Dual Antiplatelet Therapy (DAPT) with aspirin and P2Y12 receptor inhibitor remains a cornerstone in the secondary prevention of coronary artery disease (CAD). Clopidogrel is one of the most commonly used antithrombotic agent that inhibits the platelet P2Y(12) adenosine diphosphate (ADP) receptor.

Ticagrelor is an oral, reversibly-binding, direct-acting P2Y12 receptor antagonist used clinically for the prevention of atherothrombotic events in patients with acute coronary syndromes (ACS). Guideline recommendations on the use of dual antiplatelet therapy have been formulated that ticagrelor 90 mg twice daily plus aspirin in preference to clopidogrel 75mg daily plus aspirin for ACS patients. The previous studies have reported that half-dose ticagrelor had the similar inhibitory effect on platelet aggregation as the standard-dose ticagrelor, which was significantly stronger than that in the clopidogrel group. One-quarter standard-dose ticagrelor provided greater degree of platelet inhibition than standard dose clopidogrel in Chinese patients with stable CAD. But the effectiveness and safety of low-dose ticagrelor remain yet not very clearly in Chinese patients with acute coronary syndrome undergoing percutaneous coronary intervention.

Inclusion Criteria:

• After half-dose ticagrelor (loading dose 90mg, and then 45mg bidpo.) treatment for 3 days, the platelet aggregation is effectively inhibited by light transmission aggregometry method and thromboela-stogram.
• planned to undergo PCI recently
• planned to DAPT for 1 year after PCI

Exclusion Criteria:

• taken adenosine diphosphate (ADP) receptor antagonists within 2 weeks
• Platelet count <100g/L;
• A history of bleeding tendency;
• Aspirin, ticagrelor or clopidogrel allergies;
• Severe liver injury.