Carotid artery disease is common in the general population (75% in men and 65% in women >64). Clinical management of patients with a degree of carotid stenosis >70% is well established. However, in a large majority of cases (>90% of cases), carotid stenosis is <70%. While <70% carotid stenosis is associated with a low individual risk of ischemic stroke (1.3% to 3.3% annually), its high prevalence in the general population translates into a large number of ischemic strokes on a population level. In these patients with <70% carotid stenosis, the exact degree of luminal narrowing fails to predict the associated risk of stroke. Recently, a concept has emerged that direct assessment of the atherosclerotic process within the carotid wall would be a better predictor of the risk of stroke than characterizing its indirect impact on the adjacent lumen—an approach that is made possible by the ability of imaging techniques, such as ultrasound, MRI, and CT, to assess the carotid artery wall in addition to the lumen.
The goal of this research is to identify a carotid artery wall feature (or a combination thereof) that would allow differentiation in patients with <70% carotid stenosis between those at high risk and those at low risk of ischemic stroke. In pursuit of this goal, we propose to conduct a nested study in a retrospective cohort of patients from our institution who had a CT-angiogram of their carotid arteries between 2001 and 2007 (n=4,891). We will compare and evaluate 6 carotid artery wall features (maximal carotid wall thickness, carotid plaque ulcerations, thickness of the fibrous cap, lipid-rich necrotic core, intraplaque hemorrhage, calcifications). The primary outcome will be ischemic strokes of carotid origin. We propose three specific aims, which will test the three following hypotheses, with specific attention paid to patients with <70% carotid stenosis:
Aim 1: To test the hypothesis that a combination of one or several among 6 carotid artery wall features discriminates carotid stroke patients from non-carotid stroke patients.
Aim 2: To test the hypothesis that a combination of one or several among 6 carotid artery wall features discriminates the side ipsilateral to the stroke from the contralateral side in carotid stroke patients.
Aim 3: Among patients free of stroke at baseline, to test the hypothesis that a combination of one or several among 6 carotid artery wall features predicts incident carotid ischemic stroke during follow-up.