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Coronary Artery Calcium Scoring (CAC)

Posted 09 October 2018

What is CAC?

Coronary calcification is a highly sensitive and specific marker of atherosclerosis. The more calcium is present, the greater the burden of atherosclerosis.

What information does CAC scoring by CT give me?

A high calcium score predicts a high risk of adverse cardiovascular (CV) events. Conversely, a calcium score of 0 has repeatedly been shown to be the strongest negative risk marker in clinical practice, with a ‘warranty period’ that extends as far as 10 years.

How do I interpret the numerical CAC score in the report?

Calcium scoring is a prognostic test; the absolute value allows you to accurately risk-stratify your patient’s future risk of adverse cardiovascular events. Scores are bracketed as 0 (very low CV risk), 1-99 (low risk), 100-400 (intermediate risk), and >400 (high risk). The score is also benchmarked against age-matched peers (percentile), and an estimated “arterial age” can be generated.

Why not just use traditional calculators like the NVDPA calculator?

CAC score repeatedly outperforms clinical risk prediction in research studies. Some older studies found only one-third of heart attack patients would have been found to be “high risk” by traditional calculators, whereas 95 per cent of heart attack patients will have evidence of coronary calcium. CAC also tells us what is actually happening in that specific patient, whereas risk factors can only ever tell us what is likely to happen in a population. CAC scoring thus allows a far more personalised CV risk evaluation.

How much radiation is incurred?

The radiation burden is very low indeed, approximately 0.1-0.5mSv (equivalent to about 2 months of background radiation from living in Perth).

When is CAC scoring most useful?

A prognostic test is only useful if it changes management. CAC is most helpful in those deemed at intermediate CV risk using traditional calculators (defined as a ten-year risk of 5%-20%). In the Heinz-Nixdorf Recall study nearly half of such patients were re-categorised into either high or low risk which in turn informstreatment. CAC is also extremely useful for those with risk factors that are not captured by traditional calculators, such as a family history of CVD or rheumatoid arthritis. Finally, the personalised nature of CAC scoring is a powerful individualised motivator when a high-risk patient is unconvinced of the need for treatment and lifestyle changes.

When is CAC scoring least useful?

CAC is unlikely to be helpful in those who are already clearly at high CV risk (e.g. known coronary disease, diabetics aged 60+ etc); these individuals already have a clear indication for treatment. CAC should also not be requested in those individuals who wouldn’t accept treatment or lifestyle changes even if their CAC score turns out to be high.

Should I use CAC to evaluate chest pain or suspected angina?

No. CAC sore is very good at detecting coronary calcium atheroma but cannot reliably determine whether the atheroma is obstructive or not. CTCA or stress testing is more advisable in symptomatic patients.

How do I choose between CT calcium score vs. CT coronary angiography?

CAC is a prognostic test – it is best applied in asymptomatic individuals to guide the appropriateness of primary prevention. CTCA is a diagnostic test for the evaluation of patients with chest pain (symptomatic patients).

Does my patient need a CTCA if the calcium score is very high?

This is an uncertain area with inadequate evidence base. In most cases CTCA is not necessary, assuming there are no symptoms like chest pain or exertional breathlessness, because the treatment in any case remains medical (lifestyle, diet, aspirin and statins). Further evaluation for obstructive atheroma is only necessary if there are accompanying symptoms. In equivocal cases where symptoms are difficult to gauge it may be reasonable to consider further testing, although stress testing may be more appropriate than CTCA. If you have concerns about your patient’s high calcium score, please feel free to contact our reporting cardiologist via our reception or the patient’s own cardiologist.

Should the CAC be repeated in the future?

If the score is >400, there is no value in repeat testing as treatment is already indicated. For individuals with lower scores the answer is uncertain and there is currently no consensus. In most cases however it will not be useful to repeat the study for at least 5 years, and probably not at all if the patient is already on statin therapy.