Sex Difference of Fibrous Cap Collagen Content in Patients With Coronary Artery Disease: An Intravascular Polarimetry Study

Introduction: Intracoronary optical coherence tomography (OCT) polarimetry (OCT-polarimetry) enables to provide polarization properties (birefringence and depolarization) of the tissues in the coronary arterial wall together with coronary plaque microstructures. Collagen and smooth muscle cells exhibit birefringence, while depolarization is increased by the presence of macrophages and lipid components. Hypothesis: We hypothesized that there exists sex difference in collagen content of coronary plaques by measuring polarization properties of the coronary arterial walls. Methods: We analyzed 41 coronary lesions imaged with intracoronary OCT-polarimetry in 38 patients with CAD (ACS, n = 24 and chronic CAD, n = 14). Conventional OCT analysis included lesion-level qualitative analysis (fibrous cap thickness, presence of plaque rupture, macrophages, thrombus, layered plaque, cholesterol crystals) and quantitative analysis (lipid-burden index, calcium arc and length, and vessel lumen area). Polarimetric analysis was performed on OCT cross-sectional images with the thinnest fibrous cap of the lesion, blinded to the conventional OCT analysis results. The measurements were compared between male (n = 27) and female (n =11) using a generalized linear model with generalized estimating equations. Results: In this study population, ACS was more frequently observed in female patients compared to male patients (91% v.s. 52%, p<0.05). There was no significant difference in the conventional OCT measurements, while male patients exhibited a greater lipid-index compared to female patients. Although depolarization was comparable between the two groups, significantly lower birefringence was observed in female patients as compared to male patients (p-values < 0.05). A GEE model demonstrated that birefringence was independently and positively associated with male sex (beta, 1.4; 95% confidence interval 0,42-2,4; p =0.005), even after adjusting for age, ACS, and lipid-burden index. Conclusions: This study is the first to report sex difference in the polarization properties of coronary plaque fibrous cap. Intracoronary OCT-polarimetry opens the possibility of elucidating the mechanism of plaque destabilization through collagen remodeling.