Risk of stroke in relation to degree of asymptomatic carotid stenosis: a population-based cohort study, systematic review, and meta-analysis

There is uncertainty around which patients with asymptomatic carotid stenosis should be offered surgical intervention. Although stroke rates were unrelated to the degree of stenosis in the medical-treatment-only groups in previous randomised trials, this could simply reflect recruitment bias and there has been no systematic analysis of a stenosis-risk association in cohort studies. We aimed to establish whether there is any association between the degree of asymptomatic stenosis and ipsilateral stroke risk in patients on contemporary medical treatment. We did a prospective population-based study (Oxford Vascular Study; OxVasc), and a systematic review and meta-analysis. All patients in OxVasc with a recent suspected transient ischaemic attack or stroke, between April 1, 2002, and April 1, 2017, who had asymptomatic carotid stenosis were included in these analyses. We commenced contemporary medical treatment and determined ipsilateral stroke risk in this cohort by face-to-face follow-up (to Oct 1, 2020). We also did a systematic review and meta-analysis of all published studies (from Jan 1, 1980, to Oct 1, 2020) reporting ipsilateral stroke risk in patients with asymptomatic carotid stenosis. We searched MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials, and included both observational cohort studies and medical treatment groups of randomised controlled trials if the number of patients exceeded 30, ipsilateral stroke rates (or the raw data to calculate these) were provided, and were published in English. Between April 1, 2002, and April 1, 2017, 2354 patients were consecutively enrolled in OxVasc and 2178 patients underwent carotid imaging, of whom 207 had 50–99% asymptomatic stenosis of at least one carotid bifurcation (mean age at imaging: 77·5 years [SD 10·3]; 88 [43%] women). The 5-year ipsilateral stroke risk increased with the degree of stenosis; patients with 70–99% stenosis had a significantly greater 5-year ipsilateral stroke risk than did those with 50–69% stenosis (six [14·6%; 95% CI 3·5–25·7] of 53 patients vs none of 154; p