Final Recommendation Statement
Carotid Artery Stenosis: Screening
July 08, 2014
Recommendations made by the USPSTF are independent of the U.S. government. They should not be construed as an official position of the Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services.
The U.S. Preventive Services Task Force (USPSTF) makes recommendations about the effectiveness of specific clinical preventive services for patients without related signs or symptoms.
It bases its recommendations on the evidence of both the benefits and harms of the service and an assessment of the balance. The USPSTF does not consider the costs of providing a service in this assessment.
The USPSTF recognizes that clinical decisions involve more considerations than evidence alone. Clinicians should understand the evidence but individualize decision making to the specific patient or situation. Similarly, the USPSTF notes that policy and coverage decisions involve considerations in addition to the evidence of clinical benefits and harms.
Stroke is a leading cause of death and disability in the United States. Although asymptomatic carotid artery stenosis is a risk factor for stroke, it causes a relatively small proportion of strokes.
The most feasible screening test for carotid artery stenosis (defined as 60% to 99% stenosis) is ultrasonography. Although adequate evidence indicates that this test has high sensitivity and specificity, in practice, ultrasonography yields many false-positive results in the general population, which has a low prevalence of carotid artery stenosis (approximately 0.5% to 1%). There are no externally validated, reliable tools that can determine who is at increased risk for carotid artery stenosis or for stroke when carotid artery stenosis is present. Adequate evidence indicates that the accuracy of screening by auscultation of the neck is poor.
Benefits of Detection and Early Intervention
There is no direct evidence on the benefits of screening for carotid artery stenosis. Adequate evidence indicates that in selected trial participants with asymptomatic carotid artery stenosis, carotid endarterectomy (CEA) performed by selected surgeons reduces the absolute incidence of all strokes or perioperative death by approximately 3.5% compared with (outdated) medical management. However, this difference is probably smaller with current optimal medical management 1. The magnitude of these benefits would be smaller in asymptomatic persons in the general population. For the general primary care population, the magnitude of benefit is small to none. There is no evidence that identification of asymptomatic carotid artery stenosis leads to any benefit from adding or increasing medication doses (beyond current standard medical therapy for cardiovascular disease prevention).
Harms of Detection and Early Intervention
Adequate evidence indicates that both the testing strategy for carotid artery stenosis and treatment with CEA can cause harms. Although screening with ultrasonography has few direct harms, all screening strategies, including those with or without confirmatory tests (that is, digital subtraction or magnetic resonance angiography), have imperfect sensitivity and specificity and could lead to unnecessary interventions and result in serious harms. In selected centers similar to those in the trials, CEA is associated with a 30-day stroke or mortality rate of approximately 2.4%; reported rates are as high as approximately 5% in low-volume centers and 6% in certain states 1. Myocardial infarctions are reported in 0.8% to 2.2% of patients after CEA. The 30-day stroke or mortality rate after carotid angioplasty and stenting (CAAS) is approximately 3.1% to 3.8%. The overall magnitude of harms of screening and subsequent treatment of asymptomatic carotid artery stenosis is small to moderate depending on patient population, surgeon, center volume, and geographic location.
The USPSTF concludes with moderate certainty that the harms of screening for asymptomatic carotid artery stenosis outweigh the benefits.
Patient Population Under Consideration
This recommendation applies to adults without a history of transient ischemic attack, stroke, or other neurologic signs or symptoms. It was based on evidence of the benefits and harms of screening using ultrasonography to detect narrowing of the carotid arteries. A previous USPSTF review on the assessment of carotid intima–media thickness in 2009 found insufficient evidence to support its use as a screen for coronary heart disease risk. For this recommendation, the USPSTF did not review new evidence on ultrasonography to characterize carotid plaque structure or intima–media thickness and their association with cardiovascular disease events. However, clinicians considering using ultrasonography to characterize carotid plaque to stratify patient risk for cardiovascular disease should consider the same harms that the USPSTF evaluated for this recommendation (stroke, myocardial infarction, and death from CEA) because surgery may result from this screen.
Assessment of Risk
The major risk factors for carotid artery stenosis include older age, male sex, hypertension, smoking, hypercholesterolemia, diabetes mellitus, and heart disease. Despite evidence on important risk factors, there are no externally validated, reliable methods to determine who is at increased risk for carotid artery stenosis or for stroke when carotid artery stenosis is present.
Although screening with ultrasonography has few direct harms, all screening strategies, including those with or without confirmatory tests (that is, digital subtraction or magnetic resonance angiography), have imperfect sensitivity and specificity and could lead to unnecessary surgery and result in serious harms, including death, stroke, and myocardial infarction. There is no evidence that screening by auscultation of the neck to detect carotid bruits is accurate or provides benefit.
