Note: This draft Recommendation Statement is not the final recommendation of the U.S. Preventive Services Task Force. This draft is distributed solely for the purpose of pre-release review. It has not been disseminated otherwise by the USPSTF. It does not represent and should not be interpreted to represent a USPSTF determination or policy.
This draft Recommendation Statement is based on an Evidence Report that is also available for public comment. To read the accompanying draft Evidence Report on Screening for Carotid Artery Stenosis and provide comments, go to http://www.uspreventiveservicestaskforce.org/draftrep2.htm.
The 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 decisionmaking 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.
This draft Recommendation Statement is available for comment from February 18 until March 17, 2014, at 5:00 PM ET. You may wish to read the entire Recommendation Statement before you comment. A fact sheet that explains the draft recommendations in plain language is available here.
Screening for Carotid Artery Stenosis: U.S. Preventive Services Task Force Recommendation Statement
Summary of Recommendation and Evidence
The U.S. Preventive Services Task Force (USPSTF) recommends against screening for asymptomatic carotid artery stenosis (CAS) in the general adult population.
This is a D recommendation.
Stroke is a leading cause of death and disability in the United States. Although CAS is a risk factor for stroke, only a relatively small proportion of strokes is caused by CAS.
The most feasible screening test for CAS (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, where CAS is low in prevalence (approximately 0.5% to 1%). There are no validated, reliable tools that can determine who is at increased risk for CAS or stroke when CAS is present. There is adequate evidence 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 CAS. Adequate evidence indicates that in selected trial participants with asymptomatic CAS, carotid endarterectomy (CEA) by selected surgeons reduces the absolute incidence of all strokes or perioperative death by approximately 3.5% compared with medical management, though this difference is likely smaller with current optimal medical management (1). The magnitude of these benefits would be less among 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 CAS leads to any benefit from adding or increasing doses of medications (beyond current standard medical therapy for cardiovascular disease prevention).
Harms of Detection and Early Intervention
Adequate evidence indicates that both the testing strategy for CAS 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 (i.e., 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 about 2.4%; reported rates range up to about 5% for low-volume centers and up to 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 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 CAS outweigh the benefits.
Patient Population Under Consideration
This recommendation applies to adults without neurologic signs or symptoms, including a history of transient ischemic attack or stroke.
Assessment of Risk
The major risk factors for CAS include older age, male sex, hypertension, smoking, hypercholesterolemia, diabetes mellitus, and heart disease. Despite evidence on important risk factors, there are no validated, reliable methods to determine who is at increased risk for CAS or stroke when CAS is present.
Although screening with ultrasonography has few direct harms, all screening strategies, including those with or without confirmatory tests (i.e., digital subtraction or magnetic resonance angiography), have imperfect sensitivity 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, and counseling on smoking and healthful diet and physical activity. In addition, the USPSTF recommends that clinicians discuss aspirin chemoprevention with 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 CAS or stroke from CAS 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-2) study may provide important data for future recommendations. CREST-2 will study 2,400 patients with greater than 70% stenosis who are randomized to CAAS with intensive medical management versus intensive medical management alone or CEA with intensive medical management versus intensive medical management alone.
Burden of Disease
While stroke is a leading cause of death and disability in the United States, strokes resulting from large artery atherothrombotic disease (e.g., CAS) in previously asymptomatic patients (the focus of this recommendation) account for a relatively small proportion of all strokes. Mortality from all strokes has declined significantly over the last five decades; improved blood pressure control is thought to be the most important factor accounting for this decline (2). Other factors, including treatment and control of diabetes and hyperlipidemia, are also reported to be important contributors.
The best available data from U.S.-based studies report that the overall estimated prevalence of CAS (defined as 70% or 75% to 99% stenosis) is 0.5% to 1% (1). Studies have found that CAS is more prevalent in older adults, smokers, persons with hypertension, and persons with heart disease. Evidence shows that the incidence of stroke caused by CAS has been decreasing (1). Research has not found any single risk factor or clinically useful risk stratification tool that can reliably and accurately distinguish between persons who have clinically important CAS and those who do not.
