Assessment of platelet-derived thrombogenicity with the total thrombus-formation analysis system in coronary artery disease patients receiving antiplatelet therapy

Use of heated tobacco products (IQOS) causes an acute increase in arterial stiffness and platelet thrombus formation

BACKGROUND AND AIMS

Heated tobacco products (HTPs) are novel alternative tobacco products being promoted as an alternative to cigarettes. To evaluate the impact of HTP use on vascular function, we investigated the effects of a brief HTP usage on arterial stiffness and platelet thrombus formation in healthy volunteers.

METHODS

In a randomised crossover study, twenty-four healthy young adults with occasional tobacco use smoked the HTP IQOS 3 Multi (Phillip Morris Int.) and "no-exposure" was used as a control, with a wash-out period of at least one week in-between. Arterial stiffness was assessed through pulse wave velocity and pulse wave analysis. Blood samples, collected at baseline and 5 min following exposure, were analysed with the Total-Thrombus-formation analysis system evaluating platelet and fibrin-rich thrombus formation tendency.

RESULTS

HTP exposure caused immediate heightened pulse wave velocity (+0.365 m/s, 95% CI: +0.188 to 0.543; p = 0.004) and enhanced augmentation index corrected to heart rate (+6.22%, 95% CI: +2.33 to 10.11; p = 0.003) compared to the no-exposure occasion. Similarly, blood pressure and heart rate transiently increased immediately following HTP inhalation. Platelet thrombus formation significantly increased following HTP exposure (area under the curve +59.5, 95% CI: +25.6 to 93.4; p < 0.001) compared to no-exposure. No effect was seen on fibrin-rich thrombus formation following HTP-exposure.

CONCLUSIONS

Brief HTP use in healthy young adults had immediate adverse effects on vascular function resulting in increased arterial stiffness and platelet thrombus formation, known risk factors for the development of atherosclerosis. Further research is needed to address long term health impacts.

The oxylipin analog CS585 prevents platelet activation and thrombosis through activation of the prostacyclin receptor

Cardiovascular disease remains the primary cause of morbidity and mortality globally. Platelet activation is critical for maintaining hemostasis and preventing the leakage of blood cells from the vessel. There has been a paucity in the development of new drugs to target platelet reactivity. Recently, the oxylipin 12(S)-hydroxy-eicosatrienoic acid (12-HETrE), which is produced in platelets, was shown to limit platelet reactivity by activating the prostacyclin receptor. Here, we demonstrated the synthesis of a novel analog of 12-HETrE, known as CS585. Human blood and mouse models of hemostasis and thrombosis were assessed for the ability of CS585 to attenuate platelet activation and thrombosis without increasing the risk of bleeding. Human platelet activation was assessed using aggregometry, flow cytometry, western blot analysis, total thrombus formation analysis system, microfluidic perfusion chamber, and thromboelastography. Hemostasis, thrombosis, and bleeding assays were performed in mice. CS585 was shown to potently target the prostacyclin receptor on the human platelet, resulting in a highly selective and effective mechanism for the prevention of platelet activation. Furthermore, CS585 was shown to inhibit platelet function in human whole blood ex vivo, prevent thrombosis in both small and large vessels in mouse models, and exhibit long-lasting prevention of clot formation. Finally, CS585 was not observed to perturb coagulation or increase the risk of bleeding in the mouse model. Hence, CS585 represents a new validated target for the treatment of thrombotic diseases without the risk of bleeding or off-target activation observed with other prostaglandin receptor agonists.

Hemostatic disorders in patients with infective endocarditis undergoing urgent surgical valve replacement - Rethinking current beliefs

BACKGROUND

Although infective endocarditis (IE) represents a unique model of thrombo-inflammatory disease, the most frequent early complications of surgical valve replacement (SVR) in IE population are coagulopathy and bleeding. The hemostatic capacity and procedure-related coagulation disorders of IE patients undergoing SVR are unknown. The aims of this study were to test periprocedural hemostasis in IE patients undergoing urgent SVR, and to assess the association between disorders of hemostasis and early bleeding as well as with thromboembolic events.

METHODS

A prospective, two-center, hypothesis generating, observational study was performed between Dec 2017 and Jan 2020. Periprocedural hemostasis of IE patients was assessed using Total Thrombus-formation Analysis System (T-TAS Plus) within 24 h before and 72 h post SVR.

RESULTS

Overall, 25 patients with active IE undergoing urgent SVR were tested. Hemostatic capacity of IE patients was significantly impaired pre-SVR as well as post-SVR compared to normal values, in most aspects of T-TAS assays under high and low shear forces, including prolonged activation of coagulation (T10), final clot formation (OT) and clot strength (AUC30). Post-SVR T-TAS results were significantly associated with early bleeding and with red blood cell, platelet, and fresh frozen plasma administration. No association with thrombo-embolic events was found.

CONCLUSIONS

Patients with active IE undergoing urgent SVR have significantly reduced hemostatic capacity before and after SVR. Hemostatic insufficiency post-SVR is related to bleeding and blood products transfusion. T-TAS may be helpful in assessment of periprocedural hemostasis in patients with IE undergoing SVR.

Electronic Cigarette Vaping with Nicotine Causes Increased Thrombogenicity and Impaired Microvascular Function in Healthy Volunteers: A Randomised Clinical Trial

Electronic cigarette (EC) vaping is increasingly popular, despite growing evidence of adverse health effects. To further evaluate the impact of EC use on vascular health, we investigated the effects of brief EC inhalation on flow-dependent thrombus formation and microcirculation in healthy volunteers. The study was performed with a randomised double-blind crossover design. Twenty-two healthy subjects aged between 18 and 45 years with occasional tobacco use were recruited. Subjects inhaled 30 puffs of EC aerosol with and without nicotine on two occasions separated by a wash-out period of at least 1 week. Blood samples were collected at baseline and at 15 and 60 min following exposure and analysed with the Total-Thrombus-formation analysis system evaluating fibrin-rich thrombus formation and platelet thrombus formation in whole blood under flow. Microvascular function was assessed at baseline and 30 min after exposure by laser speckle contrast imaging and iontophoresis of acetylcholine and sodium nitroprusside (SNP) to evaluate the endothelium-dependent and independent pathways of vasodilation. Compared with nicotine free EC aerosol, exposure to EC aerosol with nicotine significantly increased platelet thrombus formation and fibrin-rich thrombus formation at 15 min (p = 0.017 and p = 0.037, respectively) with normalisation after 60 min. Peak SNP-mediated microvascular perfusion, i.e. endothelium-independent vasodilation, was reduced following EC vaping with nicotine compared with baseline (p = 0.006). Thirty puffs of EC aerosol with nicotine increased platelet and fibrin-dependent thrombus formation and reduced microvascular dilatation capacity. No compelling effects of EC vaping without nicotine were observed, indicating nicotine as the main effector. Trial registration: ClinicalTrials.gov Identifier: NCT04175457 URL: https://clinicaltrials.gov/ct2/show/NCT04175457.

