Role of Microparticles in Thrombin Generation in Patients at Risk for Atherothrombosis.

We have shown recently (Hron et al. JAMA 2006) that measuring thrombin generation can identify patients at low risk for recurrent venous thromboembolism and that peak thrombin is a suitable parameter to differentiate low risk from high risk patients. In this study we used the same assay (Technothrombin®TGA) to analyze patients at high risk of atherothrombosis (a swiss study of patients with a history of myocardial infarction). Moreover, we investigated the influence of microparticles on thrombin generation in these patients. Thrombin generation was measured using Technothrombin®TGA. The reagent used contained low levels of phospholipid and 5 pM tissue factor. Platelet poor plasma from 178 patients (n=178, age =55±8 ys, male/female = 157/21) who had a previous myocardial infarction and 79 normal age and sex matched controls. (n=79, age = 55±8 ys, male/female = 70/9) was analyzed. Microparticle-free plasma was generated from PPP plasma by filtration through a membrane (0.2 μm pore size) using a standardized filtration device (Ceveron®MFU 500, Technoclone). In the control group the mean value for peak thrombin in platelet poor plasma was 252±7.7 nM (mean±SD). A significantly higher (p< 0,05) peak thrombin was found in the group of patients (355±49 nM) when patients without medication were analyzed. In patients on aspirin (n=109) the peak thrombin was not significantly different from untreated patients (297±10 nM) while in patients on oral anticoagulation (n=34) peak thrombin was significantly lower (225±27 nM). In the group of patients on oral anticoagulation also the lag period was significantly longer as compared to controls or patients without medication (21.9±2 minutes versus 14.8±0.2 minutes) whereas aspirin treatment did not affect the lag period significantly. After removing microparticles from the samples, the peak thrombin values between patient and control group were no longer significantly different. The difference between microparticle free plasma and platelet poor plasma was significantly higher (p<0.05) in the patient groups without therapy (304±39nM) and in patients on Aspirin therapy (257±23nM) as compared to the normal controls(182.6±10.4nM). These data indicate that thrombin generation is significantly increased in patients with previous myocardial infarction and that this increased thrombin generation is likely due to microparticles contained in these samples.