Coronary artery disease (CAD) remains the leading cause of mortality worldwide, responsible for approximately 17.9 million deaths annually. CT Coronary Angiography (CCTA) has emerged over the past two decades as a powerful, non-invasive alternative to invasive catheter-based coronary angiography for evaluating patients with suspected CAD. With modern 256- and 320-detector CT scanners, CCTA can image all three major coronary arteries and their branches in a single breath-hold acquisition — delivering detailed anatomical information about coronary plaque, stenosis degree, and vessel calcification without the risks associated with arterial catheterization.

When is CCTA Indicated?

CCTA is most valuable in the evaluation of patients with intermediate pre-test probability of obstructive CAD (typically 15–65% based on age, sex, symptom characteristics, and risk factors). In this group — which includes most patients presenting with stable chest pain to outpatient cardiology clinics — CCTA's extremely high negative predictive value (greater than 99%) makes it ideal for safely excluding significant coronary disease without invasive angiography. Major clinical applications include:

  • Stable chest pain evaluation in intermediate pre-test probability patients (replacing exercise stress testing per 2019 ESC guidelines for stable CAD)
  • Acute chest pain evaluation in the emergency department (CCTA pathway in the HEART pathway protocol)
  • Evaluation of coronary anomalies (anomalous origin, coronary fistulas)
  • Pre-operative assessment before non-cardiac surgery in selected patients
  • Follow-up of coronary artery bypass grafts (CABG) patency assessment

CT Acquisition Protocol: Heart Rate Control is Critical

Successful CCTA requires a stable, low heart rate — ideally below 65 beats per minute — to minimize cardiac motion artifact, which is the primary technical source of non-diagnostic or degraded image quality. Standard patient preparation includes: oral or intravenous beta-blocker administration (typically metoprolol) to achieve heart rate below 65 bpm; sublingual nitroglycerin spray immediately prior to scanning to dilate coronary arteries and improve vessel visibility; and adequate patient breath-hold coaching (typical scan duration under 5 seconds on modern scanners). Retrospective ECG-gating acquires data throughout the cardiac cycle and allows retrospective reconstruction at multiple cardiac phases — higher radiation dose but more robust motion correction. Prospective ECG-triggering acquires data only during the target cardiac phase (typically mid-diastole at 70–75% of the R-R interval) — lower radiation dose but less flexible for patients with irregular rhythms.

Coronary Artery Anatomy on CCTA

A systematic approach to coronary anatomy review is essential. The three major coronary arteries and their primary branches are assessed using the standard 15-segment model of the American Heart Association. The Left Main Coronary Artery (LMCA) arises from the left coronary sinus and bifurcates into the Left Anterior Descending (LAD) and Left Circumflex (LCx) arteries. The Right Coronary Artery (RCA) arises from the right coronary sinus. Dominant circulation — which artery supplies the posterior descending artery — must be determined: right dominant (85%), left dominant (8%), or co-dominant (7%).

Coronary Plaque Characterisation

One of the major advantages of CCTA over invasive angiography is the ability to characterize the composition of coronary atherosclerotic plaque — not merely the degree of luminal stenosis. CT plaque types include: Calcified plaque (greater than 130 HU, dense white deposits — strongly associated with stable, less vulnerable lesions); Non-calcified plaque (low attenuation soft plaque — including lipid-rich, fibrofatty, and fibrous subtypes); and Mixed plaque (combination of calcified and non-calcified components). High-risk plaque features associated with acute coronary syndrome risk include: low-attenuation plaque, napkin-ring sign, positive remodeling, and spotty calcification.

Stenosis Grading and Reporting

Coronary stenosis on CCTA is graded as: Minimal (1–24% diameter reduction), Mild (25–49%), Moderate (50–69%), and Severe (70–99%). Complete occlusion represents 100% stenosis. Hemodynamically significant stenosis is conventionally defined as 50% or greater in the LMCA or 70% or greater in other major vessels. The structured CCTA report should address: coronary dominance, calcification burden (Agatston calcium score if acquired), plaque presence and characteristics for each of the 15 segments, degree of stenosis, and overall coronary artery disease classification (absent, minimal, mild, moderate, severe, or complete occlusion).