and activated partial thromboplastin time (APTT) clot waveform analysis were investigated in a cohort of patients with severe, moderate, and mild HA and compared with conventional assays.

RESULTS

The maximum velocity (MaxVel) parameter of modified thromboelastometry analysis, initiated by tissue factor and in the presence of corn trypsin inhibitor (CTI), had 92% sensitivity and 95% specificity for hemophilia diagnosis. The MaxVel also strongly correlated with factor VIII (FVIII) levels of patients with HA (r = .805, P < .0001). CTI improved the sensitivity of TGA, providing more accurate results. In particular, peak height parameter of platelet-rich plasma samples with CTI had a sensitivity and specificity of 100% and 94%, respectively, in all patients with HA. APTT clot waveform analysis minimum value of first derivative (Min1) and minimum value of second derivative (Min2) parameters (representing speed and acceleration of clot formation, respectively) were sensitive and correlated more strongly with FVIII levels than APTT clotting times did (Min1: r = 0.786, P < 0.0001; Min2: r = 0.759, P < 0.0001; APTT: r = -0.513, P = 0.001).

CONCLUSIONS

The sensitivity and specificity of the global assays was method dependent. Correlation between clinical end points and thrombin generation might also be valuable in the era of non-factor replacement therapy.

Clinical utility and impact of the use of the chromogenic vs one-stage factor activity assays in haemophilia A and B

Treatment of haemophilia A/B patients comprises factor VIII (FVIII) or factor IX (FIX) concentrate replacement therapy, respectively. FVIII and FIX activity levels can be measured in clinical laboratories using one‐stage activated partial thromboplastin time (aPTT)‐based clotting or two‐stage chromogenic factor activity assays. We discuss strengths and limitations of these assays, providing examples of clinical scenarios to highlight some of the challenges associated with their current use for diagnostic and monitoring purposes. Substantial inter‐laboratory variability has been reported for one‐stage assays when measuring the activity of factor replacement products due to the wide range of currently available aPTT reagents, calibration standards, factor‐deficient plasmas, assay conditions and instruments. Chromogenic activity assays may avoid some limitations associated with one‐stage assays, but their regulatory status, perceived higher cost, and lack of laboratory expertise may influence their use. Haemophilia management guidelines recommend the differential application of one or both assays for initial diagnosis and disease severity characterisation, post‐infusion monitoring and replacement factor potency labelling. Efficient communication between clinical and laboratory staff is crucial to ensure application of the most appropriate assay to each clinical situation, correct interpretation of assay results and, ultimately, accurate diagnosis and optimal and safe treatment of haemophilia A or B patients.

Novel Cellulose-Halloysite Hemostatic Nanocomposite Fibers with a Dramatic Reduction in Human Plasma Coagulation Time

High-performance cellulose-halloysite hemostatic nanocomposite fibers (CHNFs) are fabricated using a one-step wet-wet electrospinning process and evaluated for human plasma coagulation by activated partial thromboplastin time. These novel biocompatible CHNFs exhibit 2.4 times faster plasma coagulation time compared with the industry gold standard QuikClot Combat Gauze (QCG). The CHNFs have superior antileaching property of clay with 3 times higher post-wetting clotting activity compared to QCG. The CHNFs also coagulate whole blood 1.3 times faster than the QCG and retain twice the clotting performance after washing. Halloysite clay is also more effective in plasma coagulation than commercial kaolin clay. The physical and thermal properties of the CHNFs were evaluated using scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, Brunauer-Emmett-Teller surface area analysis, and thermogravimetric analysis. CHNFs show a 7-fold greater clay loading than QCG and their small average diameter of 450 ± 260 nm affords a greater specific surface area (33.6 m² g^-1) compared with the larger average diameter of 12.6 ± 0.9 μm for QCG with a specific surface area of 1.6 m² g^-1. The CHNFs were shown to be noncytotoxic and human primary fibroblasts proliferated on the composite material. The drastic reduction in coagulation time makes this novel nanocomposite a potential lifesaving material for victims of rapid blood loss such as military personnel and patients undergoing major surgical procedures or to aid in the treatment of unexpected bleeding episodes of patients suffering from hereditary blood clotting disorders. Since a person can die within minutes of heavy bleeding, every second counts for stopping traumatic hemorrhaging.

