Clopidogrel monotherapy has been found effective in reducing ischaemic cardiovascular and haemorrhagic complications in patients with drug-eluting stent (DES) placement. However, concerns remain about the safety of long-term clopidogrel monotherapy in high-risk patients with HPR (high platelet reactivity) who do not respond adequately to clopidogrel. This study aims to evaluate the effectiveness of a patient-tailored antiplatelet therapy strategy that considers platelet aggregation in high-risk patients with DES placement beyond 12 months after stenting.

This study will randomly assign eligible participants who underwent drug-eluting stent placement and have maintained the standard antiplatelet therapy for 12 months to either a control group or an intervention group. The control group will continue receiving clopidogrel monotherapy for 24 months regardless of their PRU (platelet reactivity unit) values. The intervention group will receive personalized antiplatelet therapy based on their PRU values: for non-HPR patients (PRU<208), clopidogrel monotherapy will be continued; for HPR patients (PRU≥208), dual antiplatelet therapy will be prescribed based on clinical diagnosis at the time of stent implantation and individual patients' ischemic/bleeding risk profiles. Patients (≥50 years) who presented with acute myocardial infarction at the time of coronary intervention, and have high-risk characteristics (① ≥65 years ② multi-vessel disease ③ diabetes mellitus ④ chronic kidney disease ⑤ recurrent myocardial infarction) will receive ticagrelor 60 mg twice daily with aspirin, whereas the remainder will receive clopidogrel with aspirin. For high-bleeding-risk patients with two or more major bleeding risk factors according to ARC-HBR, the investigator may consider early discontinuation of dual antiplatelet therapy or de-escalation therapy like aspirin monotherapy based on the patient's risk profile. The treatment assignment ratio is 1:1. The study period will be up to 24 months from the time of randomization.

Inclusion Criteria:

1. Patients > 18 years old
2. Patients who previously underwent percutaneous coronary intervention with drug-eluting stent implantation 12 months (± 3 months) ago.
3. At least one high risk characteristics of ischemic events

High risk patients

1. Acute coronary syndrome
2. Previous history of cerebrovascular accidents
3. Previous history of peripheral artery intervention
4. Heart failure
5. Diabetes mellitus requiring medication
6. Chronic kidney disease (regardless of requirement of renal replacement therapy)

High risk lesions

1. Left main disease
2. Multivessel disease, 2- or 3- vessels
3. Bifurcation lesions requiring 2 or more stents
4. Chronic total occlusion
5. In-stent restenosis
6. Graft lesions
7. Diffuse long lesion requiring stent(s) with total stent length ≥28 mm
8. Lesion at small sized vessel requiring stent(s) with stent diameter ≤2.5 mm
9. Calcified lesions requiring atherectomy

Exclusion Criteria:

1. Patients > 80 years old
2. Pregnant women or women with potential childbearing
3. Life expectancy < 1 year
4. Refusal or inability to understand of informed consent
5. Patients eligible to long-term anticoagulation therapy
6. Patients with major bleeding events in previous 3 months before randomization