7 Symptomatic Extracranial Carotid Artery Stenosis
Abstract
Stroke is the fourth most common cause of death and leading cause of disability in the United States; therefore, treatment of internal carotid artery (ICA) stenosis is of paramount importance. All patients should receive best medical treatment including glycemic control and blood pressure control, smoking cessation, and antiplatelet therapy. Symptomatic patients with ≥50% extracranial ICA stenosis should be considered for intervention. In asymptomatic patients with ICA stenosis, intervention should be reserved for those harboring ≥70% stenosis. Carotid revascularization in symptomatic patients should not be delayed and should be viewed as an urgent procedure. Early revascularization has been shown to prevent more strokes than delaying the procedure until it can be performed with negligible risks. The choice of revascularization treatment in patients with extracranial ICA stenosis has been a topic of debate. Carotid endarterectomy should be avoided in patients considered high risk for open surgical intervention and in those high risk for undergoing anesthesia. Carotid artery stenting (CAS) should be avoided in severe ICA tortuosity, concentric calcifications, carotid pseudoocclusion, and difficult distal landing zone for distal protection devices. Proximal protection devices such as balloon guide catheters and flow-reversal devices occlude forward flow from the heart and common carotid artery creating a gradient that reverses flow away from the ICA toward the bifurcations. The Safety and Efficacy Study for Reverse Flow Used During Carotid Artery Stenting Procedure (ROADSTER) multicenter trial of transcarotid stenting has the lowest stroke risk of any CAS trials reported to date. Hyperperfusion syndrome is a well-recognized phenomenon following CAS, caused by altered cerebral autoregulation secondary to long-standing stenosis. In order to prevent this complication, it is important to maintain relative hypotension in the immediate period following CAS.
Introduction
Stenosis at the bifurcation of the carotid artery is the most common site of stenosis among all blood vessels supplying the brain. Extra-cranial carotid artery stenosis is responsible for up to one-third of all strokes, amounting to 750,000 strokes per year in the United States. These strokes are most commonly the result of atherosclerotic emboli from plaque rupture rather than from vessel occlusion. The risk of stroke is proportional to the degree of ipsilateral internal carotid artery (ICA) stenosis. Although the management of carotid artery disease has been investigated in many clinical trials, it remains a topic of strong contention between various medical and surgical practitioners.
Major controversies in decision making addressed in this chapter include:
Whether or not treatment is indicated.
Endarterectomy versus stenting for symptomatic carotid artery stenosis.
Complications, outcome, and durability of the treatment.
Current trials and controversies in management.
Whether to Treat
Because stroke is the fourth most common cause of death and the leading cause of disability in the United States, treatment of carotid artery stenosis is of paramount importance. However, the decision to treat relies profoundly on the degree of stenosis and the presence of symptomatology. Furthermore, the choice of treatment, whether by open carotid endarterectomy (CEA), endovascular carotid artery stenting (CAS), or medical management, depends on the patient′s overall health and the existence of comorbidities.
Symptomatic patients with ≥50% extracranial carotid artery stenosis should be considered for intervention ( 1 in algorithm ). According to the North American Symptomatic Carotid Endarterectomy Trial (NASCET), CEA in these patients reduces the 2-year risk of stroke from 26 to 9% when compared to best medical management ( 1 in algorithm ). Similarly, the European Carotid Surgery Trial (ECST) reported a stroke-risk reduction from 27 to 15% in patients with ≥80% symptomatic carotid disease following CEA compared to the best medical management ( 1 in algorithm ).
Very few strokes involve patients with previously asymptomatic carotid disease. Therefore, the degree of carotid stenosis in this patient population must be higher than that in symptomatic patients for the treatment to be warranted and beneficial. Thus, in asymptomatic patients with carotid occlusive disease, intervention should be reserved for those harboring ≥70% stenosis. In these patients, the Asymptomatic Carotid Atherosclerosis Study (ACAS) and the Asymptomatic Carotid Surgery Trial (ACST) demonstrated a 5-year reduction in stroke risk from 11 to 6% following CEA compared to the best medical management.
