 To assess the efficacy of TEG in monitoring Rivaroxaban activity, the investigators will also perform a battery of coagulation tests at the same timepoints described above in order to attempt to assess the degree of functional factor X inhibition. The coagulation battery will include: thrombin time, thrombin generation, PT with neoplastine, ecarin chromogenic assay, as well as the anti-factor Xa chromogenic assay Rivaroxaban assay run by our Institute for Transfusion Medicine. 