The clinical implications of incidental coronary artery calcification in routine, non-triggered high-resolution thoracic computed tomography: a retrospective study

Abstract

Background: Coronary artery calcium (CAC) is a marker of atherosclerosis and an independent risk factor for cardiac-related mortality. The measurement of this score has traditionally been based on using ECG triggered computed tomography (CT). However, CAC, identified on non-contrast high resolution chest computed tomography (HRCT), should be considered diagnostic for coronary artery disease (CAD). We aimed to evaluate the incidental prevalence and burden of CAC on non-gated HRCT thorax used for patients undergoing lung cancer screening or follow-up for interstitial lung disease. We also assessed how often Radiologists reported CAC as an incidental finding on these scans. Method(s): Computerised Radiology Information Service (CRIS) was manually searched to determine all HRCT scans performed in our Trust from 01/05/2018 to 01/05/2019. The reports issued by Radiologists and images of selected studies were reviewed. Result(s): 2185 HRCT scans were performed over this period. Patients were divided into three groups of age <50 (Group 1); 50-<60 (Group 2) and 60 (Group 3). 100 scans were randomly selected from each group using a random number generator to give a total of 300 patients. The mean ages of patients in Group 1, 2 and 3 were 48.3+/-2.3, 54.8+/-2.4 and 65+/-3.2 respectively. There was, approximately, the same number of males as females in each group. CAC was noted in 15% of scans in Group 1, 82% of scans in Group 2 and 94% scans in Group 3. CAC was only noted in 1/15 (6.7%) of scan reports in Group 1, 41/82 (50%) in Group 2 and 37/94 (39.4%) in Group 3. Among the 79 patients with radiologist-reported incidental CAC, statin and aspirin prescriptions increased by approximately 7 percentage points each. A diagnosis of CAD was eventually made in 9 (11.4%) patients through functional imaging or coronary angiogram. Two authors independently calculated the Agatston scores of HRCT scans whose reports did not comment on the degree of calcification. We excluded 15/112 (13.4%) scans as they were uninterpretable due to motion artefacts. Of the remaining 97 scans analysed 58/97 (59.8%) had severe CAC with an Agatston score of >400 with the remaining showing moderate calcification (101- 400). Cohen kappa agreement between the two authors rating was 0.90 (95% confidence interval [CI] 0.87-0.96). Group 2 and 3 had significantly more patients with severe CAC then group 1 (p<0.001). Left anterior descending artery was most commonly affected. Conclusion(s): This study shows that CAC is under reported on non-gated HRCT scans which represents a missed opportunity to implement strategies for primary and secondary prevention. Given that respiratory disease is an independent risk factor for developing cardiac disease, it is incumbent upon the interpreting clinician to report all findings and ensure that critical findings are highlighted. The images of calcified coronary arteries may also potentially have a role in convincing people to make correct lifestyle choices.