Risk factors

CAC scoring: new position statement clarifies role in reclassification of CV risk

Coronary artery calcium (CAC) scoring can be considered in patients where absolute cardiovascular risk may be underestimated or where management intensity is uncertain, according to new Australian advice.

A new position statement from the National Heart Foundation, published in The MJA, offers practical guidance on the use of CAC scoring but the strength of the recommendations remain conditional.

“The conditional status of our recommendations reflect possible benefits in CVD-related morbidity and mortality that are yet to be proven in randomised controlled clinical trials,” it said.

The position statement said people with low absolute cardiovascular risk but with risk-enhancing factors not fully captured in the National Vascular Disease Prevention Alliance algorithm may benefit from CAC scoring.

Those factors included a family history of premature atherosclerotic CVD, a history of conditions such as preeclampsia or premature menopause, lipids or biomarkers associated with increased atherosclerotic CVD risk, and high risk ethnicity such as south Asian populations and Aboriginals and Torres Strait Islanders.

It also found CAC scoring was useful in people with moderate absolute cardiovascular risk where the risk status may be close to the threshold for high risk.

The statement adopted US thresholds for CAC scoring.

“Determining CAC thresholds for reclassification of risk is challenging in the absence of Australian data for CAC-guided CVD risk management,” it said.

The recommendations for asymptomatic people with moderate absolute CV risk were:

  • A CAC score of 0 Agatston units (AU) could reclassify a person to a low absolute CV risk status.
  • A CAC score >99 AU could reclassify a person to a high absolute CV risk status.

The statement emphasised that CAC scoring is not required in people already found to be at high risk.

It also noted that given CAC scoring was not publicly funded in Australia, its costs should be included in discussions with patients about the benefits and harms of testing.

“The potential impact of the CAC scoring on health equity was an important factor in our decision to make our recommendations conditional, rather than routine.”

Lead author on the position statement and chief medical advisor of the Heart Foundation Professor Garry Jennings told the limbic there had been significant technological advances in CAC scoring.

For example, the radiation dose was now lower which mitigated some of the potential harm while the increase from 8-slice to a 256-slice CT scanner had also led to a commensurate improvement in definition and in fidelity of the signal.

Professor Jennings said risk prediction was a very crowded area.

“Firstly, the absolute risk equation is under review and we will have a new absolute risk predictor model in 2022,” he said.

“Secondly, there are other imaging tests coming along but there are also biomarkers which are being used which have incremental value and there are polygenic risk scores and other tests using the new biology to predict risk.”

He predicted no particular strategy would “win” and instead there would most likely be a combination of approaches.

“Here we are saying that CAC works well as a post classifying test. That is, if you have any uncertainty after you have done the absolute risk equation, then it is helpful.”

“It will also come down to cost benefit. The notion that everybody in the community over a certain age has a CT scan – I guess we accept that for breast cancer screening and certainly you could make the case that coronary disease is far more common than breast cancer – but there would be significant economic and cultural barriers to do that.”

“There has been very little in the way of cost effectiveness analysis in the Australian context,” he said.

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