This protocol describes a pilot study intended to test the hypothesis that patients with acute coronary syndrome (ACS) caused by plaque erosion can be stabilized by effective antithrombotic treatment without stent implantation, thereby avoiding both early and late complications related to percutaneous coronary intervention (PCI).

Inclusion Criteria:

• Men or non-pregnant women >18 years of age and < 75 years of age
• Patients undergo cardiac catheterization for ACS. Patients with STEMI, NSTEMI, and UAP will be included. STEMI will be defined as continuous chest pain for >30 minutes, arrival at the hospital within 12 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). NSTEMI will be defined as a progressive crescendo pattern of angina or angina at rest, in the absence of ST-segment elevation on the 12-lead ECG, with elevated cardiac markers. UAP will be defined as new onset angina, progressive crescendo pattern of angina, or angina at rest.
• Culprit lesion located in a native coronary artery
• TIMI flow grade 3 and diameter stenosis < 70% on angiogram
• Definite erosion defined by OCT
• Patients able to provide written informed consent

Exclusion Criteria:

Left ventricular ejection fraction < 30%.

• 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.