Neuroscience Clerkship

 
 

Management of Carotid Stenosis to Prevent Ischemic Stroke

Carotid artery stenosis is one of the most important risk factors for ischemic stroke. It is imperative to assess the carotid arteries in anyone presenting with ischemic stroke, as intervention can reduce the future risk of stroke. Atherosclerosis most commonly affects the carotid bifurcation or proximal internal carotid artery. The carotid arteries can be well visualized by doppler/ultrasound and magnetic resonance angiography, as well as by conventional angiography.
 

Epidemiology

Approximately 10% of ischemic strokes are due to carotid stenosis.


Pathophysiology

Stroke may occur due to carotid artery stenosis in several ways:

• Unstable atheromatous plaque in the carotid artery may rupture and result in thrombosis, thus occluding the lumen of the vessel. A stroke will then ensue secondary to lack of blood flow to the corresponding area of brain the carotid artery supplies.

• An unstable plaque in the carotid artery may rupture and embolize distally to affect a branch of the carotid artery, most often the middle cerebral artery (i.e., artery to artery embolism).

• In a patient with a critical stenosis (near occlusion), any drop in systemic blood pressure may result in hypoperfusion across the already compromised carotid artery resulting in a “watershed” territory stroke.

Management

The definitive management for patients with symptomatic severe carotid stenosis is carotid endarterectomy. “Severe” stenosis is defined as greater than 70% stenosis of the carotid artery. The designation of “symptomatic stenosis” requires that a patient has a stroke or TIA ipsilateral to the side of carotid stenosis. In these patients with symptomatic stenosis of greater 70%, the North American Symptomatic Carotid Endarterectomy Trial (NASCET) demonstrated a highly significant reduction of future stroke risk. In patients with symptomatic carotid stenosis of 50-69%, the benefits were still present but not as profound. In practice, in a patient with moderate symptomatic carotid stenosis, the risks and benefits need to be weighed based on the patient’s other co-morbidities, and the complication rate of the local surgeons.

If the risk of disabling stroke and death associated with endarterectomy exceeds 3%, then the benefit of endarterectomy compared to medical therapy is lost. Carotid endarterectomy should be performed only at institutions and by surgeons whose patients have low rates of complications.

Above: Intraoperative carotid endarterectomy.

In addition to surgery, patients with carotid stenosis should be on an antiplatelet agent such as aspirin or plavix. Additionally, aggressive risk factor modification should be undertaken including improving cholesterol profile, smoking cessation and blood pressure control.

Above: Kaplan–Meier Curves for Event-free Survival among Patients with Severe and Moderate Stenosis. The curves show the probability of avoiding an ipsilateral stroke of any degree of severity (left-hand panels) and a disabling ipsilateral stroke (right-hand panels) among patients with carotid stenosis of 70 to 99 percent (top), 50 to 69 percent (center), and less than 50 percent (bottom) who were randomly assigned to undergo carotid endarterectomy (surgical-therapy group) or to receive medical therapy alone (medical-therapy group). Also shown are the P values from the Mantel–Haenszel chi-square test used to compare the survival curves, with the 95 percent confidence interval (CI) for each curve and the overlap between the confidence intervals indicated by bands of color. The numbers below the panels are the numbers of patients in each group who were still at risk during each year of follow-up. These analyses were conducted according to the intention-to-treat principle and include patients who crossed over to the other treatment. The survival curves for medically treated patients differ significantly among the three severity-of-stenosis groups (P=0.02 for all ipsilateral strokes and P<0.001 for disabling ipsilateral strokes); the curves did not differ significantly for surgically treated patients (P=0.58 and P=0.51, respectively). From Barnett H. et. al. Benefit of Carotid Endarterectomy in Patients with Symptomatic Moderate or Severe Stenosis. NEJM, 1998; 339: 1415-1425.
In patients with incidentally discovered “asymptomatic carotid stenosis,” surgery may be beneficial, but only if the patient’s surgical risk is low (<3%) and life expectancy is at least 5 years. The recommendations below are from the AHA guidelines for Carotid Endarterectomy.


Patients With Asymptomatic Carotid Artery Disease
For patients with a surgical risk <3% and life expectancy of at least 5 years:

• Proven indications: Ipsilateral carotid endarterectomy is acceptable for stenotic lesions ( 60% diameter reduction of distal outflow tract with or without ulceration and with or without antiplatelet therapy, irrespective of contralateral artery status, ranging from no disease to occlusion [Grade A recommendation]).

• Acceptable indications: Unilateral carotid endarterectomy simultaneous with coronary artery bypass graft for stenotic lesions (60% with or without ulcerations with or without antiplatelet therapy irrespective of contralateral artery status [Grade C recommendation]).

• Uncertain indications: Unilateral carotid endarterectomy for stenosis >50% with large or complex ulcers irrespective of contralateral internal carotid artery status (Grade C recommendation).

Adapted from: Biller J, et. al. Guidelines for Carotid Endarterectomy: A Statement for Healthcare Professionals From a Special Writing Group of the Stroke Council, American Heart Association. Stroke, Feb 1998; 29: 554 - 562.

Carotid Stenting

More recently, the use of carotid angioplasty with stenting has come into practice. It should be noted however that there are not good clinical trials yet which compare carotid stenting with surgical intervention. Carotid stenting offers some apparent advantages to surgery in that the perioperative mortality may be less, especially in patients with many co-morbidities. However, only time will tell what the true efficacy is based on direct head-to-head comparisons with carotid endarterectomy.

Above: Stenting is performed similar to angioplasty. A catheter is passed to the area of stenosis and a balloon is inflated to expand the stent. The balloon is then taken down and the stent remains.