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Aortic Arch Calcification and Novel Markers of Subclinical Atherosclerosis on Lung CT: Methodology and Reproducibility in the COPD Gene Study

Matthew J Budoff*, Ilana S Golub, Suvasini Lakshmanan, Suraj Dahal, Stephanie Kristo, Lucia Schroeder, Orly Termeie, Venkat Manubolu, Luay Hussein, Dhiran Verghese, Ahmed M Shafter, Richard Casaburi, Sion K Roy

Background: COPD, smoking, and risk for CVD are closely associated. CAC offers a well-established assessment of CVD risk and subclinical atherosclerosis on both ECG-gated/cardiac and non-gated/lung CT. However, the predictive value of CAC for stroke is limited. Frequently detected on ungated lung CT scans due to large field view, aortic arch calcium (AAC) can serve as a marker of subclinical atherosclerotic burden. We hypothesized that AAC is more proximal to the carotids and may better predict stroke. This unmeasured marker may be an independent and/or incremental predictor of both stroke and atherosclerotic cardiovascular disease (ASCVD) but the prognostic value of AAC on adverse cardiovascular events, remains to be established. Our study will evaluate novel cardiac screening metrics of subclinical atherosclerosis, by measuring AAC measurements obtained with ungated Lung CT scans in a large cohort study.

Methods: We will evaluate 10,300 ungated lung CT scans obtained in the COPD GENE cohort study, a longitudinal study of current and former smokers aged 45 to 80 years, sponsored by the National Institutes of Health. The following measures were summed to yield total Arch Calcium Score and total Arch Volume: aortic valve and root; south and north aortic arch segment; brachiocephalic, common carotid and subclavian artery; ascending and descending aorta. We also report the inter-reader variability of this measure, by randomly selecting 90 ungated lung CT scans from this cohort, and Bland-Altman plot analysis was used to test the reproducibility of this measure.

Results: We present here the methods used to determine multiple metrics of calcification not previously reported in any epidemiologic cohort study. We also demonstrate that inter-reader reproducibility was excellent for both total Arch Calcium Score at 98% and for total Arch Volume at 96%.

Conclusion: This metric may prove to be an important measure of ASCVD risk and easily obtainable on every non-contrast lung CT performed. Importantly, high rates of inter-observer reproducibility at ungated lung CT attest to the proposed arch calcium measurement methods. This introduces a new method with the potential of ASCVD risk stratification among patients undergoing lung CT evaluation, without requiring additional scanning, radiation or patient burden. This method can help measure AAC on lung CT, allowing recognition of CV risk and enabling targeted preventive strategies for CVD.