Platelet Function in Minimal Extracorporeal Circulation Versus Conventional Extracorporeal Circulation in Coronary Artery Bypass Grafting

Platelet function test

Thromboelastography (TEG) TEG is a test which provides information on the complete haemostasis. Also fibrinolysis can be measured. The strength of the clot can be measured. This provides information about platelet concentration, -function and platelet-fibrin interaction. It is measured in a medium with added heparinase, an enzyme that degrades heparin,, which makes TEG measurement possible during ECC. The results from the TEG will be displayed graphically and numerically. The letter R (reaction time) represents the time before the clot formation starts. This time is predominately dependent on coagulation factors and inhibitors such as heparin. The velocity at which the clot is then formed is displayed as the letter K (time between 2 mm en 20 mm amplitude in the thromboelastogram). The firmness of the clot is the maximum amplitude in the thromboelastogram (MA) and is dependent on the amount and function of the thrombocytes, fibrinogen concentration and factor XIII concentration of the sample. Fibrinolysis will be visualised in the parameter that displays the velocity of dissolving the clot (LY30= fibrinolysis 30 minutes after MA).

In case of a severe coagulation factor independency or use of heparin, the R parameter will be elongated. In severe thrombocytopathy, thrombocytopenia or a low fibrinogen concentration the graphic will show a lowered MA. In hyperfibrinolysis the LY30 will be elongated.

Multiple electrode Aggregometry (MEA) MEA is a technique to test platelet function in whole blood based on classical impedance aggregometry. The use of whole blood makes centrifugation redundant. The use of agonist ADP, arachidonic acid, collagen and TRAP provides information about platelet aggregation, and simultaneously provides specific information of the routes inhibited by clopidogrel and acetylsalicylic acid.

MEA calculates three parameters. The most important parameter, the area under the curve (AUC), reflexes the overall platelet activity . The area under the curve is influenced by the total height of the aggregation curve as well as by its slope. The other parameters are the height of the curve that describes the aggregation. The maximum slope of the curve describes the reflex velocity.