Monitoring platelet glycoprotein IIb/IIIa-fibrin interaction with tissue factor-activated thromboelastography

Utility of thromboelastography with platelet mapping (TEG-PM) for monitoring platelet transfusion in qualitative platelet disorders

Patients with pathogenic variants in RASGRP2 (inherited platelet disorder (IPD)-18) have normal platelet counts but show impaired platelet aggregation due to diminished activation of αIIbβ3 integrin. This defect results in moderate to severe bleeding episodes, especially following surgical procedures, which require patients to be transfused with platelets and/or pro-hemostatic agents. We recently demonstrated that the hemostatic efficacy of transfused platelets is limited by dysfunctional endogenous platelets in a mouse model of IPD-18 ( Rasgrp2 -/- mice), as dysfunctional platelets were recruited to the forming hemostatic plug but did not participate in clot contraction. Consequently, higher amounts of transfused platelets were required to outcompete these dysfunctional cells and to reverse bleeding. We here studied the usefulness of thromboelastography with platelet mapping (TEG-PM), a method to evaluate platelet-dependent clot contraction, for ex vivo monitoring of the hemostatic potential in Rasgrp2 -/- mice transfused with various amounts of wild-type (WT) platelets. Rasgrp2 -/- whole blood samples did not contract in TEG-PM, consistent with a critical role of this protein in αIIbβ3 activation. Addition of WT platelets improved TEG parameters (K time, α-angle, MA) in a ratio dependent manner, consistent with our recent in vivo studies showing impaired hemostasis at a 5:1, but not at a 2:1 ratio of mutant to WT platelets. Interestingly, K and α values were identified as better predictors of transfusion efficacy than MA, the most platelet-dependent TEG parameter. In conclusion, this proof-of-concept study supports the use of TEG-PM to monitor platelet transfusion ratios and hemostatic potential in IPD-18 and potentially other platelet disorders.

Protease-activated receptors and glycoprotein VI cooperatively drive the platelet component in thromboelastography

BACKGROUND

Thromboelastography (TEG) is used for real-time determination of hemostatic status in patients with acute risk of bleeding. Thrombin is thought to drive clotting in TEG through generation of polymerized fibrin and activation of platelets through protease-activated receptors (PARs). However, the specific role of platelet agonist receptors and signaling in TEG has not been reported.

OBJECTIVES

Here, we investigated the specific receptors and signaling pathways required for platelet function in TEG using genetic and pharmacologic inhibition of platelet proteins in mouse and human blood samples.

METHODS

Clotting parameters (R time, α-angle [α], and maximum amplitude [MA]), were determined in recalcified, kaolin-triggered citrated blood samples using a TEG 5000 analyzer.

RESULTS

We confirmed the requirement of platelets, platelet contraction, and αIIbβ3 integrin function for normal α and MA. Loss of the integrin adaptor Talin1 in megakaryocytes/platelets (Talin1mKO) also reduced α and MA, but only minimal defects were observed in samples from mice lacking Rap1 GTPase signaling. PAR4mKO samples showed impaired α but normal MA. However, impaired TEG traces similar to those in platelet-depleted samples were observed with samples from PAR4mKO mice depleted of glycoprotein VI on platelets or with addition of a Syk inhibitor. We reproduced these results in human blood with combined inhibition of PAR1, PAR4, and Syk.

CONCLUSION

Our results demonstrate that standard TEG is not sensitive to platelet signaling pathways critical for integrin inside-out activation and platelet hemostatic function. Furthermore, we provide the first evidence that PARs and glycoprotein VI play redundant roles in platelet-mediated clot contraction in TEG.

Coronary Revascularization in Patients With Cancer

Purpose of review

The treatment of coronary artery disease (CAD) in cancer patients is an evolving landscape. Recent data emphasizes the importance of aggressive management of cardiovascular risk factors and diseases in improving cardiovascular health in this unique group of patients regardless of cancer type or stage.

Recent findings

Novel cancer therapeutics such as immune therapies and proteasome inhibitors have been associated with CAD. Recent stent technologies may safely allow for shorter duration (< 6 months) of dual antiplatelet therapy post-percutaneous coronary interventions. Intracoronary imaging may be useful in the decision making process in terms of stent positioning and healing.

Summary

Large registry studies have partially filled a gap left by the lack of randomized controlled trials in the treatment of CAD in cancer patients. Cardio-oncology is gaining traction as a major sub-specialty in the cardiology field given the release of the first European Society of Cardiology - Cardio-oncology guidelines in 2022.

Prognostic Factors and Overall Survival After Pericardiocentesis in Patients With Cancer and Thrombocytopenia

Background: Pericardiocentesis is an important diagnostic and therapeutic tool for cancer-associated pericardial effusion. Limited safety and outcomes data exists regarding the management of malignancy-related pericardial effusion in patients with thrombocytopenia.

Objectives: Our study aimed to analyze prognostic factors and overall survival (OS) after pericardiocentesis in thrombocytopenic cancer patients.

Methods and Results: A retrospective review of 136 thrombocytopenic cancer patients who underwent primary percutaneous pericardiocentesis was performed. Degree of thrombocytopenia was classified by platelet count recorded on day of pericardiocentesis: 75–149 × 10³ cells/μL (41%); 50–74 × 10³ cells/μL (10%); 25–49 × 10³ cells/μL (24%); <25 × 10³ cells/μL (25%). Median OS was 2.6 months and median follow-up was 37.4 months. Kaplan-Meier survival analysis showed significant OS differences among thrombocytopenia severity groups (p = 0.023), and worse OS with platelets <100 vs. ≥100 × 10³ cells/μL (p = 0.031). By univariate analysis, thrombocytopenia severity was associated with increased risk of death (HR 0.993; 95% CI 0.989–0.997; p = 0.002). Poor prognostic factors for OS were advanced cancer, malignant effusion, elevated international normalized ratio (INR), quantity of platelet transfusions, and platelet transfusion resistance. However, thrombocytopenia severity became insignificant for OS (p = 0.802), after adjusting for advanced cancer and INR.

Conclusions: For patients with malignancy-related large pericardial effusion and thrombocytopenia, pericardiocentesis is a feasible intervention and should be considered due to low complication rates. There is no absolute contraindication to pericardiocentesis in case of hemodynamic instability, even with severe thrombocytopenia.

Fibrinogen Diagnostics in Major Hemorrhage

Fibrinogen is one of the first factors to fall to critically low levels in the blood in many coagulopathic events. Patients with hypofibrinogenemia are at a significantly greater risk of major hemorrhage and death. The rapid replacement of fibrinogen early on in hypofibrinogenemia may significantly improve outcomes for patients. Fibrinogen is present at concentrations between 2 and 4 g/L in the plasma of healthy people. However, hypofibrinogenemia is diagnosed when the fibrinogen level drops below 1.5-2 g/L. This review analyses different types of fibrinogen assays that can be used for diagnosing hypofibrinogenemia. The scientific mechanisms and limitations behind these tests are then presented. Additionally, the current state of clinical major hemorrhage protocols (MHPs) is presented and the structure, function and physiological role of fibrinogen is summarized.

Identifying Hemostatic Thresholds in Cancer Patients Undergoing Coronary Angiography Based on Platelet Count and Thromboelastography

Objectives: To evaluate the role of platelet count and thromboelastogram (TEG) in the treatment of thrombocytopenic cancer patients with suspected coronary artery disease (CAD).

