Reduced inflammation assessed by pericoronary adipose tissue is associated with coronary plaque calcification

Abstract
Introduction
Pericoronary adipose tissue attenuation (PCAT) quantified from coronary computed tomography angiography (CCTA) is increasingly recognized as an inflammation marker in coronary artery disease (CAD). Inflamed PCAT has been linked to non-calcified plaque (NCP) and cardiovascular morbidity and mortality. Nevertheless, gaps remain in understanding how PCAT behaves during plaque stabilization.

Purpose
We investigated associations between coronary artery inflammation assessed by PCAT and the presence and type of coronary plaques, plaque burden, and coronary calcification.

Methods
An observational study involving 506 patients with suspected chronic coronary syndrome who underwent CCTA. PCAT was averaged across the proximal 40 mm segments of all three coronary vessels to represent the patient level. Plaque presence and types (calcified, mixed, and soft) were assessed. Total, NCP, and calcified plaque (CP) burdens were measured as normalized atheroma volumes. Coronary calcification was quantified using Agatson coronary artery calcification (CAC) score and categorized based on cut-offs of 0, 100, 400.

Results
The mean PCAT was -81.1 ±6.3 Hounsfield Unit (HU) without plaque and -79.7 ±6.0 HU with plaque (p= 0.01). PCAT differed between calcified (-81.8 HU), mixed (-79.8 HU), and soft (-77.0 HU) plaques (p<0.0001).

Multivariate linear analysis (adjusted for clinical risk factors, cardiovascular medication, and tube voltage) showed PCAT positively associated with total plaque burden (estimate= 1.1 [95% CI: 0.3-1.8], p=0.004) and NCP burden (estimate= 2.4 [95% CI: 1.4-3.4]; p<0.0001), while the association with CP burden was negative, but not statistically significant (estimate= -1.7 [95%CI : -4.1-0.7], p=0.2).

Multivariate linear analysis, which accounted for both calcified and non-calcified plaque, reaffirmed the positive association to NCP burden (estimate= 2.7 [95% CI: 1.7-3.7]; p<0.0001) and a significant negative association between CP burden (estimate= - 3.3 [95% CI: -5.8- -1.0]; p=0.007) and PCAT.

No significant differences in PCAT levels were found among patients with a CAC score of 0 and those with CAC scores exceeding 400, or across different stages of CAC score categories (p>0.8).

Conclusion
PCAT increased with plaque presence, rising from calcified to mixed to soft plaques. Increased NCP burden associated with higher PCAT, while higher CP burden seemed to reduce PCAT, though not statistical significant. Interestingly, when NCP was absent, higher levels of CP burden were associated with reduced inflammation. This supports the hypothesis of plaque stabilization, proposing that calcification might stabilize the vessel and indirectly contribute to reducing inflammation.