The whole blood Thrombelastograph (TEG®) Platelet Mapping™ assay measures clot strength, maximal amplitude (MA), reflecting maximal platelet function, and detects the reduction in platelet function, presented as percentage inhibition, by both aspirin and clopidogrel. A study reported that the TEG® can be used as routine monitoring of the variability in ADP receptor inhibition and of antiplatelet therapy. Therefore, using TEG Platelet Mapping assay, we could find out the perioperative clopidogrel responsiveness of the patients with ACS undergoing OPCAB.

The purpose of this study is to determine whether the rate of the major adverse cardiac events (MACE, a combined endpoint of MI, revascularization and cardiac death) is higher in the patients with high degree of clopidogrel resistance, who are scheduled to undergo the OPCAB due to ACS.

Inclusion Criteria:

1. the patients with ACS undergoing OPCAB
2. the patients over 20 years of age
3. the patient who have been taking [100 mg of Aspirin] and [75 mg of clopidogrel or 180 mg of ticagrelor] for more than one week and who continue within 3 to 5 days prior to surgery

Exclusion Criteria:

1. re-operation or emergency operation
2. the patients with bleeding tendency of decreased liver function
3. Left ventricular ejection fraction < 40% by echo
4. preoperative hematocrit < 33% or platelet count < 100,000/mm3 or creatinine > 1.4 mg/dL
5. abnormal preoperative prothrombin time or activated partial thromboplastin time
6. preoperative use of other PO antiplatelet drugs or PO anticoagulants

patients with acute coronary syndrome (ACS) undergoing off-pump coronary artery bypass surgery