Coronary artery calcium scoring in primary care

Opening Vignette

Mrs Tan, a 45-year-old woman, visits you for her annual health screening. She is a smoker, overweight with a body mass index of 27 kg/m², and has primary hypertension that is well controlled on calcium channel blocker therapy. As part of her health screening, her lipid panel returned with a total cholesterol of 6.2 mmol/L, high-density lipoprotein of 1.1 mmol/L, and low-density lipoprotein of 3.8 mmol/L. She wants to know her cardiovascular risk and how to reduce this risk.

WHAT IS CORONARY ARTERY CALCIUM SCORING?

Coronary artery calcification is a well-recognised condition and indicates the presence of coronary artery disease (CAD). It is a predictor of future cardiac events and generally correlates well with the extent of calcific CAD. Figure 1 shows a typical display format of a calcium score report. In general, a coronary artery calcium (CAC) score of 0 implies a low risk of obstructive CAD, as prior studies have reported that obstructive CAD is present in <5% of symptomatic patients with a CAC score of 0.[1] The caveat to this generality is that the diagnostic value of a CAC score of 0 was not uniform across age groups, as younger patients tend to have a higher incidence of non-calcified plaque.[2]

Figure 1.

Diagram shows an example of a calcium score report.

In asymptomatic patients, the absence of a CAC score of 0 has been shown to be the strongest ‘negative risk marker’ as compared to other traditional and novel markers such as carotid intima-media thickness, absence of carotid plaque, brachial flow-mediated dilation, ankle-brachial pressure index, serum high-sensitivity C-reactive protein, serum homocysteine and N-terminal pro-brain natriuretic peptide. The ‘power of zero’ provides the strongest degree of ‘de-risking’ available when compared to other currently available markers.

The imaging process is relatively simple, involving non-contrast computed tomography (CT) that requires no patient preparation. Patients should ideally be able to follow instructions and hold their breath for 3–5 seconds while lying still during the scan. The effective radiation dose is low (generally < 1 mSV), which is comparable to a screening mammogram.

In Singapore, CAC is most commonly reported using the Agaston method, which provides a summation of the total coronary calcium reported in Agatston units. This is then reported as a percentile based on the patient’s age, gender, and ethnicity using the data derived from the multi-ethnic study of atherosclerosis (MESA).[3] In general, the Agaston score is a reflection of the short-term risk, and the percentile cohort reflects the lifetime risk of obstructive CAD. Of note, the CAC score is increased following statin treatment due to its plaque stabilisation effect.[4] Therefore, the CAC scores of patients on statin therapy should be interpreted with caution.

HOW RELEVANT IS THIS TO MY PRACTICE?

Atherosclerotic cardiovascular disease (ASCVD) is one of the leading causes of death in Singapore and accounted for 31.4% of all deaths in 2022.[5] As Singapore moves from being a low-income to a high-income country and life expectancy increases, the burden of ASCVD is projected to increase. In 2020, Singapore’s expenditure on cardiovascular disease (CVD) costs amounted to SGD 11.5 billion.[6] This underscores the importance of primary prevention in alleviating the financial and societal impact of ASCVD. The Healthier Singapore initiative and the government’s focus on population and preventive health have received strong support from the cardiology community.[7] Targeted primary prevention approaches, such as CAC scoring, are a valuable tool in our arsenal for risk stratification, particularly in guiding statin initiation decisions for patients in low-moderate risk groups who are mostly managed by primary care physicians. By embracing CAC scoring and collaborative care, we can optimise primary prevention strategies and reduce the burden of ASCVD on individuals and the society.

HOW TO USE CORONARY ARTERY CALCIUM SCORING IN PRIMARY CARE?

The main utility of screening CAC lies in predicting CAD and guiding treatment decisions. Specifically, CAC scoring can be helpful in convincing hesitant patients with cardiovascular risk factors or elevated low-density lipoprotein (LDL)-cholesterol levels to initiate statin therapy. In spite of the similar goals, global best use and societal practice recommendations of CAC vary widely.

The main consensus amongst the different country guidelines for the use of CAC is that it should be used in patients aged ≥40 years and for intermediate-risk and asymptomatic patients with a CAC score >100 to initiate or consider statin therapy [Figure 2]. For patients with a CAC score of 0, their cardiovascular (CV) risk should be downgraded, and statins can be withheld with a repeat CAC test in 5–10 years. The latest edition of the Singapore lipid clinical practice guidelines published in December 2023 largely concurs with this consensus.[8] These recommendations are based on the results of the MESA study, in which 10-year event rates varied from 1.3%–5.6% for CAC score of 0 and from 13.1%–26.6% for CAC score >300.[3] The study estimated a 14% relative increment in ASCVD risk for each doubling of CAC score, with all other risk factors constant.

