Numerical modeling of stenotic arteries in the presence of micro-heterogeneities

Most finite element models used for atherosclerotic arteries do not account for the micro-heterogeneity of the plaque constituents. Failure of plaque lesions has been shown to be a local event, linked to stress concentrations caused by cap thinning, inflammation, macroscopic heterogeneity and, recently, the presence of micro-calcifications. There is growing evidence that micro-calcifications exist in the fibrous cap of plaque lesions. However, their role is not yet understood. The goal of this work is to investigate the effects of localized micro-heterogeneities on the stress field of atherosclerotic plaque caps. This is achieved by performing finite element simulations of three-dimensional fluid-structure interaction (FSI) models. The process of debonding and failure is explored by using micro-mechanical approximations to evaluate stress concentration functions of micro-calcifications embedded in fibrous tissue. A sensitivity study is conducted to determine whether the effects of the micro-heterogeneities are influenced by changes in other key parameters, such as the fibrous cap thickness, micro-calcification position in the fibrous cap, and the volume fraction of micro-calcifications. As in previous studies in the literature, the fibrous cap thickness has a significant influence on the level of stress. However, the presence of the micro-calcifications have a significant influence on the distribution of stress, shifting the maximum circumferential stress away from the shoulder of the lesion to the region of calcification. This is one possible explanation as to why 40% of cap failures occur away from the shoulder region, where failure is most common. It was found that if micro-calcifications are present, the fibrous cap can become vulnerable at a much earlier stage, and in a different location than normally expected.