The EMERALD II study is a multinational, multicenter, and retrospective study. ACS patients who underwent CCTA from 1 months to 3 years prior to the event will be retrospectively identified. Plaques in the non-culprit vessels will be regarded as a primary control group.

The mechanisms of plaque rupture are not fully understood. Hemodynamic forces, plaque vulnerability, and the interaction between these factors may cause plaque instability and subsequent acute coronary syndrome (ACS). Previously, the first-in-human study, EMERALD I, showed that the addition of hemodynamic parameters calculated noninvasively from coronary computed tomography (CCTA) using computational fluid dynamics (CFD) improved the ability to predict the risk of ACS compared with conventional approaches based on anatomical stenosis severity and adverse plaque characteristics. In addition to hemodynamic properties, quantified compositional plaque volumes such as fibrofatty and necrotic core volume (FFNC) or low-attenuation plaque burden (% plaque to vessel volume) have been proven to be robust prognostic indicators of ACS. While various hemodynamic and plaque features predictive of ACS have been introduced, the relative importance among them and the additive value of the risk model with the best features over the current diagnostic scheme of CCTA have not been proposed. In this regard, we designed the subsequent EMERALD II study to find the best hemodynamic and plaque features in prediction of ACS from comprehensive CCTA analysis, including per-lesion and per-vessel plaque quantification and hemodynamic analysis, and to investigate whether a comprehensive risk prediction model with them has an incremental value in a larger population.

Inclusion Criteria:

1. Patients who presented with ACS* and underwent invasive coronary angiography with identifiable culprit lesion

2. The patients who underwent coronary CT angiography, regardless of the reason (for example, routine healthcare check-up, or evaluation for stable angina or atypical chest pain) prior to the acute event.

3. Time limit of CCTA: 1 months ~ 3 years prior to the event.

   • Definition of ACS:

A. The patients with acute myocardial infarction should have cardiac enzyme elevation and identified culprit lesion confirmed by invasive coronary angiography, IVUS, or OCT.

B. The patients with unstable angina should have evidence of plaque rupture, which includes at least one of the following: (1) the presence of plaque rupture or haziness including thrombus at invasive coronary angiography, (2) angiographic stenosis ≥90%, or (3) the evidence of rupture confirmed by IVUS or OCT.

Exclusion criteria for Patient enrollment

1. Patients with ACS without clear evidence of culprit lesion
2. Patients with stents in two or more vessel territories prior to CCTA
3. Poor quality of CCTA which is unsuitable for plaque and CFD analysis
4. Patients with ACS culprit lesion in a stented segment
5. Patients with previous history of coronary artery bypass graft surgery
6. Patients with revascularization after CCTA and before ACS event (*Patients with elective PCI for 1 vessel within 3 month after CCTA can be enrolled.
7. Secondary ACS due to other general medical conditions, such as sepsis, arrhythmia, bleeding, etc.
8. Patients with unstable angina without evidence of plaque rupture Additional exclusion criteria for Computational Fluid Dynamics
9. Poor quality CCTA images unsuitable for CFD and plaque analysis
10. No unprocessed CCTA data

Patients who presented with acute coronary syndrome (acute myocardial infarction or unstable angina) and had undergone CCTA from 1 months to 3 years prior to the event.