What is the purpose and procedure of a CT (Computed Tomography) coronary angiogram?

CT Coronary Angiogram: Purpose and Procedure

Primary Purpose

CT coronary angiography (CCTA) is a non-invasive imaging technique that visualizes the coronary arteries to detect obstructive coronary artery disease, characterize atherosclerotic plaque, and evaluate coronary anatomy without requiring catheter-based procedures. 1, 2

Clinical Applications

Diagnostic Indications

• CCTA is recommended for symptomatic patients with chest pain and intermediate pre-test probability of coronary artery disease (CAD) to diagnose or exclude obstructive disease 1
• The test should be considered as an alternative to invasive coronary angiography in patients without prior CAD history who present with chest pain and inconclusive diagnostic assessment 1
• CCTA is appropriate for ruling out CAD in low-risk patients before valve surgery 1
• The examination can simultaneously evaluate other life-threatening causes of chest pain including pulmonary embolism and acute aortic syndrome using "triple rule-out" protocols 3, 4

Anatomical Assessment Capabilities

• CCTA provides detailed visualization of coronary artery stenosis, plaque characteristics (calcified vs. non-calcified), and vessel anatomy 1, 2
• The technique can assess bypass graft patency and coronary stents ≥3 mm in diameter in patients with new or worsening symptoms 1
• CCTA detects coronary artery anomalies and other structural abnormalities not visible on functional testing 3
• The modality can evaluate disease complexity, vessel size, lesion length, and optimal landing zones for stents or bypass grafts when planning revascularization 2

Diagnostic Performance

Strengths

• CCTA demonstrates 90-95% or greater sensitivity and specificity for occlusive CAD with current multidetector technology 1
• The test has an excellent negative predictive value—if no calcified or non-calcified plaque is found, it is highly unlikely that symptoms are due to atherosclerotic coronary disease 1, 3
• CCTA can detect up to 50% more coronary segments with increased wall thickness compared to conventional coronary angiography 1

Limitations

• The positive predictive value is lower because CCTA provides anatomic information without functional or physiological assessment of ischemia 1
• Severe coronary calcifications, coronary stents, and poor image quality can lead to overestimation of stenosis severity 5
• CCTA cannot reliably assess the hemodynamic significance of intermediate stenoses (50-70%) without additional functional testing 1, 5

Procedural Requirements

Patient Preparation

• Heart rate control is essential for optimal image quality—beta blockers are usually required to achieve a slow, regular heart rate (typically <60-70 beats per minute) 1, 6
• Patients with persistently high heart rates require scanners with high temporal resolution (such as dual-source systems) for adequate image quality 1
• The examination requires a single breath hold for image acquisition 1

Technical Considerations

• The procedure uses intravenous iodinated contrast material, requiring assessment of renal function before administration 1
• Spatial resolution is approximately 0.6 mm, providing excellent anatomic detail 1
• Radiation exposure ranges from 8-24 mSv with standard protocols, though contemporary scanner technology allows imaging at decreasing radiation doses 1

Integration with Other Testing

When CCTA is Insufficient

• Functional imaging (stress echocardiography, stress MRI, SPECT, or PET) is recommended when CCTA shows stenosis of uncertain functional significance 5
• Invasive coronary angiography with fractional flow reserve (FFR) measurement is indicated when functional imaging is positive or symptoms are severe and refractory to medical treatment 5
• In heart transplant patients, CCTA is not recommended for routine clinical use in detecting cardiac allograft vasculopathy 1

Complementary Role with Calcium Scoring

• Coronary artery calcium (CAC) scoring on non-contrast CT can be performed before CCTA to assess atherosclerotic burden 1, 7
• A zero calcium score has high negative predictive value for excluding obstructive CAD in some populations, though it does not completely exclude non-calcified plaque in symptomatic patients 1, 5
• CAC scores ≥400 are associated with higher likelihood of obstructive disease and ischemia on provocative testing 1

Common Pitfalls to Avoid

• Do not use CCTA as a screening tool in asymptomatic individuals—it should be reserved for symptomatic patients or specific high-risk scenarios 5
• Avoid ordering CCTA in patients with severe coronary calcifications where image quality will be inadequate for accurate stenosis assessment 5
• Do not interpret anatomic stenosis on CCTA as automatically indicating hemodynamically significant disease requiring revascularization without functional correlation 1, 5
• Recognize that CCTA accuracy is compromised in patients with prior coronary stents or bypass grafts due to blooming artifacts 5

Recent Evidence on Clinical Outcomes

• The 2022 DISCHARGE trial demonstrated that among patients with stable chest pain and intermediate pretest probability of CAD, CT-guided strategy resulted in similar rates of major adverse cardiovascular events compared to invasive angiography, but with significantly lower procedure-related complications (0.5% vs. 1.9%) 8