Background: Cancer patients with CAD and thrombocytopenia are often treated non-invasively (i.e., without coronary angiography when clinically indicated) due to perceived high risk of bleeding. We sought to evaluate coagulability based on TEG and determine if platelet count and TEG could predict bleeding risk/mortality among cancer patients undergoing coronary angiography (CA).

Methods: Baseline demographics, platelet count, and TEG parameters were recorded among cancer patients that underwent CA and had a concomitant TEG. Logistic regression and univariate proportional hazards regression analysis were performed to determine the impact of platelet count and coagulability on 24-month overall survival (OS).

Results: All patients with platelet count <20,000/mm³ and nearly all patients with platelet count 20,000–49,000/mm³ were hypocoagulable based on TEG results. In contrast, nearly all patients with platelet counts of 50,000–99,999/mm³ had normal TEG results and OS similar to those with platelet counts of ≥100,000/mm³. Coagulability based on TEG was not associated with OS. However, a platelet count of <50,000/mm³ was associated with worse 24-month OS (hazard ratio = 2.76; p = 0.0072) when compared with a platelet count of ≥100,000/mm³. No major bleeding complications were observed in all groups.

Conclusion: The majority of cancer patients with platelet counts of <50,000/mm³ were hypocoagulable based on TEG and had worse OS at 24 months. The relatively normal TEGs in the >50,000/mm³ groups, as well as the improved survival, suggest that with appropriate clinical indication and risk/benefit assessment, a cut-off of 50,000/mm³ platelets can be considered for CA in cancer patients.

Prospective Longitudinal Evaluation of Coagulation with Novel Thromboelastography Technology in Patients After Subarachnoid Hemorrhage: A Pilot Study

BACKGROUND

There is limited knowledge of whether hypercoagulability is present after subarachnoid hemorrhage (SAH) or about its timing of onset, duration, and severity. To conduct a pilot new-generation thromboelastography (TEG) technology (TEG6s)-based and conventional coagulation test-supported longitudinal assessment of coagulation in patients with SAH.

METHODS

We prospectively enrolled patients with nontraumatic SAH on admission from May 2015 to May 2016. We performed TEG6s measurements and conventional coagulation tests on days 1, 2, 3, 5, 7, 10, and 14 and compared them with TEG6s parameters in healthy volunteers.

RESULTS

We studied 14 patients and 72 TEG6s measurements. Of these patients, 10 (71.4%) were admitted to the intensive care unit. Mean age was 57.5 (±14.5) years, Acute Physiology and Chronic Health Evaluation III score 58.2 (±26.6), length of hospital stay was 23 (±11.7) days, and mortality was 14.3%. At baseline, conventional coagulation tests were within normal range. However, TEG6s parameters already showed increased coagulability. Thereafter, alpha angle, reaction time, functional fibrinogen level, and maximum amplitude rapidly and significantly increased (P < 0.01) compared with healthy controls. Ten (71.4%) patients demonstrated a >20% increase in coagulability based on TEG6s parameters from their baseline. Moreover, TEG6s hypercoagulability peaked at day 10 and only showed an initial partial decline towards normal by day 14. Similarly, platelet counts and fibrinogen levels increased over this period (P < 0.01) CONCLUSIONS: Using TEG6s technology, we found significant and progressive hypercoagulability in 70% of patients, with an early dominant contribution from hyperfibrinogenemia and increased fibrin formation and partial contribution from thrombocytosis, beginning on the first day, increasing to peak values by day 10, and then partly declining toward normal by day 14.

Effects of preoperative plasma exchange therapy with albumin replacement fluid on blood coagulation in patients undergoing ABO-incompatible living-donor kidney transplantation using rotational thromboelastometry

BACKGROUND

ABO-incompatible living-donor kidney transplantation (LDKT) requires immunotherapy and plasma exchange therapy (PEX). PEX with albumin replacement fluid reportedly decreases fibrinogen levels. However, no reports have described the effects of PEX with albumin replacement fluid on blood coagulation parameters and blood loss during the perioperative period. Therefore, we investigated the effects of preoperative PEX on blood coagulation parameters and blood loss during the perioperative period in patients undergoing ABO-incompatible LDKT as measured by rotational thromboelastometry (ROTEM®).

METHODS

Twenty-eight patients undergoing LDKT were divided into the PEX group (ABO incompatible with PEX, n = 13) and non-PEX group (ABO compatible without PEX, n = 15). ROTEM® parameters, standard laboratory test parameters, bleeding volume, and transfusion volume were compared between PEX and non-PEX group. MCE_platelet, which represents platelet contribution to clot strength and where "MCE" stands for maximum clot elasticity, was calculated from the difference in MCE between EXTEM and FIBTEM.

RESULTS

The bleeding volume during surgery and the intensive care unit (ICU) stay was significantly higher in the PEX than non-PEX group (p < 0.01). Maximum clot firmness (MCF) of EXTEM (MCF_EXTEM), MCF_FIBTEM, and MCE_platelet was significantly lower in the PEX than non-PEX group (p < 0.01). In the PEX group, the bleeding volume during surgery was very strongly correlated with the baseline MCF_EXTEM and MCE_platelet, and the bleeding volume during the ICU stay was strongly correlated with the postoperative MCF_EXTEM and MCE_platelet.

CONCLUSIONS

These results suggest that the increased blood loss in the PEX group during surgery and the ICU stay was associated with decreased platelet contribution to clot strength as measured by ROTEM®.

TRIAL REGISTRATION

UMIN-Clinical Trial Registry UMIN000018355 . Registered 21 July 2015.

Prediction of Ischemic Events after Percutaneous Coronary Intervention: Thrombelastography Profiles and Factor XIIIa Activity

Background  High plasma fibrin clot strength (MA) measured by thrombelastography (TEG) is associated with increased risk of cardiac events after percutaneous coronary interventions (PCIs). Factor XIIIa (FXIIIa) cross-links soluble fibrin, shortens clot formation time (TEG-K), and increases final clot strength (MA).

Methods  We analyzed platelet-poor plasma from patients with previous PCI. Kaolin-activated TEG (R, K, MA) in citrate platelet-poor plasma and FXIIIa were measured ( n  = 257). Combined primary endpoint was defined as recurrent myocardial infarction (MI) or cardiovascular death (CVD). Relationship of FXIIIa and TEG measurements on cardiac risk was explored.

Results  FXIIIa correlated with TEG-MA ( p  = 0.002) and inversely with TEG-K ( p  < 0.001). High MA (≥35.35 mm; p  = 0.001), low K (<1.15 min; p  = 0.038), and elevated FXIIIa (≥83.51%; p  = 0.011) were associated with increased risk of CVD or MI. Inclusion of FXIIIa activity and low TEG-K in risk scores did not improve risk prediction as compared with high TEG-MA alone.

Conclusion  FXIIIa is associated with higher plasma TEG-MA and low TEG-K. High FXIIIa activity is associated with a modest increase in cardiovascular risk after PCI, but is less sensitive and specific than TEG-MA. Addition of FXIIIa does not provide additional risk stratification beyond risk associated with high fibrin clot strength phenotype measured by TEG.

