Investigating the impact of non-gated thoracic CT prior to CTCA to reduce layered testing

Abstract

To determine the proportion of computed tomography (CT) coronary angiography (CTCA) referrals with coronary artery calcification (CAC) evident on previous non-cardiac CT imaging and how this impacted the diagnostic yield for CTCA, the requirement for additional diagnostic testing, and the associated costs to confirm or refute obstructive coronary artery disease (CAD). A retrospective review of CTCA examinations was undertaken between 01/05/2018 and 31/05/2020 in which the examinations were cross referenced for previous non-gated thoracic CT at Royal United Hospitals Bath. Major epicardial vessel CAC on baseline CT was re-evaluated by published semi-quantitative methods, giving a per-patient CAC score (mild=1-3, moderate=4-6, severe >6). Subsequent incomplete CTCA diagnostic yield, further testing, and cost implications were examined. Of the 2140 CTCA examinations identified, 13% (280/2140) had a preceding non-gated thoracic CT (53% female, age 63±11 years). The incomplete diagnostic rate increased with CAC grade, mild 32%, (RR 12; 95% CI 4-40), moderate 64% (RR 25; 95% CI 8-80), severe 75%, (RR 29; 95% CI 9-94). Additional diagnostic testing occurred in 4% for the mild CAC category, and 14% and 42% for moderate and severe, respectively. When severe CAC was identified on a non-gated thoracic CT a cost saving of £171/patient (dobutamine stress echo [DSE]) and £61/patient (myocardial perfusion scintigraphy [MPS]) was established with a direct to functional testing pathway. In patients referred for CTCA where severe CAC was identified on a preceding non-gated thoracic CT a direct to functional testing altered management in 42% of cases and was cost-effective.