Traditional and non-traditional anticoagulation management during extracorporeal membrane oxygenation

Unfractionated heparin (UFH) is the anticoagulant of choice during extracorporeal membrane oxygenation (ECMO) support. Despite its favorable pharmacologic properties, management of heparin anticoagulation during ECMO remains a major challenge. To date, little is known about the optimal monitoring strategy or the heparin dose offering the best safety/efficacy profile. Therefore, it remains unclear if the heparin dose should be adapted to target a specific "clotting time" [e.g., activated clotting time (ACT) or activated partial thromboplastin time (aPTT)] or a heparin concentration, measured by coagulation factor anti-Xa assay. In addition, no study has compared the relevance of modern viscoelastic coagulation tests over the single value of a clotting time or heparin concentration value. Although guidelines for anticoagulation during ECMO support have been published, the absence of evidence limits the quality of the recommendations provided, which explains the major intra- and inter-institutional variability observed. Large prospective multicenter trials are urgently needed to investigate the optimal anticoagulation management strategy during ECMO support.

Blood Coagulation Testing Smartphone Platform Using Quartz Crystal Microbalance Dissipation Method

Blood coagulation function monitoring is important for people who are receiving anticoagulation treatment and a portable device is needed by these patients for blood coagulation self-testing. In this paper, a novel smartphone based blood coagulation test platform was proposed. It was developed based on parylene-C coated quartz crystal microbalance (QCM) dissipation measuring and analysis. The parylene-C coating constructed a robust and adhesive surface for fibrin capturing. The dissipation factor was obtained by measuring the frequency response of the sensor. All measured data were sent to a smartphone via Bluetooth for dissipation calculation and blood coagulation results computation. Two major coagulation indexes, activated partial thromboplastin time (APTT) and prothrombin time (PT) were measured on this platform compared with results by a commercial hemostasis system in a clinical laboratory. The measurement results showed that the adjusted R-square (R²) value for APTT and PT measurements were 0.985 and 0.961 respectively. The QCM dissipation method for blood coagulation measurement was reliable and effective and the platform together with the QCM dissipation method was a promising solution for point of care blood coagulation testing.

Low-molecular-weight sulfonated chitosan as template for anticoagulant nanoparticles

PURPOSE

In this work, low-molecular-weight sulfoethyl chitosan (SECS) was used as a model template for the generation of silver core-shell nanoparticles with high potential as anticoagulants for medical applications.

MATERIALS AND METHODS

SECS were synthesized by two reaction pathways, namely Michael addition and a nucleophilic substitution with sodium vinylsulfonate or sodium 2-bromoethanesulfonate (NaBES). Subsequently, these derivatives were used as reducing and capping agents for silver nanoparticles in a microwave-assisted reaction. The formed silver-chitosan core-shell particles were further surveyed in terms of their anticoagulant action by different coagulation assays focusing on the inhibition of either thrombin or cofactor Xa.

RESULTS

In-depth characterization revealed a sulfoalkylation of chitosan mainly on its sterically favored O6-position. Moreover, comparably high average degrees of substitution with sulfoethyl groups (DSSE) of up to 1.05 were realized in reactions with NaBES. The harsh reaction conditions led to significant chain degradation and consequently, SECS exhibits masses of <50 kDa. Throughout the following microwave reaction, stable nanoparticles were obtained only from highly substituted products because they provide a sufficient charge density that prevented particles from aggregation. High-resolution transmission electron microscopy images reveal that the silver core (diameter ~8 nm) is surrounded by a 1-2 nm thick SECS layer. These core-shell particles and the SECS itself exhibit an inhibiting activity, especially on cofactor Xa.

CONCLUSION

This interesting model system enabled the investigation of structure-property correlations in the course of nanoparticle formation and anticoagulant activity of SECS and may lead to completely new anticoagulants on the basis of chitosan-capped nanoparticles.

Reversible covalent direct thrombin inhibitors

INTRODUCTION

In recent years, the traditional treatments for thrombotic diseases, heparin and warfarin, are increasingly being replaced by novel oral anticoagulants offering convenient dosing regimens, more predictable anticoagulant responses, and less frequent monitoring. However, these drugs can be contraindicated for some patients and, in particular, their bleeding liability remains high.

METHODS

We have developed a new class of direct thrombin inhibitors (VE-DTIs) and have utilized kinetics, biochemical, and X-ray structural studies to characterize the mechanism of action and in vitro pharmacology of an exemplary compound from this class, Compound 1.

RESULTS

We demonstrate that Compound 1, an exemplary VE-DTI, acts through reversible covalent inhibition. Compound 1 inhibits thrombin by transiently acylating the active site S195 with high potency and significant selectivity over other trypsin-like serine proteases. The compound inhibits the binding of a peptide substrate with both clot-bound and free thrombin with nanomolar potency. Compound 1 is a low micromolar inhibitor of thrombin activity against endogenous substrates such as fibrinogen and a nanomolar inhibitor of the activation of protein C and thrombin-activatable fibrinolysis inhibitor. In the thrombin generation assay, Compound 1 inhibits thrombin generation with low micromolar potency but does not increase the lag time for thrombin formation. In addition, Compound 1 showed weak inhibition of clotting in PT and aPTT assays consistent with its distinctive profile in the thrombin generation assay.

