Coronary CT Angiography and CAD-RADS Reporting

Definition and Clinical Role

Coronary computed tomographic angiography (CCTA) is a non-invasive anatomical examination that depicts the coronary arterial lumen, atherosclerotic plaque, and the severity and distribution of coronary stenosis. Modern cardiac CT can acquire a three-dimensional cardiac dataset within approximately 5–15 seconds, with submillimetre spatial resolution. Iodinated contrast is generally required for coronary angiography because the intrinsic contrast between the cardiac chambers, blood pool, and vascular structures is limited.

CCTA has become an important first-line investigation for selected patients with suspected coronary artery disease (CAD), particularly those with stable chest pain, no previous diagnosis of CAD, and a low clinical likelihood of obstructive disease when good image quality is expected. It is also an alternative to invasive coronary angiography (ICA) for excluding non-ST-segment elevation acute coronary syndrome (NSTE-ACS) in patients with a low-to-intermediate likelihood of CAD when cardiac troponin and/or the ECG is normal or inconclusive.

The principal diagnostic strength of CCTA is its ability to exclude significant anatomical CAD with high sensitivity and a high negative predictive value, particularly when disease prevalence is low. It also identifies non-obstructive plaque, which may have important prognostic and preventive implications even when stenosis is not flow-limiting.

CCTA should be distinguished from coronary artery calcium (CAC) scoring. CAC imaging is a rapid, non-contrast, low-radiation CT examination that quantifies coronary calcification, whereas CCTA uses iodinated contrast to assess the coronary lumen and plaque morphology.

Pathophysiological and Imaging Basis

CT generates cross-sectional images from x-ray attenuation measurements obtained at multiple angles. Tissue attenuation is expressed relative to water in Hounsfield units. Bone is highly attenuating, air has very low attenuation, and blood and myocardium have intermediate values. Iodinated contrast increases the attenuation of the blood pool and permits delineation of the coronary lumen.

Coronary imaging is technically demanding because the vessels are small and are subject to both cardiac and respiratory motion. Image quality is therefore improved by:

• A slow, regular heart rate

• Adequate breath-holding

• ECG-synchronised acquisition

• Appropriate intravenous iodinated contrast timing

• Sublingual nitroglycerin immediately before contrast administration to enlarge the coronary lumen

• Contemporary scanners, generally including 64-slice technology or above

• An experienced imaging team

Prospective ECG-triggered axial acquisition has reduced radiation exposure compared with earlier techniques. Radiation exposure depends on the protocol and scanner; CAC scanning is associated with a particularly low dose, approximately 1–2 mSv, while contemporary combined coronary, pulmonary, and aortic angiography can achieve less than 5 mSv in appropriate settings.

Clinical Presentation and Indications

CCTA is relevant to several clinical presentations.

Stable chest pain

CCTA is recommended as an initial test for diagnosing CAD in stable patients with:

• Low clinical likelihood or no previous diagnosis of CAD

• Characteristics suggesting that good-quality imaging is achievable

It is particularly useful when the clinical question is whether CAD is present and when an anatomical examination is preferred over an initial functional test. CCTA may be advantageous in adults younger than 65 years and in patients with a lower suspicion of obstructive disease.

Patients with no plaque or stenosis on CCTA should be reassured, and non-atherosclerotic causes of symptoms should be considered. When plaque is present but stenosis is minimal or mild, symptoms are also unlikely to be caused by flow-limiting epicardial disease, and alternative causes should remain under consideration.

Acute chest pain and suspected NSTE-ACS

CCTA may be used as an alternative to ICA for excluding NSTE-ACS in patients with low-to-intermediate CAD likelihood when troponin and/or ECG findings are normal or inconclusive. In emergency-care populations with low-to-intermediate risk, CCTA has been associated with reduced emergency-department costs and length of stay without a difference in death or rehospitalisation in the cited randomized evidence. More recent data have also indicated that an upfront CCTA strategy may reduce the need for invasive angiography in selected patients with suspected myocardial infarction.

CCTA should not replace the clinical assessment, serial ECGs, rapid biomarker testing, and structured clinical decision pathways. In patients with acute chest pain, the possibility of pulmonary embolism, aortic dissection, or other non-coronary causes may influence the choice of CT protocol.