Effects of Antiplatelet Drugs on Platelet-Dependent Coagulation Reactions

Activated platelets are involved in blood coagulation by exposing phosphatidylserine (PS), which serves as a substrate for assembling coagulation complexes. Platelets accelerate fibrin formation and thrombin generation, two final reactions of the coagulation cascade. We investigated the effects of antiplatelet drugs on platelet impact in these reactions and platelet ability to expose PS. Washed human platelets were incubated with acetylsalicylic acid (ASA), ticagrelor, ASA in combination with ticagrelor, ruciromab (glycoprotein IIb-IIIa antagonist), or prostaglandin E1 (PGE1). Platelets were not activated or activated by collagen and sedimented in multiwell plates, and plasma was added after supernatant removal. Fibrin formation (clotting) was monitored in a recalcification assay by light absorbance and thrombin generation in a fluorogenic test. PS exposure was assessed by annexin V staining using flow cytometry. Ticagrelor (alone and in combination with ASA), ruciromab, and PGE1, but not ASA, prolonged the lag phase and decreased the maximum rate of plasma clotting and decreased the peak and maximum rate of thrombin generation. Inhibition was observed when platelets were not treated with exogenous agonists (activation by endogenous thrombin) and pretreated with collagen. Ticagrelor (alone and in combination with ASA), ruciromab, and PGE1, but not ASA, decreased PS exposure on washed platelets activated by thrombin and by thrombin + collagen. PS exposure on activated platelets in whole blood was lower in patients with acute coronary syndrome receiving ticagrelor + ASA in comparison with donors free of medications. These results indicate that antiplatelet drugs are able to suppress platelet coagulation activity not only in vitro but also after administration to patients.

The association between platelet reactivity and lipoprotein levels in Framingham Heart Study participants

BACKGROUND

Hypertriglyceridemia is an independent risk factor for major adverse cardiovascular events, though the mechanisms linking triglycerides and platelet function with thrombosis, remain elusive. The aim of this study was to assess the association between platelet function and triglyceride levels.

METHODS

We included participants from the Framingham Heart Study Third Generation cohort, OMNI, and New Offspring Spouse cohort who attended the third examination cycle (2016-2019). Eligible participants were categorized into four triglyceride subgroups.

RESULTS

The study comprised a total of 1897 (55.53 %) participants with normal TG levels; 883 (25.85 %) participants with high-normal TGs; 378 (11.07 %) with borderline high TGs; and 258 (7.55 %) participants with hypertriglyceridemia. After adjusting for age, sex, alcohol consumption, aspirin, statin and P2Y₁₂ inhibitors, the levels of ADP-induced platelet aggregation were inversely associated with total cholesterol levels (P < 0.0001). Platelet disaggregation was associated with low-density lipoprotein and high-density lipoprotein cholesterol levels (P < 0.0001). Lastly, in a shear-stress chamber assay mimicking arterial flow velocities, TG levels in the normal-high group were associated with increased levels of collagen-dependent thrombogenicity (β = 24.16, SE = 6.65, P < 0.0001).

CONCLUSION

Triglyceride levels are associated with altered platelet activation and aggregation. Furthermore, increased platelet-driven thrombogenicity is directly associated with triglyceride levels after adjusting for medications and other covariates.

Monitoring of Antiplatelet Therapy

In the late 1990s, the antithrombotic antiplatelet agent, clopidogrel, a P2Y12 inhibitor, was introduced. Around the same time, there was an increase in a number of new methods to measure platelet function (e.g., PFA-100 in 1995), and this has continued. It became evident that not all patients responded to clopidogrel in the same way and that some patients had a relative "resistance" to therapy, termed "high on-treatment platelet reactivity." This then led to some publications to advocate platelet function testing being used for patients on antiplatelet therapy. Platelet function testing was also suggested for use in patients awaiting cardiac surgery after stopping their antiplatelet therapy as a way of balancing thrombotic risk pre-surgery and bleeding risk perioperatively. This chapter will discuss some of the commonly used platelet function tests used in these settings, particularly those that are sometimes referred to as point-of-care tests or that require minimal laboratory sample manipulation. The latest guidance and recommendations for platelet function testing will be discussed following several clinical trials looking at the usefulness of platelet function testing in these clinical settings.

Atherothrombosis-on-Chip: A Site-Specific Microfluidic Model for Thrombus Formation and Drug Discovery

Atherothrombosis, an atherosclerotic plaque disruption condition with superimposed thrombosis, is the underlying cause of cardiovascular episodes. Herein, a unique design is presented to develop a microfluidic site-specific atherothrombosis-on-chip model, providing a universal platform for studying the crosstalk between blood cells and plaque components. The device consists of two interconnected microchannels, namely main and supporting channels: the former mimics the vessel geometry with different stenosis, and the latter introduces plaque components to the circulation simultaneously. The unique design allows the site-specific introduction of plaque components in stenosed channels ranging from 0% to above 50%, resulting in thrombosis, which has not been achieved previously. The device successfully explains the correlation between vessel geometry and thrombus formation phenomenon as well as the influence of shear rate on platelet aggregation, confirming the reliability and the effectiveness of the design. The device exhibits significant sensitivity to aspirin. In therapeutic doses (50 × 10^-6 and 100 × 10^-6 m), aspirin delays and prevents platelet adhesion, thereby reducing the thrombus area in a dose-dependent manner. Finally, the device is effectively employed in testing the targeted binding of the RGD (arginyl-glycyl-aspartic acid) labeled polymeric nanoparticles on the thrombus, extending the use of the device to examine targeted drug carriers.

Malnutrition-associated high bleeding risk with low thrombogenicity in patients undergoing percutaneous coronary intervention

BACKGROUND AND AIMS

Although antithrombotic treatments are established for coronary artery disease (CAD), they increase the bleeding risk, especially in malnourished patients. The total thrombus-formation analysis system (T-TAS) is useful for the assessment of thrombogenicity in CAD patients. Here, we examined the relationships among malnutrition, thrombogenicity and 1-year bleeding events in patients undergoing percutaneous coronary intervention (PCI).

METHODS AND RESULTS

This was a retrospective analysis of 300 consecutive CAD patients undergoing PCI. Blood samples obtained on the day of PCI were used in the T-TAS to compute the thrombus formation area under the curve. We assigned patients to two groups based on the geriatric nutritional risk index (GNRI): 102 patients to the lower GNRI group (≤98), 198 patients to the higher GNRI group (98<). The primary endpoint was the incidence of 1-year bleeding events defined by Bleeding Academic Research Consortium criteria types 2, 3, or 5. The T-TAS levels were lower in the lower GNRI group than in the higher GNRI group. Kaplan-Meier analysis showed worse 1-year bleeding event-free survival in the lower GNRI group compared with the higher GNRI group. The combined model of the GNRI and the Academic Research Consortium for High Bleeding Risk (ARC-HBR) had good calibration and discrimination for bleeding risk prediction. In addition, having a lower GNRI and ARC-HBR positivity was associated with 1-year bleeding events.

CONCLUSION

A lower GNRI could reflect low thrombogenicity evaluated by the T-TAS and determine bleeding risk in combination with ARC-HBR positivity.

