Ischaemic heart disease

CSANZ endorses CAC score in asymptomatic, intermediate risk

The role of coronary artery calcium (CAC) scoring to predict heart disease risk has been bolstered as Australian experts move to support its use in people who are at intermediate risk of a cardiovascular event based on traditional risk scores.

In a position statement published in the MJA this week the Cardiac Society of Australia and New Zealand said the test is the strongest independent predictor of future myocardial infarction and mortality providing risk information beyond traditional risk calculators such as the Framingham Risk Score.

The test, which is not government funded and costs patients around $200, has now been given a strong recommendation by the Society for use in asymptomatic patients who have been identified as having intermediate risk who do not have known coronary artery disease and are aged between 45 and 75 years.

In this group, a calcium score can help doctors to home in on a patient’s individual risk and reclassify patients into lower- or higher-risk groups to help determine whether patients might benefit from early and more aggressive therapies or lifestyle interventions or potentially eliminate some patients from the consideration of statins.

Professor Clara Chow, Director of the Cardiovascular Division at The George Institute for Global Health and a member of the CAC position statement Working Group said the CSANZ recommendations should remove a lot of the confusion about which patient groups stand to gain the most benefit from the test.

“There has been a huge amount of research and discussion about the role of calcium scoring in risk assessment but the clinical interpretation has been confusing,” she told the limbic in an interview.

“This statement makes it fairly clear that calcium scoring is useful in a subset of people over the age of 40 who would normally have a routine cardiovascular risk assessment. If these patients were to get an intermediate risk assessment based on those traditional clinical parameters then a calcium score would be useful in that subset of people.”

She added that the position statement should also ease fears the test would be overused with the Group recommending a tiered assessment strategy.

“It needs to be used alongside the risk assessment tools we already have and really as a second step in risk assessment.”

She also noted that the scan has very low radiation exposure – about 0.5e1.0 mSv, which is similar to breast mammography.

Ultimately the test, in addition to traditional risk factor scoring, will reduce the number of people categorised into intermediate risk – an ambiguous classification when it comes to deciding whether or not to initiate primary pharmacotherapy prevention therapies over lifestyle modification, she added.

“There’s no clear clinical pathway for people at intermediate risk but the research shows that calcium scoring give us a substantial jump in our ability to risk stratify – it is fantastic for splitting intermediate risk up or down so you can tailor the treatment.”

The position statement includes a recommendation to initiate aspirin and a high efficacy statin in high risk patients, defined as those with a CAC score ≥400, or a CAC score of 100–399 and above the 75th percentile for age and sex.

It’s also reasonable to treat patients with CAC scores ≥100 with aspirin and a statin, the Group said while patients with a score of 1-99 are considered low risk and should be managed with diet and lifestyle interventions unless there are other clinical factors present like a strong family history of premature infarction for instance. These patients could also be reassessed the Group suggested.

Meanwhile asymptomatic patients with a CAC score of zero are considered very low risk and do not benefit from treatment.

However, Professor Chow said that that calcium scores do miss early soft fatty atheroma and some patients may be incorrectly classified.

“There will still be people who probably will be misclassified even with all the information from risk assessment combined with a calcium score such as those who might have a fair burden of non calcified plaque,” she noted.

But whether the Government will fund the test in patients at intermediate risk of a cardiovascular event remains to be seen.

In its most recent review the Health Policy Advisory Committee on Technology (HealthPACT), a sub-committee of the Australian Health Ministers’ Advisory Council, failed to recommend the routine use of CAC scoring, citing concerns about the radiation dose involved – the equivalent of 50 chest x-rays per scan, it claimed – as well as the impact on downstream tests and treatments.

Its advice to the ministers was that the test “is of unproven clinical benefit or utility”.

Despite that, its report also said there was evidence that calcium scoring could accurately predict cardiovascular events in individuals not showing symptoms of heart disease and the scanning “has been shown to perform better than traditional risk factor assessment, although the magnitude of that difference in clinical terms is not clear”.

Professor Chow described that decision as ‘unfortunate’.

“Calcium scoring is very useful  – it significantly improves our ability to stratify risk unfortunately at the moment patients do pay out of pocket costs for that test, which detracts from people using it,” Professor Chow said.

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