The Role of Platelet Activation and Inflammation in Early Brain Injury Following Subarachnoid Hemorrhage

BACKGROUND

Early brain injury (EBI) following aneurysmal subarachnoid hemorrhage (SAH) is an important predictor of poor functional outcome, yet the underlying mechanism is not well understood. Animal studies suggest that platelet activation and inflammation with subsequent microthrombosis and ischemia may be a mechanism of EBI.

METHODS

A prospective, hypothesis-driven study of spontaneous, SAH patients and controls was conducted. Platelet activation [thromboelastography maximum amplitude (MA)] and inflammation [C-reactive protein (CRP)] were measured serially over time during the first 72 h following SAH onset. Platelet activation and inflammatory markers were compared between controls and SAH patients with mild [Hunt-Hess (HH) 1-3] versus severe (HH 4-5) EBI. The association of these biomarkers with 3-month functional outcomes was evaluated.

RESULTS

We enrolled 127 patients (106 SAH; 21 controls). Platelet activation and CRP increased incrementally with worse EBI/HH grade, and both increased over 72 h (all P < 0.01). Both were higher in severe versus mild EBI (MA 68.9 vs. 64.8 mm, P = 0.001; CRP 12.5 vs. 1.5 mg/L, P = 0.003) and compared to controls (both P < 0.003). Patients with delayed cerebral ischemia (DCI) had more platelet activation (66.6 vs. 64.9 in those without DCI, P = 0.02) within 72 h of ictus. At 3 months, death or severe disability was more likely with higher levels of platelet activation (mRS4-6 OR 1.18, 95 % CI 1.05-1.32, P = 0.007) and CRP (mRS4-6 OR 1.02, 95 % CI 1.00-1.03, P = 0.041).

CONCLUSIONS

Platelet activation and inflammation occur acutely after SAH and are associated with worse EBI, DCI and poor 3-month functional outcomes. These markers may provide insight into the mechanism of EBI following SAH.

Adaptation of global hemostasis to therapeutic hypothermia in patients with out-of-hospital cardiac arrest: Thromboelastography study

BACKGROUND

The use of mild therapeutic hypothermia (MTH) in patients after out-of-hospital cardiac arrest (OHCA) who are undergoing primary percutaneous coronary intervention (pPCI) can protect patients from thromboembolic complications. The aim of the study was to evaluate the adaptive mecha- nisms of the coagulation system in MTH-treated comatose OHCA survivors.

METHODS

Twenty one comatose OHCA survivors with acute coronary syndrome undergoing imme- diate pPCI were treated with MTH. Quantitative and qualitative analyses of physical clot properties were performed using thromboelastography (TEG). Two analysis time points were proposed: 1) during MTH with in vitro rewarming conditions (37°C) and 2) after restoration of normothermia (NT) under normal (37°C) and in vitro cooling conditions (32°C).

RESULTS

During MTH compared to NT, reaction time (R) was lengthened, clot kinetic parameter (a) was significantly reduced, but no effect on clot strength (MA) was observed. Finally, the coagulation index (CI) was significantly reduced with clot fibrinolysis attenuated during MTH. The clot lysis time (CLT) was shortened, and clot stability (LY60) was lower compared with those values during NT. In vitro cooling generally influenced clot kinetics and reduced clot stability after treatment.

CONCLUSIONS

Thromboelastography is a useful method for evaluation of coagulation system dysfunc- tion in OHCA survivors undergoing MTH. Coagulation impairment in hypothermia was associated with a reduced rate of clot formation, increased weakness of clot strength, and disturbances of fibrinoly- sis. Blood sample analyses performed at 32°C during MTH, instead of the standard 37°C, seems to enhance the accuracy of the evaluation of coagulation impairment in hypothermia.

New-Generation Thromboelastography: Comprehensive Evaluation of Citrated and Heparinized Blood Sample Storage Effect on Clot-Forming Variables

Context.—

Thromboelastography (TEG) is a whole blood, real-time analyzer measuring the viscoelastic properties of the hemostasis process and allowing for individualized goal-directed therapy. However, routine use of TEG requires validation of sample storage effect on clot parameters.

Objectives.—

To establish the minimum time required for equilibration time and the maximum time for sample storage for all commercially available TEG tests for the new-generation TEG 6s and to determine how those times compare with the older generation TEG 5000.

Design.—

Citrated and heparinized whole blood samples obtained from 20 healthy donors were analyzed for clot parameters at multiple time points for both the TEG 6s and the TEG 5000. Samples were activated with the citrated multichannel cartridge or the platelet-mapping cartridge in the TEG 6s or with recalcified kaolin in the TEG 5000.

Results.—

All blood samples yielded TEG parameter results within reference ranges and had a tendency toward hypercoagulable profiles with increased storage time. Sample storage resulted in increased platelet inhibition with significant differences at 4 hours in the platelet-mapping cartridge (arachidonic acid percentage of inhibition, P = .002; adenosine diphosphate percentage of inhibition, P = .02).

Conclusions.—

For nonemergent cases or in a central laboratory setting, all tests provided reliable results for up to 4 hours in the citrated multichannel cartridge and for 3 hours for platelet function information in the platelet-mapping cartridge. In emergent/urgent situations in which the sample needs to be run immediately, RapidTEG and functional fibrinogen tests may be preferred.

Platelet Function and Cardiopulmonary Bypass

Cardiopulmonary bypass (CPB) is a nonphysiologic state that has many detrimental effects on a patient's hemostatic integrity. Exposure to the extracorporeal circuit and subsequent activation of the coagulation and fibrinolytic systems are factors that contribute to morbidity and mortality in cardiac surgical patients. These effects can be prevented in part or appropriately treated if practitioners understand the basic mecha nisms. This article reviews the effects of CPB on platelet function, the relationship of platelet function to post operative bleeding, the monitors available to measure platelet function, and the impact of antiplatelet therapy on bleeding in cardiac surgery.

Effects of gabexate mesilate on coagulopathy and organ dysfunction in rats with endotoxemia: a potential use of thrombelastography in endotoxin-induced sepsis

Sepsis and its associated multiple organ failure are related to high mortality in critical patients. Several studies have reported that gabexate mesilate, a synthetic inhibitor of trypsin-like serine protease, protects tissues/organs against injury in the models of endotoxemia. The aim of this study was to examine whether gabexate mesilate could attenuate coagulopathy and organ dysfunction in lipopolysaccharide (LPS)-induced sepsis model by using thrombelastography (TEG). LPS (7.5  mg/kg/h, intravenouly for 4  h) was administered to male adult Wistar rats. Some of the LPS rats received a continuous infusion of gabexate mesilate (10  mg/kg/h, intravenously for 8.5  h) for 30  min before the LPS administration. Variable parameters of hemodynamics, biochemistry, hemostasis and inflammatory response were measured for 6  h after the LPS infusion. TEG variables (R-time, K-time, α-angle, and maximal amplitude) were also measured. The pretreatment of LPS rats with gabexate mesilate significantly attenuated the lung, liver and kidney dysfunction, consumptive coagulopathy, the increases in serum tumor necrosis factor-α, interleukin-6, plasma thrombin-antithrombin complex and plasminogen activator inhibitor-1, and neutrophils infiltration score in lung, liver and kidney, compared with the LPS alone group. In addition, TEG parameters correlated with tissue and liver injury in the late phase of endotoxemia. In particular, a strong negative correlation between maximal amplitude at 4  h and Ln (lactate dehydrogenase) at 6  h after LPS infusion was noted (r = -0.752, P < 0.001, R = 0.566). These results indicate that beneficial effects of anticoagulants (e.g. gabexate mesilate) in endotoxemia could be monitored by TEG per se.

