Shear rate is a better marker of symptomatic ischemic cerebrovascular events than velocity or diameter in severe carotid artery stenosis

Objective: This study was designed to test the hypothesis that the high shear rate of flow in the area of carotid stenosis is associated with the incidence of ischemic symptoms in patients with a high degree of carotid stenosis. Methods: This is a case-control study of patients with > 70% stenosis of the internal carotid artery (ICA) identified by duplex ultrasound in an Intersocietal Accreditation Commission-accredited laboratory during 1 year. Symptomatic patients were included in the study group, and asymptomatic patients served as controls. Shear rates were calculated from high-resolution ultrasound images. Descriptive statistics and univariate and multivariate analysis were performed to account for confounding factors. Receiver operating characteristic curves were used to compare diagnostic values of shear rate, velocities, and diameters of the ICA. Results: The study included 308 patients (55.5% male; mean age, 73 6 10 years); 209 of them were asymptomatic and 99 were symptomatic. The mean shear rate was 7930 s(-1) for asymptomatic and 9338 s(-1) for symptomatic patients. Receiver operating characteristic curve identified a cutoff value of 8000 s(-1) to differentiate between symptomatic and asymptomatic patients; 92% of asymptomatic patients and 8.0% of symptomatic patients had a shear rate of < 8000 s(-1) compared with 48.5% asymptomatic and 51.5% symptomatic who had a shear rate $ 8000 s(-1). Patients who had a shear rate higher than this cutoff value were 12 times more likely to be symptomatic than those with a shear rate < 8000 s(-1) (odds ratio, 12.1; 95% confidence interval, 6.12-24.09). Sensitivity and specificity were 84.8% and 61.2%, respectively. Conclusions: In patients with > 70% ICA stenosis, the shear rate is associated with the prevalence of symptomatic cerebrovascular ischemic events. A shear rate of 8000 s(-1) and above may be used as a predictor for having symptomatic cerebrovascular ischemic events. Further validation as well as further study of the pathologic mechanism connecting the high shear rate and ischemic cerebrovascular events is needed.