This protocol describes a prospective, multi-center study intended to test the hypothesis that patients with STEMI caused by plaque rupture or plaque erosion without obstructive stenosis (diameter stenosis <70%) can be stabilized by effective antithrombotic treatment without stent implantation, thereby avoiding both early and late complications related to percutaneous coronary intervention (PCI) with stent implantation. All the patients will be followed by intracoronary OCT and physiological assessment at 1-month and 12-month follow-up.

EROSION (Effective anti-thrombotic therapy without stenting: intravascular optical coherence tomography-based management in plaque erosion) study, a single-center, uncontrolled, prospective, proof-of concept study, showed that for patients with ACS caused by non-obstructive plaque erosion, conservative treatment with anti-thrombotic therapy without stenting may be an option. However, it is unknown whether plaque rupture with large lumen area and non-obstructive stenosis can be treated medically without stenting. EROSION II study is a prospective, multi-center, observational study to test the hypothesis that patients with STEMI caused by plaque rupture or plaque erosion without obstructive stenosis (diameter stenosis <70% by visual assessment) can be stabilized and healed by effective antithrombotic treatment without stent implantation. Patients presenting with STEMI within 24 hours from the onset of ischemic symptoms will be included for screening. Thrombus aspiration will be performed in patients with large thrombus burden and TIMI flow grade less than 2 to restore blood flow. OCT will be performed after antegrade blood flow restored to assess the underlying mechanism of culprit lesion including plaque rupture, plaque erosion, calcified nodule, spontaneous coronary artery dissection, and other uncommon reasons. OCT imaging of non-culprit vessels will be performed if feasible. Patients caused by plaque erosion or plaque rupture with minimal lumen area > 1.6mm2 or non-obstructive stenosis (diameter stenosis <70% by visual assessment) will be treated medically only with dual anti-platelet therapy for 12 months after discharge.

Serial OCT examination will be performed at 1-month and 12-month follow-up to assess the healing of original culprit lesion. Physiological assessment (either wire-based FFR or angio-based FFR) will also be performed to assess the hemodynamic function of culprit lesion. The primary endpoint is the reduction of thrombus burden assessed by OCT at 1-month follow-up. Presence of recurrent ischemia symptoms or positive FFR value are the indications for target lesion revascularization. Patients will be followed by phone calls by study coordinators or clinical visit at 1 month, 3 months, 6 months, 9 months and 12 months. Major cardiovascular adverse events (MACE) will be collected in all patients throughout the whole follow-up period. MACE is a composite of cardiac death, recurrent myocardial infarction, stroke, target lesion revascularization, major bleeding and unstable angina-induced rehospitalization.

Patients who do not meet the criteria after OCT imaging will be enrolled in registry cohort.

Blood sample will be obtained from artery sheath or coronary artery by aspiration catheter during the PCI procedure in selected sites. Blood samples will be stored at -80°C for potential biomarker test and multi-omics analysis.

Inclusion Criteria:

• Men or non-pregnant women >18 years of age and < 75 years of age.
• Patients undergo cardiac catheterization for STEMI. STEMI will be defined as continuous chest pain for >30 minutes, arrival at the hospital within 24 hours from chest pain onset, ST-segment elevation >0.1 mV in at least two contiguous leads, or new left bundle-branch block on the 12-lead electrocardiogram (ECG), and elevated cardiac markers (troponin T/I or creatine kinase-MB).
• Culprit lesion located in a native coronary artery.
• TIMI flow grade 3 and diameter stenosis < 70% by visual assessment on angiogram or MLA > 1.6mm2.
• Plaque erosion and rupture defined by OCT.
• Patients able to provide written informed consent.

Exclusion Criteria:

• Left ventricular ejection fraction < 30%.
• Lesions in LM, ostial LAD or RCA (defined as within 3 mm of the aorto-ostium).
• Long lesions, tortuous lesions and angulated lesions.
• More than 2 vessels with severe lesions.
• Massive residual thrombus after the thrombus aspiration.
• With the history of cardiopulmonary resuscitation (CPR), acute pulmonary edema and cardiac shock on the attacks.
• Life expectancy < 1 year.
• Contraindication to the contrast media.
• Creatinine level > 2.0 mg/dL or end-stage kidney disease.
• Serious liver dysfunction.
• Patients with hemodynamic or electrical instability (including shock).
• Any contraindication against the use of ticagrelor.
• Investigator considers the patient is not suitable.

Study population is STEMI patients who undergo primary cardiac catheterization.

2020