This study is to see whether the low-dose coronary computed tomographic angiography (CCTA) protocol is as safe and efficacious as conventional-dose protocol in early triage of acute chest pain.

Currently, CCTA is a valuable tool for early triage of low to intermediate risk acute chest pain patients in emergency department. However, it has been criticized for causing unnecessary radiation exposure in the population where its majority has no coronary lesion. A low-dose CCTA protocol comprised with 1) dedicated cardiac imaging protocol (rather than triple rule-out protocol), 2) prospective gating and 3) without additional imaging for calcium scoring will be used to implement the low-dose imaging. We hypothesized that the low-dose CCTA protocol will be as safe and efficacious as conventional dose protocol while decreasing the amount of radiation exposure significantly.

Inclusion Criteria:

- Patients visiting emergency department for A) acute onset (<12hr) chest pain or equivalent symptoms B) aged between 25-55, C) that requires to rule out acute coronary syndrome.

Exclusion Criteria:

1. Known coronary artery disease and/or any related intervention (STENT, CABG)
2. Elevated cardiac biomarkers (CK-MB, Troponin I)
3. Ischemic ECG changes
4. Documented evidence of low LV systolic function (ejection fraction ≤ 45%)
5. TIMI risk >4
6. Unstable vital sign (e.g. hypoxemia, shock)
7. Patients with contraindication to iodinated contrast and/or beta blockers including renal failure or reactive airway diseases such as COPD or asthma
8. Atrial fibrillation on initial ECGs
9. Active renal disease, serum creatinine ≥1.5 mg/dl
10. Negative coronary angiography or CCTA within 6 months
11. Modified Wells criteria >4 or D-dimer > 0.5ug/mL
12. Suspicious of aortic dissection or D-dimer > 0.5ug/mL