Frequency of analyses (Cohort study): No interim analyses are planned. The Data Safety Monitoring Board (DSMB, see below) will be instructed to monitor the frequency of hemorrhage in this group. If the upper limit of the 95% CI about the risk of hemorrhage exceeds 5% after a minimum of 20 patients have completed the 90 day outcome ascertainment, the DSMB will notify the Steering Committee that the risk of hemorrhage in the cohort study is excessive. The steering committee will then decide whether this arm of the study should be discontinued or the intervention modified.