Scope of Review
In 2007, the USPSTF recommended against screening for asymptomatic CAS 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 CAS with CEA or CAAS, 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 three primary studies assessed the accuracy or reliability of duplex ultrasonography (DUS) to detect CAS (1). A good-quality meta-analysis included studies published from 1966 to 2003 and used digital subtraction angiography as the reference standard (3). Authors reported a sensitivity of 98% (95% CI, 97 to 100) and a specificity of 88% (95% CI, 76 to 100) for detecting CAS of 50% or greater. Sensitivity and specificity for detecting CAS of 70% or greater were 90% (95% CI, 84 to 94) and 94% (95% 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 CAS 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 (3). Potential sources of heterogeneity in measurements include differences in patients, study designs, equipment, and techniques and different methods of classification or training. One study of 1,006 carotid arteries reported poor agreement between readers for the differentiation of stenoses of less than 70% (45% agreement; kappa=0.26 [95% CI, 0.23 to 0.29]), but excellent agreement for stenoses of 70% or greater (96% agreement; kappa=0.85 [95% CI, 0.83 to 0.87]) (4). Results of DUS screening can also vary based on the type of DUS scanner, the velocity cutpoints or ratios used, the Doppler angle employed, and inherent variability between facilities and observers (5).
Four studies assessed the use of auscultation for carotid bruits to detect CAS (6–9). 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 two studies involved patients from the general population.
No externally-validated risk stratification tools can reliably distinguish between persons who have clinically important CAS and those who do not or those who will experience harm after treatment with CEA or CAAS.
Effectiveness of Early Detection and Treatment
Three randomized, controlled trials (RCTs) studied 5,226 patients randomized to treatment with CEA or medical therapy alone for asymptomatic CAS and followed for 2.7 to 9 years: ACAS (Asymptomatic Carotid Atherosclerosis Study) (10), VACS (Veterans Affairs Cooperative Study) (11), and ACST (Asymptomatic Carotid Surgery Trial) (12). Two of the studies, ACAS and VACS, were conducted in North America; ACST was conducted in 30 mostly European countries. The mean age of subjects was 65 to 68 years, and subjects were required to have at least 50% (VACS) or 60% (ACAS and ACST) stenosis of the carotid artery. In the two North American trials, the vast majority (87% to 95%) of subjects were white. Most of the subjects were men: two thirds of enrolled subjects in ACAS and ACST and all subjects in VACS.
There are important limitations of the evidence, 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 prior 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 subjects who had a transient ischemic attack or stroke attributable to the artery under study if it was more than 6 months before enrollment; 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 subjects received aspirin in ACAS and VACS. Surgeons were highly selected and required to submit records of their last 50 cases (ACAS and ACST) or previous 24 months of experience with CEA (VACS); they were selected based on demonstrated low morbidity and mortality rates. In addition, 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 the perioperative period (>30 days after surgery). Pooled estimates from the three RCTS found that 2.0% fewer patients randomized to CEA experienced perioperative stroke or death and subsequent ipsilateral stroke compared with patients randomized to medical treatment alone. Pooled estimates on the outcome of perioperative stroke or death or any subsequent stroke reported that 3.5% fewer subjects treated with CEA had this outcome than subjects 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 confirmation test, harms from angiography were reported in two of the previously discussed RCTs. In ACAS, 1.2% (5/414) of patients who underwent angiography developed strokes, and one of these patients died. In VACS, 0.4% (3/714) of patients had nonfatal strokes following angiography (1).
The three previously discussed RCTs, eight studies based on additional trials, and eight cohort studies provided data on harms of treatment. Four of the additional trials include: CASANOVA (Carotid Artery Stenosis with Asymptomatic Narrowing: Operation Versus Aspirin) (13), MACE (Mayo Asymptomatic Carotid Endarterectomy) (14), CREST (15, 16), and SAPPHIRE (Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy) (17). MACE and CASANOVA were conducted in the early 1990s and included 252 patients with 50% to 99% CAS, confirmed by angiography, who were randomized to treatment with CEA. Subjects in both trials were predominately male (56% to 63%) and most had hypertension (60% to 64%); 42% to 44% had coronary artery disease. Harms data were provided by two other multicenter RCTs, CREST and SAPPHIRE, which compared CEA with CAAS. SAPPHIRE required that participants have at least one condition suggesting high surgical risk (e.g., older than age 80 years, severe pulmonary disease, or contralateral carotid occlusion). Prevalence of hypertension in CREST and SAPPHIRE was 85% to 88%, diabetes was 25% to 33%, and coronary artery disease was 81% in SAPPHIRE and 44% in CREST. In both trials, interventionalists had to demonstrate low complication rates before participating. Eight multicenter cohort studies reported perioperative harms of CEA using Medicare claims and enrollment databases.
