Asymptomatic carotid stenosis refers to atherosclerotic narrowing of the extracranial internal carotid artery, most commonly involving the proximal internal carotid artery at or just distal to the carotid bifurcation. To consider the stenosis asymptomatic, the patient must not have experienced ischemic stroke, transient ischemic attack (TIA), or retinal ischemia referable to the stenotic artery within the past 6 months. Randomized trials of carotid revascularization in asymptomatic patients have shown that revascularization is associated with approximately a 3% risk of perioperative stroke or death and a 1% per year absolute reduction in the risk of stroke (i.e., 2% per year with medical therapy vs. 1% per year after revascularization). Because the upfront procedural risk is substantial relative to the annual risk reduction, careful patient selection is critical. Further, recent evidence suggests that modern, more intensive medical therapy has reduced the risk of stroke attributable to asymptomatic carotid stenosis, possibly to as low as 0.5% per year. If true, this may limit the potential benefit from carotid revascularization.
Intensive medical therapy for all patients should include antithrombotic therapy, high-dose, high-intensity statin therapy, blood pressure control with a goal < 130/80 mmHg, diabetes control with a goal HgbA1c < 7.0% when applicable, and lifestyle modification including smoking cessation, healthy diet, exercise, and weight loss. Choice of antithrombotic therapy should be individualized. Low-dose aspirin monotherapy is reasonable for most patients; for those with significant carotid stenosis (> 50%) and a low risk of systemic bleeding, the addition of low-dose rivaroxaban (2.5 mg bid.) to aspirin offers additional reduction in vascular risk and should be considered.
All patients with carotid stenosis ≥ 60% should be screened to confirm that they have not had a TIA, ischemic stroke, or retinal ischemia referable to the stenotic artery within the past 6 months. If any of these has occurred, the patient should be considered symptomatic and the risk of subsequent ischemic stroke is much higher; in this scenario, carotid revascularization is of substantial benefit and should be pursued.
Age, life expectancy, and medical comorbidities are important considerations. Patients with a life expectancy < 5 years should generally avoid revascularization because the procedural risk is high relative to the short-term reduction in stroke. This is particularly true in the context of medical comorbidities that may increase the procedural risk. Current guidelines recommend carotid revascularization only be considered in asymptomatic patients if the surgical risk of stroke, death, or myocardial infarction is < 3%.
Features which convey a greater likelihood of benefit from carotid revascularization include young age, male sex, and absence of significant medical comorbidities. Transcranial Doppler ultrasonography (TCD) can be used to evaluate for microembolic signals (MES) ipsilateral to the stenotic carotid artery. If present, MES suggest a high short-term risk of stroke. Additionally, progressive stenosis over time despite aggressive medical therapy is associated with a higher risk of stroke. Plaque morphology, including the presence of heterogeneous and/or ulcerated plaque, and impaired cerebral vasoreactivity on TCD may also be associated with an increased risk of stroke. Clinical decision making should be individualized, including shared decision making with the patient that incorporates their personal preferences, age, medical comorbidities, estimated life expectancy, and surgical risk. Notably, contrary to common belief, a higher degree of stenosis at initial presentation (i.e., 80% vs. 65%) has not been associated with an increased benefit from revascularization.
In carefully selected patients who have a life expectancy of ≥ 5 years and an estimated surgical risk of stroke, death, or myocardial infarction < 3%, it is reasonable to proceed with carotid revascularization.
In the absence of high-risk features, it is reasonable to proceed with medical therapy alone. Given the equipoise between medical therapy and carotid revascularization, it is critical to engage the patient in a process of shared medical decision making. Consideration should be given to the patient’s perceptions about immediate vs. long-term risk, as well as their level of anxiety about both the carotid disease and the risks of surgery.
When carotid revascularization is planned, both carotid endarterectomy (CEA) and carotid artery stenting (CAS) are options. CEA is typically preferred due to a lower perioperative risk of stroke and death. CAS can be considered in patients < 70 years of age with high-risk cardiac disease and/or contralateral carotid occlusion. In some cases, carotid artery anatomy precludes CEA (e.g., high bifurcation), in which case CAS can be considered.
Patients treated with medical therapy alone should receive an annual carotid ultrasound. If there is progressive stenosis despite medical therapy, or the development of other high-risk features, it is reasonable to consider carotid revascularization.