The USPSTF has made recommendations on many factors related to stroke prevention, including screening for hypertension, screening for dyslipidemia, the use of nontraditional coronary heart disease risk factors, counseling on smoking, and counseling on healthful diet and physical activity. In addition, the USPSTF recommends the use of aspirin for persons at increased risk for cardiovascular disease. These recommendations are available on the USPSTF Web site (www.uspreventiveservicestaskforce.org).
Research Needs and Gaps
Valid and reliable tools are needed to determine which persons are at high risk for carotid artery stenosis or for stroke due to carotid artery stenosis and who might experience harm from treatment with CEA or CAAS. Studies comparing CEA or CAAS with current standard medical therapy are needed. The planned CREST-2 (Carotid Revascularization Endarterectomy versus Stenting Trial 2) may provide important data for future recommendations. CREST-2 will study 2400 patients with greater than 70% stenosis who are randomly assigned to CAAS with intensive medical management versus intensive medical management alone or to CEA with intensive medical management versus intensive medical management alone.
Burden of Disease
Stroke is a leading cause of death and disability in the United States. Mortality from all strokes has decreased substantially over the past 5 decades; improved blood pressure control is believed to be the most important factor accounting for this decrease 2. Other factors, including treatment and control of diabetes and hyperlipidemia, are also reported to be important contributors. Most strokes are ischemic (80% to 90%), and approximately 10% to 20% are from hemorrhagic causes.
In a population-based U.S. study from 1999, the age-adjusted incidence rates for ischemic stroke subtypes were 40 per 100,000 persons for stroke due to cardioembolic causes, 27 per 100,000 persons for stroke due to atherostenosis causes, 25 per 100,000 persons for lacunar stroke (small vessel disease), and 52 per 100,000 persons for stroke due to unknown causes 3. Strokes resulting from large artery atherothrombotic disease (such as carotid artery stenosis) in previously asymptomatic patients (the focus of this recommendation) account for a relatively small proportion of all strokes.
The best available data from U.S.-based studies report that the overall estimated prevalence of carotid artery stenosis (defined as 70% or 75% to 99% stenosis) is 0.5% to 1% 1. Studies have found that the condition is more prevalent in older adults, smokers, persons with hypertension, and persons with heart disease. Evidence shows that the incidence of stroke caused by carotid artery stenosis has been decreasing 1. Research has not shown any single risk factor or clinically useful risk stratification tool that can reliably and accurately distinguish between persons who have clinically important carotid artery stenosis and those who do not.
Scope of Review
In 2007, the USPSTF recommended against screening for asymptomatic carotid artery stenosis in the general adult population. To update its recommendation, the USPSTF commissioned a systematic review to synthesize the evidence on the accuracy of screening tests, externally validated risk stratification tools, the benefits of treatment of asymptomatic carotid artery stenosis with CEA or CAAS, the benefits from medications added to current standard medical therapy, and the harms of screening and treatment with CEA or CAAS.
Accuracy of Screening Tests
Three meta-analyses and 3 primary studies assessed the accuracy or reliability of duplex ultrasonography (DUS) to detect carotid artery stenosis 1. A good-quality meta-analysis included studies published from 1966 to 2003 and used digital subtraction angiography as the reference standard 4. Authors reported a sensitivity of 98% (95% CI, 97% to 100%) and a specificity of 88% (CI, 76% to 100%) for detecting carotid artery stenosis of 50% or greater. Sensitivity and specificity for detecting carotid artery stenosis of 70% or greater were 90% (CI, 84% to 94%) and 94% (CI, 88% to 97%), respectively. This evidence is limited by the lack of reporting on whether (or what proportion of) asymptomatic patients were included.
The reliability of DUS to detect potentially clinically important carotid artery stenosis is limited. A good-quality meta-analysis reported wide variation in measurement properties between laboratories, with clinically important variation in the magnitude of the variation 4. Potential sources of heterogeneity of measurements include differences in patients, study designs, equipment, techniques, and methods of classification or training. One study of 1006 carotid arteries reported poor agreement between readers for the differentiation of stenoses of less than 70% (45% agreement; κ = 0.26 [CI, 0.23 to 0.29]) but excellent agreement for stenoses of 70% or greater (96% agreement; κ = 0.85 [CI, 0.83 to 0.87]) 5. Results of DUS screening can also vary on the basis of the type of scanner, the velocity cut points or ratios used, the Doppler angle employed, and inherent variability between facilities and observers 1 , 6.
