Coronary Artery Calcium Scoring

Authors: Dr Charles Lott*

What is a coronary artery calcium scoring?

Coronary artery scoring is a CT scanning technique for identifying and quantifying calcium deposits in the coronary arteries reflecting underlying atherosclerosis. It relies on the ability of the CT scanner to detect small areas of calcium within atheromatous plaques. As there is no intravenous contrast medium given to the patient to enhance intravascular blood (as in CT angiography), this examination cannot show coronary artery anatomy or pathology.

Coronary artery calcium scores are of most use in those patients with intermediate risk of cardiovascular disease, where the result will either lower or raise the risk profile and, potentially, provide a change in management.

Potential clinical cardiovascular risk for any patient can be assessed¹ and calculated into low-, medium- or high-risk categories.²

Those at low risk (such as an asymptomatic 35-year-old male non-smoker who exercises and has no significant family history) and those at high risk (such as a 60-year-old obese male long-term smoker with chest pain on exertion) would not benefit from this study.

What are the generally accepted indications for coronary artery calcium scoring?

Review of risk classification in asymptomatic intermediate-risk patients (aged 35–75 years) without known coronary heart disease.
Intermediate-risk patients have been defined as:³

1. Patients (absolute 10-year cardiovascular risk of 10–20%) who are asymptomatic, do not have known coronary artery disease and are aged 45–75 years, where coronary artery scoring has the ability to reclassify patients into lower- or higher-risk groups.
2. Lower-risk patients might also be considered (absolute 10-year cardiovascular risk 6–10%), particularly those where traditionally risk scores underestimate risk; for example, especially in the context of a family history of premature cardiovascular disease, and possibly in patients with diabetes aged 40–60 years.

What are the prerequisites for having coronary artery calcium scoring done?

Asymptomatic intermediate-risk patients: women aged between 35 and 70 years and men aged between 40 and 60 years.

In these intermediate-risk patients, the test is valid for main ethnic groups; however, the result is most accurate in patients of Caucasian origin.

It must be stressed that there is potential for a technically false negative result. A score of zero does not exclude the possibility of myocardial infarction in the future.

What are the absolute contraindications for coronary artery calcium scoring?

Any contraindication to X-ray exposure, of which pregnancy is the most common.

What are the relative contraindications for coronary artery calcium scoring?

Any patient with a high risk of a coronary event and symptoms should have appropriate investigation and treatment urgently. These patients are not suitable for coronary artery scoring.

The information from a coronary calcium score study will not be of any benefit to anyone who has already had a myocardial infarction or coronary revascularisation.

Coronary artery calcium scoring in patients on dialysis and with established long-term diabetes is not recommended, due to the high likelihood of a high score and the current scientific uncertainty over the interpretation of the result.

All scanners have physical limitations due to table weight limits and the diameter of the scanner aperture. Older scanners are able to scan patients up to 150 kg. Newer scanners can in some cases accommodate patient weights of 220–250 kg. Some obese patients have large abdominal girths. Most scanners have a gantry diameter of about 68 cm, with newer scanners up to 78 cm. If you are concerned that your patient may exceed any of these limits, it is best to contact the hospital or practice to find out whether this may preclude scanning.

What are the adverse effects of coronary artery calcium scoring?

Radiation risks are discussed in detail in another information item on InsideRadiology (see Radiation risk of medical imaging for adults and children). Radiation dose used in low-dose CT examinations are significantly lower than most other CT studies. Current examination techniques would deliver a radiation dose equivalent to approximately two breast mammogram examinations.

Are there any alternative imaging tests, interventions or surgical procedures to coronary artery calcium scoring?

Alternative strategies exist to assess the personal risk of a cardiovascular event. Risk stratification techniques to assess a 10-year individual risk of a cardiovascular event include:

• Framingham risk score
• PROCAM score
• European SCORE system

These are in wide use, but tend to have a heavy weighting to the patient’s age and may not adequately take into account lifestyle factors, such as smoking, diet, exercise and body mass index.

Alternative non-angiographic methods of imaging or testing to better stratify the individual’s risk include:

• Intima-media thickness (IMT) – ultrasound measurement of carotid artery wall intimal layer thickness. This requires a very high level of experience to perform well and is difficult to reproduce routinely.
• Inflammation markers, such as CRP/ESR – general non-specific screening tests that have an association with atherosclerosis and risk.
• Biochemical screening – including lipid and lipoprotein profile, diabetes, plasma homocysteine levels, and lipoprotein A levels. These are very general in their use, but either of low prevalence or poor at discrimination between risk levels.
• Exercise stress test – this assesses the functional ability of the cardiovascular system compared with an age- and sex-matched cohort. This common test provides information above that of the Framingham risk, but has a high false negative rate.
• Stress echocardiography – a functional imaging of myocardium with and without cardiac stress. An excellent test of myocardial function. It does not provide a good indication of atherosclerosis and is better used in assessment of symptomatic patients.
• Stress nuclear myocardial scintigraphy – a functional imaging test of myocardium with and without cardiac stress. Requires a significant radiation dose. An excellent test of myocardial function. It does not provide a good indication of atherosclerosis and is better used in assessment of symptomatic patients.

In those patients who fit into high-risk categories or who are symptomatic, then detailed imaging of the coronary arteries may be required. This will require either CT coronary angiography or direct catheter angiography.

Useful websites:

• Radiology Info ACR
  www.radiologyinfo.org/en/info.cfm?pg=ct_calscoring
• MESA Trial NEJM
  www.nejm.org/doi/full/10.1056/NEJMoa072100

References

1. Royal Australian College of General Practitioners. National, P. and C. Community Medicine (2001). Guidelines for preventive activities in general practice. Aust Fam Physician 9th ed: S1i-xvi, 86-87.
   www.racgp.org.au/your-practice/guidelines/redbook/8-prevention-of-vascular-and-metabolic-disease/81-assessment-of-absolute-cardiovascular-risk/ [accessed 12 June 2018]
2. National Vascular Disease Prevention Alliance. Australian absolute cardiovascular disease risk calculator. www.cvdcheck.org.au [accessed 12 June 2018]
3. Gary Liew et al: Heart Lung and Circulation. December 2017 Vol 26, Issue 12, P 1239-1251 Cardiac Society of Australia and New Zealand Position Statement: Coronary Artery Calcium Scoring.
   http://www.csanz.edu.au/wp-content/uploads/2016/11/CAC_Position-Statement_Exec-Summary_ratified-4-August-2016.pdf [accessed 12 June 2018]

*The author has no conflict of interest with this topic.

Page last modified on 13/6/2018.