Emerging Use of Viscoelastography in Thrombosis and Hemostasis: A Challenge to Conventional Coagulation Tests? Part I: The Use of Thromboelastography and Thromboelastometry in the Assessment of Hemostatic Function

The clotting of blood in vitro involves the activation of clotting factors and platelets. Retraction of the clot then takes place followed by breakdown of the clot by fibrinolysis. All of these steps can be followed by studying the tensile strength of the clot by thromboelastography (TEG) and rotational thromboelastometry (ROTEM), both methods identified under the umbrella term “viscoelastography.” This methodology was first described by Helmut Hartert as “thrombus stressography” in 1948.[1] Further technologic advance has led to the development of several new devices. TEG and ROTEM represent the two most commonly used methods. In the former, a sample of citrated blood is placed in an oscillating cup containing kaolin. Calcium is added to start the clotting process. A plot of the reaction is shown in [Fig. 1]. The initial reaction time is designated as R-time with normal values ranging from 4 to 8 minutes. This measures the function of clotting factors and is thus affected by anticoagulants. The time to reach a clot strength of 20 mm is the K-time and ranges from 1 to 3 minutes. The α-angle, ranging from 55 to 78 degrees, is the slope of the tracing that represents the rate of clot formation. The maximal amplitude (MA) of the tracing represents the greatest clot strength ranging from 50 to 60 mm. As fibrinolysis takes place, the MA decreases. The percentage of the MA at 30 minutes is the lysis index and ranges from 0 to 15%. The first part of the tracing (R-time, K-time, α-angle, and MA) is a function of the quantity and quality of the clotting factors and of platelets, and the second part those of fibrinolysis. In the rapid version of TEG, clotting is further accelerated by addition of tissue factor. In thromboelastometry, also known as ROTEM, the cup containing the test sample is stationary while the torque of the clot is picked up by a rotating pin.

Fig. 1 A plot of the reaction for thromboelastography. MA, maximal amplitude.

In this issue of Seminars in Thrombosis and Hemostasis, the utility of both TEG and ROTEM is presented by many experts in this field. In the first article, TEG and ROTEM are compared with conventional coagulation tests.[2] Then its use in the management of blood product replacement in the bleeding patient is discussed.[3] The advantages and disadvantages of these methods are discussed. Viscoelastographic measures can be done at point of care with rapid turnaround time. Such advantage is fully utilized in the management of trauma patients, as discussed previously by Moore and colleagues, and in the current issue by Meizoso et al.[4] [5] Another potential application of this methodology is in the monitoring of anticoagulant therapy.[6] This is especially useful in patients with marked variation in the coagulation status such as in complicated cases in the emergency department. This is followed in this issue by the use of viscoelastographic tests in patients on mechanical circulatory support devices such as for extracorporeal membrane oxygenation.[7] The next two articles deal with the use of viscoelastography in neurological practice. They are used in subarachnoid hemorrhage and intracranial hemorrhage[8] as well as in acute ischemic stroke.[9] In addition, these methods are used in the management of COVID-19 patients.[10] [11]

As its use becomes more popular, improvement in both the technique and knowledge of viscoelastography is indeed a challenge for continued and future research.

Publication History

Article published online:
29 September 2022

• References

• 1 Hartert H. Blood clotting studies with thrombus stressography; a new Investigation procedure. Klin Wochenschr 1948; 26 (37-38): 577-583
• 2 Bunch CM, Berquist M, Ansari A. et al. The choice between plasma-based common coagulation tests and cell-based viscoelastic tests in monitoring hemostatic competence: not an either-or proposition. Semin Thromb Hemost 2022; 48 (07) 769-784
• 3 Matkovic E, Lindholm PF. Role of viscoelastic and conventional coagulation tests for management of blood product replacement in the bleeding patient. Semin Thromb Hemost 2022; 48 (07) 785-795
• 4 Meizoso JP, Barrett CD, Moore EE, Moore HB. Advances in management of coagulopathy in trauma: the role of viscoelastic hemostatic assays across all phases of trauma care. Semin Thromb Hemost 2022; 48 (07) 796-807
• 5 Moore HB, Walsh M, Kwaan HC, Medcalf RL. The complexity of trauma-induced coagulopathy. Semin Thromb Hemost 2020; 46 (02) 114-115
• 6 Artang R, Brod C, Nielsen JD. Application of activators Ecarin and factor Xa in thrombelastography for measurement of anticoagulant effect of direct oral anticoagulants using TEG® 500. Semin Thromb Hemost 2022; 48 (07) 808-813
• 7 Volod O, Wegner J. Viscoelastic testing in the management of adult patients on mechanical circulatory support devices with focus on extracorporeal membrane oxygenation. Semin Thromb Hemost 2022; 48 (07) 814-827
• 8 Hvas A-M, Hvas CL. Viscoelastic testing in the clinical management of subarachnoid hemorrhage and intracerebral hemorrhage. Semin Thromb Hemost 2022; 48 (07) 828-841
• 9 Pîrlog BO, Grotta JC. The applicability of thromboelastography in acute ischemic stroke. A literature review. Semin Thromb Hemost 2022; 48 (07) 842-849
• 10 Bösch J, Rugg C, Schäfer V. et al. Low-molecular-weight heparin resistance and its viscoelastic assessment in critically ill COVID-19 patients. Semin Thromb Hemost 2022; 48 (07) 850-857
• 11 Grobbelaar LM, Kruger A, Venter C. et al. Relative hypercoagulopathy of the SARS-CoV-2 beta and delta variants when compared to the less severe omicron variants is related to TEG parameters, the extent of fibrin amyloid microclots, and the severity of clinical illness. Semin Thromb Hemost 2022; 48 (07) 858-868