Can the Viscoelastic Parameter α-Angle Distinguish Fibrinogen from Platelet Deficiency and Guide Fibrinogen Supplementation?

Viscoelastic tests such as thrombelastography (TEG, Haemoscope Inc., Niles, IL) and thromboelastometry (ROTEM, Tem International GmbH, Munich, Germany), performed in whole blood, are increasingly used at the point-of-care to characterize coagulopathic states and guide hemostatic therapy. An algorithm, based on a mono-analysis (kaolin-activated assay) approach, was proposed in the TEG patent (issued in 2004) where the α-angle and the maximum amplitude parameters are used to guide fibrinogen supplementation and platelet administration, respectively. Although multiple assays for both the TEG and ROTEM devices are now available, algorithms based on TEG mono-analysis are still used in many institutions. In light of more recent findings, we discuss here the limitations and inaccuracies of the mono-analysis approach. Research shows that both α-angle and maximum amplitude parameters reflect the combined contribution of fibrinogen and platelets to clot strength. Therefore, although TEG mono-analysis is useful for identifying a coagulopathic state, it cannot be used to discriminate between fibrin/fibrinogen and/or platelet deficits, respectively. Conversely, the use of viscoelastic methods where 2 assays can be run simultaneously, one with platelet inhibitors and one without, can effectively allow for the identification of specific coagulopathic states, such as insufficient fibrin formation or an insufficient contribution of platelets to clot strength. Such information is critical for making the appropriate choice of hemostatic therapy.

Assessing the Methodology for Calculating Platelet Contribution to Clot Strength (Platelet Component) in Thromboelastometry and Thrombelastography

The viscoelastic properties of blood clot have been studied most commonly using thrombelastography (TEG) and thromboelastometry (ROTEM). ROTEM-based bleeding treatment algorithms recommend administering platelets to patients with low EXTEM clot strength (e.g., clot amplitude at 10 minutes [A10] <40 mm) once clot strength of the ROTEM® fibrin-based test (FIBTEM) is corrected. Algorithms based on TEG typically use a low value of maximum amplitude (e.g., <50 mm) as a trigger for administering platelets. However, this parameter reflects the contributions of various blood components to the clot, including platelets and fibrin/fibrinogen. The platelet component of clot strength may provide a more sensitive indication of platelet deficiency than clot amplitude from a whole blood TEG or ROTEM® assay. The platelet component of the formed clot is derived from the results of TEG/ROTEM® tests performed with and without platelet inhibition. In this article, we review the basis for why this calculation should be based on clot elasticity (e.g., the E parameter with TEG and the CE parameter with ROTEM®) as opposed to clot amplitude (e.g., the A parameter with TEG or ROTEM®). This is because clot elasticity, unlike clot amplitude, reflects the force with which the blood clot resists rotation within the device, and the relationship between clot amplitude (variable X) and clot elasticity (variable Y) is nonlinear. A specific increment of X (ΔX) will be associated with different increments of Y (ΔY), depending on the initial value of X. When calculated correctly, using clot elasticity data, the platelet component of the clot can provide a valuable insight into platelet deficiency in emergency bleeding.

Endogenous Fibrinolysis: An Important Mediator of Thrombus Formation and Cardiovascular Risk

Most acute cardiovascular events are attributable to arterial thrombosis. Plaque rupture or erosion stimulates platelet activation, aggregation, and thrombosis, whilst simultaneously activating enzymatic processes that mediate endogenous fibrinolysis to physiologically maintain vessel patency. Interplay between these pathways determines clinical outcome. If proaggregatory factors predominate, the thrombus may propagate, leading to vessel occlusion. However, if balanced by a healthy fibrinolytic system, thrombosis may not occur or cause lasting occlusion. Despite abundant evidence for the fibrinolytic system regulating thrombosis, it has been overlooked compared with platelet reactivity, partly due to a lack of techniques to measure it. We evaluate evidence for endogenous fibrinolysis in arterial thrombosis and review techniques to assess it, including biomarkers and global assays, such as thromboelastography and the Global Thrombosis Test. Global assays, simultaneously assessing proaggregatory and fibrinolytic pathways, could play a role in risk stratification and in identifying impaired fibrinolysis as a potential target for pharmacological modulation.

A Single Controlled Exposure to Secondhand Smoke May Not Alter Thrombogenesis or Trigger Platelet Activation

INTRODUCTION

Chronic secondhand smoke (SHS) exposure increases cardiovascular events, particularly acute thrombotic events. There are little human data on acute SHS exposure. The aim of this study was to determine whether a single controlled exposure of humans to SHS increased thrombogenesis.

METHODS

After 6-8 hours fast, subjects (n = 50) were exposed to constant dose SHS (particulate level of 500 μg/m(3)) for 120 minutes in a temperature-regulated and ventilated, simulated bar environment. Blood was drawn before and immediately after SHS exposure for thromboelastography (TEG) and flow cytometry. Maximum clot strength (MA) was measured using TEG and platelet leukocyte aggregates (LPA) were measured as an index of platelet activation. Anti-CD 14 antibodies were used as leukocyte markers and anti-CD 41 antibodies as platelet markers for cytometry. Data were analyzed using students' t test for paired samples.

RESULTS

There was no effect of acute exposure to SHS on platelet activation or thrombogenesis. Also, intra group (smokers [n = 19] and nonsmokers [n = 31]) comparisons of LPA and TEG parameters did not show changes with SHS exposure.

CONCLUSIONS

While there are abundant data showing enhanced thrombogenesis and platelet activation following repeated exposure to SHS, our study suggests that a single exposure does not appear to significantly alter thrombin kinetics nor result in platelet activation. The effects of SHS on thrombogenesis might be nonlinear.

Integration of acoustic radiation force and optical imaging for blood plasma clot stiffness measurement

Despite the life-preserving function blood clotting serves in the body, inadequate or excessive blood clot stiffness has been associated with life-threatening diseases such as stroke, hemorrhage, and heart attack. The relationship between blood clot stiffness and vascular diseases underscores the importance of quantifying the magnitude and kinetics of blood's transformation from a fluid to a viscoelastic solid. To measure blood plasma clot stiffness, we have developed a method that uses ultrasound acoustic radiation force (ARF) to induce micron-scaled displacements (1-500 μm) on microbeads suspended in blood plasma. The displacements were detected by optical microscopy and took place within a micro-liter sized clot region formed within a larger volume (2 mL sample) to minimize container surface effects. Modulation of the ultrasound generated acoustic radiation force allowed stiffness measurements to be made in blood plasma from before its gel point to the stage where it was a fully developed viscoelastic solid. A 0.5 wt % agarose hydrogel was 9.8-fold stiffer than the plasma (platelet-rich) clot at 1 h post-kaolin stimulus. The acoustic radiation force microbead method was sensitive to the presence of platelets and strength of coagulation stimulus. Platelet depletion reduced clot stiffness 6.9 fold relative to platelet rich plasma. The sensitivity of acoustic radiation force based stiffness assessment may allow for studying platelet regulation of both incipient and mature clot mechanical properties.

