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Raman G, Kitsios GD, Moorthy D, et al. Management of Asymptomatic Carotid Stenosis [Internet]. Rockville (MD): Agency for Healthcare Research and Quality (US); 2012 Aug 27.
This publication is provided for historical reference only and the information may be out of date.
Background
Stroke is a leading cause of death in the United States. Although the number of deaths from stroke has declined in recent years, it continues to be a major public health problem in the United States, with an estimated $34.3 billion in direct cost and indirect cost of stroke in the year 2008.1 Carotid artery stenosis represents an important risk factor for ischemic stroke, which accounts for nearly 90 percent of all strokes among U.S. men and women. Carotid artery stenosis is increasingly prevalent from the fifth decade of life onward. Patients with vascular disease and multiple risk factors (e.g., diabetes, hypertension, hyperlipidemia, and smoking) have a higher probability of having asymptomatic carotid stenosis. Since carotid artery atherosclerosis can largely proceed silently and unpredictably, the first manifestation can be a debilitating or fatal stroke. Asymptomatic carotid artery stenosis affects approximately 7 percent of women and over 12 percent of men, older than 70 years of age.2 Clinically important stenosis, at which the risk of stroke is increased, is defined as stenosis of over 50 or 60 percent.3 Natural history studies have reported that patients with asymptomatic carotid stenosis are at an increased risk of ipsilateral carotid territory ischemic stroke ranging from 5 to 17 percent.4,5
The goal of management of asymptomatic carotid stenosis is to decrease the risk of stroke and stroke-related deaths. However, screening asymptomatic patients for carotid stenosis is not part of common clinical practice as noted in a review by the U.S. Preventive Services Task Force from 1996, which concluded that evidence was insufficient to recommend either for or against screening.3 As the general U.S. population ages, and with the availability of noninvasive imaging studies, asymptomatic carotid artery stenosis may be more frequently detected in the course of patient management. Auscultation of the carotid arteries to listen for bruits is by convention an initial means of clinical assessment of high-risk patients, but the presence of bruits is not necessarily indicative of significant stenosis.6 Since carotid auscultation has limited sensitivity in detecting significant carotid stenosis,7 additional imaging modalities including digital subtraction angiography (DSA), Doppler ultrasound (DUS), computed tomography angiography (CTA), and magnetic resonance angiography (MRA) are being increasingly utilized.8
The most commonly used measurement method of carotid stenosis used in clinical trials or most common angiographic method was introduced in the North American Symptomatic Carotid Endarterectomy Trial (NASCET).9 In the NASCET method, the stenosis is measured as the ratio of the linear luminal diameter of the narrowest portion of the artery's diseased segment divided by the diameter of the healthy distal carotid artery (above the post-stenotic dilation). An alternative method was used in the European Carotid Surgery Trial (ECST), which utilized the estimated carotid bulb at the site of maximal stenosis as the denominator.10 The ECST method tends to yield higher degrees of stenosis, but measurements made by each method can be converted to those of the other using a simple arithmetic equation.11 According to the 2003 Society of Radiologists in Ultrasound consensus criteria, a carotid stenosis is not quantified as an exact percentage of luminal stenosis but can be classified by range of stenoses that represent clinically relevant categories (normal, < 50 percent, 50-69 percent, ≥ 70 percent but less than near occlusion, near occlusion, or total occlusion).8
Therapeutic options in asymptomatic carotid stenosis include medical therapy alone, carotid endarterectomy (CEA) and medical therapy, or carotid angioplasty and stenting (CAS) and medical therapy. However, the optimal therapeutic management strategy for patients with asymptomatic carotid stenosis is unclear. The Centers for Medicare and Medicaid Services (CMS) is interested in a systematic review of the literature on these three treatment strategies in patients with asymptomatic carotid stenosis. The Coverage and Analysis Group at the CMS requested the present report from the Technology Assessment Program (TAP) at the Agency for Healthcare Research and Quality (AHRQ). AHRQ assigned this report to the Tufts Evidence-based Practice Center (Tufts EPC) (Contract number, HSSA 290 2007 10055 I).
