Aim: Plaque rupture is likely to occur if mechanical loading induced by blood pressure and heart motion exceeds the material strength of fibrous cap (FC). Fine fibre structures in the FC may affect such loading in ways that have not been fully investigated.
Methods: Fibre structures in 16 coronary atherosclerotic lesions were analysed based on histology. Misalignment of fibres along the lumen contour and dispersion of fibres were calculated. Differences in fibre orientation and critical mechanical condition (stress) in shoulder regions, mid FC and regions with intima thickening (RIT) were compared.
Results: Compared with the shoulder region, fibres in mid FC and RIT regions had better alignment with the local lumen boundary (Median [Inter quartile range] 11.5 [8.8, 19.5] vs. 6.4 [5.7, 7.7] or 5.4 [4.9, 6.2], p<0.05; unit: degree). Although, in general, the dispersion increased when the misalignment increased, there was no significant difference between either shoulder and mid FC (p=0.09) or shoulder and RIT regions (p=0.08). Mechanical loading within the FC was not over-/under-estimated if the fibre structure was ignored. However, anisotropic analyses indicated that shear (sliding) stress between fibres at the shoulder, mid FC and RIT were 13.61 [9.30, 25.05], 5.66 [2.75, 10.38] and 20.08 [17.04, 24.69] (unit: kPa), respectively, corresponding to 14.2%, 20.6% and 16.2% of the maximal principal stress in each sub-region. Conclusions: Although fine fibre orientation had little impact on the mechanical loading within the FC, considerable shear stress existed between fibres which might cause fibre debonding leading to FC rupture.