Article

Thrombelastography: A novel bedside tool to assess the effects of antiplatelet therapy?

Wessex Cardiac Unit, Southampton University Hospital, Southampton, UK.
Platelets (Impact Factor: 2.98). 10/2006; 17(6):385-92. DOI: 10.1080/09537100600757521
Source: PubMed
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.

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    • "TEG â MA is strongly correlated to the platelet count but has a poor sensitivity for platelet dysfunction (Swallow et al, 2006 ). Although PlateletMapping â identifies drug-induced platelet dysfunction (Swallow et al, 2006), it still may lack sensitivity (Chang et al, 2009). The test has mainly been used in the perioperative setting. "
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    • "The VHA's (TEG, ROTEM and ReoRox) have the advantage that they can measure coagulation, platelet function , clot retraction and fibrinolysis simultaneously. However, in contrast to the aggregation assays, VHA are in general insensitive to anti-platelet treatment with aspirin and ADP-receptor inhibitors with the exception of the Platelet Mapping assay [34]. PFA-100 has also shown variable sensitivity to aspirin and variable sensitive to clopidogrel with the ADP cartridge [80] but a newer cartridge called INNOVANCE PFA P2Y has shown promise in detecting clopidogrel resistance [83] . "
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