Increased thrombogenicity is associated with revascularization outcomes in patients with chronic limb-threatening ischemia

OBJECTIVES

Clinically driven target lesion revascularization (CD-TLR) frequently occurs after endovascular therapy (EVT) in patients with chronic limb-threatening ischemia (CLTI). The total thrombus-formation analysis system (T-TAS) can quantitatively evaluate thrombogenicity. Therefore, we aimed to elucidate the association of T-TAS parameters with CD-TLR.

METHODS

We analyzed 34 CLTI patients and 62 Non-CLTI patients who underwent EVT. Blood samples collected on the day of EVT were used in T-TAS to compute the thrombus formation area under the curve (PL₂₄-AUC₁₀ in the platelet chip and AR₁₀-AUC₃₀ in the atheroma chip). After the EVT procedure, clinical follow-up was performed, and the presence of CD-TLR was assessed.

RESULTS

During the follow-up period (median 574 days), 10 patients (29%) in the CLTI group and 11 patients (18%) in the Non-CLTI group showed CD-TLR. In the CLTI group, patients who showed CD-TLR had a higher AR₁₀-AUC₃₀ than those who did not (1694 [1657, 1799] vs. 1561 [1412, 1697], p=0.01). In contrast, the PL₂₄-AUC₁₀ showed no significant differences depending on CD-TLR in both groups. For the CLTI patients, multivariable Cox regression analysis using propensity scores revealed that the AR₁₀-AUC₃₀ was an independent predictor of CD-TLR even after adjusting for baseline demographics, lesion characteristics, and anticoagulant use (HR=2.04, 95%CI=1.18-3.88, p=0.01; per 100 increase). In contrast, in Non-CLTI patients, neither the AR₁₀-AUC₃₀ and nor the PL₂₄-AUC₁₀ was significantly associated with CD-TLR. Receiver operating characteristics curve analysis identified an AR₁₀-AUC₃₀ level of 1646 as an optimal cutoff value to predict CD-TLR (AUC = 0.85, sensitivity = 0.93, specificity = 0.56).

CONCLUSIONS

In CLTI patients, but not in Non-CLTI patients, the AR₁₀-AUC₃₀ showed a potential to predict CD-TLR. This finding suggests that hypercoagulability may play a predominant role in the progression of CLTI and anticoagulants may be useful in preventing revascularization.

Protease-activated receptor antagonists prevent thrombosis when dual antiplatelet therapy is insufficient in an occlusive thrombosis microfluidic model

Background

Platelet activation and arterial thrombosis on a ruptured atherosclerotic plaque is a major cause of myocardial infarction. Dual antiplatelet therapy (DAPT), the combination of platelet aggregation inhibitors, aspirin and a P2Y12 antagonist, is used to prevent arterial thrombosis. However, many people continue to have arterial thrombosis and myocardial infarction despite DAPT, indicating that additional therapies are required where DAPT is insufficient.

Objectives

To determine whether antagonists of protease-activated receptors (PARs) can prevent occlusive thrombosis under conditions where DAPT is insufficient.

Methods

We used human whole blood in a microfluidic model of occlusive thrombosis to compare conditions under which DAPT is effective to those under which DAPT was not. Cangrelor (a P2Y12 antagonist) and aspirin were used to mimic DAPT. We then investigated whether the PAR1 antagonist vorapaxar or the PAR4 antagonist BMS 986120, alone or in combination with DAPT, prevented occlusive thrombosis.

Results and Conclusions

A ruptured plaque exposes collagen fibers and is often rich in tissue factor, triggering activation of platelets and coagulation. Occlusive thrombi formed on type I collagen in the presence or absence of tissue factor (TF). However, although DAPT prevented occlusive thrombosis in the absence of TF, DAPT had little effect when TF was also present. Under these conditions, PAR antagonism was also ineffective. However, occlusive thrombosis was prevented by combining DAPT with PAR antagonism. These data demonstrate that PAR antagonists may be a useful addition to DAPT in some patients and further demonstrate the utility of in vitro models of occlusive thrombosis.

Temporary Rise in Blood Thrombogenicity in Patients with Acute Myocardial Infarction

Objective  Although blood thrombogenicity seems to be one of the determinant factors for the development of acute myocardial infarction (MI), it has not been dealt with in-depth. This study aimed to investigate blood thrombogenicity and its change in acute MI patients. Methods and Results  We designed a prospective, observational study that included 51 acute MI patients and 83 stable coronary artery disease (CAD) patients who underwent cardiac catheterization, comparing thrombogenicity of the whole blood between: (1) acute MI patients and stable CAD patients; and (2) acute and chronic phase in MI patients. Blood thrombogenicity was evaluated by the Total Thrombus-Formation Analysis System (T-TAS) using the area under the flow pressure curve (AUC ₃₀ ) for the AR-chip. Acute MI patients had significantly higher AUC ₃₀ than stable CAD patients (median [interquartile range], 1,771 [1,585-1,884] vs. 1,677 [1,527-1,756], p  = 0.010). Multivariate regression analysis identified acute MI with initial TIMI flow grade 0/1 as an independent determinant of high AUC ₃₀ ( β  = 0.211, p  = 0.013). In acute MI patients, AUC ₃₀ decreased significantly from acute to chronic phase (1,859 [1,550-2,008] to 1,521 [1,328-1,745], p  = 0.001). Conclusion  Blood thrombogenicity was significantly higher in acute MI patients than in stable CAD patients. Acute MI with initial TIMI flow grade 0/1 was significantly associated with high blood thrombogenicity by multivariate analysis. In acute MI patients, blood thrombogenicity was temporarily higher in acute phase than in chronic phase.

Cardiovascular risk factors are associated with augmented thrombogenicity in healthy individuals: analysis using the Total Thrombus-formation Analysis System

BACKGROUND

Rupture of an atherosclerotic plaque and subsequent exposure of the subendothelial prothrombotic matrix to blood cause arterial thrombosis. Circulating platelets play an indispensable role in the growth of arterial thrombi partially owing to their unique ability to adhere to the subendothelial matrix and to aggregate to each other under flow conditions. Recently, the Total Thrombus-formation Analysis System (T-TAS) was developed for ex vivo analysis of the thrombogenic potential of whole blood samples under flow conditions. Despite the potential clinical utility of the T-TAS in assessing the risk for thrombosis and bleeding, reference intervals for T-TAS analysis in healthy individuals have not been determined.

METHODS

In total, 122 whole blood samples were collected from healthy volunteers ranging in age from 25 to 45 years. T-TAS analysis and hematological, physiological, and lifestyle assessments were conducted in these subjects. Whole blood samples anticoagulated with hirudin were perfused into a collagen-coated microchip (PL chip). The time to 10 kPa and the area under the flow pressure curve up to 10 min (AUC₁₀) were analyzed as representative variables for thrombogenic potential. Reference intervals, which were defined as 2.5-97.5 percentiles, were determined. Additionally, univariate and multivariate analyses were performed to identify factors associated with the AUC₁₀ in the T-TAS.

