Carotid Plaque Hemodynamics

Internal carotid artery (ICA) plaques constitute one major source of retinal and cerebral brain embolism. Current guidelines recommend optimal treatment of cardiovascular risk factors and recanalization based on the degree of ICA stenosis. However, ICA plaque composition, motion, vascularization, and local hemodynamics have only received limited attention as potential and independent risk factors for plaque rupture. The European Carotid Surgery Trial (ECST) showed an increased risk of stroke recurrence even in moderate stenosis if the plaque surface was ulcerated in angiography. Further indicators of plaque instability and thus vulnerability were established by native or contrast-enhanced two-dimensional duplex ultrasound, CT, and MRI. Due to high soft tissue contrast, multi-contrast MRI seems to be ideally suited to identify plaque compositions that are prone to rupture, although data from large clinical trials proving the independent predictive value of plaque morphology are lacking. The role of cardiovascular risk factors for atherosclerosis of the common carotid artery is well established. Nevertheless, little is known concerning the impact of local hemodynamics on plaque development, progression, and rupture. Wall shear stress, the friction force acting on the endothelium of the vessel wall, was shown to be able to induce local atherosclerosis and vulnerable plaques in animal models. Plaque movement and deformation was limited to investigations using ultrasound in order to identify plaques at risk. Similarly, models to calculate tensile plaque stress seem to be able to identify peak mechanical stress acting on plaque surfaces that make such regions susceptible to rupture. In this review, current evidence regarding the correlation of plaque location, composition, and local hemodynamics at the carotid artery bifurcation will be presented. Moreover, the potential benefit of a future comprehensive and individual risk assessment will be discussed.