Coronary artery calcium scoring is emerging as an important tool in a primary care physician’s toolkit
Coronary artery calcium scoring is a valuable method for identifying those at both low-risk and high-risk for cardiovascular events.
Calcium scoring can be used for reclassifying patients identified at intermediate risk of cardiovascular disease using traditional risk scoring methods, such as the Framingham risk score. These stratification methods involve calculating and stratifying risk according to risk factors such as age, gender, systolic blood pressure, lipid profile, the presence of diabetes, and smoking status of the patient.
Coronary artery calcium scoring adds to this by introducing a direct evaluation of the severity of atherosclerosis in the coronary vasculature.
The technique was developed in the US in the 1980s, and involves a calculation based on the density of calcium seen in atherosclerotic plaque within the coronary arteries on a CT scan and the total area involved. This score, termed the Agatston score, appears to effectively predict the risk of cardiovascular disease.
WHO MAY BENEFIT?
Coronary artery calcium scoring is of most value in asymptomatic patients who have been identified as having intermediate risk using calculators such as Framingham (a 10-year risk of cardiovascular events of 10% to 20%), who do not have known coronary artery disease and are aged between 45 and 75 years. In this group, a calcium score can reclassify patients into lower- or higher-risk groups. This, in turn, can help determine whether primary prevention measures are warranted.
Calcium scoring may also be considered for lower-risk patients (10-year risk of cardiovascular events of 6% to 10%), particularly where risk scores potentially underestimate risk e.g. in context of a strong family history of early coronary disease, in women and younger men, and in individual patients from certain ethnic groups, such as patients from the Pacific Islands or from the Indian subcontinent.
Coronary artery calcium scoring is not recommended for patients at very low risk (10-year risk of cardiovascular events of less than 5%), as testing is unlikely to alter the recommended management.
Modifications in lifestyle factors and optimising diet are the mainstays of preventative treatment in this patient group.
Another group unlikely to benefit from coronary artery calcium scoring is patients who are already considered to be high risk of cardiovascular disease, such as diabetics over 60 years of age, or individuals with familial hypercholesterolaemia.
These patients, in view of their established high levels of risk, should be managed aggressively with optimal medical therapy.
Similarly, coronary artery calcium scoring is not useful for patients who have established coronary artery disease and/or a past history of myocardial infarction or coronary artery revascularisation.
The investigation also has no place in the assessment of a symptomatic patient with possible cardiac chest pain.
THE AGATSTON SCORE
Based on the literature to date, the following stratifications are used to relate the coronary artery calcium score to the extent of atherosclerotic coronary artery disease.
• Coronary calcium score 0: No identifiable plaque. Risk of coronary artery disease very low (<5%)
• Coronary calcium score 1-10: Mild identifiable plaque. Risk of coronary artery disease low (<10%)
• Coronary calcium score 11-100: Definite, at least mild atherosclerotic plaque. Mild or minimal coronary narrowings are likely.
• Coronary calcium score 101-300: Definite, at least moderate atherosclerotic plaque. Mild coronary artery disease is highly likely. Significant narrowings possible
• Coronary calcium score > 300: Extensive atherosclerotic plaque. Significant narrowings possible.
When interpreting the score, it is important to take into account the normal variation that can occur related to age, gender and ethnicity. For this reason, scores are commonly provided along with the normal distributions of scores based on these factors, and it is vital to not only look at the absolute score, but to look at that score as a percentile.
A calcium score of zero in an appropriate patient group portends a very good prognosis and a low cardiovascular event rate (less than 0.5%) out to greater than five years of follow up in large studies. It should be cautioned however, that calcium scores do miss early soft fatty atheroma.
Recently the US Multi-Ethnic Study of Atherosclerosis study group published an algorithm that incorporates coronary artery calcium scoring along with traditional risk factors including age, gender, ethnicity, systolic blood pressure, family history in a first degree relative, lipid profile, use of anti-hypertensive or lipid lowering medication, presence of diabetes and smoking status.
This online tool clearly reports the patient’s 10-year risk of developing cardiovascular disease, both with and without their calcium being taken into consideration.
Coronary calcium scoring has been shown to improve patient adherence to preventative measures, including interventions to lower blood pressure, maintain an optimum weight, and improve medication compliance.
This may be due to the patient’s perception that the result describes the potentially damaging impact of atherosclerosis visualised directly in the coronary arteries, compared with their perception of more abstract concepts such as risk related to high blood pressure or high cholesterol.
Calcium scoring has also begun to help guide decision-making with regards to the benefit of aspirin therapy.
It is also helpful in making recommendations for statin therapy and allows shared decision-making in primary prevention strategies.
While a cardiac stress test can be very helpful in patients with abnormal coronary calcium scores to evaluate functional capacity and the presence or absence of ischaemia, an abnormal calcium score in an asymptomatic patient is not an indication for coronary angiography, stents or bypass surgery.
The cost of a calcium score is approximately $50 to $200 depending on the radiology provider. The radiation dose is usually less than 1.0 mSV and with modern CT scanners can be as low as 0.2 mSV, which is approximately equivalent to the radiation exposure from four chest X-rays. Unfortunately, there is currently no Medicare rebate for calcium scoring as a standalone study.
An elevated coronary artery calcium score should be viewed as documentation of coronary atherosclerosis, the best treatment for which is lifestyle modification, normalising of blood pressure, reducing LDL cholesterol levels, and the possible use of antiplatelet agents.
Coronary calcium scoring should be ordered by the primary care physician and the result incorporated into the cardiac evaluation alongside other cardiovascular risk factors.
Patients found to be at elevated risk should be treated aggressively with risk factor control and referred for specialist opinion if indicated, while low risk patients can be encouraged to maintain healthy lifestyle in order to manage their cardiovascular risk.
Dr Jason Kaplan is cardiologist and clinical lead of the cardiovascular program, Macquarie University Health Sciences Centre. His clinical interests include sports cardiology, integrative and preventative cardiology and cardiac imaging (cardiac CT and echocardiography)
References
1. CSANZ position statement on coronary calcium scoring 2016
2. Robyn L. McClelland, PhD; Neal W. Jorgensen, MS; Matthew Budoff, MD; et al., MS 10-Year Coronary Heart Disease Risk Prediction Using Coronary Artery Calcium and Traditional Risk Factors: Derivation in the MESA (Multi-Ethnic Study of Atherosclerosis) With Validation in the HNR (Heinz Nixdorf Recall) Study and the DHS (Dallas Heart Study). J Am Coll Cardiol. 2015 Oct 13;66(15):1643-53.
3. Grayburn , P N Engl J Med 2012; 366:294-296.
Interpreting the Coronary Calcium Score.
