Study Design and Participants

The study population was selected from the multicenter international registry “Identification of Predictors for Coronary Plaque Erosion in Patients With Acute Coronary Syndrome Study” (http://www.clini​caltr​ials.gov; {"type":"clinical-trial","attrs":{"text":"NCT03479723","term_id":"NCT03479723"}}NCT03479723). Patients presenting with ACS who underwent OCT imaging of the culprit lesion were eligible. Among 1699 patients, 586 patients were excluded and 1113 cases were included in the final analysis (Figure S1). Although the study cohort consists of patients from 6 countries, the majority of patients (75.6%) were from Japan (Table S1). The study period at each institution and the number of cases per year are shown in Figures S2 and S3. The diagnosis of ACS, which included ST‐segment–elevation myocardial infarction (STEMI) and non‐ST‐segment–elevation ACS, was made according to the current American Heart Association/American College of Cardiology guidelines.9, 10 STEMI was defined as continuous chest pain that lasted >30 minutes, arrival at the hospital within 12 hours from the onset of symptoms, ST‐segment elevation >0.1 mV in ≥2 contiguous leads or new left bundle branch block on the 12‐lead ECG, and elevated cardiac markers (creatine kinase myocardial band or troponin T/I). Non–ST‐segment–elevation ACS included non–ST‐segment–elevation myocardial infarction (NSTEMI) and unstable angina pectoris. NSTEMI was defined as ischemic symptoms in the absence of ST‐segment elevation on ECG with elevated cardiac markers. Unstable angina pectoris was defined as having newly developed or accelerating chest symptoms on exertion or rest angina within 2 weeks. The culprit lesion was determined based on angiographic findings, ECG changes, and/or left ventricular wall motion abnormalities. Demographic and OCT findings of the culprit lesions were evaluated. All images were deidentified, digitally stored, and sent to Massachusetts General Hospital (Boston, MA). The protocol was approved by the institutional review board at each site, and written informed consent was obtained from all patients before enrollment.