Pre-operative assessment

The role of pre-operative CCTA before non-cardiac surgery remains selective. In patients with a history of or risk factors for CAD, or a history of congestive heart failure, CCTA improved estimation of postoperative cardiovascular death and non-fatal myocardial infarction when added to the Revised Cardiac Risk Index. However, it also produced substantial overestimation of risk among patients who did not experience the primary outcome.

CCTA combined with CT-derived fractional flow reserve (FFR-CT) has identified functionally severe coronary stenosis in asymptomatic patients undergoing carotid endarterectomy or peripheral vascular surgery. Nevertheless, pre-operative coronary angiography and revascularisation should follow the same indications used outside the surgical setting. Routine invasive angiography may cause procedural risk and unpredictable delays to surgery.

Structural and valvular heart disease

Cardiac CT is frequently used for procedural planning before transcatheter aortic or mitral valve replacement. It can assess:

• Aortic root and valve anatomy

• Ventricular size and function

• The great vessels

• Coronary arteries and collateral vessels

• Prosthetic valve structure and function

• Paravalvular complications

• Cardiac masses and selected extracardiac structures

In patients being evaluated for transcatheter aortic valve implantation (TAVI), CCTA has high sensitivity but more modest specificity for obstructive CAD because severe aortic valve disease is often accompanied by extensive coronary calcification and atrial fibrillation. If the CCTA acquired during standard pre-TAVI assessment is of sufficient quality to exclude relevant CAD, omission of invasive coronary angiography should be considered.

Evaluation and Pre-Examination Assessment

Before referral for CCTA, the following should be assessed:

• Heart rate and rhythm: A slow, regular rhythm is desirable. Tachycardia that cannot be adequately controlled reduces accuracy.

• Ability to follow breath-holding instructions: Respiratory motion can compromise coronary assessment.

• Renal function: Kidney function should be reviewed before iodinated contrast administration.

• Contrast allergy: A history of allergy to contrast agents should be assessed.

• Coronary calcification: Heavy calcification reduces interpretability because of blooming artefact.

• Prior coronary stents: Stent evaluation may be limited by artefact, although newer photon-counting CT technology may improve visualisation.

• Scanner and institutional capability: High-quality imaging requires appropriate contemporary CT technology and an experienced team.

Beta-blocker premedication, administered orally or intravenously when appropriate, may be used to slow the heart rate. Suitability for such treatment should be considered before the examination. The source material does not provide specific beta-blocker regimens or dosing schedules.

CCTA is less useful when there is:

• Poorly controlled tachycardia

• Heavy coronary calcification

• Extensive stent-related artefact

• Inability to comply with breath-holding

• Technical limitations related to temporal or spatial resolution

In older patients with extensive calcification, functional testing may be preferable.

Diagnostic Assessment

Coronary calcium scoring

CAC scoring is performed without iodinated contrast. It detects calcified coronary atherosclerosis and can support decisions regarding preventive therapies, particularly statins and aspirin, in selected patients without established CAD when cardiovascular risk or the role of lipid-lowering treatment is uncertain.

The Agatston score may be categorised as follows:

CAC scores may also be normalised according to age and sex and reported as percentile values.

A CAC score of zero, particularly in patients with stable symptoms, is associated with a low likelihood of obstructive CAD, and further evaluation may not be necessary in appropriately selected low-risk individuals. CAC may also be identified opportunistically on non-gated chest CT examinations and can provide additional cardiovascular risk information.

CAC scoring is not equivalent to CCTA. It quantifies calcification but does not directly visualise the coronary lumen, non-calcified plaque, or stenosis.

CCTA acquisition and interpretation

A standard coronary CT examination uses:

• ECG synchronisation

• Weight-based, appropriately timed intravenous iodinated contrast

• Breath-holding

• Heart-rate control when required

• Sublingual nitroglycerin to enlarge the coronary lumen

• Three-dimensional post-processing for assessment of coronary anatomy and stenosis

CCTA can depict:

• The presence or absence of CAD

• Coronary plaque burden

• Calcified and non-calcified plaque

• High-risk plaque features

• The location and severity of stenosis

• Proximal and distal disease distribution

• Coronary stents, when technically assessable

• Ventricular function

It can also provide information about the pericardium, lungs, ascending aorta, pulmonary arteries, and other structures. Alternative causes of chest pain identified on cardiac CT include pulmonary embolism, pulmonary infarction, aortic dissection, pericardial effusion, hiatal hernia, and pulmonary artery dilatation.

