As outlined here, CT calcium scoring is a safe, non-invasive and accurate way to detect the presence, burden and extent of atherosclerotic plaque in the coronary arteries, in other words the degree of “hardening” in the walls of the arteries that supply blood to the heart muscle. This test is one of the earliest ways to detect atherosclerotic plaque in people with no symptoms of heart disease, with the calcium score result correlating well with the risk of heart attack in the next five years. A calcium score above 0, measured in Agatston units (AU), is a marker of atherosclerosis, with increasing scores correlating to increasing risk of heart attack, whereas a score of 0 AU indicates absence of coronary calcification and is associated with a very low risk of heart attack in the subsequent five years.  So if calcium scoring is so useful in predicting risk of heart attack, why is it not recommended in everybody, and more specifically, is a CT calcium score right for you?

This month, a new position statement was published by the National Heart Foundation of Australia, offering practical guidance on the appropriate use of CT calcium scoring in our community. While the position statement did not add any new evidence to the existing body of knowledge regarding the utility and predictive outcomes of CT calcium scoring, it is an important document based on best available expert opinion that provides practical guidance for doctors considering this test, particularly given its increasing availability and use in Australia over the last few years.

Determining your risk of heart attack is the starting point in determining what preventative lifestyle changes, and perhaps preventative medical therapy, your doctor will recommend to minimise your risk of heart attack in the future. When you see your doctor for cardiac risk assessment, before they consider whether you need a calcium score to determine your risk of heart attack, they will take into account several modifiable and non-modifiable risk factors to determine your risk. Firstly, they will consider non-modifiable risk factors such as your age, sex, ethnicity and whether you have any family history of premature heart disease in any first-degree relatives. Generally, risk assessment should commence by the age of 45 (or 30 in Aboriginal and Torres Strait Islander peoples), although this may occur at a younger age if there is a family history of premature heart disease. Your doctor will then consider whether you have any modifiable risk factors for heart disease, such as smoking, high blood pressure, high cholesterol, diabetes, high waist circumference, high body mass index, physical inactivity or poor nutrition.  

These modifiable and non-modifiable risk factors are then collectively entered into well-studied and evidence-based risk calculators which provide a rough estimate of your risk of heart attack over the next five years.  If the risk of heart attack is calculated to be more than 15% over the next five years, this is considered to be high risk. That means if everyone with a risk score of more than 15% was grouped together, about 1 in 7 would have a heart attack within the next 5 years. If the risk of heart attack is calculated to be 10-15% over the next five years, this is considered to be moderate risk. If the risk of heart attack is calculated to be less than 10% over the next five years, this is considered to be low risk. However, the problem with these risk calculators is that while they provide a crude assessment of heart attack risk, they can be inaccurate in particular situations, for example in individuals with a family history of premature heart attack, which the calculators do not account for well. In fact, several studies have reported significant improvement in the predictive performance of these risk calculators with the addition of CT calcium scores into the risk models, indicated by improvement in reclassification of heart attack risk, especially in individuals with moderate risk scores or low risk scores with risk enhancing factors (see below). Reclassification by CT calcium scoring of individuals with high risk scores into lower risk groups has been shown to be far less common.

On this basis, the new position statement made the following four recommendations:

• Calcium scoring could be considered for selected people with moderate absolute cardiovascular risk using absolute cardiovascular risk algorithms
• Calcium scoring could be considered for selected people with low absolute cardiovascular risk, as assessed by absolute cardiovascular risk algorithms, and who have additional risk-enhancing factors that may result in the underestimation of risk – these risk enhancing factors include family history of premature heart disease, LDL (“bad”) cholesterol above 4.1, history of premature menopause, pregnancy-associated conditions that increase later heart disease risk (e.g., preeclampsia), chronic inflammatory conditions (e.g. rheumatoid arthritis), high risk ethnicity (e.g. south Asian populations, Aboriginal and Torres Strait Islander peoples) or other biomarkers associated with increased heart disease risk such as elevated high sensitivity C-reactive protein (hs-CRP) level on blood test.
• A calcium score of 0 AU could reclassify a person to a low absolute cardiovascular risk status, with subsequent management to follow recommendations for low absolute cardiovascular risk.
• A calcium score above 99 AU or ≥ 75th percentile for age and sex could reclassify a person to a high absolute cardiovascular risk status, with subsequent management to follow recommendations for high absolute cardiovascular risk.

So, in summary, CT calcium scoring may be right for you to determine your risk of heart attack if your doctor estimates that your risk is low or moderate using traditional risk calculators, especially if you have a family history of heart disease in your first-degree relatives. In this setting, calcium scoring improves the accuracy of this prediction, and guides the decision as to whether your prognosis will improve with preventative medical therapy such as aspirin and/or statins. On the other hand, if your doctor estimates that your risk of heart attack is high using traditional risk calculators, CT calcium scoring will generally not reclassify this estimate of risk and is therefore not recommended, and preventative medical therapy will likely already have been instituted to minimise your risk of heart attack.  Finally, CT calcium scoring is also not right for you if you have any symptoms of possible narrowed or blocked heart arteries, for example, chest discomfort or breathing difficulties – if you have any such symptoms you may require stress echocardiography or CT coronary angiography to evaluate this possibility, which if diagnosed, requires prompt management. 

Reference:

National Heart Foundation of Australia: Position Statement On Coronary Artery Calcium Scoring For The Primary Prevention of Cardiovascular Disease in Australia. Med J Aust. 2021 May 17. G Jennings, R Audehm, W Bishop et al.