Subtraction CT Angiography Improves Evaluation of Significant Coronary Artery Disease in Patients with Severe Calcifications or Stents-the C-Sub 320 Multicenter Trial

Objectives: Diagnostic accuracy of conventional coronary CT angiography (CCTA) may be compromised by blooming artifacts from calcifications or stents. Blooming artifacts may be reduced by subtraction coronary CT angiography (CCTA) in which non-contrast and contrast CT data sets are subtracted digitally. We tested whether CCTA in patients with severe coronary calcification or stents reduces the number of false-positive stenosis evaluations compared with CCTA.

Methods: In this study, 180 symptomatic patients scheduled for invasive coronary angiography (ICA) were prospectively enrolled and CT scanned (2013-2016) at three international centers. CCTA, and CCTA data sets were reconstructed. Target segments were defined as motion-free coronary segments with a suspected stenosis (> 50% of lumen) potentially due to blooming of either calcium or stents. Target segments were evaluated with respect to misregistration artifacts from the CCTA reconstruction process, in which case evaluation was omitted. CCTA and CCTA were compared with ICA. Primary outcome measure was the frequency of false positives by CCTA versus CCTA to identify > 50% coronary stenosis by ICA on a per-segment level.

Results: After exclusion of 76 patients, 104 (14% females) with mean age 67 years and median Agatston score 852 were included. There were 136 target segments with misregistration and 121 target segments without. Accuracy calculations in target segments without misregistration showed a reduction of the false positives from 72% [95% confidence interval (CI): 63-80%] in CCTA to 33% (CI:25-42%) in CCTA, at the expense of 7% (CI:3-14%) false negatives in CCTA.

Conclusions: In severely calcified coronary arteries or stents, CCTA reduces the false-positive rate in well-aligned, calcified or stent segments suspected of significant stenosis on CCTA. Nevertheless, misregistration artifacts are frequent in CCTA.

Key Points: • A high calcium-score reduces the diagnostic accuracy in patients scanned with cardiac CT. • These patients would normally need an invasive angiogram for diagnosis. • In this prospective, multicenter study, subtraction CT, when evaluable, reduces false-positive stenosis evaluations. • Subtraction coronary CT angiography may, when evaluable, reduce excessive downstream testing.