Aim: To define the relationship between CAC score, coronary stenosis and MBF.
Methods: Consecutive patients (n=63) with suspected angina that underwent both CTCA and 82Rb PET as a part of routine clinical care between 2016 and 2018 were identified. Clinical history ascertained the chest pain characteristics, medications and traditional risk factors. The Agatston CAC score (CACS) and visual grading of coronary stenosis were quantified by CTCA in accordance with SCCT reporting guidelines. Semi-quantitative visual interpretation of the 82Rb PET rest and stress perfusion images was performed using a 17-segment heart model; abnormal perfusion was defined as SSS=4. Quantitative assessment of resting MBF, hyperemic MBF and global myocardial perfusion reserve (MPR) was made using the Syngo MBF platform. Four subjects were excluded: 3 had insufficient CTCA image quality and 1 was unable to tolerate adenosine stress.
Results: In the 59 patients (age 56±10 yr, male 48%) included in the analysis, in total 177 vascular territories were assessed. On semi-quantitative assessment of the relative 82Rb PET perfusion images, 18 subjects (31%) had abnormal perfusion. In the 45 subjects with no prior history of CAD in whom CACS was quantified, abnormal perfusion was associated with a higher mean CACS (472 vs. 149; P=0.009). There was an inverse association between CACS and both hyperemic global MBF (?=-0.45, p=0.003) and global MPR (?=-0.23, p=0.039). There was no significant association between CACS and the SSS (?=0.25, p=0.11). Stenoses in the territory of the left anterior descending artery graded as =50% and =70% were associated with reduced global MPR (2.2±0.2 vs. 2.8±0.1, p=0.04 and 2.0±0.3 vs. 2.7±0.1, p=0.02, respectively) but there was no such relationship for the right coronary or left circumflex territories. Across all 3 coronary territories, on a per-vessel analysis there was no association between the visual grading of stenosis and MPR.
Conclusion: While there is a robust association between the extent of CAC and global MBR, there is no correlation between the visual grading of coronary stenoses on CTCA and the functional ischaemia quantitated by MPR, which reflects both epicardial and microvascular disease. Future work aims to establish the relationship between CT-guided FFR and MPR.