Atherosclerosis - A finite element study of plaque distribution and stability

Sammanfattning: Atherosclerosis is a chronic disease of arteries. Cardiovascular diseases, of which atherosclerosis is an underlying mechanism, are the most common causes of death globally. The disease is characterised by lipids having penetrated the intima of the artery wall, accompanied by inflammation, fibrosis and endothelial hyperplasia. Accumulated cells, lipids, connective-tissue elements and debris from the blood gives rise to atherosclerotic plaques. These lesions may cause stenosis or rupture, exposing thrombotic materials to the circulatory system. Two-dimensional finite element simulations of coronary arteries afflicted by atherosclerosis were carried out, with the aim of studying how structural parameters of a lesion affect plaque stability. The Holzapfel-Gasser-Ogden material model was used to model the arterial layers and the plaque excluding the necrotic core, while the hyperelastic neo-Hookean material model covered the necrotic core. Four parameters were studied; plaque circumference, lumen coverage, necrotic core thickness and necrotic core angle. The load was applied as static intraluminal pressure in two steps, first at 80 mmHg and second at 120 mmHg, and the differences in stress distributions between these steps were used as output results. A Tresca stress map over the artery and lesion was created and peak circumferential and Tresca stresses along the plaque-lumen boundary was saved in each simulation. Results indicate that all parameters considered had an effect on plaque stability, by the increase and/or change in distribution of stresses induced into the lesion. Differences in stress levels due to structural changes in the plaque were in general small when comparing with values available in the literature, but within reason. The most influential parameter on plaque stability was the necrotic core thickness, which directly affects the thickness of the fibrous cap. Changing this parameter gave the largest increase in peak cap stresses of all four parameters, which may be considered significant in terms of plaque stability.