Thromboelastography: Potential bedside tool to assess the effects of antiplatelet therapy?

Abstract

Modified thrombelastography (TEG) is a simple point of care test that provides an overall assessment of ex vivo clot formation and currently has limited clinical application. We evaluated the ability of TEG to assess the effects of antiplatelet therapy on clot formation using a novel assessment parameter (the area under curve). Forty healthy volunteers were divided into four groups of 10. Group A took aspirin 75 mg once daily for 7 days followed by aspirin 75 mg and clopidogrel 75 mg once daily in combination for 7 more days. Blood samples were taken for analysis at day 0 and days 7 and 14. Group B took a single 300 mg dose of aspirin. Group C took 600 mg of clopidogrel only. Group D took 300 mg of aspirin and 600 mg of clopidogrel at the same time. For groups B, C and D blood was taken prior to drug administration and at 2, 6 and 24 h afterwards. Each sample was tested by TEG in four channels following activation using (1) kaolin, (2) activator F (Act F), a direct activator of fibrin, (3) Act F + arachidonic acid (AA) and (4) Act F + adenosine diphosphate (ADP). Parameters measured included the maximum amplitude (MA) of the clot and the area under the TEG-generated curve at 1 h. Significant, time-dependent reductions in MA and area were seen in the AA-activated samples following administration of aspirin in all groups as compared to baseline. By contrast, there were no significant differences in MA or area in the AA-activated samples with clopidogrel alone. Significant reductions were also seen in MA and area in ADP-activated samples from volunteers treated with clopidogrel as compared to baseline. Three out of 10 subjects receiving 600 mg clopidogrel had a reduction in their responses of 30% or less, thus identifying them as relatively resistant to the drug. This study identifies a rapid, reliable method for assessing the time-dependent effects of antiplatelet therapy on clotting using a novel parameter of area of the TEG trace, which could have an important clinical application as a point of care test of efficacy, particularly in the context of acute coronary syndromes and percutaneous coronary intervention.

How I treat patients with massive hemorrhage

“…24 It should be noted that the standard VHA tests, TEG and ROTEM, cannot measure pharmacological platelet inhibition and thus identify bleeding secondary to aspirin and/or adenosine 59-diphosphate receptor inhibitors such as clopidogrel, effient, or ticagrelor. 12 In these patients, the TEG Platelet Mapping Assay (Haemonetics Corp., Braintree, MA) or the whole blood platelet impedance aggregometry assay Multiplate (Roche, Basel, Switzerland) should be used, enabling identification of potential increased bleeding risk secondary to pharmacological platelet inhibition.…”

“…However, the conventional plasma based tests only describe isolated fragments of the hemostatic process 10,11 and are poorly associated with bleeding and transfusion requirements, as well as the platelet count itself does not reflect whether the platelets are hemostatically intact. 12 The criticism of using the conventional coagulation tests were inspired by a new understanding of the hemostatic process, introduced by Hoffman and colleagues in the mid-1990s. 13 A final major problem with the conventional coagulation analysis is that the time from blood sampling to availability of the results is too slow to be of clinical relevance in the massively bleeding patient.…”

Advances in the understanding of trauma-induced coagulopathy

“…44 Viscoelastic tests provide some information on platelet function, but the angle and maximum amplitude/clot firmness variables on TEG and rotational thromboelastometry (ROTEM) are also dependent on fibrinogen levels, 45 and these tests are furthermore not effective at detecting inhibition by antiplatelet agents. 46 Specialized assays including TEG platelet mapping (TEG-PM) and aggregometry modalities assay platelet function by measuring their response to various agonists. However, diagnostic cutoffs for pathologic platelet dysfunction after trauma have not been well established.…”

A Randomized Crossover Study Comparing the Antiplatelet Effect of Plavix Versus Generic Clopidogrel

“…As blood clots, changes in its viscoelasticity are transmitted to the pin and the resulting torque generates an electrical signal producing a TEG trace, which is a graphic representation of the speed and strength of clot formation. 17 The following parameters are derived from the TEG trace:…”