Use of Thromboelastography (TEG) for Detection of New Oral Anticoagulants

CONTEXT

The clinical introduction of new oral anticoagulants (NOACs) has stimulated the development of tests to quantify the effects of these drugs and manage complications associated with their use. Until recently, the only treatment choices for the prevention of venous thromboembolism in orthopedic surgical patients, as well as for stroke and systemic embolism in patients with atrial fibrillation, were vitamin K antagonists, antiplatelet drugs, and unfractionated and low-molecular-weight heparins. With the approval of NOACs, treatment options and consequent diagnostic challenges have expanded.

OBJECTIVE

To study the utility of thromboelastography (TEG) in monitoring and differentiating between 2 currently approved classes of NOACs, direct thrombin inhibitors (dabigatran) and factor Xa inhibitors (rivaroxaban and apixaban).

DESIGN

Blood samples from healthy volunteers were spiked with each NOAC in both the presence and absence of ecarin, and the effects on TEG were evaluated.

RESULTS

Both the kaolin test reaction time (R time) and the time to maximum rate of thrombus generation were prolonged versus control samples and demonstrated a dose response for apixaban (R time within the normal range) and dabigatran. The RapidTEG activated clotting time test allowed the creation of a dose-response curve for all 3 NOACs. In the presence of anti-Xa inhibitors, the ecarin test promoted significant shortening of kaolin R times to the hypercoagulable range, while in the presence of the direct thrombin inhibitor only small and dose-proportional R time shortening was observed.

CONCLUSIONS

The RapidTEG activated clotting time test and the kaolin test appear to be capable of detecting and monitoring NOACs. The ecarin test may be used to differentiate between Xa inhibitors and direct thrombin inhibitors. Therefore, TEG may be a valuable tool to investigate hemostasis and the effectiveness of reversal strategies for patients receiving NOACs.

Does incorporation of thromboelastography improve bleeding prediction following adult cardiac surgery?

Cardiopulmonary bypass (CPB) coagulopathy increases utilization of allogenic blood/blood products, which can negatively affect patient outcomes. Thromboelastography (TEG) is a point-of-care measurement of clot formation and fibrinolysis. We investigated whether the addition of TEG parameters to a clinically based bleeding model would improve the predictability of postoperative bleeding. A total of 439 patients’ charts were retrospectively investigated for 8-h chest tube output (CTO) postoperatively. For model 1, the variables recorded were patient age, gender, body surface area, clopidogrel use, CPB time, first post-CPB fibrinogen serum level, first post-CPB platelet count, first post-CPB international normalized ratio, the total amount of intraoperative cell saver blood transfused, and postoperative first ICU hematocrit level. Model 2 had the model 1 variables, TEG angle, and maximum amplitude. The outcome was defined as 0–8-h CTO. The predictor variables were placed into a forward stepwise regression model for continuous outcomes. Analysis of variance with adjusted R² was used to assess the goodness-of-fit of both predictive models. The predictive accuracy of the model was examined using CTO as a dichotomous variable (75th percentile, 480 ml) and receiver operating characteristic curves for both models. Advanced age, male gender, preoperative clopidogrel use for 5 days or less, greater cell saver blood utilization, and lower postoperative hematocrit levels were associated with increased 8-h CTO (P < 0.05). Adding TEG angle and maximum amplitude to model 1 did not improve CTO predictability. When TEG angle and maximum amplitude were added as predictor factors, the predictability of the bleeding model did not improve.

A time course study of acute traumatic coagulopathy prior to resuscitation: from hypercoagulation to hypocoagulation caused by hypoperfusion?

INTRODUCTION

Coagulopathy after sever injury predicts the requirements of blood products, organ failure and mortality in traumatic patients. The early onset and complexity of traumatic coagulopathy preclude the understanding the underlying mechanism. The aim of the study is to characterize the early coagulation alteration in a swine model with multi-trauma and shock.

METHODS

Twelve pigs were subjected to multi-trauma (femur fracture, laparotomy, 10 cm intestine resection and grade III injury of liver) and hemorrhaged to a mean arterial pressure (MAP) of 40 mmHg. Physiologic parameters and coagulation variables (prothrombin time (PT), international normalized ratio (INR), fibrinogen, antithrombin-III (AT-III) activity, D-dimer and thromboelastography (TEG)) were measured after instrumentation (baseline), 5 min after multi-trauma (after trauma), 10 min (early shock) and 40 min (late shock) after hemorrhage. A group of 6 instrumented pigs were used as control.

RESULTS

Multi-trauma and hemorrhage caused significant increase of base excess (BE) and lactate (p<0.05). PT shortened after multi-trauma but increased significantly at late shock (p<0.05). Fibrinogen reduced greatly after trauma and at early shock (p<0.05), while remained stable afterwards. AT-III activity decreased throughout the experiment. Reaction time (R) shortened after trauma and at early shock (both p<0.05). Maximal amplitude (MA) decreased significantly during the shock period.

CONCLUSION

After traumatic hemorrhagic shock, hypercoagulation turned into hypocoagulation in a short period, which was probably caused by hypoperfusion.

Thromboelastographic phenotypes of fibrinogen and its variants: clinical and non-clinical implications

INTRODUCTION

Thromboelastography (TEG), a widely used clinical point of care coagulation test, is poorly understood. To investigate its fibrin determinants we used normal and variant fibrinogen isolates.

MATERIALS AND METHODS

We focused mainly on the TEG maximum signal amplitude (MA), a shear modulus and clot stiffness indicator. Isolates included normal des-αC, cord, and abnormal congenital variants with amino acid substitutions or deletions that impaired fibrin polymerization. Heterophenotypic congenital isolates were from cryoprecipitate-depleted plasma owing to their more diminished clot MA than their cryoprecipitate counterparts. By colorimetric assay, the amount of fibrinogen adsorbed by untreated TEG cups was 83.5±12.4 pM/cm(2), n=18. Thrombin-induced clots were obtained at pH6.4 or 7.4, the latter containing 8mM CaCl2, and 14% afibrinogenemic plasma with and without gel-sieved platelets.

RESULTS AND CONCLUSIONS

Measured by the water droplet contact angle, >90% reduction of surface hydrophobicity by exposure of TEG cup and pin to ozone plasma decreased MA by 74%. Increasing normal fibrinogen or thrombin concentrations progressively increased MA. Platelets increased MA further ~2 fold, except for ≥10 fold for des-αC clots. Examined in the absence of platelets, MA of heterophenotypic fibrin variants averaged 21%, n=15. The results imply that essential MA determinants include hydrophobic fibrinogen/fibrin adsorption and each polymerization contact site, with substantial enhancement by platelets. Also, cryoprecipitate-harvested soluble fibrinogen/fibrin complexes contained mostly normal molecules, while cryoprecipitate-depleted plasma contained mostly variant molecules. Moreover, significantly decreased MA by fibrinogen anomalies and/or low level thrombin generation can potentially impact clinical interpretation of MA.

Discrepant fibrinolytic response in plasma and whole blood during experimental endotoxemia in healthy volunteers

Background

Sepsis induces early activation of coagulation and fibrinolysis followed by late fibrinolytic shutdown and progressive endothelial damage. The aim of the present study was to investigate and compare the functional hemostatic response in whole blood and plasma during experimental human endotoxemia by the platelet function analyzer, Multiplate and by standard and modified thrombelastography (TEG).

