Diagnostic Accuracy of Calcified Aortic Knob Found in Chest Radiograph for Detection of Coronary Artery Calcification

Aims: To validate the diagnostic performance of a calcified aortic knob found in chest radiographs in relation to coronary calcification. Study Design: This study is an observational analytical cross-sectional study. Place and Duration of Study: This study examined participants who were referred for a CT coronary calcium scoring (CT-CAC). at the Central Chest Institute of Thailand, Department of Medical Services, Ministry of Public Health, during the period from November 1, 2019, to October 31, 2021. Methodology: This cross-sectional study aims to evaluate the association between calcified aortic knobs on chest radiographs and coronary artery calcification as determined by CT-CAC. The study included 664 patients who underwent CT-CAC between November 1, 2019 and October 31, 2021. We selected participants aged 40 to 75 years without known history of coronary artery disease (CAD) or diabetes (fasting blood sugar levels under 126 mg/dl within past 6 months). A total of 441 eligible patients were included in the final analysis. Standard chest radiographs within 6 months interval were evaluated and classified into 4 grades, Grade 0 (no visible calcification), Grade 1 (<50% calcification of aortic knob), Grade 2 (>50% calcification of the aortic knob), and Grade 3 (circular calcification of the aortic knob). These findings were then compared with CAC obtained via dual source CT scanner to evaluate the diagnostic accuracy of chest radiographs. Key performance metrics, including sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV), were calculated to determine the effectiveness of aortic knob calcification as a predictor for coronary calcification. Results: Positive CAC (CAC >0) was strongly associated with a calcified aortic knob (grades 1-3), with a high positive predictive value of 88.07%. The diagnostic accuracy, sensitivity, and specificity were 66.9%, 61.5%, and 79.8%, respectively. The negative predictive value was low, at 41.8%. Conclusion: A calcified aortic knob (grades 1-3) correlates strongly with positive CAC (positive predictive value 88.07%). The study’s findings of low sensitivity (61.5%) and negative predictive value (46.18%) indicate limitations in using calcified aortic knob on chest radiograph as a standalone screening tool for coronary artery calcification.