RESULTS

The time to 10 kPa and the AUC₁₀ widely varied, even in healthy volunteers. The reference intervals were 1.50-4.02 min and 223.4-456.8, respectively, at a shear rate of 1500 s^- 1. Univariate and multivariate analyses showed that platelet counts were most significantly associated with the AUC₁₀ of the T-TAS. The presence of one or more cardiovascular risk factors of a high body mass index, a high pulse pressure, high fasting serum glucose levels, high low-density lipoprotein-cholesterol levels, a history of smoking, and no habitual exercise, had the second largest effect on the AUC₁₀ of the T-TAS.

CONCLUSIONS

Healthy volunteers who had any cardiovascular risk factors showed augmented thrombogenicity, even in artificial uniform capillaries, compared with those without any risk factors in the T-TAS.

[Integral tests of the hemostasis system in assessing the efficiency of acetylsalicylic acid in patients with ischemic heart disease]

Despite the fact that acetylsalicylic acid (ASA) is the "gold" standard for the prevention of cardiovascular complications in patients with coronary heart disease (CAD), a number of patients still have risks of atherothrombosis. In the present study, the antithrombotic effect of ASA in patients with CAD was assessed in platelet-rich plasma (PRP) using integral tests of the hemostasis study: the T-TAS system (Total Thrombus-formation Analysis System) and the thrombin generation test (TGT). The study involved 34 patients with stable CAD (11 women, 23 men) and people (15 women, 18 men) in the control group. As a result of assessing the activity of thrombus formation using the T-TAS system, a significant decrease in the area under the curve (AUC10) was found in the group with CAD patients compared with the control (135.6 [88.0-222.3] and 260.5 [217.3-301.9], respectively, p.

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.

Development of anti-thrombotic vaccine against human S100A9 in rhesus monkey

In post-stroke patients, a decreased adherence to antiplatelet drugs is a major challenge in the prevention of recurrent stroke. Previously, we reported an antiplatelet vaccine against S100A9 in mice, but the use of Freund’s adjuvant and the difference in amino acid sequences in epitopes between mice and humans were problematic for clinical use. Here, we redesigned the S100A9 vaccine for the common sequence in both humans and monkeys and examined its effects in cynomolgus monkeys with Alum adjuvant. First, we assessed several candidate epitopes and selected 102 to 112 amino acids as the suitable epitope, which could produce antibodies. When this peptide vaccine was intradermally injected into 4 cynomolgus monkeys with Alum, the antibody against human S100A9 was successfully produced. Anti-thrombotic effects were shown in two monkeys in a mixture of vaccinated serum and fresh whole blood from another cynomolgus monkey. Additionally, the anti-thrombotic effects were partially inhibited by the epitope peptide, indicating the feasibility of neutralizing anti-thrombotic effects of produced antibodies. Prolongation of bleeding time was not observed in vaccinated monkeys. Although further studies on increasing the effect of vaccine and safety are necessary, this vaccine will be a promising approach to improve adherence to antiplatelet drugs in clinical settings.

The Total Thrombus Formation (T-TAS) platelet (PL) assay, a novel test that evaluates whole blood platelet thrombus formation under physiological conditions

Dual antiplatelet therapy (DAPT, aspirin, and a P2Y₁₂ inhibitor) reduces thrombotic events in patients with coronary artery disease (CAD). The T-TAS PL assay uses arterial shear flow over collagen surface, better mimicking in vivo conditions compared to conventional agonist-based platelet function assays, to evaluate platelet function. Here, the platelet function in patients taking DAPT is evaluated with the T-TAS PL assay. In 57 patients with CAD, taking DAPT ≥7 days (n = 22 for clopidogrel, n = 15 for prasugrel, n = 20 for ticagrelor), T-TAS PL assessments were performed in duplicate, and expressed as area under the flow pressure curve within a 10-minute period (AUC10). The duplicate measurements were strongly correlated (r = 0.90, p < .001), with an intra-assay coefficient of variation (CV) of 11,5%. For clopidogrel, the median AUC10 was 11.5 (IQR5.9-41.8), for prasugrel 28.8 (IQR10.3-37.6), and for ticagrelor 8.9 (IQR 6.4-10.9). All measurements were below the AUC10 cutoff of 260 measured in healthy volunteers, suggesting excellent discrimination of DAPT-treated and untreated persons. The new T-TAS PL assay demonstrated complete discrimination of platelet function in patients on DAPT based on an established cutoff. Ticagrelor showed lower levels of platelet function and a more uniform response compared to prasugrel and clopidogrel.

Hemodialysis-related low thrombogenicity measured by total thrombus-formation analysis system in patients undergoing percutaneous coronary intervention

BACKGROUND

Established antithrombotic therapies can increase bleeding risk, especially in hemodialysis (HD) patients. The Total Thrombus-formation Analysis System (T-TAS) is useful for evaluating thrombogenicity. The aim of this study was to examine the relationship between HD and thrombogenicity, or bleeding events in patients undergoing percutaneous coronary intervention (PCI).

METHODS

In this retrospective cohort study, 300 patients undergoing elective PCI were enrolled between April 2017 and March 2019. Blood samples obtained on the day of PCI were analyzed with T-TAS to compute the thrombus formation area under the curve (AUC; PL₁₈-AUC₁₀ for platelet chip; AR₁₀-AUC₃₀ for atheroma chip). The patients were divided into three groups according to estimated glomerular filtration rate (eGFR): 33 HD patients, 124 non-HD patients with eGFR <60 mL/min/1.73m², and 143 non-HD patients with eGFR ≥60. We examined the thrombogenicity and spontaneous bleeding events within 1-year post-PCI.

RESULTS

HD was significantly associated with both low PL₁₈-AUC₁₀ and AR₁₀-AUC₃₀ levels determined by T-TAS. Bleeding events defined by the Bleeding Academic Research Consortium criteria types 2, 3, or 5 occurred during follow-up in 27 patients (9.0%): 7 in HD, 10 in non-HD with eGFR <60, and 10 in non-HD with eGFR ≥60. Both T-TAS parameters in the patients with bleeding were lower compared with those in the patients without bleeding, and HD was significantly associated with 1-year bleeding events.

CONCLUSIONS

The results suggested that HD patients undergoing PCI might be a predictor for low thrombogenicity measured by T-TAS and 1-year bleeding risk.

Development and assessment of total thrombus-formation analysis system-based bleeding risk model in patients undergoing percutaneous coronary intervention

BACKGROUND

Antithrombotic therapy is established for the treatment of various cardiovascular events. However, it has been shown to increase the bleeding risk. Total Thrombus-formation Analysis System (T-TAS) is reported to be useful for evaluating thrombogenicity. Here, we estimated whether T-TAS is useful for predicting bleeding events risk in patients undergoing percutaneous coronary intervention (PCI).

METHODS

This was a retrospective, observational study at Kumamoto University Hospital between April 2017 and March 2019. Blood samples obtained on the day of PCI were used in T-TAS to compute the thrombus formation area under the curve (AUC) (AR₁₀-AUC₃₀, AUC for AR chip). We divided the study population into 2 groups according to the Academic Research Consortium for High Bleeding Risk (ARC-HBR) (182 patients in ARC-HBR positive, 118 in ARC-HBR negative). The primary endpoint was 1-year bleeding events that were defined by Bleeding Academic Research Consortium type2, 3, or 5.