Methods

Prospective physiologic study of nine healthy male volunteers undergoing endotoxemia by means of a 4-hour infusion of E. coli lipopolysaccharide (LPS, 0.5 ng/kg/hour), with blood sampled at baseline and at 4 h and 6 h. Physiological and standard biochemical data and coagulation tests, TEG (whole blood: TEG, heparinase-TEG, Functional Fibrinogen; plasma: TEG±tissue-type plasminogen activator (tPA)) and Multiplate (TRAPtest, ADPtest, ASPItest, COLtest) were recorded. Mixed models with Tukey post hoc tests and correlations were applied.

Results

Endotoxemia induced acute SIRS with increased HR, temperature, WBC, CRP and procalcitonin and decreased blood pressure. It also induced a hemostatic response with platelet consumption and reduced APTT while INR increased (all p<0.05). Platelet aggregation decreased (all tests, p<0.05), whereas TEG whole blood clot firmness increased (G, p = 0.05). Furthermore, during endotoxemia (4 h), whole blood fibrinolysis increased (clot lysis time (CLT), p<0.001) and Functional Fibrinogen clot strength decreased (p = 0.049). After endotoxemia (6 h), whole blood fibrinolysis was reduced (CLT, p<0.05). In contrast to findings in whole blood, the plasma fibrin clot became progressively more resistant towards tPA-induced fibrinolysis at both 4 h and 6 h (p<0.001).

Conclusions

Endotoxemia induced a hemostatic response with reduced primary but enhanced secondary hemostasis, enhanced early fibrinolysis and fibrinogen consumption followed by downregulation of fibrinolysis, with a discrepant fibrinolytic response in plasma and whole blood. The finding that blood cells are critically involved in the vasculo-fibrinolytic response to acute inflammation is important given that disturbances in the vascular system contribute significantly to morbidity and mortality in critically ill patients.

Comparing citrated native, kaolin-activated, and tissue factor–activated samples and determining intraindividual variability for feline thromboelastography

Thromboelastography (TEG) is a point-of-care whole blood test of hemostasis. While TEG is becoming more widely used in veterinary medicine, few studies describe the use of TEG in cats. The objectives of the current study were to: 1) document the range of TEG variables produced in healthy cats using 3 sample types (citrated native, kaolin-activated, and tissue factor–activated), and 2) determine if there was a significant difference between 2 separate samples obtained from individual healthy cats on the same day. Jugular venipuncture was performed in 20 cats, and citrated blood collected for TEG. TEG analysis was performed on citrated native, kaolin-activated, and tissue factor–activated blood for each sample. Two hours later, the procedure was repeated from the opposite jugular vein, yielding a total of 120 analyses. Reaction time ( R), alpha angle (α), kappa value (κ), and maximum amplitude (MA) were recorded from each tracing. No significant differences were found between TEG tracings from the first and second venipuncture samples. Significant differences were found between sample types for R, α, κ, and MA. Means for citrated native/kaolin-activated/tissue factor–activated methods were R = 4.1/3.7/0.6 min; κ = 2.5/1.8/2.2 min; α = 59.9/65.1/70.4 degrees; MA = 47.4/49.9/44.7 mm. A limitation of this study was the small number of cats used. Thromboelastography analysis may be a suitable method of evaluating hemostasis in cats.

The acute coagulopathy of trauma is due to impaired initial thrombin generation but not clot formation or clot strength

BACKGROUND

Acute coagulopathy of trauma (ACOT) has been described as a very early hypocoagulable state, but the mechanism remains controversial. One proposed mechanism is tissue hypoperfusion leading to protein C activation, with subsequent inhibition of Factors V and VIII. Variability in trauma has impeded the use of clinical data towards the elucidation of the mechanisms of ACOT, but thrombelastography (TEG) may provide insight by assessing hemostatic function from initial thrombin activation to fibrinolysis. We hypothesized that in a controlled animal model of trauma/hemorrhagic shock, clotting factor dysfunction is the predominant mechanism in early ACOT.

METHODS

Rats anesthetized by inhaled isoflurane (n = 6) underwent laparotomy, and hemorrhage was induced to maintain a MAP of 35 mm Hg for 30 min. Rats were then resuscitated with twice their shed blood volume in normal saline. TEG was performed at baseline, shock, and post-resuscitation periods. No heparin was given. Statistical analysis was performed by ANOVA with post-hoc Fisher's test.

RESULTS

Coagulation factor function was significantly impaired in the early stages of trauma/hemorrhagic shock. TEG R and SP-values were significantly increased from baseline to shock (P < 0.001) and from shock to post-resuscitation periods (P < 0.05). Delta (R-SP), a measure of thrombin generation, showed a significant increase (P < 0.05) from baseline to shock. No significant changes were found in K, Angle, MA, and LY30 values.

CONCLUSION

Clotting factor derangement leading to impaired thrombin generation is the principle etiology of ACOT in this model and not the dynamics of clot formation, fibrin cross-linking, clot strength/platelet function, or fibrinolysis.

The effects of cytochalasin D and abciximab on hemostasis in canine whole blood assessed by thromboelastography and the PFA-100® platelet function analyzer system

The selective inhibition of platelet function in whole blood coagulation testing may allow insights into the nature of hypercoagulability in dogs with critical illness. To determine the effects of cytochalasin D and abciximab on hemostatic parameters in canine citrated whole blood, an in-vitro study was designed using thromboelastography (TEG) and a platelet function analyzer (PFA-100®). 8 clinically healthy mixed breed dogs donated blood that was anticoagulated with 3.2% sodium citrate in a 9:1 blood-to-citrate ratio. Addition of cytochalasin D to citrated whole blood from 6 dogs at concentrations ranging from 0 µg/ml to 10 µg/ml caused a maximal reduction of TEG maximum amplitude (MA) at a concentration of 7.5 µg/ml (52.7 ± 4.3 to 14.3 ± 7.8 mm). Addition of abciximab to canine citrated whole blood at concentrations of either 20 µg/ml or 40 µg/ml did not affect the TEG tracing; however, addition of abciximab to citrated canine whole blood at concentrations of 10 µg/ml and 20 µg/ml significantly prolonged PFA-100 closure times (72.5 ± 15 to 149.2 ± 91 sec and 275.6 ± 54 sec, respectively, P < 0.04). Inhibition of canine platelet function by cytochalasin D is demonstrated by TEG, but abciximab did not change TEG tracings. Abciximab does, however, inhibit platelet aggregation under shear stress as measured by the PFA-100. Inhibition of canine platelet function with cytochalasin D may allow further TEG studies in dogs with clinical disease.

Coagulation abnormalities in the trauma patient: the role of point-of-care thromboelastography

Current recommendations for resuscitation of the critically injured patient are limited by a lack of point-of-care (POC) assessment of coagulation status. Accordingly, the potential exists for indiscriminant blood component administration. Furthermore, although thromboembolic events have been described shortly after injury, the time sequence of post-injury coagulation changes is unknown. Our current understanding of hemostasis has shifted from a classic view, in which coagulation was considered a chain of catalytic enzyme reactions, to the cell-based model (CBM), representing the interplay between the cellular and plasma components of clot formation. Thromboelastography (TEG), a time-sensitive dynamic assay of the viscoelastic properties of blood, closely parallels the CBM, permitting timely, goal-directed restoration of hemostasis via POC monitoring of coagulation status. TEG-based therapy allows for goal-directed blood product administration in trauma, with potential avoidance of the complications resulting from overzealous component administration, as well as the ability to monitor post-injury coagulation status and thromboprophylaxis. This overview addresses coagulation status and thromboprophylaxis management in the trauma patient and the emerging role of POC TEG.

