Key Points

Cardiac Computed Tomography Overview

CT coronary calcium score (CCS) and CT coronary angiography (CTCA) are well-established imaging modalities for cardiac risk scoring and diagnosing coronary artery disease.

CCS offers risk stratification and is highly predictive of future cardiovascular events (Kalia, 2012).

CTCA has high diagnostic accuracy to detect and exclude coronary artery disease (CAD) in comparison with invasive coronary angiography (von Ballmoos, 2011).

Coronary Calcium Score – Pathophysiology

In the development of coronary atherosclerosis, calcification of coronary arteries is an active process. It is almost always absent in the normal vessel wall. It can be sometimes seen in early atherosclerotic lesions, but is more commonly seen in complex lesions. It is frequently seen in plaques that have evidence of healed plaque rupture by histology.

Clinical Utility of Computed Tomography Coronary Calcium Score

Above literature reviews have shown the clinical utility of the Agatston coronary calcium score in:

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  Prediction of coronary artery disease deaths or myocardial infarcts in asymptomatic patients. This is especially true for those patients who are at low to intermediate risk of cardiovascular disease as derived from Framingham study risk calculators. CCS can improve traditional risk stratification in multiple patient cohorts.

  
  
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  In symptomatic patients, a zero CCS has a high negative predictive value for >50 per cent stenosis on angiography.

  
  
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  In patients with a pre-test probability of <30 per cent for coronary artery disease, CCS is more cost-effective than exercise treadmill testing.

  
  
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  Serial measures of CCS may be used to monitor the efficacy of statin treatment. More research is needed to assess the impact of various treatments for CAD. In intermediate risk patients, by traditional Framingham risk stratification, who have negative coronary calcium scores, there may be a cost saving by stopping statin therapy.

NICE guidelines (2010) for people suspected of having stable angina that cannot be diagnosed or excluded based on clinical assessment alone recommend that those who have an estimated 10–29 per cent likelihood of CAD be offered CTCCS as a first-line investigation.

Calcium score is independently associated with future cardiovascular events (see Table 5.D.1).

Strengths and limitations of CTCCS are described in Table 5.D.2.

Computed Tomography Coronary Angiography – Pathophysiology

For patients with stable chest pain of unknown aetiology, non-invasive CT imaging obtains high-resolution thin slice (submillimetre) 3D images of the coronary arteries. It also images the remaining cardiac and extra-cardiac structures in the field of view, such as neighbouring mediastinum, lungs and osseous anatomy. It directly identifies coronary artery calcified and non-calcified plaques and allows stenosis estimation. This can guide further cardiac intervention by detection of significant stenoses. Occasionally, non-cardiac chest pain aetiologies may also be identified in the osseous anatomy, mediastinum, chest wall, lung parenchyma and pleura.

Clinical Utility of Cardiac Computed Tomography Coronary Angiography

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  Diagnosis. In patients with intermediate pre-test probability risk of having coronary artery disease, CTCA can be a first-line investigation. Compared to the gold standard invasive angiography, multicentre trials show a per-patient diagnostic sensitivity and specificity ranging from 85–99 per cent and 64–90 per cent respectively (Budoff, 2008; Meijboom, 2008; Miller, 2008). Conversely, in low pre-test probability of having CAD, a negative CTCA scan does not significantly decrease the post-test probability in these patients as this is already low. However, a positive scan is associated with a considerable number of false positive outcomes, leading to over-diagnosis and unnecessary referral to invasive angiography.

  
  
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  Prognosis. Excellent prognostic value in symptomatic patients for normal CTCA, ranging from 0.2 per cent major coronary event rate over 20 months to 0.28 per cent annualised all cause death rate (Min, 2011).

  
  
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  Therapeutic efficacy guidance. Accuracy of a negative CTCA scan to rule out CAD is high in patients with intermediate pre-test probability of CAD. This allows safe discharge and there is no need for further diagnostic testing. In contrast, patients with a positive CTCA resulting in a high post-test probability should be referred for invasive coronary angiogram +/- pressure wire studies to consider revascularisation to relieve symptoms and improve prognosis.

  
  
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  Cost-effectiveness and clinical outcomes of CTCA compared with functional cardiac imaging. Currently, there is no difference in clinical outcomes and cost of first-line CTCA vs. exercise electrocardiography, nuclear stress testing or stress echocardiography (Douglas, 2015). Compared to nuclear tests, CTCA might be the safer test with fewer catheterisations without obstructive disease and lower radiation exposure.

  
  
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  Evaluation of coronary stents. In-stent restenosis may be assessed for large stents and simple left main stents.

  
  
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  Investigation of left bundle branch block. This carries an increased risk of cardiac events and can be associated with CAD. It often requires invasive coronary angiography because stress testing and imaging can be unreliable. CTCA demonstrated excellent negative predictive value compared with invasive angiography.

  
  
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  Evaluation of suspected coronary anomalies/complex congenital heart disease.

  
  
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  Exclusion of CAD in new-onset heart failure/cardiomyopathy.