CONCLUSION

Compound 1, while maintaining strong potency comparable to the current DTIs, has a distinct mechanism of action which produces a differentiating pharmacological profile. Acting through reversible covalent inhibition, these direct thrombin inhibitors could lead to new anticoagulants with better combined efficacy and bleeding profiles.

Chemical clocks, oscillations, and other temporal effects in analytical chemistry: oddity or viable approach?

Most analytical methods are based on "analogue" inputs from sensors of light, electric potentials, or currents. The signals obtained by such sensors are processed using certain calibration functions to determine concentrations of the target analytes. The signal readouts are normally done after an optimised and fixed time period, during which an assay mixture is incubated. This minireview covers another-and somewhat unusual-analytical strategy, which relies on the measurement of time interval between the occurrences of two distinguishable states in the assay reaction. These states manifest themselves via abrupt changes in the properties of the assay mixture (e.g. change of colour, appearance or disappearance of luminescence, change in pH, variations in optical activity or mechanical properties). In some cases, a correlation between the time of appearance/disappearance of a given property and the analyte concentration can be also observed. An example of an assay based on time measurement is an oscillating reaction, in which the period of oscillations is linked to the concentration of the target analyte. A number of chemo-chronometric assays, relying on the existing (bio)transformations or artificially designed reactions, were disclosed in the past few years. They are very attractive from the fundamental point of view but-so far-only few of them have be validated and used to address real-world problems. Then, can chemo-chronometric assays become a practical tool for chemical analysis? Is there a need for further development of such assays? We are aiming to answer these questions.

Antithrombotic potential of esculin 7, 3', 4', 5', 6'-O-pentasulfate (EPS) for its role in thrombus reduction using rat thrombosis model

Currently available anticoagulants for prevention and treatment of thrombosis have several limitations, thus, small organic scaffolds that can dissolve clots in vivo in a dose dependent manner with lesser side effects are highly desirable. Here we report the synthesis of esculin pentasulfate (EPS) and assessment of its in vitro, in vivo and ex vivo anticoagulant and antithrombotic potential. Assessment of in vitro clotting times showed prolonged activated partial thromboplastin time (APTT), prothrombin time (PT) and thrombin time (TT) in the presence of EPS. EPS also showed remarkable reduction in thrombus formation when administered in occlusion induced thrombotic rats at a low dose (2.5 mg/kg). Further, assessment of clot rate with plasma isolated from EPS treated rats confirmed its anticoagulation potential. EPS at varying concentrations showed no significant cytotoxic effect on HEK293 cell line. Further, molecular docking analysis of EPS with known anticoagulant proteins [(antithrombin (ATIII) and heparin cofactor II (HCF II)] that require heparin revealed good binding affinity (-7.9 kcal/mol) with ATIII but not with HCF II. ATIII when incubated with EPS showed increased fluorescence intensity, with no change in secondary structure. Overall, our results clearly show the in vivo modulation of thrombus formation using a modified natural scaffold EPS.

Managing transitions from oral factor Xa inhibitors to unfractionated heparin infusions

PURPOSE

Published evidence regarding the effects of oral factor Xa inhibitors on anticoagulation monitoring tests is reviewed with a focus on monitoring concerns that can arise during transitions to i.v. heparin therapy.

SUMMARY

Assays that measure inhibition of factor Xa activity (i.e., anti-Xa assays) are widely used in U.S. institutions to monitor i.v. heparin therapy and, in some cases, for monitoring other types of anticoagulation therapy. Clinicians have raised concerns that the use of anti-Xa assays to monitor heparin levels in hospitalized patients who must be transitioned from oral factor Xa inhibitor therapy to i.v. unfractionated heparin (UFH) infusions could yield unquantifiable or inaccurate results, leading to unnecessary UFH dose reductions and potential treatment failures; the manufacturer labeling of oral factor Xa inhibitors (apixaban, edoxaban, and rivaroxaban) does not provide specific guidance on this issue. Results of a literature review indicated that residual effects of oral factor Xa inhibitor use can result in substantial interference with the currently available chromogenic anti-Xa assays but negligible to moderate effects on global coagulation assays, which measure activated partial thromboplastin time (aPTT) or prothrombin time. Therefore, during the transition from an oral factor Xa inhibitor to i.v. UFH therapy, it may be prudent to consider an aPTT assay for anticoagulation monitoring.

CONCLUSION

The use of oral factor Xa inhibitors appears to affect the accuracy of anti-Xa assay results, with results of global coagulation assays affected to a lesser degree.