What is the preferred initial test for suspected coronary artery disease, Coronary Artery Calcium (CAC) scan or Computed Tomography (CT) angiogram?

CT Angiography is Superior to CAC Scoring for Suspected Coronary Artery Disease

For patients with suspected coronary artery disease, CT angiography (CCTA) is the preferred initial test over coronary artery calcium (CAC) scoring, as CCTA directly visualizes obstructive disease, guides treatment decisions, and improves clinical outcomes including mortality reduction. 1, 2

Why CCTA Over CAC Scoring

Direct Visualization vs. Indirect Marker

• CCTA provides direct anatomical visualization of both obstructive and non-obstructive coronary disease, allowing definitive diagnosis and risk stratification in a single test 1
• CAC scoring only detects calcium as an indirect marker of atherosclerosis burden but cannot identify obstructive stenoses or guide revascularization decisions 1, 3
• The 2024 ESC Guidelines explicitly state that "coronary calcium detection by CT is not recommended to identify individuals with obstructive CAD" 1

Proven Mortality and Morbidity Benefits

• CCTA demonstrates superior outcomes compared to standard care, with the SCOT-HEART trial showing a 41% reduction in cardiovascular death or non-fatal MI (2.3% vs 3.9% over 5 years) when CCTA was added to routine evaluation 1, 2
• The PROMISE trial demonstrated equivalent safety with CCTA compared to functional testing, with fewer non-diagnostic invasive angiograms (12% vs 8% showing no obstructive disease) 1
• Knowledge of plaque presence from CCTA motivates patients to implement lifestyle changes and adhere to preventive therapies, translating to improved long-term outcomes 2, 4

Clinical Algorithm for Test Selection

Low to Moderate Pre-Test Likelihood (>5%-50%)

• CCTA is the Class I, Level A recommendation as first-line test 1, 2
• This population represents the majority of symptomatic patients where ruling out obstructive disease is the primary goal 1
• CCTA's exceptional negative predictive value allows safe exclusion of CAD without further testing 1

Moderate to High Pre-Test Likelihood (>15%-85%)

• Functional imaging (stress echo, SPECT, PET, or CMR) is recommended as first-line to directly assess hemodynamic significance and quantify ischemia 1
• Functional tests have better "rule-in" power for obstructive disease in this higher-risk population 1
• If functional testing is equivocal or non-diagnostic, CCTA should be considered next 2

Very High Pre-Test Likelihood (≥85%)

• Proceed directly to invasive coronary angiography with FFR/iFR availability for patients with severe refractory symptoms or high-risk clinical features 1

Critical Contraindications to CCTA

CCTA should NOT be performed when:

• Extensive coronary calcification is present (limits accurate stenosis assessment) 1, 2
• Irregular heart rate or atrial fibrillation (causes motion artifact) 1, 2
• Inability to cooperate with breath-hold commands 1, 2
• Significant obesity (degrades image quality) 1, 2
• Severe renal insufficiency or documented iodinated contrast allergy 1

In these scenarios, functional imaging becomes the preferred alternative 1

Why CAC Scoring Alone is Insufficient

Limited Diagnostic Utility

• CAC scoring cannot diagnose obstructive CAD and provides no information about stenosis severity or location 1, 3
• Research demonstrates that adding CAC scoring to CCTA provides no incremental prognostic value in symptomatic patients (AUC 0.892 for CCTA alone vs 0.902 with CAC added, P=0.198) 3
• CAC scoring has low specificity for obstructive disease, as extensive calcification can occur without significant stenosis 1

Role Limited to Asymptomatic Screening

• CAC scoring's primary utility is risk stratification in asymptomatic individuals to guide preventive therapy intensity 1, 5
• A CAC score of zero predicts excellent prognosis in asymptomatic patients (annual cardiovascular event rate <1%) 1, 6
• For symptomatic patients with suspected CAD, CAC scoring should not be used as the diagnostic test 1

Sequential Testing Strategy

If CCTA shows stenosis of uncertain functional significance (typically 40-90% diameter stenosis):

• Proceed to functional imaging (stress testing) to assess hemodynamic significance 1
• Alternatively, consider FFR-CT (fractional flow reserve derived from CCTA) to avoid additional testing 2

If functional testing is negative but symptoms persist:

• Consider CCTA to detect obstructive CAD and assess atherosclerotic plaque burden 2

Common Pitfalls to Avoid

• Do not order CAC scoring when you need to diagnose obstructive CAD in symptomatic patients - it cannot answer this clinical question 1
• Do not proceed with CCTA in patients with extensive calcification - image quality will be inadequate and functional testing is preferred 1, 2
• Do not skip functional assessment of intermediate stenoses (50-90%) found on CCTA before revascularization - FFR/iFR is required unless stenosis is >90% 1
• Do not ignore non-obstructive plaque on CCTA - this finding should trigger intensification of preventive therapies including statins 1, 4