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
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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[Show abstract] [Hide abstract] ABSTRACT: Hellmut Hartert was the first person to exploit the viscoelastic properties of clotting blood to measure blood coagulation in 1948. Since then, the technology has improved, allowing these analyses to be performed as point-of-care tests with immediately-available results. The addition of several activators and inhibitors to the original assay creates a panel of tests able to quantify the different aspects of blood clotting that can rival conventional laboratory assays. However, although much progress has been made, the standardization and validation of these tests still need improvement. Viscoelastic analyses of blood coagulation are mainly used to guide haemostatic therapy in bleeding patients and have proven superior to standard clotting tests in some circumstances. There is potential to extend their use to other areas, such as drug monitoring, and diagnosis and management of congenital bleeding disorders. The forthcoming cartridge-based assays are expected to improve the reliability and usability of viscoelastic assays of blood coagulation but high quality clinical trials remain urgently needed to determine their exact place, benefit and cost effectiveness.
- "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. "
[Show abstract] [Hide abstract] ABSTRACT: Haemostasis is a complex process affected by many factors including both cellular and plasma components. It is a multistep process starting with platelet adhesion to damaged endothelium and ending in clot fibrinolysis. There are several methods available to study different aspects of haemostasis including adhesion, aggregation, coagulation and fibrinolysis. This review describes the different methods, what aspects of haemostasis they measure and their limitations. Methods discussed include methods to study adhesion (e.g. PFA-100, cone and platelet(let) analyzer and perfusion chambers) and aggregation (e.g. Multiplate, VerifyNow and Plateletworks). Furthermore the principles behind viscoelastic haemostatic assays are presented as well as methods that can analyse aspects of haemostasis in plasma or platelet-rich-plasma samples (thrombin generation, overall haemostasis potential and Thrombodynamics Analyzer).
- "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 . PFA-100 has also shown variable sensitivity to aspirin and variable sensitive to clopidogrel with the ADP cartridge  but a newer cartridge called INNOVANCE PFA P2Y has shown promise in detecting clopidogrel resistance  . "
[Show abstract] [Hide abstract] ABSTRACT: Severe trauma-related bleeding is associated with high mortality. Standard coagulation tests provide limited information on the underlying coagulation disorder. Whole-blood viscoelastic tests such as rotational thromboelastometry or thrombelastography offer a more comprehensive insight into the coagulation process in trauma. The results are available within minutes and they provide information about the initiation of coagulation, the speed of clot formation, and the quality and stability of the clot. Viscoelastic tests have the potential to guide coagulation therapy according to the actual needs of each patient, reducing the risks of over- or under-transfusion. The concept of early, individualized and goal-directed therapy is explored in this review and the AUVA Trauma Hospital algorithm for managing trauma-induced coagulopathy is presented.
- "Platelet count provides quantitative information on platelet numbers, but it provides no information on platelet function. Prior treatment with platelet inhibitors such as aspirin or thienopyridines is commonly encountered among emergency room patients and, although platelet function may potentially influence patient outcomes , platelet inhibitor therapy cannot be assessed adequately by standard viscoelastic analyses . POC monitoring devices allowing rapid assessment of platelet function (e. g. "