Diagnostic accuracy

Against invasive angiography, CCTA has demonstrated high sensitivity for stenosis greater than 50%. In one meta-analysis, sensitivity was 97% and specificity was 78%. For functionally significant CAD defined by invasive FFR ≤0.80, sensitivity was 93% and specificity was 53%.

In a prospective comparison involving multiple non-invasive tests, CCTA demonstrated sensitivity of 91% and specificity of 92% for significant CAD defined by invasive angiography. In another head-to-head comparison using invasive FFR ≤0.80 as the reference standard, CCTA had a sensitivity of 90%.

These findings support CCTA as a sensitive anatomical test and an effective rule-out examination. Its ability to identify lesion-specific ischaemia is more limited, and anatomical stenosis does not necessarily establish haemodynamic significance.

CT-derived fractional flow reserve

FFR-CT uses computational algorithms applied to CCTA data to estimate lesion-specific coronary flow. It may be useful for lesions of uncertain haemodynamic significance. A normal FFR-CT can help avoid unnecessary invasive angiography.

For intermediate lesions, particularly in proximal or mid-vessel locations, current guidance supports consideration of FFR-CT or other functional assessment. FFR-CT may also be incorporated into pre-operative evaluation in selected patients.

CT myocardial perfusion

Stress myocardial CT perfusion provides anatomical and physiological information in a single protocol. It can be combined with CCTA, with a radiation exposure reported to be similar to that of nuclear perfusion imaging. In the cited multicentre study, CT perfusion had sensitivity of 88% and specificity of 55% for CAD defined by at least 50% stenosis, compared with sensitivity of 62% and specificity of 67% for SPECT.

Photon-counting CT

Photon-counting CT detectors permit higher spatial resolution. This may improve visualisation of coronary stents and reduce calcium blooming artefacts. Ultra-high-resolution imaging has demonstrated the ability to distinguish mild disease from occlusion in heavily calcified vessels, although the clinical role of these newer techniques continues to evolve.

Other cardiac CT applications

Aortic stenosis

The severity of aortic stenosis can be assessed using the aortic valve Agatston calcium score. Values above 2065 in males and above 1274 in females have been reported to provide good discrimination for severe aortic stenosis and to identify patients with adverse prognosis.

Direct planimetry at the leaflet tips can measure aortic valve area. Multiphase imaging may also identify aortic valve closure during diastole, supporting evaluation of aortic regurgitation. Direct planimetry of the regurgitant orifice can be used to estimate the severity of aortic regurgitation.

Prosthetic valves

CCT is particularly valuable when echocardiography is limited by prosthetic valve artefact. It can assess:

• Prosthetic valve thrombosis

• Hypoattenuated leaflet thickening (HALT)

• Reduced leaflet motion, also called hypoattenuation affecting motion (HAM)

• Pannus

• Mechanical prosthetic leaflet opening and closing

• Paravalvular pseudoaneurysm

• Abscess

• Fistula

• Other complications of prosthetic valve endocarditis

HALT appears as meniscal-shaped hypoattenuating leaflet thickening, generally more prominent at the leaflet base than centrally. Reports should document its location, longitudinal extent, and thickness, and should state whether restricted leaflet motion is present.

Most HALT with reduced leaflet motion is probably subclinical. Oral anticoagulation is associated with a lower incidence of HALT or HAM, and starting oral anticoagulation after detection has been associated with reduction in leaflet thickening. However, the clinical benefit of treating subclinical leaflet thrombosis, including whether it reduces valve degeneration, remains uncertain. The source material does not specify an anticoagulant or dose for this indication.

CCT can detect vegetations on native valves with high diagnostic accuracy, although very small vegetations may be difficult to visualise. In prosthetic valves, it can identify paravalvular pseudoaneurysm, abscess, or fistula. In the cited infective endocarditis guidance, paravalvular lesions detected by CCT constitute a major diagnostic criterion within the modified diagnostic criteria.

CAD-RADS Reporting

Purpose and structure

CAD-RADS, the Coronary Artery Disease-Reporting and Data System, is recommended for standardised reporting of CCTA. The report should communicate:

• The maximum degree of coronary stenosis

• The extent of plaque

• High-risk plaque features when present

• Relevant non-coronary findings

• A management-oriented recommendation

Plaque burden may be incorporated using the P modifier:

• P1: mild plaque burden

• P2: moderate plaque burden

• P3: severe plaque burden

• P4: extensive plaque burden

The source material does not provide formal quantitative thresholds for each plaque-burden category.