Four studies assessed the use of auscultation for carotid bruits to detect carotid artery stenosis 7–10. Reported sensitivity ranged from 46% to 77%, and specificity ranged from 71% to 98%. However, none of the studies used angiography as a gold standard, and only 2 studies involved patients from the general population.
No externally validated risk stratification tools can reliably distinguish between persons who have clinically important carotid artery stenosis and those who do not or those who will experience harm after treatment with CEA or CAAS.
Effectiveness of Early Detection and Treatment
There are no studies on the direct benefit of screening for asymptomatic carotid artery stenosis. Three randomized, controlled trials (RCTs) evaluated the benefit of treating asymptomatic carotid artery stenosis with CEA: ACAS (Asymptomatic Carotid Atherosclerosis Study) 11, VACS (Veterans Affairs Cooperative Study) 12, and ACST (Asymptomatic Carotid Surgery Trial) 13. These RCTs studied 5226 patients randomly assigned to treatment of asymptomatic carotid artery stenosis with CEA or medical therapy alone and followed the patients for 2.7 to 9 years. Two of the studies (ACAS and VACS) were conducted in North America, and ACST was conducted in 30 countries, primarily in Europe. The mean age of patients was 65 to 68 years, and they were required to have at least 50% (VACS) or 60% (ACAS and ACST) stenosis of the carotid artery. In the 2 North American trials, most patients (87% to 95%) were white. Two thirds of the patients in ACAS and ACST and all of the patients in VACS were men.
The evidence has important limitations, including the lack of studies focusing on a population identified by screening in primary care. In addition, many of the enrolled patients were not completely asymptomatic. Although study patients were required to be recently asymptomatic for the carotid artery under study, 20% to 24% had a history of contralateral CEA and 25% to 32% had a history of contralateral transient ischemic attack or stroke in trials reporting baseline data for these characteristics. ACST allowed the enrollment of patients who had a transient ischemic attack or stroke attributable to the carotid artery under study if it occurred more than 6 months before enrollment, and ACAS included patients if their symptoms referable to the contralateral artery occurred more than 45 days before enrollment. Medical therapy varied across trials and was not clearly defined or standardized, although all patients received aspirin in ACAS and VACS. Surgeons were highly selected and were required to submit records of their 50 most recent cases (ACAS and ACST) or previous 24 months performing CEA (VACS); they were selected on the basis of demonstrated low morbidity and mortality rates. In addition, the ACAS and ACST trial protocols did not allow further enrollment of patients by surgeons or institutions that showed unacceptably high morbidity or mortality during the trial.
In general, the RCTs reported results combining stroke and death outcomes during the perioperative period 30 days after surgery and during the time subsequent to this period. Pooled estimates from the 3 RCTs found that, compared with patients receiving medical treatment alone, 2.0% fewer patients randomly assigned to CEA had perioperative stroke or death and subsequent ipsilateral stroke. Pooled estimates on the outcome of death, perioperative stroke, or any subsequent stroke reported that 3.5% fewer patients treated with CEA had this outcome than those in medical treatment groups 1.
No studies compared CAAS with medical therapy or studied the incremental benefit of additional medications beyond current standard medical therapy.
Potential Harms of Screening and Treatment
No studies examined the direct harms of screening. Although angiography is less commonly used now as a confirmatory test, harms from it occurred in 2 of the previously discussed RCTs. In ACAS, 1.2% of patients (5 of 414) who had angiography developed strokes, and 1 of these patients died. In VACS, 0.4% of patients (3 of 714) had nonfatal strokes after angiography 1.
The 3 previously discussed RCTs, 8 studies based on additional trials, and 8 cohort studies provided data on harms of treatment. Four of the additional trials include the CASANOVA (Carotid Artery Stenosis with Asymptomatic Narrowing: Operation Versus Aspirin) trial 14, the MACE (Mayo Asymptomatic Carotid Endarterectomy) trial 15, CREST 16 , 17, and the SAPPHIRE (Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy) trial 18. The MACE and CASANOVA trials were conducted in the early 1990s and included 252 patients with 50% to 99% carotid artery stenosis, confirmed by angiography, who were randomly assigned to treatment with CEA. Patients in both trials were predominantly male (56% to 63%); most (60% to 64%) had hypertension, and 42% to 44% had coronary artery disease. Data on harms were provided by 2 other multicenter RCTs (CREST and the SAPPHIRE trial), which compared CEA with CAAS. The SAPPHIRE trial required that participants have at least 1 condition suggesting high surgical risk (for example, age older than 80 years, severe pulmonary disease, or contralateral carotid occlusion). Prevalence of hypertension in CREST and the SAPPHIRE trial was 85% to 88%, prevalence of diabetes in the trials was 25% to 33%, and prevalence of coronary artery disease was 81% in the SAPPHIRE trial and 44% in CREST. In both trials, interventionalists had to demonstrate low complication rates before participating. Eight multicenter cohort studies using Medicare claims and enrollment databases reported perioperative harms of CEA.
