Temporal Trends and Determinants of Stroke Risk in Patients With Medically Treated Asymptomatic Carotid Stenosis

Effectiveness of carotid procedures (surgery and stenting) in patients with asymptomatic carotid artery stenosis (ACAS) depends on the absolute risk reduction that patients might receive from these procedures. We aimed to quantify the risk of ipsilateral ischemic stroke and examined temporal trends and determinants of these risks in patients with ACAS treated conservatively. We conducted a systematic review from inception to March 9, 2023, of peer-reviewed trials and cohort studies describing ipsilateral ischemic stroke risk in medically treated patients with ACAS of ≥50%. Risk of bias was assessed with an adapted version of the Quality in Prognosis Studies tool. We calculated the annual incidence rates of ipsilateral ischemic stroke. We explored temporal trends and associations of sex and degree of stenosis with ipsilateral ischemic stroke using Poisson metaregression analysis and incidence rate ratios, respectively. After screening 5915 reports, 73 studies describing ipsilateral ischemic stroke rates of 28 625 patients with midyear of recruitment ranging from 1976 to 2014 were included. The incidence of ipsilateral ischemic stroke was 0.98 (95% CI, 0.93-1.04) per 100 patient-years (median duration of follow-up, 3.3 years). The incidence decreased 24% with every 5 years more recent midyear of recruitment (rate ratio, 0.76 [95% CI, 0.73-0.78]). Incidence rates of ipsilateral ischemic stroke were lower in female patients (rate ratio, 0.74 [95% CI, 0.63-0.87]) and in patients with moderate versus severe stenosis when assessed in cohort studies, with incidence rate ratios of 0.41 ([95% CI, 0.35-0.49] cutoff, 70%) and 0.42 ([95% CI, 0.30-0.59] cutoff, 80%). Reported risks of ipsilateral ischemic stroke in patients with ACAS have declined 24% every 5 years from mid-1970s onward, further challenging the routine use of carotid procedures. Risks were lower in female patients and more than twice as high with severe compared with moderate ACAS. Inclusion of these findings in individualized risk assessment can help to determine the benefit of carotid procedures in selected individual patients with ACAS. URL: https://www.crd.york.ac.uk/PROSPERO/; Unique identifier: CRD42021222940.