Long-term risk of stroke and other vascular events in patients with asymptomatic carotid artery stenosis

Context: The annual risk of ischemic stroke in patients with asymptomatic carotid artery stenosis is about 2% during the short-term (2-3 years), but the long-term risks of stroke and other vascular events are unknown, although they may affect surgical decision making. Objective: To evaluate the long-term risk of stroke and other vascular events in patients with asymptomatic carotid artery stenosis. Design: Cohort study with a median follow-up of 10 years (range, 5-18 years). Setting: The teaching hospital of the University of Toronto, Toronto, Ontario. Patients: From the initial cohort of 500 patients, 106 patients with asymptomatic carotid artery stenosis were selected because they had completed at least 5 years of follow-up. Main Outcome Measures: Ipsilateral stroke, myocardial infarction, and nonstroke vascular death. Results: The 10- and 15-year actuarial risks of ipsilateral stroke were 5.7% (95% confidence interval [CI], 0%-12%) and 8.7% (95% CI, 1%-17%), respectively, in patients with 0% to 49% internal carotid artery stenosis, and 9.3% (95% CI, 1%-18%) and 16.6% (95% CI, 1%-32%) in patients with 50% to 99% internal carotid artery stenosis. The 10- and 15-year risks of myocardial infarction and nonstroke vascular death were 10.1% (95% CI, 4%-16%) and 24.0% (95% CI, 14%-34%). Age (P=.02), diabetes mellitus (P=.02), and internal carotid artery stenosis of 50% or more (P=.04) were predictive of increased risks of myocardial infarction and nonstroke vascular death. Internal carotid artery stenosis of 50% or more did predict the risk of ipsilateral stroke (P=.003) when all 181 asymptomatic carotid arteries were included. Conclusions: The annual stroke risk in patients with asymptomatic carotid artery stenosis was low and remained stable during long-term follow-up. Any benefit from carotid surgery is therefore unlikely to increase significantly with long-term follow-up. The high longterm risks of myocardial infarction and nonstroke vascular death suggest that prevention strategies should concentrate on coronary risk more than stroke risk.