The Effect of Carotid Plaque Morphology on Longitudinal Fibrous Cap Stress Levels

Background and Purpose: Rupture of vulnerable carotid atherosclerotic plaques is a major cause of stroke. Stress levels may reflect risk of rupture in patients with carotid atherosclerotic plaques. Features thought to influence the risk of plaque rupture include the degree of stenosis, lipid-rich necrotic core (LR-NC) size, and thickness of the protective fibrous caps. We used computational models to investigate the effect of these variables on fibrous cap stress levels. Methods: Two-way coupled fluid-structure interaction longitudinal 2D simulations were performed on a bifurcation model based on idealized geometry derived from a symptomatic patient. Models with varying degrees of stenosis (50%-95%), fibrous cap thicknesses (0.05-1 mm), and LR-NC sizes (2 × 1 mm-6 × 3 mm) were simulated. The stress distribution for each model was calculated and peak principal stresses extracted. Regression analysis was used for assessing the relationship between the variables and stress levels. Results: Mechanical stresses increased with decreasing fibrous cap thicknesses ( β= -0.905, p < 0.001) and increasing LR-NC sizes (β = 0.262, p < 0.001). The degree of steno-sis (β = 0.024, p = 0.344) and LR-NC placement (ß = -0.001, p = 0.979) had insignificant effects on mechanical stress levels. Conclusions: Thin-capped plaques with large atheromas, known predictors of plaque vulnerability, were shown to exhibit the greatest mechanical stress levels.