RESULTS

The AR₁₀-AUC₃₀levels were significantly lower in the ARC-HBR positive group than in the ARC-HBR negative group (median [interquartile range] 1571.4 [1277.0-1745.3] vs. 1726.2 [1567.7-1799.6], p < 0.001). The combination of ARC-HBR and AR₁₀-AUC₃₀ could discriminate the bleeding risk, and improved predictive capacity compared with ARC-HBR by c-statistics. Decision-curve analysis also revealed that combining AR₁₀-AUC₃₀ with ARC-HBR ameliorated bleeding risk-prediction. In multivariate Cox hazards analyses, combining ARC-HBR with lower AR₁₀-AUC₃₀ levels was significantly associated with 1-year bleeding events.

CONCLUSIONS

The results highlight that AR₁₀-AUC₃₀ evaluated by T-TAS could be a potentially useful marker for predicting high bleeding risk in patients undergoing PCI.

Advances in Platelet Function Testing-Light Transmission Aggregometry and Beyond

Platelet function testing is essential for the diagnosis of hemostasis disorders. While there are many methods used to test platelet function for research purposes, standardization is often lacking, limiting their use in clinical practice. Light transmission aggregometry has been the gold standard for over 60 years, with inherent challenges of working with live dynamic cells in specialized laboratories with independent protocols. In recent years, standardization efforts have brought forward fully automated systems that could lead to more widespread use. Additionally, new technical approaches appear promising for the future of specialized hematology laboratories. This review presents developments in platelet function testing for clinical applications.

Detection of acquired von Willebrand syndrome after ventricular assist device by total thrombus-formation analysis system

AIMS

Bleeding is a serious complication in patients with continuous-flow left ventricular assist device (CF-LVAD). Acquired von Willebrand syndrome (AVWS; type 2A) develops because of high shear stress inside the pumps and is a cause of bleeding complication. Although von Willebrand factor (vWF) multimer analysis is useful for diagnosing AVWS, it is only performed in specialized research institutes. A novel microchip flow chamber system, the total thrombus-formation analysis system (T-TAS), is a point-of-care system to evaluate the thrombus-formation process and useful for monitoring platelet thrombus-formation capacity in patients receiving antiplatelet therapy and the diagnosis and evaluation of the clinical severity of von Willebrand disease type 1. However, little is known about the association between AVWS and platelet thrombus-formation capacity evaluated by T-TAS in patients with CF-LVAD. We aimed to evaluate the utility of T-TAS for easy detection of AVWS in patients with CF-LVAD.

METHODS AND RESULTS

We simultaneously evaluated the vWF large multimers and T-TAS parameters in four consecutive patients with axial-type CF-LVAD and eight control patients treated with aspirin and warfarin. vWF large multimer index was defined as the proportion of large multimers in total vWF derived from a normal control plasma. T-TAS analyses different thrombus-formation processes using two microchips with different thrombogenic surfaces. PL₂₄ -AUC₁₀ levels in the platelet (PL) chip are highly sensitive for platelet functions, while AR₁₀ -AUC₃₀ levels in the atheroma (AR) chip allow the assessment of the overall haemostatic ability. vWF large multimer index and T-TAS parameters were decreased in all patients with CF-LVAD. The mean PL₂₄ -AUC₁₀ level (5.4 ± 2.9 vs. 219 ± 67; P < 0.01), AR₁₀ -AUC₃₀ level (338 ± 460 vs. 1604 ± 160; P < 0.01) and vWF large multimer index (49 ± 11% vs. 112 ± 27%; P < 0.01) were significantly lower in the patients with CF-LVAD than in control patients. One patient showed changes in T-TAS levels before and after implantation of CF-LVAD. PL₂₄ -AUC₁₀ and AR₁₀ -AUC₃₀ levels decreased from 438.1 to 5.0 and from 1667.9 to 1134.3, respectively.

CONCLUSIONS

In patients with CF-LVAD, the platelet thrombus-formation capacity was extremely impaired because of AVWS, and T-TAS parameters could detect the presence of AVWS. T-TAS can be used for easy detection of AVWS as a point-of-care testing. Further studies with a large sample size are needed to validate our results in several LVAD models and evaluate the prognostic value of bleeding complications and thromboembolism in patients with LVAD.

A Novel Microchip Flow Chamber (Total Thrombus Analysis System) to Assess Canine Hemostasis

Hemorrhagic diseases are common in dogs. Current coagulation assays do not model all aspects of in vivo hemostasis and may not predict bleeding risk. The Total-Thrombus Analysis System (T-TAS) is a novel hemostasis assay system in which whole blood flows through microfluidic channels at defined shear rates to provide qualitative and quantitative evaluation of platelet function (PL-chip) and coagulation function (AR-chip). The present study evaluated the T-TAS in dogs with hereditary bleeding disorders and with acquired hemorrhagic syndromes (Group 1), and healthy controls (Group 2). Hereditary defects included von Willebrand's disease (VWD; n = 4), hemophilia A (n = 2), and canine Scott syndrome (n = 2). Acquired hemorrhagic disorders included neoplastic hemoperitoneum (n = 2) and acute hemorrhagic diarrhea syndrome (n = 1). Citrate anticoagulated samples were collected from diseased dogs (Group 1, n = 11) and controls (Group 2, n = 11) for coagulation screening tests, fibrinogen analyses, D-dimer concentration, antithrombin activity, von Willebrand Factor antigen, PFA-100 closure time (PFA-CT), and thromboelastography (TEG). Citrate and hirudin anticoagulated samples were used for T-TAS analyses at two shear rates. Qualitative thrombus formation in each chip was recorded using the T-TAS video camera. Numeric parameters, derived from the instrument software, included occlusion start time (OST; time to 10 kPa), occlusion time (OT; time to 60 kPa (PL-chip) or 80 kPa (AR-chip)), and area under the pressure curve (AUC). Correlations between continuous variables were evaluated by Spearman's rank. Continuous variables were compared between groups by Student's t-test or the Mann-Whitney U-test. Alpha was set at 0.05. In combined analyses of all dogs, significant correlations were identified between T-TAS variables, between the PFA-CT and PL-chip parameters and between TEG variables and AR-chip parameters. The prothrombin time correlated with the AR-chip AUC at both shear rates. In Group 1 dogs, the AR-chip AUC at low shear was significantly reduced compared with Group 2 dogs. Aberrant thrombus formation was seen in video images recorded from dogs with VWD and hemophilia A. The T-TAS AR-chip analysis distinguished dogs with bleeding risk compared to healthy controls. Initial evaluations of the T-TAS suggest it may aid characterization of hemostasis in patients at-risk of bleeding and assist with delineating bleeding phenotypes.

