The purpose of the study is to evaluate diagnostic performance of high iodine (iopamidol 370 mg/dl) content versus low iodine (iodixanol 300 mg/dl) content for diagnostic accuracy by contrast-enhanced Coronary Cardiac Computed Tomography (CCTA) using a 64-detector-row CT scanner for detection of presence or absence of coronary artery obstruction when compared against invasive coronary angiography, the standard of truth.

Coronary Cardiac CT (CCTA) is a widely accepted modality for non-invasive evaluation of coronary atherosclerosis. The diagnostic performance of CCTA for detecting coronary artery plaque burden has been validated in numerous studies, reaching a negative predictive value of 99%.

The current gold standard for anatomic coronary imaging is Invasive Coronary Angiography (ICA) which portends a small but significant procedural-related complication of 1.7%. Non-invasive coronary imaging has the potential to replace ICA but the variability in diagnostic performance of CCTA remains under study. Among the potential variables causing differences in diagnostic performance is perhaps the degree of opacification of coronary artery by iodinated contrast. While numerous contrast agents exist, those that provide improved low and high contrast resolution (for delineating plaque from arterial wall and lumen from plaque, respectively) are hypothetically, the most optimal agents. To date, however, this has not been well evaluated. Further, use of a contrast agent which maximizes patient comfort is desired, as this may reduce heart rate increases and heart rate variability, which may in turn improve diagnostic image quality of CCTA.

We hypothesize that the use of lower iodine content iso-osmolar agent - iodixanol - will improve diagnostic performance and patient comfort, as compared to higher iodine content low osmolar iodinated contrast - iopamidol.

Inclusion Criteria:

• The subject is ≥18 years old.
• The subject has typical or atypical chest pain suspected of Coronary Artery Disease (CAD) and is referred for an elective coronary angiography.
• The subject must be scheduled to undergo a CATH procedure between 72 hours and 3 weeks of the CCTA procedure.
• The subject must not undergo any cardiac interventional treatment between the 2 procedures.
• The subject must have a sinus rhythm with stable heart rate of ≤75 beats per minute (bpm) and if heart rate is >65 bpm, the subject must agree to the use of beta-blocker(s) prior to the CT scan procedure to achieve stable heart rate of ≤65 bpm.

Exclusion Criteria:

• The subject has an established diagnosis of CAD by a) previous ICA, b) prior myocardial infarction confirmed by electrocardiogram (ECG), or c) prior revascularization (balloon angioplasty, stent placement, or coronary artery bypass grafting (CABG).
• The subject has a known allergy to iodinated contrast agent, including but not limited to hives, anaphylactoid or cardiovascular reactions, laryngeal edema and bronchospasm.
• The subject has impaired renal function with a serum creatinine level of 1.7 mg/dL (150 μmol/L) or above.
• The subject has atrial fibrillation/flutter or any irregular heart rhythm considered by the investigator to interfere with temporal acquisition of cardiac CT images.
• The subject has a resting heart rate of >100 bpm and/or a resting systolic blood pressure of <100 mm Hg.
• The subject has an artificial heart valve(s).
• The subject has had prior pacemaker or internal defibrillator lead implantation.
• The subject's resting heart rate is >65 bpm and beta-blocker therapy is contraindicated.
• The subject has a contraindication to Verapamil when beta-blocker therapy cannot be administered.
• The subject has a contraindication to nitroglycerin.
• The subject has evidence of ongoing or active clinical instability.

Subjects are over 18 years or older. They have been referred to a cardiologist for suspected CAD and then scheduled for an elective invasive coronary angiography.