Coronary artery disease (CAD) is a very common cause of heart failure affecting millions of people worldwide, which is caused by build-up of plaque inside arteries of the heart. Build-up of plaque eventually impacts the blood supply to the heart. In medicine, techniques (invasive or non-invasive) such as coronary angiography, intravascular ultrasound, computed tomography, magnetic resonance imaging, positron emission tomography and transthoracic echocardiography can be used to diagnose CAD.

The investigators aim to study Coronary Artery Disease significance with the combination of computed tomography angiography (CTA), and computational fluid dynamics (CFD) methods. CTA is a non-invasive technique to visualize arterial vessels, which uses computer-processed x-rays. Computational Fluid Dynamics employs digital computers and numerical methods to solve complex flow patterns inside arterial vessels. Combining these two methods, the investigators are able to provide detailed blood flow information and mechanical stress distributions on the vessels. This study therefore, aims to propose a non-invasive methodology to assess the significance of CAD.

Cardiovascular disease is the leading cause of death in Singapore, and accounts for 31.9% of all deaths in 2010. Coronary vascular dysfunction has been linked to the development of cardiovascular-related events, such as death, myocardial infarction (MI), stroke and unstable angina. Recently, impaired coronary vaso-motion has been suggested as an independent predictor of poor prognosis, which can predict cardiovascular events in patients with epicardial Coronary Artery Disease . Coronary vaso-motion refers to the change in diameter of a coronary vessel in response to vasoactive agent, which is measured via quantitative coronary angiography (QCA). Better coronary vaso-motion response has been associated with improved survival for both obstructive and non-obstructive CAD.

Another widely used invasive clinical imaging technology to assess CAD is intravascular ultrasound (IVUS), which uses ultrasound technology for imaging the endothelium of vessels. Since detailed histological information of plaques on the endothelium of coronary arteries can be provided by IVUS, it is used as gold standard in evaluating progression or regression of plaque.

Although coronary vaso-motion, FFR and IVUS have been shown to improve clinical outcomes and procedural cost-efficiency in terms of guiding percutaneous interventions, they are invasive procedures. Non-invasive option for the diagnosis of myocardial ischemia is required to relief the patients' pain and medical cost due to the invasive cath. This study aims to fill in the gap. The investigators hypothesize that non-invasive FFRCT can be obtained by combining CT images and CFD methods, which can be used to assess the physiologic significance of CAD.

Inclusion Criteria:

1. Aged 21-98.
2. Undergoing coronary angiography, who had received coronary CTA within 2 months before the scheduled coronary angiography.

Exclusion Criteria:

1. Individuals unable to provide informed consent.
2. Non-cardiac illness with life expectancy <2 years.
3. Pregnant or breastfeeding state. Female patients who have a chance of becoming pregnant will receive pregnancy testing to exclude pregnant women from entering the study.
4. Allergy to iodinated contrast.
5. Significant arrhythmia; heart rate ≥ 100 beats/min; systolic blood pressure ≤90 mmHg.
6. Renal dysfunction (Glomerular filtration rate (GFR) <30 mL/min/1.73m2).
7. Contraindication to beta blockers or nitroglycerin.
8. Canadian Cardiovascular Society class IV angina.
9. Significant valvular pathology
10. Previous coronary artery bypass surgery
11. Previous Percutaneous coronary intervention
12. Contraindication to adenosine administration (e.g. asthma, chronic obstructive pulmonary disease, heart rate <50 beats/min)
13. Patients with an acute myocardial infarction or unstable arrhythmias
14. Patients with a left ventricular ejection fraction less than 30%

Patients with diagnosed Coronary Artery Disease