Platelet-Derived Thrombogenicity Measured by Total Thrombus-Formation Analysis System in Patients With ST-Segment Elevation Myocardial Infarction Undergoing Primary Percutaneous Coronary Intervention

BACKGROUND

Prompt and potent antiplatelet effects are important aspects of management of ST-elevation myocardial infarction (STEMI) patients undergoing primary percutaneous coronary intervention (PPCI). We evaluated the association between platelet-derived thrombogenicity during PPCI and enzymatic infarct size in STEMI patients.Methods and Results:Platelet-derived thrombogenicity was assessed in 127 STEMI patients undergoing PPCI by: (1) the area under the flow-pressure curve for the PL-chip (PL₁₈-AUC₁₀) using the total thrombus-formation analysis system (T-TAS); and (2) P2Y₁₂reaction units (PRU) using the VerifyNow system. Patients were divided into 2 groups (High and Low) based on median PL₁₈-AUC₁₀during PPCI. PRU levels during PPCI were suboptimal in both the High and Low PL₁₈-AUC₁₀groups (median [interquartile range] 266 [231-311] vs. 272 [217-317], respectively; P=0.95). The percentage of final Thrombolysis in Myocardial Infarction (TIMI) 3 flow was lower in the High PL₁₈-AUC₁₀group (75% vs. 90%; P=0.021), whereas corrected TIMI frame count (31.3±2.5 vs. 21.0±2.6; P=0.005) and the incidence of slow-flow/no-reflow phenomenon (31% vs. 11%, P=0.0055) were higher. The area under the curve for creatine kinase (AUC_CK) was greater in the High PL₁₈-AUC₁₀group (95,231±7,275 IU/L h vs. 62,239±7,333 IU/L h; P=0.0018). Multivariate regression analysis identified high PL₁₈-AUC₁₀during PPCI (β=0.29, P=0.0006) and poor initial TIMI flow (β=0.37, P<0.0001) as independent determinants of AUC_CK.

CONCLUSIONS

T-TAS-based high platelet-derived thrombogenicity during PPCI was associated with enzymatic infarct size in patients with STEMI.

Effects of glycemic control and hypoglycemia on Thrombus formation assessed using automated microchip flow chamber system: an exploratory observational study

Background

Thrombus formation is an important factor affecting cardiovascular events and venous thromboembolism in type 2 diabetes. However, it is unclear whether glycemic control reduces thrombogenicity. We investigated the effect of short-term glycemic control (STUDY 1) and hypoglycemia (STUDY 2) on thrombus formation using an automated microchip flow chamber system.

Methods

For STUDY 1, we recruited 10 patients with type 2 diabetes. Before and after 2 weeks of treatment, blood glucose was analyzed with a continuous glucose monitoring system, and thrombogenicity was analyzed with an automated microchip flow chamber system. For STUDY 2, we recruited 10 subjects without diabetes who underwent an insulin tolerance test. We evaluated the change in thrombogenic potential with hypoglycemia.

Results

STUDY1: The mean blood glucose level reduced from 10.1 ± 2.6 to 6.9 ± 0.97 mM (P < 0.01). T10, an indicator of thrombogenicity, significantly attenuated after glycemic control (338 ± 65 vs. 425 ± 117 s, P < 0.05). The attenuation in T10 was significantly correlated with changes in mean blood glucose level after treatment (r = - 0.718, P < 0.05). STUDY 2: Platelet function was enhanced with decreasing blood glucose; increased platelet function was strongly correlated with an increase in epinephrine.

Conclusions

We demonstrated attenuation in thrombogenicity with short-term comprehensive diabetes care and enhancement in thrombogenicity with hypoglycemia, using a new flow chamber system.

Trial registration

UMIN-CTR UMIN 000019899, registered 26-Jan-2015 (STUDY 2).

Active Micropump-Mixer for Rapid Antiplatelet Drug Screening in Whole Blood

There is a need for scalable automated lab-on-chip systems incorporating precise hemodynamic control that can be applied to high-content screening of new more efficacious antiplatelet therapies. This paper reports on the development and characterization of a novel active micropump-mixer microfluidic to address this need. Using a novel reciprocating elastomeric micropump design, we take advantage of the flexible structural and actuation properties of this framework to manage the hemodynamics for on-chip platelet thrombosis assay on type 1 fibrillar collagen, using whole blood. By characterizing and harnessing the complex three-dimensional hemodynamics of the micropump operation in conjunction with a microvalve controlled reagent injection system we demonstrate that this prototype can act as a real-time assay of antiplatelet drug pharmacokinetics. In a proof-of-concept preclinical application, we utilize this system to investigate the way in which rapid dosing of human whole blood with isoform selective inhibitors of phosphatidylinositol 3-kinase dose dependently modulate platelet thrombus dynamics. This modular system exhibits utility as an automated multiplexable assay system with applications to high-content chemical library screening of new antiplatelet therapies.

Total Thrombus-Formation Analysis System can Predict 1-Year Bleeding Events in Patients with Coronary Artery Disease

Aims: The assessment of bleeding risk in patients with coronary artery disease (CAD) is clinically important. We recently developed the Total Thrombus-Formation Analysis System (T-TAS) for the quantitative analysis of thrombus formation using microchips with thrombogenic surfaces. Here, we assessed the utility of T-TAS parameters in predicting 1-year bleeding events in patients with CAD.

Methods: The study subjects were 561 consecutive patients who underwent coronary angiography (CAG) between August 2013 and September 2016 for suspected CAD. Blood samples collected at the time of CAG were used for T-TAS to compute the area under the curve (AUC) (AR₁₀-AUC₃₀) in the AR chip. Patients were divided into three groups according to AR₁₀-AUC₃₀ (low: ≤ 1603, intermediate, and high: > 1765, n = 187 each). One-year bleeding events were defined by the Platelet Inhibition and Patient Outcomes criteria.

Results: Bleeding occurred in 21 (3.7%) patients and was classified as major (8 [1.4%]) and minor (13 [2.3%]). The AR₁₀-AUC₃₀ levels were significantly lower in the bleeding group than the non-bleeding group (median [interquartile range] 1590 [1442–1734] vs. 1687 [1546–1797], p = 0.04). Univariate Cox regression analysis demonstrated that low AR₁₀-AUC₃₀, high prothrombin time-international normalized ratio levels, and diabetes correlated with bleeding events. Multivariate Cox regression analysis identified low AR₁₀-AUC₃₀ levels as a significant determinant of bleeding events. Kaplan-Meier survival curves showed a higher rate of bleeding events in the low than the high AR₁₀-AUC₃₀ group (p = 0.007).

Conclusions: The results highlight the potential usefulness of the AR₁₀-AUC₃₀ levels in the prediction of 1-year bleeding events in patients with CAD treated with various antithrombotic therapies.

Reduction in thrombogenic activity and thrombocytopenia after transcatheter aortic valve implantation - The ATTRACTIVE-TTAS study

Introduction

Bleeding complications after transcatheter aortic valve implantation (TAVI) is a major problem in clinical practice. However, there is few information on thrombogenicity after TAVI. The aim of this study was to establish a monitoring of total thrombogenicity in perioperative TAVI using the Total Thrombus-formation Analysis System (T-TAS), a microchip-based flow chamber system for analysis of thrombus formation under flow condition.