Pooled analysis of data from 6 trials (n = 3435) showed that 2.4% (CI, 1.7% to 3.1%) of patients died or had a stroke in the 30-day period after CEA, which was 1.9% more (CI, 1.2% to 2.6%) than in the medical therapy groups in the 3 trials (n = 5223) directly comparing CEA with medical therapy 1. Pooled data from cohort studies showed a 3.3% rate of death or stroke after CEA at 30 days. One cohort study on harms from CAAS, the CREST lead-in study, found a stroke or death rate of 3.8% (CI, 2.9% to 5.1%) 19. A meta-analysis of 2 trials (n = 6152) found a stroke or death rate of 3.1% (CI, 2.7% to 3.6%) after CAAS 1.
Other important harms after surgical intervention for carotid artery stenosis include myocardial infarction and surgical complications. In ACST, myocardial infarctions occurred in 0.6% more patients in the CEA group than in the medical group. VACS reported 4 events in the CEA group and none in the medical therapy group. One cohort study of 6 New York hospitals, which included 1378 Medicare beneficiaries who received CEA for asymptomatic carotid artery stenosis during 1997 to 1998, reported a 0.85% rate of nonfatal myocardial infarction 20. A similar 1993 study of Medicare beneficiaries in Georgia (n = 1002) reported a 0.8% rate of myocardial infarction and a 0.6% rate of myocardial infarction–related death 21. Cranial nerve injury is another important potential harm; it occurred in 3.8% of patients (8 of 211) who received CEA in VACS, but none had permanent disability. The CASANOVA trial reported such CEA complications as lung embolism (1.4%), permanent cranial nerve damage (4.2%), pneumonia (1.4%), and local hematoma requiring surgery (2.8%). The total frequency of major complications (such as death, stroke, minor stroke, myocardial infarction, and permanent cranial nerve damage) in the group randomly assigned to immediate surgery was 7.9%. The MACE trial reported a 1.1% rate of minor cranial nerve injury in the 36 patients randomly assigned to CEA.
The volume of patients treated by individual surgeons and centers is often suggested as an important factor that may affect outcomes. The USPSTF reviewed studies using Medicare data that reported the relationship between patient volume and adverse events after CEA. One study of Medicare beneficiaries who had CEA (350 procedures) during 1993 to 1994 in Oklahoma found combined 30-day stroke and death rates of 3.5% at high-volume hospitals (>100 Medicare-covered CEAs performed over the study period) and 5.2% at low-volume centers 22. A similar study of Medicare beneficiaries who received CEA at 115 hospitals in Ohio (167 procedures) reported stroke or death rates of 0% at high-volume centers and 4.9% at low-volume centers during 1993 to 1994 23. A major limitation of the evidence on harms associated with CEA is the dearth of recent data: all of the observational studies reporting on 30-day perioperative harms after CEA were based on data from the 1990s.
Estimate of Magnitude of Net Benefit
The USPSTF found no evidence that screening for carotid artery stenosis leads to additional treatment and benefit beyond standard preventive treatments based on traditional cardiovascular risk factors. In patients and surgeons similar to those in the RCTs, treatment with CEA for asymptomatic carotid artery stenosis can result in a net absolute reduction in stroke rates, but this benefit has only been shown in selected patients with selected surgeons and must be weighed against a small increase in nonfatal myocardial infarctions. The net benefit of CEA largely depends on patients surviving the perioperative period without complications and living for at least 5 years. The magnitude of these benefits would be smaller in asymptomatic persons in the general population than among patients in RCTs.
For the general primary care population, the magnitude of benefit is small to none. Adequate evidence indicates that both the testing strategy for carotid artery stenosis and treatment with CEA or CAAS can cause serious harms. In selected centers similar to those in the trials, CEA is associated with a 30-day stroke or mortality rate of approximately 2.4%; reported rates are as high as approximately 5% in low-volume centers and 6% in certain states. Myocardial infarctions are reported in 0.8% to 2.2% of patients after CEA. The 30-day stroke or mortality rate after CAAS is approximately 3.1% to 3.8%. The overall magnitude of harms is small to moderate depending on patient population, surgeon, center volume, and geographic location.
