Abstract Body (Do not enter title and authors here): Background: Collagen is the major extracellular matrix that imparts mechanical strength to fibrous caps covering fibroatheromas. Intracoronary polarimetry with polarization-sensitive (PS) optical frequency domain imaging (OFDI) measures polarization properties, such as birefringence and depolarization (Figure 1). Birefringence is elevated in collagen and collagen-synthesizing smooth muscle cells, while depolarization is increased by the presence of macrophages and lipid/necrotic cores.

Purpose: This study aimed to investigate polarimetric signatures of coronary lesions with healed coronary plaques (HCP) in patients with ACS and chronic coronary syndrome (CCS). Furthermore, we aimed to investigate diagnostic value for birefringence and depolarization of ACS culprit lesions discriminating from CCS target lesions.

Methods: We conducted a single center prospective registry of intracoronary PS-OFDI imaging in patients with coronary artery disease (n = 50). A total of 862 OFDI frames selected from culprit or target lesions were analyzed. Coronary plaque phenotypes were assessed using conventional OFDI imaging. HCP was defined as plaques with one or more layers of different optical density and a clear demarcation from underlying components on intensity images. Birefringence and depolarization of the newer intima was measured in cross-sectional images. Birefringence and depolarization of ACS- and CCS-lesions were compared using a generalized estimating equation model. Receiver operating characteristic (ROC) analysis was used to investigate the diagnostic performance of polarimetric signatures for identifying ACS-lesions.

Results: Compared to CCS-lesions, ACS-lesions featured significantly higher lipid-burden index and maximum lipid arc (both p < 0.05). Compared to the CCS-lesions, ACS-lesions exhibited significantly lower birefringence (p < 0.05) and higher depolarization (p < 0.05). In the ROC analysis for differentiating ACS-lesions from CCS-lesions, area under the curves (AUC) for birefringence and depolarization were 0.712 and 0.672, respectively. In the multivariable ROC analysis in diagnosing ACS lesions, combination of birefringence with depolarization improved the AUC to 0.755 (p ＝ 0.025).

Conclusions: Intracoronary polarimetry provides quantitative assessment of plaque composition in patients. Further research is warranted to investigate whether birefringence can serve as a marker of healing failure following plaque rupture and erosion.