Therapeutic options in asymptomatic carotid stenosis
Medical therapy alone
The specifics of optimal medical management for asymptomatic carotid stenosis continue to evolve. Recent systematic reviews and their analyses of asymptomatic patients with medical therapy alone have shown decreased risk estimates for stroke.12 13 Contemporary medical management of vascular diseases includes use of dual antiplatelet drugs, use of statins, blood-pressure targets in patients with hypertension, and newer classes of antihypertensive drugs, such as angiotensin-converting enzyme inhibitors (ACE-I) or angiotensin receptor blockers. Statin therapy, in particular, may have beneficial effects on carotid plaque morphology and attenuate the underlying inflammatory response.14 Management of diabetes and lifestyle modifications (smoking cessation, physical activity, improved diet) may also be beneficial for the prevention of carotid stenosis-related stroke.15 Primary prevention of stroke with aspirin remains to be of uncertain value, and other antiplatelet regimens (clopidogrel, ticlopidine, aspirin/extended-release dipyridamole, and cilostazol) have not been tested for primary prevention of stroke.
CEA and medical therapy
CEA was initially indicated in patients with symptomatic carotid stenosis, which was subsequently expanded to asymptomatic patients following the demonstrated modest benefit of CEA over medical therapy in RCTs of asymptomatic carotid stenosis.16 The procedure involves surgical incision and removal of fatty plaque blockage. Different techniques of CEA have been developed, with the standard longitudinal arteriotomy modified to an ‘eversion endarterectomy,’ which allows full exposure of the plaque and removal through a transverse incision.
The perioperative antithrombotic management with heparin, low-molecular weight heparinoids, followed by antiplatelet drugs is routinely used. Antiplatelet treatment is an important element in the conduct of the procedure; more recently both aspirin and Clopidogrel are administered. In general, there are a wide range of practices in terms of the selection of technical and anesthesia modules for CEA. Additional techniques during CEA can include cerebral protection with the use of an in-line shunt to perfuse blood from the common carotid to the internal carotid and is applied on the operated side. The use of shunting varies widely. Selective shunting may be based on the surgeons' own observations (e.g. amount of ‘back bleeding’ or retrograde internal carotid artery flow following proximal common carotid artery occlusion) monitoring with electroencephalography, or transcranial ultrasound during CEA. There has also been a change in the management of the arteriotomy closure following CEA. Carotid patching is based on the creation of a wider internal carotid artery (ICA) diameter with improved flow dynamics associated with the patch.
CAS and medical therapy
CAS is a less invasive carotid revascularization technique. CAS is performed intravascularly and does not involve a surgical incision. CAS does not require general anesthesia; the procedure is more commonly conducted under conscious sedation and local anesthesia. Antiplatelet treatment is an integral part of CAS, with dual antiplatelet regimens (aspirin plus clopidogrel), which are continued beyond the periprocedural period. The procedure involves a diagnostic arteriogram of both carotids, the advancement of a guide wire over the stenosis, optional pre dilation of the lesion with a balloon, and then deployment of a self-expandable stent (with varying diameters, lengths, and shapes) into the lesion. The stent selection is tailored to the optimal ICA diameter. Finally, a completion arteriogram of the bifurcation and intracranial carotid vessels is carried out to ensure that the stent is deployed correctly and to identify any potential dissection, vasospasm, or embolization. Because of the concerns regarding distal embolization related to catheter manipulation and stent deployment, embolic protection devices have been developed (e.g., distal balloon occlusion, flow reversal or filter trapping devices) with filter traps being the most commonly used.