Pooled analysis of trial data showed that 2.4% (95% CI, 1.7 to 3.1) of patients experienced death or stroke in the 30-day perioperative period, which was 1.9% more than in the medical therapy groups (1). Pooled data from cohort studies showed a 3.33% 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% (95% CI, 2.86 to 5.09) (18). A meta-analysis of trials (N=6,152; two trials) found a stroke or death rate of 3.1% (95% CI, 2.7 to 3.6) after CAAS (1).
Other important harms after surgical intervention for CAS include myocardial infarction and surgical complications. Myocardial infarctions occurred in 0.6% more patients receiving CEA in ACST compared with patients in the medical arm. VACS reported four events in the CEA group and none in the medical therapy group. One cohort study of six New York hospitals that included 1,378 Medicare beneficiaries undergoing CEA for asymptomatic CAS during 1997 to 1998 reported a 0.85% rate of nonfatal myocardial infarction (19). A similar 1993 study in Georgia Medicare beneficiaries (N=1,002) reported a 0.8% rate of myocardial infarction and a 0.6% rate of myocardial infarction–related death (20). Cranial nerve injury complicating CEA is another important potential harm; it occurred in 3.8% of subjects undergoing CEA (8/211) in VACS, but none resulted in permanent disability. CASANOVA reported rates of CEA complications: 1.4% rate of lung embolism, 4.2% rate of permanent cranial nerve damage, 1.4% rate of pneumonia, and 2.8% rate of local hematoma requiring surgery. The total frequency of major complications (e.g., death, stroke, minor stroke, myocardial infarction, permanent cranial nerve damage) in the group randomized to immediate surgery was 7.9%. MACE reported a 1.1% rate of minor cranial nerve injury in the 36 patients randomized to CEA.
The volume of patients treated by individual surgeons and centers is often suggested as an important potential factor that may affect outcomes. The USPSTF reviewed studies using Medicare data that reported on the relationship between patient volume and adverse events following CEA. One study of Medicare beneficiaries who underwent CEA (350 procedures) during 1993 to 1994 in Oklahoma found a combined 30-day stroke and death rate of 3.5% at high-volume hospitals (>100 Medicare CEAs performed over the study period) and 5.2% at low-volume centers (21). A similar study of Medicare beneficiaries undergoing CEA at 115 hospitals in Ohio (167 procedures) reported a stroke or death rate of 0% at high-volume centers and 4.9% at low-volume centers during 1993 to 1994 (22). A major limitation of the evidence on harms associated with CEA is the dearth of recent data; all 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 CAS leads to additional treatment and benefit beyond standard preventive treatments based on traditional cardiovascular risk factors. Among patients and surgeons similar to those in the RCTs, treatment with CEA for asymptomatic CAS 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 less among asymptomatic persons in the general population compared with the outcomes 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 CAS 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 about 2.4%; reported rates range up to about 5% for low-volume centers and up to 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 CAS outweigh the benefits.
How Does Evidence Fit With Biological Understanding?
The medical treatment group in the RCTs was poorly defined and probably did not include the intensive blood pressure and lipid control that is standard practice today 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.
Update of Previous Recommendation
This recommendation is an update of the 2007 recommendation on screening for CAS, which also concluded that the general asymptomatic adult population should not be screened for CAS.
Recommendations of Others
In 2010, the American Heart Association and the American Stroke Association recommended against screening the general population for asymptomatic carotid stenosis (23). 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 (24). The Society for Vascular Surgery also released a guideline in 2011 stating that routine screening to detect clinically asymptomatic CAS in the general population is not recommended (25).
