Management of Asymptomatic Carotid Artery Stenosis

Introduction

Asymptomatic stenosis of the carotid artery is not an uncommon finding encountered by many doctors in clinical practice.

The common question that comes up is

What is the management of these patients?

Should they undergo carotid revascularization surgery?

Current guidelines recommend revascularization in most patients with severe asymptomatic carotid artery stenosis. However, these guidelines are based on older studies that do not reflect the changing natural history of asymptomatic carotid artery stenosis with current optimal medical management.

Conventional treatment

Current recommendations for revascularization for asymptomatic carotid artery stenosis are predominantly based on two landmark studies performed in the 1990s.

The Asymptomatic Carotid Artery Study (ACAS) was a well-conducted study that assessed carotid endarterectomy (CEA) in asymptomatic carotid artery stenosis (>60%) for stroke prevention. The study was halted because of a projected safety favoring carotid endarterectomy (CEA). The perioperative stroke rate was 2.3%. The five-year projected rate of ipsilateral stroke was 11% for the medical group versus 5.1% for the surgical group.

In the Asymptomatic Carotid Surgery Trial (ACST), the 30-day risk of stroke or death was 3.1%. The five-year rates were 6.4% for CEA and 11.7% for medical therapy arm.

However, medical therapy in these trials was not up to current standards, with only a minority of patients receiving lipid-lowering therapy (Statins) and blood pressure (BP) was also significantly higher than today's standards.

Evolving Natural History of Asymptomatic Carotid Artery Stenosis

Recent evidence suggests that the natural history of asymptomatic carotid artery stenosis has improved remarkably, and the risk-benefit analysis of revascularization will need to be re-evaluated. Current optimal medical management consists of high-dose statin drugs, optimal BP control, smoking cessation, antiplatelet therapy (generally aspirin alone), optimal diabetes control and other lifestyle changes. Hence, the annual risk of stroke with current OMT is likely <1%.

Who is a "High-Risk" Patient?

The reality is that the majority of patients with asymptomatic carotid artery stenosis will never become symptomatic and may undergo unnecessary procedures if these studies do show benefit of endarterectomy or stenting

Clinical Features

There are few clinical predictors of increased stroke risk in asymptomatic carotid artery stenosis. Certain clinical characteristics, such as male sex, current smoking, poorly controlled hypertension, and history of contralateral transient ischemic attack (TIA)/stroke impart a higher risk of future stroke. However these are too non-specific to serve as useful guides for deciding about revascularization.

Stenosis Severity

Patients with 50-69% stenosis had a lower risk compared to those with 70-89% and 90-99% stenosis. However, stenosis severity alone is not a strong enough predictor to be used alone in decision making.

Progression of Stenosis

Progression of stenosis on periodic examination has been shown to impart at least twice the risk of stroke in patients.

Plaque Characteristics

Using ultrasound, atherosclerotic plaques can be characterized based on their surface irregularity, ulcerations, echolucency and gray-scale values. Studies show that patients with predominantly echolucent, lipid-rich plaque have significantly higher stroke risk (3%) than those with mostly echodense, fibrotic plaque (0.8-0.4%). Ulceration on plaque surface detected by three-dimensional ultrasound has also been shown to identify high-risk subjects. Magnetic resonance imaging (MRI) has also been used to detect the presence of intraplaque hemorrhage as indicative of a high-risk plaque. Intraplaque hemorrhage detected by MRI is associated with an increased risk of cerebrovascular events

Silent Emboli Detection

Since both progressive stenosis and high-risk imaging features identify unstable plaque more prone to atheroembolic events, another way to identify patients at risk is to assess for active silent emboli or evidence of prior asymptomatic cerebral emboli using transcranial doppler study. However, most patients with these signals did remain stroke free at three years, and thus, this test lacks the specificity for stand-alone clinical use.

Silent Embolic Infarcts on Computed Tomography (CT) or MRI

Presence of ipsilateral silent embolic infarcts on neuroimaging may be predictive of increased risk of ipsilateral stroke.

 Reduced Cerebrovascular Reserve

In patients with severe ipsilateral carotid stenosis, the presence of an incomplete circle of Willis or presence of intracranial or contralateral occlusive disease can reduce cerebral perfusion pressure. Cerebrovascular reserve in such patients can be assessed using TCD velocity measurements in response to acetazolamide or breathing 5% CO2.

Elderly

The elderly (especially those over 80 years of age) is a group in which the benefit of revascularization for asymptomatic carotid artery stenosis is most controversial because However, age cannot be an absolute contraindication with increasing life expectancy of the overall population; certainly in carefully selected patients, excellent outcomes after both CEA (Carotid Endarterectomy) and CAS (Carotid Artery Stenting) have been demonstrated. Overall CEA has more favorable outcomes for those over 70 years of age and CAS for those under 70 years of age.

Conclusions and Recommendations for Clinical Practice

Both medical and surgical management arms of asymptomatic carotid artery stenosis are rapidly evolving and will continue to result in decreased stroke risk.

• We recommend that for asymptomatic carotid artery stenosis patients (even those with >80%) stenosis there is enough evidence for a more conservative approach and decisions regarding revascularization should be made after discussing the stroke risk with the patients.
• Serial ultrasounds should be performed and revascularization offered to those with >70% stenosis with evidence of progression of stenosis severity.
• All patients with asymptomatic carotid artery stenosis should be on Optimal Medical Management.
• For the very elderly (>80 years) and life expectancy less than five years, a conservative approach is most reasonable in most situations.
• Carotid Endarterectomy remains the gold-standard for revascularization of carotid stenosis. Carotid Artery Stenting should be considered in patients with high risk of surgery from associated cardiac co-morbidity.
• Individual patient and anatomic risks for CEA and CAS are different and should be considered and a multi-specialty approach should be followed.