The USPSTF concludes with moderate certainty that the harms of screening for asymptomatic carotid artery stenosis outweigh the benefits.
How Does Evidence Fit With Biological Understanding?
The medical treatment groups in the RCTs were poorly defined and probably did not include the intensive blood pressure and lipid control that is currently standard practice for the prevention of cardiovascular disease. It is difficult to determine what effect current standard medical therapy would have on comparative outcomes of medical and surgical treatments, including the potential incremental benefit of CEA.
Response to Public Comment
A draft version of this recommendation statement was posted for public comment on the USPSTF Web site from 18 February through 17 March 2014. All comments were reviewed and considered by the USPSTF. Many commenters agreed with the draft recommendation. Several requested clarification on the focus of this recommendation; the recommendation statement was revised to clarify that, for this recommendation, the USPSTF did not review new evidence on the use of carotid artery ultrasonography to evaluate risk for cardiovascular disease. A few commenters provided citations for related medical articles, and the USPSTF reviewed these for relevance to the current recommendation.
This recommendation is an update of the 2007 recommendation on screening for carotid artery stenosis, which also concluded that the general asymptomatic adult population should not be screened for the condition.
In 2010, the American Heart Association and the American Stroke Association recommended against screening the general population for asymptomatic carotid artery stenosis 24. In 2011, the American College of Cardiology Foundation and the American Heart Association, in collaboration with several other organizations, including the American Stroke Association, American Association of Neurological Surgeons, American College of Radiology, American Society of Neuroradiology, Society for Vascular Surgery, and Society for Vascular Medicine, recommended against the use of carotid DUS for routine screening of asymptomatic patients with no clinical manifestations of or risk factors for atherosclerosis 25. The Society for Vascular Surgery also released a guideline in 2011 stating that routine screening to detect clinically asymptomatic carotid artery stenosis in the general population is not recommended 26. The American Academy of Family Physicians recommends against screening for asymptomatic carotid artery stenosis in the general adult population 27.
Members of the U.S. Preventive Services Task Force at the time this recommendation was finalized are Michael L. LeFevre, MD, MSPH, Chair (University of Missouri School of Medicine, Columbia, Missouri); Albert L. Siu, MD, MSPH, Co-Vice Chair (Mount Sinai School of Medicine, New York, and James J. Peters Veterans Affairs Medical Center, Bronx, New York); Kirsten Bibbins-Domingo, PhD, MD, Co-Vice Chair (University of California, San Francisco, and San Francisco General Hospital, San Francisco, California); Linda Ciofu Baumann, PhD, RN (University of Wisconsin, Madison, Wisconsin); Susan J. Curry, PhD (University of Iowa College of Public Health, Iowa City, Iowa); Karina W. Davidson, PhD, MASc (Columbia University Medical Center, New York, New York); Mark Ebell, MD, MS (University of Georgia, Athens, Georgia); Francisco A.R. García, MD, MPH (Pima County Department of Health, Tucson, Arizona); Matthew W. Gillman, MD, SM (Harvard Medical School and Harvard Pilgrim Health Care Institute, Boston, Massachusetts); Jessica Herzstein, MD, MPH (Air Products, Allentown, Pennsylvania); Alex R. Kemper, MD, MPH, MS (Duke University, Durham, North Carolina); Ann E. Kurth, PhD, RN, MSN, MPH (Global Institute of Public Health, New York, New York); Douglas K. Owens, MD, MS (Freeman Spogli Institute for International Studies, Stanford University, Stanford, California); William R. Phillips, MD, MPH (University of Washington, Seattle, Washington); Maureen G. Phipps, MD, MPH (Warren Alpert Medical School, Brown University, Providence, Rhode Island); and Michael P. Pignone, MD, MPH (University of North Carolina, Chapel Hill, North Carolina).
This document is in the public domain within the United States.
Source: This article was published online first at www.annals.org on 8 July 2014.
Disclaimer: Recommendations made by the USPSTF are independent of the U.S. government. They should not be construed as an official position of the Agency for Healthcare Research and Quality or the U.S. Department of Health and Human Services.
Financial Support: The USPSTF is an independent, voluntary body. The U.S. Congress mandates that the Agency for Healthcare Research and Quality support the operations of the USPSTF.
Potential Conflicts of Interest: None disclosed. Disclosure forms from USPSTF members can be viewed at www.acponline.org/authors/icmje/ConflictOfInterestForms.do?msNum=M14-1333.
Requests for Single Reprints: Reprints are available from the USPSTF Web site (www.uspreventiveservicestaskforce.org).
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