CAD-RADS categories

For CAD-RADS 3 or 4A, additional modifiers may include a “1+” designation, prompting consideration of ICA where symptoms or anatomy warrant. CAD-RADS 5 requires particular urgency when acute occlusion is suspected.

Reporting non-coronary information

Prior myocardial infarction should be reported when its features are visible on CTA. Remote infarction is appropriately reported when fatty metaplasia or calcification is present within an infarcted region.

Reports should also identify relevant findings involving:

• The aortic root and ascending aorta

• The pericardium

• The pulmonary arteries

• The lungs

• Cardiac masses

• Prosthetic valves

• Paravalvular structures

CAD-RADS-Based Management in Stable Chest Pain

The intensity of preventive therapy should reflect the total cardiovascular risk, the amount and distribution of plaque, the presence of high-risk plaque features, lesion location, and the severity of obstruction. Extensive plaque burden, particularly P3 or P4, may confer an event rate similar to that of secondary-prevention populations and should prompt aggressive risk-factor modification. The source material identifies high-intensity lipid-lowering therapy and antiplatelet therapy as therapies from which such patients may be more likely to benefit when there are no contraindications, but it does not provide drug names, doses, or patient-specific prescribing criteria.

CAD-RADS-Based Management in Acute Chest Pain

A positive troponin in the presence of CAD-RADS 0–2 should not automatically be attributed to obstructive CAD. Other sources of troponin elevation should be considered.

Guideline Recommendations

The source material supports the following recommendations:

• Use CAD-RADS for CCTA reporting.

• Consider CAC testing when cardiovascular risk or the role of lipid-lowering treatment is uncertain in patients without known CAD.

• Use CCTA as an initial diagnostic test in stable patients with low clinical likelihood or no previous CAD when good image quality is expected.

• Use CCTA as an alternative to ICA for excluding NSTE-ACS in selected low-to-intermediate-risk patients with normal or inconclusive ECG and troponin findings.

• Recognise that high coronary calcium reduces the practical utility of CCTA.

• Use FFR-CT for selected lesions of uncertain haemodynamic significance; a normal result may help avoid unnecessary invasive angiography.

• Consider CT perfusion or stress testing for intermediate CCTA lesions.

• Consider ICA or functional assessment for CAD-RADS 4 disease.

• Recommend ICA for CAD-RADS 4B disease.

• Expedite ICA and revascularisation when CAD-RADS 5 represents suspected acute occlusion.

• In patients undergoing valve surgery, CABG is recommended for coronary stenosis ≥70% and should be considered for stenosis of 50%–70% when concomitant complete revascularisation is appropriate.

• In patients undergoing TAVI, PCI should be considered for high-grade stenosis ≥90% in large vessels ≥2.5 mm. For stenosis ≥70%, PCI may be considered according to symptom status.

• In patients with a primary indication for TAVI, the presence of CAD should influence valve selection, coronary access planning, implantation technique, and commissural alignment.

• When CCTA acquired during pre-TAVI assessment is of sufficient quality to exclude relevant CAD, omission of invasive coronary angiography should be considered.

• In patients undergoing non-cardiac surgery, pre-operative coronary angiography and revascularisation should follow indications used in the non-surgical setting.

Treatment and Preventive Management

CCTA is primarily a diagnostic and risk-stratification examination, but its findings should directly inform preventive care.

No plaque or stenosis

Patients with CAD-RADS 0 should be reassured that the prognosis is excellent in the context described by the source material. Lifestyle-based preventive treatment should be the main strategy for reducing future risk, and non-atherosclerotic causes of symptoms should be considered.

Non-obstructive plaque

Minimal and mild stenoses are unlikely to be flow-limiting. Management should include:

• Evaluation for non-atherosclerotic symptom mechanisms

• Risk-factor modification

• Preventive pharmacotherapy when appropriate

• More intensive preventive therapy when plaque is extensive or high-risk features are present

The identification of plaque, especially extensive plaque, should prompt initiation or intensification of pharmacotherapy in patients not already receiving appropriate prevention. The source material does not specify particular lifestyle targets, lipid concentrations, drug doses, or antiplatelet regimens.