Methods

Twenty-three patients with severe aortic stenosis who underwent TAVI between August 2017 and March 2018 at Kumamoto university hospital were enrolled. After exclusion, data of 21 patients were analyzed. Blood samples were obtained before, 2, 7, and 30 days after TAVI. Thrombogenicity were assessed by the T-TAS to compute the area under the curve (AUC) (AR₁₀-AUC₃₀) in the AR chip. We also measured platelet count, high-molecular-weight von Willebrand factor (HMW-vWF) multimers, and plasma thrombopoietin. Computational fluid dynamics (CFD) analysis was performed to calculate the wall shear stress (WSS).

Results

The AR₁₀-AUC₃₀ levels and platelet counts were significantly lower at 2 days post-TAVI, and then increased gradually. HMW-vWF multimers, and plasma thrombopoietin, were significantly higher at 2 days post-TAVI, compared with before TAVI. CFD analysis showed that WSS of the aortic valve and posterior ascending aortic wall were significantly lower after TAVI than before-TAVI. Multivariate analysis identified max velocity measured by echocardiography, platelet count, and D-dimer as significant determinants of AR₁₀-AUC₃₀, representing total thrombogenicity.

Conclusions

Although HMW-vWF multimers improved earlier after TAVI, total thrombogenic activity evaluated by T-TAS remained relatively low followed by improvement in thrombogenic activity at 30 days after TAVI.Clinical Trial Registration: https://clinicaltrials.gov. Unique identifiers: NCT03248232.

Impact of Total Antithrombotic Effect on Bleeding Complications in Patients Receiving Multiple Antithrombotic Agents

BACKGROUND

Few reports have evaluated the total antithrombotic effect of multiple antithrombotic agents. Methods and Results: Thrombus formation was evaluated with the Total Thrombus-formation Analysis System (T-TAS^®) using 2 types of microchips in 145 patients with stable coronary artery disease receiving oral anticoagulants plus single- or dual-antiplatelet therapy. The PL-chip coated with collagen is designed for analysis of the platelet thrombus formation process under shear stress condition (18 µL/min). The AR-chip coated with collagen and tissue thromboplastin is designed for analysis of the fibrin-rich platelet thrombus formation process under shear stress condition (4 µL/min). The results were expressed as an area under the flow pressure curve (PL₁₈-AUC₁₀and AR₄-AUC₃₀, respectively). Bleeding events occurred in 43 patients during a 22-month follow-up. AR₄-AUC₃₀was significantly lower in patients with bleeding events than in those without (584 [96-993] vs. 1,028 [756-1,252], P=0.0003). Multivariate logistic regression analysis identified AR₄-AUC₃₀(odds ratio 3.18) as a significant predictor of bleeding events, in addition to baseline anemia and usage of the standard dose of direct oral anticoagulants. However, PL₁₈-AUC₁₀was not significantly related to bleeding events.

CONCLUSIONS

A lower AR₄-AUC₃₀level was associated with increasing risk of subsequent bleeding complications in patients with stable coronary artery disease who received multiple antithrombotic agents.

Preclinical Development of a vWF Aptamer to Limit Thrombosis and Engender Arterial Recanalization of Occluded Vessels

Endothelial surface and circulating glycoprotein von Willebrand factor (vWF) regulates platelet adhesion and is associated with thrombotic diseases, including ischemic stroke, myocardial infarction, and peripheral vascular disease. Thrombosis, as manifested in these diseases, is the leading cause of disability and death in the western world. Current parenteral antithrombotic and thrombolytic agents used to treat these conditions are limited by a short therapeutic window, irreversibility, and major risk of hemorrhage. To overcome these limitations, we developed a novel anti-vWF aptamer, called DTRI-031, that selectively binds and inhibits vWF-mediated platelet adhesion and arterial thrombosis while enabling rapid reversal of this antiplatelet activity by an antidote oligonucleotide (AO). Aptamer DTRI-031 exerts dose-dependent inhibition of platelet aggregation and thrombosis in whole blood and mice, respectively. Moreover, DTRI-031 can achieve potent vascular recanalization of platelet-rich thrombotic occlusions in murine and canine carotid arteries. Finally, DTRI-031 activity is rapidly (<5 min) and completely reversed by AO administration in a murine saphenous vein hemorrhage model, and murine toxicology studies indicate the aptamer is well tolerated. These findings suggest that targeting vWF with an antidote-controllable aptamer potentially represents an effective and safer treatment for thrombosis patients having platelet-rich arterial occlusions in the brain, heart, or periphery.

Vascular Nitric Oxide-Superoxide Balance and Thrombus Formation after Acute Exercise

INTRODUCTION

An acute bout of strenuous exercise in humans results in transient impairment of nitric oxide (NO)-dependent function, but it remains unknown whether this phenomenon is associated with increased risk of thrombotic events after exercise. This study aimed to evaluate effects of a single bout of exhaustive running in mice on the balance of vascular NO/reactive oxygen species production, and on thrombogenicity.

METHODS

At different time points (0, 2, and 4 h) after exercise and in sedentary C57BL/6 mice, the production of NO and superoxide (O2) in aorta was measured by electron paramagnetic resonance spin trapping and by dihydroethidium/high-performance liquid chromatography-based method, respectively, whereas collagen-induced thrombus formation was analyzed in a microchip-based flow-chamber system (total thrombus-formation analysis system). We also measured pre- and postexercise plasma concentration of nitrite/nitrate and 6-keto-PGF1α.

RESULTS

An acute bout of exhaustive running in mice resulted in decreased production of NO and increased production of O2 in aorta, with maximum changes 2 h after completion of exercise when compared with sedentary mice. However, platelet thrombus formation was not changed by exercise as evidenced by unaltered time to start of thrombus formation, capillary occlusion time, and total thrombogenicity (area under the flow pressure curve) as measured in a flow-chamber system. Strenuous exercise increased the plasma concentration of nitrite but did not affect nitrate and 6-keto-PGF1α concentrations.

CONCLUSION

An acute bout of strenuous exercise in mice reduced NO and in parallel increased O2 production in aorta. This response was most pronounced 2 h after exercise. Surprisingly, the reduced NO and increased O2 production in mice after exercise did not result in increased platelet-dependent thrombogenicity. These results show that transient reduction in NO bioavailability does not modify thromboresistance in healthy mice after exercise.