Figure 2.

Possible simplified algorithm for the use of coronary artery calcium (CAC) score. ASCVD: atherosclerotic cardiovascular disease CT: computed tomography

The following is a summary of the main recommendations of international guidelines that aid risk stratification and guide statin initiation. As mentioned above, there is broad consensus amongst the international guidelines.

The American College of Cardiology recommends using the pooled cohort equation to estimate the 10-year risk of ASCVD. This calculator can be conveniently found on many different medical calculator smartphone applications. It should be noted that this pooled cohort equation may not be representative of our local population, and the use of the Singapore-modified Framingham risk score (SG-FRS) can be considered for a better representation of the CVD risk amongst the local population. For patients at borderline (5%–7.5% 10-year risks) or intermediate (7.5%–20% 10-year risks) CV risk, with risk-based choices for preventive intervention with statin therapy remaining ambiguous, CAC can be considered as an adjudicator to upgrade risk (e.g., young patients or women of child-bearing age) or de-risk if CAC score is 0 with no statin therapy and repeat CAC test in 5–10 years. A CAC score of 1–99 favours statin use, especially after the age of 55 years. If CAC score is >100 and ≥75th percentile for age/gender, statin therapy should be initiated.[9]

Academy of Medicine, Singapore has since published a new local lipid guideline in December 2023 that supersedes the old guideline from 2016. In the updated guidelines, the SG-FRS score is recommended to estimate 10-year risk of CVD. For patients at borderline to intermediate risk (5%–20% 10-year risks), and for whom the decision to commence cholesterol-lowering therapy remains uncertain, the use of imaging modalities like CAC screening can be helpful for decision-making. In patients with a CAC score of 0, it is reasonable to withhold statins; for CAC score of 1–99, the risk reclassification utility is limited, and for CAC score of >100, statins are recommended to achieve the lipid targets.[9]

The Canadian Cardiovascular Society recommends using the FRS to estimate the 10-year ASCVD risk. Coronary artery calcium screening is indicated for asymptomatic adults aged > 40 years with intermediate risk and for whom treatment choices are unclear. In patients with a CAC score > 100, pharmacotherapy is reasonable regardless of the FRS.[10]

The European Society of Cardiology (ESC) recommends the calculation of a patient’s total CV risk, and CAC score assessment may be considered in individuals with low or moderate CV risk, for whom the respective LDL goal is not achieved with lifestyle intervention alone, and pharmacotherapy is an option. This would aid in the upward reclassification of risk for consideration of statin therapy.[11] The guidelines also recommend CAC scoring in patients with hypertension when it is likely to change management (class IIb recommendation).[11]

The National Lipid Association (NLA) guidelines[12] make more recommendations on the use of CAC scoring:

1. Family history of premature ASCVD: CAC score of 0 for lifestyle therapy and consider repeat CAC screening in 5–7 years; CAC score >0, consider initiation of statin therapy

2. Diabetes mellitus with no additional risk factors: CAC score of 0 for moderate-intensity statin therapy; CAC score of 1–99 for moderate or high-intensity statin therapy; CAC score >100 for high-intensity statin therapy

3. Intermediate ASCVD risk: CAC score of 0, defer statin and repeat CAC screening in 3–5 years; CAC score of 1–99 favours statin; CAC score of 100–299 favours statin therapy and aspirin if not at high risk of bleeding; CAC score >300 favours high-intensity statin therapy and aspirin if not at high risk of bleeding

4. Extreme LDL elevation (LDL >4.9 mmol/L): CAC score of 0, favours high-intensity statin therapy; CAC score >0 favours high-intensity statin therapy with addition of LDL-lowering therapy

5. For adults aged 76–80 years for whom there are doubts about statin initiation: CAC score of 0–10 favours statin avoidance; CAC score >100 favours statin initiation

The Society of Cardiovascular Computed Tomography (SCCT) recommends the calculation of a patient’s 10-year ASCVD risk; for patients with 5%–20% 10-year ASCVD risk, CAC scoring can aid further risk stratification and guide therapy.[13] In patients with a CAC score of 0, the risk is considered very low, and statins are not recommended. A CAC score of 0–99 puts the patient at mildly increased risk; a moderate-intensity statin is recommended if the patient is <75^th percentile, and a moderate-high-intensity statin is recommended if the patient is >75^th percentile. A CAC score of 100–299 puts the patient at a moderately increased risk and a moderate-high-intensity statin together with low-dose aspirin is recommended. A CAC score >300 puts the patient at a moderately to severely increased risk and a high-intensity statin together with low-dose aspirin is recommended.

Table 1 shows the areas of consensus and controversy amongst the major societal guidelines. The guidelines differ in the use of CAC to guide aspirin therapy. While specialty guidelines (like the NLA and SCCT) have covered this at great length, the main international guidelines remain largely silent on this matter and recommend aspirin therapy only in patients with high-ASCVD risk.

