At the recent Amgen-sponsored CV Academy 2021, Professor Clara Chow from the University of Sydney shared her views on the importance of targeted clinical imaging. Her expertise and knowledge in this area has been summarised below with an emphasis on “From a clinician point of view, trying to work out where do these tests best help us with respect to risk prediction when looking at primary prevention patients,” she said.

Primary prevention guidelines for assessing cardiovascular risk

Prof Chow discussed what current guidelines say – or, more importantly, don’t say – about clinical imaging. “In the 2009/2012 Australian National Vascular Disease Prevention Alliance (NVDPA) Absolute cardiovascular disease (CVD) risk guidelines it states: there is no current support for the use of ancillary cardiac imaging such as coronary CT angiography to refine FRE based risk assessment and decisions to initiate therapy,” said Prof Chow. She also briefly discussed the 2016 European CVD Primary prevention guidelines for calcium scores, along with the 2017 CSANZ Position statement on CAC and 2021 Position statement CAC score for primary prevention of CVD in Australia.

2019 ACC/AHA guideline on the primary prevention of CVD

“They try to tackle this issue of a combination of evidence-free zone with the current evidence and how we deal with it as a clinician in this space,” said Prof Chow when describing guidelines on primary prevention.  Prof Chow highlighted what is new in the most recent guidelines, including the use of Pooled Cohort Equation, risk-enhancing factors, and the utility of calcium score in reclassifying individuals with intermediate CV risk.

Prof Chow described the simplified summary of the guidelines and where calcium scoring is positioned. Of note, the guidelines have introduced a borderline risk group, which is where risk-enhancing factors are described and, in the intermediate risk group, where coronary artery calcium score is discussed.¹ “If risk decision is uncertain, consider measuring calcium score in selected adults,” suggested Prof Chow.

Looking at other guidelines, Prof Chow discussed ‘appropriateness,’ defined as: An appropriate imaging study is one in which the expected incremental information, combined with clinical judgment, exceeds the expected negative consequences by a sufficiently wide margin for a specific indication that the procedure is generally considered acceptable care and a reasonable approach for the indication. Prof Chow explained that there is a growing body of evidence that calcium score reclassifies risk. She discussed a review that looked at coronary artery calcium score and CTCA against principles of screening as applied to coronary disease.²

What evidence is there that cardiac imaging helps in primary prevention CV risk assessment?

“Does adding cardiac imaging to a risk projection score improve outcomes? The answer is not there. There isn’t a clear clinical trial,” said Prof Chow. She explained that the only trial in this area is the Early Identification of Subclinical Atherosclerosis by Noninvasive Imaging Research, or the EISNER trial from 2011.³ It was a prospective RCT that compared the clinical impact of conventional risk factor modification to that associated with the addition of CAC.  “This is the one piece of evidence that we have to say that adding calcium scoring is better than not adding, with respect to risk protection, and it’s weak and underpowered and leaves us with many questions,” she said.

Australia specific study of CAC scoring in CV risk assessment (Caught-CAD)

Prof Chow highlighted work by Tom Marwick’s group in Australia which assessed the predictive value of the Australian CV risk calculator (ACVDR) and other assessment tools for identifying Australians with family histories of early onset CAD who have coronary artery calcification.⁴ She highlighted key takeaways, including the sensitivity of the ACVDR calculator for identifying people with non-zero calcium scores being not as good as the pooled cohort equation and, similarly, the sensitivity for ACVDR for CAC>100 was also not as good as the pooled cohort equation.

Prof Chow concluded by stating guidelines suggest that CAC probably has utility in selected intermediate risk patients because they recognise the challenges of implementing imprecise cardiovascular risk guidance. Reduced cost and reduced risks of atherosclerosis imaging has become increasingly attractive and the growing evidence of improved prognostic accuracy with CAC has improved confidence in clinicians. Finally, Prof Chow reiterated that there is little clinical trial evidence that cardiac imaging helps in primary prevention CV risk assessment, and that in the future we need to look at the role of CAC in younger and older adults and ethnic subgroups.

References

1. Arnett DK, et al. J Am Coll Cardiol 2019;Mar 17.
2. Chow ALS, et al. J Clin Med 2021;10(4): 625.
3. Rozanski A, et al. JACC 2011: 57 (15):1622-32.
4. Venkataraman P, et al. Med J Aust 2020; 213 (4): 170-177.