Moderate and severe stenosis

For CAD-RADS 3 lesions, further functional assessment with FFR-CT, CT perfusion, or stress testing may clarify the need for invasive assessment. Preventive treatment should be aggressive, and antianginal therapy should be considered according to guideline-directed care.

For CAD-RADS 4 disease, ICA or functional assessment should be considered. Revascularisation options should be evaluated in conjunction with symptom burden, lesion anatomy, plaque characteristics, and the results of functional assessment.

For CAD-RADS 5 disease, ICA, functional assessment, and/or viability assessment may be appropriate. When acute occlusion is suspected, invasive angiography and revascularisation should be expedited.

Invasive Coronary Angiography

Although CCTA provides highly sensitive non-invasive anatomical assessment, precise evaluation of coronary anatomy may still require ICA. Invasive angiography remains particularly relevant when:

• CCTA demonstrates high-risk anatomy

• Symptoms persist despite medical therapy

• Non-invasive tests are inconclusive

• There is suspected left main or extensive multivessel disease

• Revascularisation is being considered

• CAD-RADS 4B or 5 findings are present

• Acute coronary occlusion is suspected

Angiographic risk depends on the number of diseased vessels, the severity and location of stenosis, proximal involvement, left main disease, and left ventricular function. Severe left main disease and its anatomical equivalent—severe proximal LAD and proximal left circumflex disease—are especially high-risk subsets and remain indications for revascularisation.

The presence of myocardial ischaemia does not necessarily imply obstructive epicardial CAD. A substantial proportion of patients with angina may have no obstructive disease on invasive angiography, and ischaemia may occur in the absence of epicardial stenosis.

CCTA in Relation to Other Diagnostic Strategies

CCTA and functional testing provide complementary information.

• CCTA identifies plaque and anatomical stenosis.

• Functional imaging assesses the physiological consequences of disease.

• FFR-CT adds lesion-specific flow information to CCTA.

• CT perfusion combines anatomical and physiological assessment.

• Invasive angiography provides detailed anatomy but does not by itself reliably establish whether a stenosis is haemodynamically significant.

In stable chest pain, randomized comparisons have shown similar clinical outcomes between initial CCTA and functional testing strategies, although CCTA may lead to more catheterisations while reducing the frequency of finding no obstructive disease at invasive angiography.

An important advantage of CCTA is its ability to detect non-obstructive plaque. In the cited evidence, many coronary events occurred in patients with less than 70% stenosis, a group that may not be identified by perfusion imaging alone. CCTA findings can therefore influence preventive treatment even when revascularisation is not indicated.

Prognosis and Follow-Up

Prognostic implications

A normal CCTA, defined as CAD-RADS 0, is associated with an excellent prognosis in the setting described. Increasing plaque burden, high-risk plaque characteristics, obstructive disease, proximal disease, left main involvement, multivessel disease, and impaired left ventricular function are associated with progressively greater risk.

CCTA has prognostic value beyond the identification of severe stenosis because non-obstructive plaque is itself associated with future cardiovascular events. In stable chest pain, use of CCTA has been associated with reduced five-year rates of coronary death or myocardial infarction in the cited evidence, with similar relative reduction in myocardial infarction among patients whose chest pain was ultimately considered non-cardiac.

Follow-up

Follow-up should be determined by the CCTA category, plaque burden, symptoms, and the results of additional testing.

• CAD-RADS 0: Reassurance, lifestyle prevention, and evaluation for non-coronary causes if symptoms persist.

• CAD-RADS 1–2: Outpatient risk-factor modification and preventive pharmacotherapy; aggressive prevention for extensive plaque.

• CAD-RADS 3: Cardiology assessment and consideration of FFR-CT, CT perfusion, or stress testing; antianginal treatment may be added.

• CAD-RADS 4: Cardiology assessment with consideration of ICA or functional assessment and evaluation for revascularisation.

• CAD-RADS 5: Urgent cardiology assessment, with expedited ICA and revascularisation when acute occlusion is suspected.

Serial CCT is not generally favoured for routine assessment of ventricular size and function because of radiation exposure and inferior temporal resolution compared with CMR. The source material does not define routine intervals for repeat CCTA, CAC scanning, or follow-up imaging.