Table 1.

Consensus indications and treatment thresholds amongst the major global CAC guidelines.

Indication	Treatment threshold	Area of controversy
Intermediate ASCVD risk	CAC score of 0, downgrade risk and consider withholding statin	CAC score to guide aspirin use
Asymptomatic	CAC score >100, initiate statin	CAC score to guide hypertensive medications
Primary prevention	–	–

ASCVD: atherosclerotic cardiovascular disease, CAC: coronary artery calcium

In conclusion, it would be prudent to emphasise that the utility of CAC score remains in the risk stratification of asymptomatic individuals with low-intermediate risk of ASCVD. The CAC score should not be used in the evaluation or decision-making for a patient with ongoing chest symptoms. It also has no value in patients with established ASCVD, such as those with a prior myocardial infarction, stent or bypass surgery.

TAKE-HOME MESSAGES

1. Coronary artery calcium scoring is a valuable tool to aid cardiovascular risk stratification and to guide statin initiation, especially among hesitant patients.

2. Coronary artery calcium scoring may be considered in patients aged ≥40 years with borderline–intermediate cardiovascular risk (based on SG-FRS) to assist with decision-making on statin therapy.

3. In patients with no additional risk factors, statin therapy can be considered if CAC score is >100.

4. Cardiovascular risk increases proportionately with CAC score. There is a 14% increment in ASCVD risk for each doubling of CAC score, when all other risk factors remain constant.

5. There is no consensus from the major international societies on the use of CAC scoring to guide aspirin initiation for primary prevention.

Closing Vignette

Mrs Tan was deemed to be of ‘borderline’ CV risk based on her SG-FRS score. You arranged for CAC screening, which returned with an Agatston score of 105, putting her at the 99^th percentile. You counselled her regarding her increased cardiovascular risk, which favours initiation of at least moderate-intensity statin for risk reduction, and started her on atorvastatin 20 mg ON. She was also encouraged to adopt a regular exercise and diet programme. She has a follow-up consultation after 6 months for a repeat lipid panel to assess the efficacy of therapy.

Conflicts of interest

Sia CH is a member of the SMJ Editorial Board and was thus not involved in the peer review and publication decisions of this article.

SMC CATEGORY 3B CME PROGRAMME

Online Quiz: https://www.sma.org.sg/cme-programme

Deadline for submission: 6 pm, 21 April 2025

Question: Answer True or False
1. The coronary artery calcium (CAC) is a predictor of future cardiac events.
2. In general, a CAC score of 0 implies a low risk of obstructive coronary artery disease (CAD).
3. Younger patients tend to have a higher incidence of non-calcified plaque.
4. The effective radiation dose of a CAC scan is low and is comparable to a screening mammogram.
5. In Singapore, CAC is most commonly reported using the Agatston method.
6. In general, the Agatston score is a reflection of the short-term cardiovascular risk.
7. The CAC score is decreased following statin treatment due to its plaque stabilisation effect.
8. Atherosclerotic cardiovascular disease (ASCVD) is one of the leading causes of death in Singapore and accounted for 31.4% of all deaths in 2022.
9. The main utility of screening CAC lies in predicting CAD and guiding treatment decisions.
10. The main consensus amongst the different country guidelines for the use of CAC scoring is that it should be used in patients aged ≥ 40 years and for intermediate risk and asymptomatic patients with a CAC score >100 AU to initiate or consider statin therapy.
11. For patients with a CAC score of 0, their risk should be downgraded, and statins can be withheld with a repeat CAC test in 5–10 years.
12. In patients with no additional risk factors, statin therapy can be considered if CAC score is >100.
13. In the multi-ethnic study of atherosclerosis, 10-year event rates varied from 1.3%–5.6% for CAC score of 0, and 13.1%–26.6% for CAC score >300.
14. There is a 14% relative increment in ASCVD risk for each doubling of CAC score, when all other risk factors remain constant.
15. The 2023 lipid guidelines by Academy of Medicine, Singapore recommend using the Singapore-modified Framingham risk score to estimate 10-year risk of cardiovascular disease.
16. The CAC score should not be used in the evaluation or decision-making for a patient with ongoing chest symptoms.
17. There is no consensus from major international societies on the use of CAC score to guide aspirin initiation for primary prevention.
18. In asymptomatic patients, the absence of CAC (CAC score of 0) is the strongest ‘negative risk marker’ as compared to other traditional and novel markers.
19. The CAC scan requires the use of iodinated contrast.
20. The CAC score has no value in patients with established ASCVD, such as those with a prior myocardial infarction, stent or bypass surgery.

Funding Statement

Nil.