2021 Top Story in Cardiology: The Continuing Evolution of Coronary CT Imaging
Since the earliest clinical reports of the ability to noninvasively image the coronary arteries with computed tomographic angiography (CTA) over 20 years ago, there have been ongoing advances. Initially, the focus of investigative work was on simply imaging luminal stenosis and direct comparisons with invasive angiography. In parallel, a large evidence base developed on the significance of coronary calcium imaging as a sign of coronary atherosclerosis, opening a door to imaging people before they become symptomatic and enabling the potential for earlier preventive therapies. In particular, a calcium score of zero was associated with a benign prognosis and very low risk for events over several years of follow-up, implying that little or no coronary atherosclerosis was present. More recently, as the technical capability and resolution of CCTA imaging systems continued to evolve and improve, it has become possible to interrogate elements of coronary atherosclerotic plaques and image features that have become associated with elevated risk of instability and a clinical acute coronary syndrome. These features include positive remodeling, spotty calcium, low attenuation, and the napkin-ring sign.
As CCTA has become much more widely available, large data sets have emerged that have informed a more nuanced perspective on how some of these imaging features fit together. A noteworthy example of such a report was published this year in JAMA Cardiology, addressing the issue of the strength of a calcium score of zero for ruling out angiographic stenosis in symptomatic patients with suspected coronary artery disease (CAD).1 The issue is highly relevant, as it has been suggested that, for individuals with suspected CAD at the low- to intermediate-likelihood part of the risk spectrum, coronary calcium imaging might be used as a screen for further testing.
In this report,1 Mortensen and colleagues studied almost 24,000 individuals referred for CCTA testing based on symptoms suspicious for CAD over a 10-year period in the Western Denmark Heart Registry, and who were then followed for a median of over 4 years post testing. A focus of the analysis was on the influence of age on the power of the coronary calcium score to be associated with angiographically obstructive CAD, here defined as stenosis >50%. As one would expect, the prevalence of obstructive CAD varied with age. Among the patients with obstructive CAD, 14% had a CAC score of zero. This prevalence varied substantially based on age, being as high as 58% among those who were younger than 40 years, down to 5% among individuals who were 70 years or older. Consistent with these findings was that the diagnostic value of the calcium score was smaller at younger ages. Prognostically, the presence of obstructive CAD in the absence of coronary calcium was associated with an elevated risk of infarction and all-cause death among those individuals under 60 years old, suggesting that, in younger people, a calcium score of zero may not be as benign as previously suggested.
The data have implications both for testing strategies for symptomatic patients but also for the use of coronary calcium scores in primary prevention and the deployment of statin therapy, as also discussed in an editorial on the Mortensen paper by Khan and Navar.2 In younger individuals referred for evaluation of symptoms, screening with coronary calcium would miss a not-insignificant number of people who have clinically important disease, although the absolute number is relatively low. In an asymptomatic primary prevention population, while not directly applicable based on the population differences, the data should give some pause to the concept that a calcium score of zero may safely allow deferral of statin therapy among those with some indication based on risk equations.
On the heels of the Mortensen paper comes the multi-society–endorsed 2021 Guideline for the Evaluation and Diagnosis of Chest Pain,3 in which CCTA has been elevated to a class I indication for assessment of symptomatic patients with an intermediate to high likelihood of CAD, alongside stress functional imaging. The extensive data supporting this recommendation are largely based on the identification of the presence, absence, and magnitude of luminal stenoses. How the broader capabilities of the modality to more comprehensively illuminate the processes of coronary atherosclerosis might be incorporated into diagnostic and treatment algorithms should be the subject of future investigations. As always, whether the published data that emanate from expert centers can generalize more widely will be a key step to evaluate.
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Additional Info
- Mortensen MB, Gaur S, Frimmer A, et al. Association of Age With the Diagnostic Value of Coronary Artery Calcium Score for Ruling Out Coronary Stenosis in Symptomatic Patients. JAMA Cardiol. 2021 Oct 27: doi: 10.1001/jamacardio.2021.4406. Online ahead of print.
- Khan SS, Navar AM. The Potential and Pitfalls of Coronary Artery Calcium Scoring. JAMA Cardiol. 2021 Oct 27. doi: 10.1001/jamacardio.2021.4413. Online ahead of print.
- Gulati M, Levy PD, Mukherjee D, et al. 2021 AHA/ACC/ASE/CHEST/SAEM/SCCT/SCMR guideline for the evaluation and diagnosis of chest pain: executive summary: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines. J Am Coll Cardiol. 2021;78 (22) 2218-2261.
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