What is CT coronary angiography?

CT coronary angiography (CTCA) is a non-invasive imaging test that uses a computed tomography (CT) scanner and intravenous contrast dye to produce detailed three-dimensional images of the coronary arteries — the vessels that supply blood to the heart muscle. It detects atherosclerotic plaques, identifies significant stenoses and assesses coronary artery anatomy, all without a catheter or hospital admission.

CTCA has transformed the investigation of stable chest pain. Current guidelines (ESC 2019, AHA/ACC 2021) recommend CTCA as the preferred first-line investigation for intermediate-risk stable chest pain due to its high negative predictive value and excellent safety profile.

• Obstructive coronary artery disease (CAD): Stenoses causing ≥50% luminal narrowing (haemodynamically significant). Guides decision to proceed to invasive angiography or revascularisation.
• Non-obstructive atherosclerosis: Identifies early plaque before it causes symptoms. A normal CTCA is highly reassuring; non-obstructive plaque identifies a group needing aggressive risk factor modification.
• Coronary artery anomalies: Anomalous coronary origins — important cause of sudden death in young people, especially athletes.
• CABG graft patency: Assesses bypass graft status non-invasively.
• CT-derived fractional flow reserve (CT-FFR): Software-derived functional assessment of stenosis significance from CTCA data — avoids invasive pressure wire measurement.
• Plaque characteristics: High-risk plaque features (low-attenuation plaque, positive remodelling, spotty calcification) identify lesions at higher risk of acute rupture.

The Agatston calcium score (CAC score) quantifies calcified atherosclerotic plaque in the coronary arteries. It is one of the most powerful imaging biomarkers of cardiovascular risk — improving risk reclassification beyond traditional risk factors.

A CAC score of 0 is associated with very low cardiovascular event risk over 5–10 years and may avoid the need for statin therapy in truly low-risk individuals.

Appropriate indications

• Stable chest pain with low-to-intermediate pre-test probability of obstructive CAD
• Atypical symptoms (breathlessness, fatigue, jaw pain) without clear diagnosis
• Equivocal or uninterpretable exercise stress test
• Young patients (<60 years) — non-invasive coronary exclusion preferred
• Pre-operative cardiac risk assessment for major surgery
• Post-revascularisation — graft patency assessment
• Evaluation of congenital coronary artery anomalies

When CTCA is not preferred

• Very high pre-test probability of CAD (proceed directly to invasive angiography)
• High resting heart rate or irregular rhythm (AF) — may degrade image quality (though modern scanners handle this better)
• Severe renal impairment — contrast contraindicated
• Allergy to iodine contrast media

How to prepare

• Avoid caffeine for 24 hours before the scan
• Fast for 4 hours (contrast-enhanced CTCA)
• Some patients receive a beta-blocker orally or IV to slow the heart rate for optimal image quality (target HR <65 bpm)
• IV cannula is inserted for contrast injection
• The scan itself takes approximately 5–10 minutes; total appointment time is around 60 minutes
• You will be asked to hold your breath for 10–15 seconds during image acquisition

Radiation and safety

Modern CTCA uses low-dose protocols. Effective radiation dose is typically 1–5 mSv — equivalent to 6–30 months of natural background radiation. This risk is negligible compared to the diagnostic value, particularly when alternative management decisions (invasive angiography, unnecessary surgery) carry higher procedural risks.

CTCA is the ideal first-line test to exclude CAD non-invasively. If CTCA reveals obstructive disease requiring intervention, the patient can then be referred for invasive angiography with a view to PCI or CABG.