Brief Summary: This study is a prospective, multicenter, randomized, controlled trial aimed to compare the reperfusion strategy and clinical outcomes of STEMI patients treated by angiography-guided vs. OCT-guided PCI. Patients presenting STEMI with coronary artery diameter stenosis ≤70% and TIMI blood flow grade 3 at index or after thrombus aspiration are randomly assigned to either an OCT-guided group or an angiography-guided group. In OCT-guided group, stent implantation or conservative medical treatment is determined based on OCT findings. Conservative non-stenting strategy will be recommended in those with culprit plaque erosions, certain ruptures without dissection and hematoma, SCAD without obstructive stenosis. In the angiography-guided group, reperfusion strategy is decided by the operators according to the local practice. The rate of stenting during primary PCI and clinical outcomes at 1-month and 1-year are collected.

Methodology: As a multicenter, prospective, randomized, controlled trial, patients with ST-segment elevation myocardial infarction (STEMI) who have an intermediate stenotic culprit lesion (angiographic diameter stenosis ≤70%) and TIMI flow grade 3 or residual stenosis ≤70% after thrombus aspiration and TIMI grade 3 will be enrolled and randomized to OCT-guided group or angiography-guided group. In OCT-guided group, pre-PCI OCT imaging of the culprit lesion will be performed and revascularization strategy will be determined based on underlying mechanism of culprit lesion morphology. For lesions required stenting, OCT measurements will be used to guide the selection of stent size and to optimize the result of stent implantation. In the angiography-guided group, OCT will not be performed and the PCI procedures will be done according to routine practice by the operators. Primary outcome is patient-level rate of stenting during primary PCI and the incidence of recurrent myocardial ischemic events (unstable angina-induced rehospitalization, recurrent myocardial infarction, target lesion revascularization) or cardiac death within 1 month. Secondary outcomes include the incidence of cardiocerebrovascular events (cardiac death, recurrent myocardial infarction, stroke, target lesion revascularization, malignant arrhythmia, and unstable angina-induced rehospitalization) and the incidence of heart failure event within 1 year.

Patient enrollment and procedure overview: Patients with STEMI<12h in whom coronary angiography is planned will be screened. Those have a culprit lesion stenosis ≤70% by visual estimation and TIMI blood flow grade 3 at index angiography or after thrombus aspiration will be consented to participate in the study. After informed consent obtained, patients will be assigned to OCT-guided group or angiography-guided group randomly. In the OCT-guided group, OCT imaging of infarcted-related artery will be performed to assess the underlying mechanism of culprit lesion. Reperfusion strategy will be decided by the operators according to the OCT findings. Conservative medical strategy will be recommended if the underlying mechanism is plaque erosions, small ruptures without dissection and hematoma, SCAD without obstructive stenosis. Otherwise, stent implantation may be performed. The procedure of stent implantation will be guided by OCT according to current guideline and consensus documents. Before stent implantation, the landing zone and size of stent will be decided according to the pre-PCI OCT images. After implantation, OCT imaging will be performed to optimize the results of stent implantation including stent expansion, apposition, edge dissection, tissue protrusion. In the angiography-guided group, PCI procedure will be performed according to current guidelines and their daily practice. All patients are required to take dual antiplatelet treatment with aspirin (100 mg/day) and ticagrelor (180 mg/day) or clopidogrel (75mg/day) for at least 12 months. The use of low molecular weight heparin and glycoprotein IIb/IIIa inhibitor are determined by the operators.

Follow-up: Patients will be followed by phone calls or clinical visits by study coordinators at 1 month (30 days) and 1 year (12 months). Severe adverse events including heart failure event, stent failure, cardiac death, recurrent myocardial infarction, stroke, target lesion revascularization, malignant arrhythmia, and unstable angina-induced rehospitalization will be collected in all patients throughout the whole study period until the last patient completes 12 months of follow up. Additional phone follow-up may also be performed subject to executive committee approval.

Inclusion Criteria:

1. 18 years old ≤ age ≤ 80 years old;
2. Patients with STEMI<12h;
3. The target lesion is located in a native coronary artery;
4. The residual diameter stenosis (DS) is ≤70% on angiogram and thrombolysis in myocardial infarction (TIMI) flow grade is 3 after thrombus aspiration or not;
5. Written informed consent.

Exclusion Criteria:

1. Patients who are breastfeeding or pregnant or planning to pregnant during the study period;
2. Patients with a history of heart failure;
3. Hemodynamic instability;
4. Target lesion such as: left main coronary artery; three-vessel disease; ostial lesion (defined as within 3mm of the left main coronary artery or aorto-ostium); tortuous lesion; angular lesion;
5. Subjects with contraindication of contrast medium;
6. There are contraindications to aspirin or clopidogrel;
7. Severe hepatic and renal insufficiency (ALT or AST >3x upper limits of normal, creatinine>2.0 mg/dL or end-stage renal disease);
8. Patients with bleeding tendency such as peptic ulcer, bleeding or coagulation disorders;
9. AMI is caused by surgery, trauma, gastrointestinal bleeding, PCI, or its complications;
10. AMI occurs in patients who have been hospitalized for other reasons;
11. Patients who were considered with poor compliance and could not complete the study as required judged by the investigators;
12. Patient with life expectancy ≤24 months;
13. Patients with heart transplantation;
14. Patients with definite diagnosis of tumors;
15. Patients who are currently enrolled in other clinical trial (except other subjects in this project) which has not reached its primary endpoint;
16. Patients who are not suitable for the current study judged by the investigators.