Review of recent guidelines
The 2010 primary prevention guidelines from the American Heart Association/American Stroke Association (AHA/ASA) recommend the use of aspirin only in conjunction with CEA, unless otherwise contraindicated (AHA/ASA rating: Class I, Level of Evidence C).15 Recent recommendations from these guidelines state that prophylactic CEA performed with <3 percent combined operative morbidity/mortality can be useful in highly selected patients with asymptomatic carotid stenosis (AHA/ASA rating: Class IIa, Level of Evidence A).15 These guidelines also recommend that prophylactic CAS might be considered in highly selected patients with an asymptomatic carotid stenosis, although the advantage of CAS over current medical therapy alone is not well established (AHA/ASA rating: Class IIb, Level of Evidence B). The usefulness of CAS as an alternative to CEA in asymptomatic patients at high risk for the surgical procedure is also uncertain (AHA/ASA rating: Class IIb, Level of Evidence C).15
The 2011 guidelines on the management of patients with extracranial carotid and vertebral artery disease was endorsed by multiple professional associations including the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines, and the American Stroke Association, American Association of Neuroscience Nurses, American Association of Neurological Surgeons, American College of Radiology, American Society of Neuroradiology, Congress of Neurological Surgeons, Society of Atherosclerosis Imaging and Prevention, Society for Cardiovascular Angiography and Interventions, Society of Interventional Radiology, Society of NeuroInterventional Surgery, Society for Vascular Medicine, and Society for Vascular Surgery in collaboration with the American Academy of Neurology and Society of Cardiovascular Computed Tomography.17 The recommendations vary in classes (size of treatment effect, ranging from I to III based on benefit from treatment is greater than risk) and differ by levels of supporting evidence (estimate of certainty or precision of treatment effect, ranging from A to C based on the hierarchy of study designs and data available in different subpopulations).
This guideline recommends that patients with asymptomatic carotid stenosis be treated with antihypertensive medication for those with hypertension to a target blood pressure below 140/90 mmHg (Class I, Level of Evidence A); counseling patients to quit tobacco smoking (Class I, Level of Evidence B); treating with statin medication alone (Class I, Level of Evidence B) to reduce low-density lipoprotein (LDL) cholesterol <100 mg/dL, and antiplatelet therapy with aspirin, 75 to 325 mg daily (Class I, Level of Evidence A). Other suggestions include combination of statins with bile acid sequestrants or niacin (Class IIa, Level of Evidence B) to reduce LDL cholesterol < 100 mg/dL; treating with statin medication alone to reduce LDL levels < 70 mg/dL in patients with diabetes mellitus (Class IIa, Level of Evidence B); and managing diabetes mellitus with diet, exercise, and glucose-lowering drug to maintain a glycosylated hemoglobin A1c level < 7.0 percent (Class IIa, Level of Evidence A).
This guideline recommends that the selection of asymptomatic patients for carotid revascularization should be guided by assessment of comorbid conditions, life expectancy, and other individual factors. This decision should incorporate patient preferences achieved by a thorough discussion of the risks and benefits of the procedure (Class I, Level of Evidence C).
This guideline recommends that it is reasonable to perform CEA in patients with asymptomatic carotid stenosis who have >70 percent stenosis of the internal carotid artery if the risk of perioperative stroke, MI, and death is low (Class IIa, Level of Evidence A). In particular, it recommends that the choice of CEA over CAS in patients with asymptomatic carotid stenosis is reasonably indicated in older patients with unfavorable pathoanatomy for CEA, patients of any age with unfavorable neck anatomy (Class IIa, Level of Evidence B). The guideline recommends prophylactic CAS may be considered in highly selected patients with asymptomatic carotid stenosis with ≥ 60 percent by angiography or ≥ 70 percent by DUS, but recognizes that the effectiveness of CAS has not been compared with medical therapy alone (Class IIb, Level of Evidence B).
The guideline also recognizes that in patients with asymptomatic carotid stenosis who are at high risk for carotid revascularization, neither CEA nor CAS has been evaluated for their effectiveness compared with medical therapy alone (Class IIb, Level of Evidence B). This guideline recommends against performing CEA or CAS in patients with < 50 percent stenosis, chronic total occlusion, and those with severe disability caused by cerebral infarction that precludes preservation of useful function.
- Introduction - Management of Asymptomatic Carotid StenosisIntroduction - Management of Asymptomatic Carotid Stenosis
- Key Questions - Management of Asymptomatic Carotid StenosisKey Questions - Management of Asymptomatic Carotid Stenosis
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