Age has been a point of contention in the treatment of patients with extracranial carotid disease. Patients older than 70 years were shown to have a significantly higher risk of stroke or death following CAS compared to younger patients. However, we maintain that age is not a risk factor for CAS and that the higher risk of complications in older patients is a product of this population′s anatomical features, rather than age itself. As discussed later, unfavorable anatomical features for stenting are more prevalent in older patients. Therefore, patients should be stratified for treatment based on their anatomical high-risk features rather than their age ( 2, 3 in algorithm ).
Conservative Management
Treatment of extracranial ICA stenosis, either via open or endovascular means, is beneficial only under the condition that surgical complication rates are kept below a certain threshold. For instance, the superiority of CEA in the NASCET trial assumes a 30-day risk of perioperative complications (stroke, myocardial infarction, or death) of ≤6%. In the ACAS trial, this superiority assumes an even lower perioperative complications risk of ≤3%. At centers where such rates are higher, conservative management should be considered until patients are referred to facilities with more expertise and acceptable complication risks.
Current medical management comprises the use of statins, anti-platelet agents, and blood pressure control. Such conservative medical therapy is a reasonable treatment choice, particularly in patients with asymptomatic carotid disease. In fact, studies have demonstrated a progressive and sustained decrease in stroke rates in asymptomatic patients with carotid disease treated conservatively over the past 30 years. Currently, in asymptomatic patients with ≥50% carotid artery stenosis treated with best medical therapy, the average annual rate of any ipsilateral ischemic stroke is less than 0.5% and the average annual rate of any ipsilateral transient ischemic attack (TIA) is less than 2%. For symptomatic patients who have less than 50% stenosis, best medical treatment alone is indicated ( 4 in algorithm ).
Timing of Treatment
Following an initial ischemic event, the risk of stroke is 1 to 2% in the first 7 days and 2 to 4% in the first 30 days. Therefore, carotid revascularization in symptomatic patients should not be delayed and should be viewed as an urgent procedure. For these patients, delaying treatment significantly reduces the treatment benefit, even though performing CEA or CAS in an urgent fashion may increase the periprocedural risks of complication. Early revascularization has been shown to prevent more strokes than delaying the procedure until it can be performed with negligible risks.
Anatomical Considerations
Throughout the development of the CAS procedure, several anatomical features have been recognized as high risk for stenting. Such features include carotid artery tortuosity, difficult distal landing zone for the deployment of distal protection devices, concentric calcification, carotid pseudoocclusion, aortic arch type III, and difficult peripheral femoral access. Such features considerably increase the technical difficulty and duration of the CAS procedure, thus putting patients at increased risk. CAS should be avoided in such patients ( 2, 5 in algorithm ). A new scoring system known as the Buffalo Risk Assessment Scale (BRASS) has been developed to predict the safety of performing CAS in symptomatic patients with carotid artery disease with such unfavorable anatomy. Conversely, CEA should be avoided in patients with anatomical high-risk features for surgery, including tandem stenosis and surgically inaccessible high or low cervical lesions. Endovascular treatment of ICA stenosis is a more suitable option for these patients ( 2, 6 in algorithm ) (▶ Fig. 7.1 ).
Workup
Clinical Evaluation
The carotid arteries supply most of the cerebral hemispheres and are responsible for providing oxygenated blood to areas of the brain that control strength, sensation, and speech, among other functions. Thus, strokes or TIAs involving the carotid arteries are expected to produce symptoms such as contralateral weakness, contralateral numbness, inability to produce speech, or lack of speech understanding. Another symptom is amaurosis fugax, which is caused by embolization into the ophthalmic artery. The presentation of such symptoms in an acute setting in any patient should prompt an emergent workup for stroke, including a detailed history focused on the time of symptom onset and the presence of renal disease, a thorough physical examination to document a National Institute of Health Stroke Scale (NIHSS) score, as well as diagnostic imaging (including diffusion-weighted magnetic resonance imaging [MRI] [▶ Fig. 7.2 ]; and computed tomographic [CT] perfusion imaging studies [▶ Fig. 7.1 ]).
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