Differentiation of enzymatic from platelet hypercoagulability using the novel thrombelastography parameter delta (delta)

BACKGROUND

Thrombelastography (TEG) allows for rapid global assessment of coagulation function. Our previous work demonstrated that a hypercoagulable state identified by TEG's G value was associated with thromboembolic events in a cohort of critically ill surgical patients despite routine chemoprophylaxis. We hypothesized that a hypercoagulable state could be differentiated into enzymatic or platelet etiology through the use of thrombus velocity curves; specifically the time to maximum rate of thrombus generation (TMRTG) and the novel TEG parameter, delta. (Delta)

METHODS

We retrospectively studied 10 critically ill surgical patients receiving thromboprophylaxis for at least 72 h by TEG, using kaolin activated citrated samples. Thrombus velocity curves were plotted for each patient, and delta was calculated as the difference between the TEG parameters R and SP, corresponding to the time to maximum rate of thrombus generation (TMRTG), which reflects the enzymatic contribution to clot formation. The TEG parameter G, (G = 5000 x A/100-A) also was determined for each patient. As G is derived from amplitude (A), it reflects overall net clot strength. A hypercoagulable state was defined as delta < 0.6 min and/or G > 11 dynes/cm(2).

RESULTS

A hypercoagulable state was identified via delta in 6 patients (60%); all of whom remained hypercoagulable following heparinase addition, suggesting chemoprophylaxis was ineffective. Of six patients with a hypercoagulable G value, 50% had a normal delta suggesting the presence of platelet hypercoagulability. Delta closely correlated with TMRTG (r = 0.94). However, the varying contribution of platelets to hypercoagulability, was shown by a nonlinear, weak correlation of delta and TMRTG with G (r = 0.11 and r = 0.14, respectively).

CONCLUSION

Delta reflects changes in thrombin generation as measured by TMRTG, allowing for differentiation of enzymatic from platelet hypercoagulability. Future studies will be required to validate these findings.

Chemokine homeostasis vs. chemokine presentation during severe acute lung injury: the other side of the Duffy antigen receptor for chemokines

Acute lung injury (ALI) still poses a major challenge in critical care medicine. Neutrophils, platelets, and chemokines are all considered key components in the development of ALI. The Duffy antigen receptor for chemokines (DARC) is thought to be involved in scavenging, transendothelial transport, and presentation of neutrophil-specific chemokines. DARC is expressed on endothelial cells and erythrocytes but not on leukocytes. Here, we show that DARC is crucial for chemokine-mediated leukocyte recruitment in vivo. However, we also demonstrate that changes in chemokine and chemokine receptor homeostasis, associated with Darc gene deficiency, exert strong anti-inflammatory effects. Neutrophils from Darc gene-deficient (Darc(-/-)) mice display a more prolonged downregulation of CXCR2 during severe inflammation than neutrophils from wild-type mice. In a CXCR2-dependent model of acid-induced ALI, Darc gene deficiency prevents ALI. Darc(-/-) mice demonstrate fully preserved oxygenation, only a small increase in vascular permeability, and a complete lack of pulmonary neutrophil recruitment. Further analysis reveals that only neutrophils but neither endothelial cells nor erythrocytes from Darc(-/-) mice confer protection from ALI. The protection appears to be due to abolished pulmonary recruitment of neutrophils from Darc(-/-) mice. The generation of neutrophil-platelet aggregates, a key mechanism in both pulmonary neutrophil recruitment and thrombus formation, is also affected by altered CXCR2 homeostasis in Darc(-/-) mice. CXCR2 blockade enhances the formation of platelet-neutrophil aggregates and thereby corrects a formerly unknown bleeding defect in Darc(-/-) mice. In summary, our study suggests that chemokine/chemokine receptor homeostasis plays a previously unrecognized and crucial role in severe ALI.

In vitro methods of evaluating antithrombotics and thrombolytics

Platelets play a crucial role in primary hemostasis by forming hemostatic plugs at sites of vascular injury. There is abundant evidence that platelets also play a pivotal role in the pathogenesis of arterial thrombotic disorders, including unstable angina (UA), myocardial infarction (MI), and stroke. The underlying pathophysiological mechanism of these processes has been recognized as the disruption or erosion of a vulnerable atherosclerotic plaque, leading to local platelet adhesion and subsequent formation of partially or completely occlusive platelet thrombi. A variety of methods have been used to assess platelet aggregation, blood coagulation, and the ex vivo and/or in vitro efficacy of platelet antagonists, anticoagulants, and thrombolytics.

Effects of cigarette smoke exposure on clot dynamics and fibrin structure: an ex vivo investigation

OBJECTIVE

The purpose of this study was to examine the effect of cigarette smoke exposure (CSE) on clot dynamics and fibrin architecture and to isolate the relative contribution of platelets and fibrinogen to clot dynamics.

METHODS AND RESULTS

From young healthy males smokers (n=34) and nonsmokers (n=34) a baseline blood was drawn, and smokers had another blood draw after smoking 2 regular cigarettes. Using thromboelastography (TEG) the degree of platelet-fibrin interaction was measured. In additional experiments, abciximab (20 microg/mL) was added to the smokers samples (n=27) to reduce the effects of platelet function from the TEG parameters. The maximum clot strength (G) obtained with abciximab measured mainly the contribution of fibrinogen to clot strength (GF). By subtracting GF from G, the contribution of platelets to clot strength (GP) was presumed. A significant difference was found for all TEG parameters between nonsmokers versus postsmoking and pre- versus postsmoking samples. Postsmoking both GF and GP were significantly higher as compared to presmoking. On electron microscopy and turbidity analysis, postsmoking fibrin clots were significantly different compared to presmoking and nonsmoking samples.

CONCLUSIONS

Acute CSE changes clot dynamics and alters fibrin architecture. Both functional changes in fibrinogen and platelets appear to contribute to heightened thrombogenicity after acute CSE.

The effect of milrinone on platelet activation as determined by TEG platelet mapping

BACKGROUND

Milrinone is a phosphodiesterase III inhibitor that increases intracellular cyclic adenosine monophosphate resulting in improved ventricular function and vasodilation. Increased intracellular levels of cyclic adenosine monophosphate also inhibit adenosine diphosphate (ADP) and arachidonic acid (AA)-induced platelet aggregation. We hypothesized that inhibition of ADP and AA-induced platelet activation by therapeutic blood concentrations of milrinone could be quantified using TEG Platelet Mapping.

METHODS

Blood was taken from 15 healthy adults who had not been taking antiplatelet medications. Milrinone was added to whole blood in three clinically relevant concentrations (30, 100, and 300 ng/mL). Conventional thromboelastography (TEG) and TEG Platelet Mapping were performed on whole blood without milrinone and at each of these three concentrations.

RESULTS

Increased blood concentrations of milrinone were associated with increased inhibition of ADP and AA-induced platelet activation (P < 0.0001). Milrinone at a blood concentration of 300 ng/mL markedly impaired the platelet activation response to ADP and AA.