Inhibitory mechanisms of very low-dose rivaroxaban in non-ST-elevation myocardial infarction

Very low-dose (VLD) factor Xa (FXa) inhibition, in combination with acetylsalicylic acid (ASA) and clopidogrel, is associated with improved outcomes in patients with acute coronary syndrome (ACS) with a tolerable bleeding risk profile. To date, there are no data documenting platelet inhibition and the anticoagulatory effects of VLD FXa inhibition on top of guideline-adherent dual-antiplatelet therapy (DAPT) in patients with ACS. Patients with non-ST-elevation myocardial infarction (NSTEMI) receiving oral DAPT (ASA + clopidogrel, n = 20; or ASA + ticagrelor, n = 20) were prospectively enrolled in a nonrandomized study. Coagulation- and platelet-dependent thrombin generation (TG), measured by means of the calibrated automated thrombogram, were significantly decreased after in vitro and in vivo addition of rivaroxaban. As shown by a total thrombus-formation analysis approach, rivaroxaban treatment led to a significantly decreased coagulation-dependent (AR-chip) thrombus formation in patients treated with ASA plus P2Y₁₂ inhibitor (clopidogrel/ticagrelor), whereas the pure platelet-dependent (PL-chip) thrombus formation was not affected at all. Adjunctive rivaroxaban therapy was not associated with significant differences in platelet aggregation assessed by light-transmission aggregometry (LTA). Nevertheless, according to fluorescence-activated cell sorter analysis, VLD rivaroxaban treatment resulted in a significantly reduced expression of platelet HMGB-1, whereas P-selectin exposure was not affected. Furthermore, an enhanced effect of rivaroxaban on total thrombus formation and TG was observed in particular in clopidogrel nonresponder patients defined as adenosine 5'-diphosphate-induced LTA ≥40%. VLD rivaroxaban reduces thrombus formation and platelet-dependent TG in patients with ACS receiving DAPT, which can be of potential ischemic benefit. This trial was registered at www.clinicaltrials.gov as #NCT01417884.

In vitro studies show synergistic effects of a procoagulant bispecific antibody and bypassing agents

Essentials Patients with hemophilia A and inhibitors receiving emicizumab experience breakthrough bleeding. Safety concerns may exist when combining emicizumab with bypassing agents. Combined bypassing agent and bispecific antibody increased thrombin generation up to 17-fold. Thrombotic effects should be considered when combining emicizumab with plasma bypassing agent.

SUMMARY

Background Investigational non-factor products such as emicizumab offer a treatment option for patients with hemophilia and inhibitors. However, their mechanism of action raises questions regarding safety when they are combined with treatments for breakthrough bleeding. Objectives To evaluate in vitro thrombin generation (TG) and clot formation for combinations of activated prothrombin complex concentrate (aPCC), recombinant activated factor VII (rFVIIa), and a sequence-identical analog of emicizumab (SIA). Methods Therapeutic concentrations of SIA (20-600 nm) alone or with aPCC (0.05-1 U mL-1 ), isolated aPCC components or rFVIIa (0.88-5.25 μg mL-1 ) were tested for TG and compared with reference ranges for healthy donor plasma. Coagulation of FVIII-inhibited blood was determined with a widely established method, i.e. rotational thromboelastometry (ROTEM), and confirmed with the Total Thrombus-formation Analysis System. Results and conclusions SIA (600 nm) or aPCC (0.5 U mL-1 ) alone resulted in peak thrombin levels of 21.4 nm and 38.6 nm, respectively, both of which are lower than normal (83.7 ± 29.8 nm). SIA plus aPCC (0.5 U mL-1 ) increased the peak thrombin level 17-fold over SIA alone, exceeding the reference plasma value by 4.2-fold. This hypercoagulable effect occurred with 600 nmSIA combined with as little as 0.25 U mL-1 aPCC, confirmed by ROTEM. FIX was the main driver for enhanced TG. SIA plus rFVIIa (1.75 μg mL-1 ) induced a 1.8-fold increase in the peak thrombin level in platelet-rich plasma, but it did not reach the normal range. These in vitro experiments demonstrate excessive TG after administration of a combination of aPCC and SIA at clinically relevant doses. Careful judgement may be required when breakthrough bleeding is treated in patients receiving emicizumab.

Direct Oral Anticoagulants Form Thrombus Different From Warfarin in a Microchip Flow Chamber System

Direct oral anticoagulants (DOACs) have low risk of intracranial hemorrhage compared to warfarin. We sought to clarify the different mechanisms responsible for suppression of bleeding events using the Total Thrombus-formation Analysis System (T-TAS), a flow-microchip chamber with thrombogenic surfaces. Blood samples were obtained at Off- and On-anticoagulant (trough) from 120 consecutive patients with atrial fibrillation (warfarin; n = 29, dabigatran; n = 19, rivaroxaban; n = 47, apixaban; n = 25), which were used for T-TAS to compute the area under the curve (AUC) (AR₁₀-AUC₃₀) in the AR chip, and to measure plasma concentrations of DOACs at On-anticoagulant. In addition, the two-dimensional area covered by thrombi (%) in the capillary was analyzed every 3 minutes after sample applications. The AR₁₀-AUC₃₀ correlated weakly and negatively with plasma concentrations of DOACs, and the levels at On-anticoagulant were lower in all groups than at Off-anticoagulant. AR₁₀-AUC₃₀ levels at Off- and On-anticoagulant were identical among the groups. The thrombi areas in early phase were significantly larger in rivaroxaban and apixaban than warfarin and dabigatran groups. The findings suggested that visual analysis of the AR-chip can identify the differential inhibitory patterns of warfarin and DOACs on thrombus formation under flow condition.

Total Thrombus-formation Analysis System Predicts Periprocedural Bleeding Events in Patients With Coronary Artery Disease Undergoing Percutaneous Coronary Intervention

BACKGROUND

Periprocedural bleeding events are common after percutaneous coronary intervention. We evaluated the association of periprocedural bleeding events with thrombogenicity, which was measured quantitatively by the Total Thrombus-formation Analysis System equipped with microchips and thrombogenic surfaces (collagen, platelet chip [PL]; collagen plus tissue factor, atheroma chip [AR]).

METHODS AND RESULTS

Between August 2013 and March 2016, 313 consecutive patients with coronary artery disease undergoing elective percutaneous coronary intervention were enrolled. They were divided into those with or without periprocedural bleeding events. We determined the bleeding events as composites of major bleeding events defined by the International Society on Thrombosis and Hemostasis and minor bleeding events (eg, minor hematoma, arteriovenous shunt and pseudoaneurysm). Blood samples obtained at percutaneous coronary intervention were analyzed for thrombus formation area under the curve (PL₂₄-AUC₁₀ for PL chip; AR₁₀-AUC₃₀ for AR chip) by the Total Thrombus-formation Analysis System and P2Y12 reaction unit by the VerifyNow system. Periprocedural bleeding events occurred in 37 patients. PL₂₄-AUC₁₀ levels were significantly lower in patients with such events than those without (P=0.002). Multiple logistic regression analyses showed association between low PL₂₄-AUC₁₀ levels and periprocedural bleeding events (odds ratio, 2.71 [1.22-5.99]; P=0.01) and association between PL₂₄-AUC₁₀ and periprocedural bleeding events in 176 patients of the femoral approach group (odds ratio, 2.88 [1.11-7.49]; P=0.03). However, PL₂₄-AUC₁₀ levels in 127 patients of the radial approach group were not significantly different in patients with or without periprocedural bleeding events.

CONCLUSIONS

PL₂₄-AUC₁₀ measured by the Total Thrombus-formation Analysis System is a potentially useful predictor of periprocedural bleeding events in coronary artery disease patients undergoing elective percutaneous coronary intervention.