Ticagrelor Monotherapy Compared to Aspirin Monotherapy in Patients With History of ACS

Antiplatelet agents are cornerstones for management of ischemic heart disease. For patients suffering from acute coronary syndrome (heart attack), treatment with aspirin and ticagrelor are typically given for one year after index heart attack and then patients will continue to take aspirin lifelong. However, these patients are still having increased risk of suffering from another heart attack. Recently data showed that adding ticagrelor to aspirin in the long term can decrease the chance of recurrent heart attack but at the cost of increased risk of major bleeding. On the other hand, ticagrelor is a potent antiplatelet agent and has been showed to have additional benefit on blood vessels and platelets. The investigator hypothesize that monotherapy with ticagrelor may have further benefit over monotherapy with aspirin in the long term management in patients with history of heart attack. The investigator plan to perform a randomized study to compare the outcome in patients taking either ticagrelor or aspirin. The primary endpoint is measurement of endothelial function by flow mediated dilatation of brachial artery which is a surrogate marker of adverse cardiovascular outcome 3 months after treatment. The investigator would also investigate secondary endpoints of patients' blood level of adenosine activity, platelet function, endothelial progenitor cell count and biomarkers