CONCLUSIONS

Therapeutic blood concentrations of milrinone exhibit a significant inhibitory effect on ADP and AA-induced platelet activation as determined by TEG Platelet Mapping, without affecting the conventional kaolin-activated TEG. We suggest that TEG Platelet Mapping results be interpreted with caution in patients being treated with milrinone, and other drugs that modify platelet cyclic nucleotide concentrations.

Bivalirudin and clopidogrel with and without eptifibatide for elective stenting: effects on platelet function, thrombelastographic indexes, and their relation to periprocedural infarction results of the CLEAR PLATELETS-2 (Clopidogrel with Eptifibatide to Arrest the Reactivity of Platelets) study

OBJECTIVES

The primary objective of this study was to compare the effect of therapy with bivalirudin alone versus bivalirudin plus eptifibatide on platelet reactivity measured by turbidometric aggregometry and thrombin-induced platelet-fibrin clot strength (TIP-FCS) measured by thrombelastography in percutaneous coronary intervention (PCI) patients. The secondary aim was to study the relation of platelet aggregation and TIP-FCS to the occurrence of periprocedural infarction.

BACKGROUND

Bivalirudin is commonly administered alone to clopidogrel naïve (CN) patients and to patients on maintenance clopidogrel therapy (MT) undergoing elective stenting. The effect of adding eptifibatide to bivalirudin on platelet reactivity (PR) and TIP-FCS, and their relation to periprocedural infarction in these patients are unknown.

METHODS

Patients (n = 200) stratified to clopidogrel treatment status were randomly treated with bivalirudin (n = 102) or bivalirudin plus eptifibatide (n = 98). One hundred twenty-eight CN patients were loaded with 600 mg clopidogrel immediately after stenting, and 72 MT patients were not loaded. The PR, TIP-FCS, and myonecrosis markers were serially determined.

RESULTS

In CN and MT patients, bivalirudin plus eptifibatide was associated with markedly lower PR at all times (5- and 20-microM adenosine diphosphate-induced, and 15- and 25-microM thrombin receptor activator peptide-induced aggregation; p < 0.001 for all) and reduced mean TIP-FCS (p < 0.05). Patients who had a periprocedural infarction had higher mean 18-h PR (p < 0.0001) and TIP-FCS (p = 0.002).

CONCLUSIONS

For elective stenting, the addition of eptifibatide to bivalirudin lowered PR to multiple agonists and the tensile strength of the TIP-FCS, 2 measurements strongly associated with periprocedural myonecrosis. Future studies of PR and TIP-FCS for elective stenting may facilitate personalized antiplatelet therapy and enhance the selection of patients for glycoprotein IIb/IIIa blockade. (Peri-Procedural Myocardial Infarction, Platelet Reactivity, Thrombin Generation, and Clot Strength: Differential Effects of Eptifibatide + Bivalirudin Versus Bivalirudin [CLEAR PLATELETS-2]; NCT00370045.

The effects of fibrinogen levels on thromboelastometric variables in the presence of thrombocytopenia

BACKGROUND

The binding of fibrinogen and fibrin to platelets is important in normal hemostasis. The extent of platelet-fibrin interaction can be measured as the viscoelastic strength of clot by rotational thromboelastometry (ROTEM). In this study, we investigated the effect of fibrinogen concentration and its relative contribution to overall clot strength using ROTEM.

METHODS

Blood samples were collected from healthy volunteers. The effects of platelet count on clot strength, determined by maximum clot elasticity (MCE), were evaluated on ROTEM using platelet-rich plasma (PRP) adjusted with autologous plasma to generate a range of platelet counts. PRPs were adjusted to 10 x 10(3) mm(-3), 50 x 10(3) mm(-3), and 100 x 10(3) mm(-3) and spiked with fibrinogen concentrates at 550 and 780 mg/dL. The effect of fibrin polymerization on clot strength, independent of platelet attachment, was analyzed by the cytochalasin D-modified thromboelastometry (FIBTEM) method. Additional retrospective analysis of clot strength (MCE) in two groups of thrombocytopenic patients was conducted.

RESULTS

Clot strength (MCE) decreased at a platelet count below 100 x 10(3) mm(-3), whereas increases in MCE peaked and reached a plateau at platelet counts from 400 x 10(3) mm(-3). Increasing fibrinogen concentrations in PRP increased clot strength in a concentration-dependent manner, even at low platelet counts (10 x 10(3) mm(-3)). The positive correlation between clot strength and plasma fibrinogen level was also confirmed in the analysis of the data obtained from 904 thrombocytopenic patients.

CONCLUSIONS

These in vitro and clinical data indicate that the clot strength increases in a fibrinogen concentration-dependent manner independent of platelet count, when analyzed by ROTEM. The maintenance of fibrinogen concentration is critical in the presence of thrombocytopenia. EXTEM (extrinsic activation) and FIBTEM may be useful in guiding fibrinogen repletion therapy.

Laboratory investigation of hypercoagulability in cancer patients using rotation thrombelastography

The goal of this study was laboratory testing for hypercoagulability in patients with solid tumors using rotation thrombelastogram (ROTEM) and correlate ROTEM parameters with routine coagulation tests. A total of 78 untreated patients with cancer were included: 28 gastrointestinal system tumors (group 1), 27 respiratory system tumors (group 2), and 23 miscellaneus group of ovarian, renal, nasopharyngeal, mesothelioma, and unknown origin (group 3). Platelet count was significantly increased in group 2 in respect to group 3 (P < 0.05) and fibrinogen level was significantly increased in group 2 in respect to group 1 (P < 0.05). There was no statistically significant difference between subgroups in respect to TEG parameters. Tumor-node-metastasis (TNM) stages of patients was not also associated with either of TEG parameters. Correlation analysis revealed significant correlation between laboratory parameters and ROTEM parameters. Fibrinogen showed the strongest correlation with MCF (r > 0.7) and CFT in all assays (INTEM, EXTEM, FIBTEM, APTEM). There were also statistically significant correlations between platelet number and other ROTEM parameters (INTEM-CFT, -MCF, EXTEM-CFT, -MCF, FIBTEM-MCF, APTEM-CFT, -MCF). In conclusions, our data demonstrates thromboelastographic signs of hypercoagulability in patients with solid tumors. ROTEM is able to identify the contribution of fibrinogen and platelets to clot strength in this patient population.

Monitoring antiplatelet therapy with point-of-care platelet function assays: a review of the evidence

Multiple studies have demonstrated that subgroups of patients receiving combination therapy with aspirin and clopidogrel fail to produce the anticipated antiplatelet effect, and various terms such as ‘aspirin resistance’, ‘clopidogrel resistance’, ‘heightened post-treatment platelet reactivity’ and ‘residual platelet reactivity’ have been introduced in the medical literature. Light transmittance aggregometry is generally considered to be the gold standard for determining platelet function, but its relevance to in vivo platelet function is questionable and the logistical demands of the method make it impossible to use in daily practice. The introduction of several point-of-care platelet function assays may be the key to the widespread clinical use of platelet function testing and may identify patients who are at risk for the occurrence of adverse cardiac events. In the present paper, we discuss the current commercially available methods of assaying platelet function, including their advantages and limitations and whether they have been shown to correlate with clinical outcomes.