Table 1: What the Grades Mean and Suggestions for Practice
Table 2: Levels of Certainty Regarding Net Benefit
|Level of Certainty*||Description|
|High||The available evidence usually includes consistent results from well-designed, well-conducted studies in representative primary care populations. These studies assess the effects of the preventive service on health outcomes. This conclusion is therefore unlikely to be strongly affected by the results of future studies.|
|Moderate||The available evidence is sufficient to determine the effects of the preventive service on health outcomes, but confidence in the estimate is constrained by factors such as:
As more information becomes available, the magnitude or direction of the observed effect could change, and this change may be large enough to alter the conclusion.
|Low||The available evidence is insufficient to assess effects on health outcomes. Evidence is insufficient because of:
More information may allow an estimation of effects on health outcomes.
*The U.S. Preventive Services Task Force defines certainty as "likelihood that the USPSTF assessment of the net benefit of a preventive service is correct." The net benefit is defined as benefit minus harm of the preventive service as implemented in a general, primary care population. The USPSTF assigns a certainty level based on the nature of the overall evidence available to assess the net benefit of a preventive service.
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11. Hobson RW 2nd, Weiss DG, Fields WS, Goldstone J, Moore WS, Towne JB, et al; Veterans Affairs Cooperative Study Group. Efficacy of carotid endarterectomy for asymptomatic carotid stenosis. N Engl J Med. 1993;328(4):221-7.
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13. CASANOVA Study Group. Carotid surgery versus medical therapy in asymptomatic carotid stenosis. Stroke. 1991;22(10):1229-35.
14. Mayo Asymptomatic Carotid Endarterectomy Study Group. Results of a randomized controlled trial of carotid endarterectomy for asymptomatic carotid stenosis. Mayo Clin Proc. 1992;67(6):513-8.
15. Brott TG, Hobson RW 2nd, Howard G, Roubin GS, Clark WM, Brooks W, et al; CREST Investigators. Stenting versus endarterectomy for treatment of carotid-artery stenosis. N Engl J Med. 2010;363(1):11-23.
16. Silver FL, Mackey A, Clark WM, Brooks W, Timaran CH, Chiu D, et al; CREST Investigators. Safety of stenting and endarterectomy by symptomatic status in the Carotid Revascularization Endarterectomy Versus Stenting Trial (CREST). Stroke. 2011;42(3):675-80.
17. Yadav JS, Wholey MH, Kuntz RE, Fayad P, Katzen BT, Mishkel GJ, et al; Stenting and Angioplasty with Protection in Patients at High Risk for Endarterectomy Investigators. Protected carotid-artery stenting versus endarterectomy in high-risk patients. N Engl J Med. 2004;351(15):1493-501.
18. Hopkins LN, Roubin GS, Chakhtoura EY, Gray WA, Ferguson RD, Katzen BT, et al. The Carotid Revascularization Endarterectomy versus Stenting Trial: credentialing of interventionalists and final results of lead-in phase. J Stroke Cerebrovasc Dis. 2010;19(2):153-62.
19. Halm EA, Chassin MR, Tuhrim S, Hollier LH, Popp AJ, Ascher E, et al. Revisiting the appropriateness of carotid endarterectomy. Stroke. 2003;34(6):1464-71.
20. Karp HR, Flanders WD, Shipp CC, Taylor B, Martin D. Carotid endarterectomy among Medicare beneficiaries: a statewide evaluation of appropriateness and outcome. Stroke. 1998;29(1):46-52.
21. Bratzler DW, Oehlert WH, Murray CK, Bumpus LJ, Moore LL, Piatt DS. Carotid endarterectomy in Oklahoma Medicare beneficiaries: patient characteristics and outcomes. J Okla State Med Assoc. 1996;89(12):423-9.
22. Cebul RD, Snow RJ, Pine R, Hertzer NR, Norris DG. Indications, outcomes, and provider volumes for carotid endarterectomy. JAMA. 1998;279(16):1282-7.
23. Goldstein LB, Bushnell CD, Adams RJ, Appel LJ, Braun LT, Chaturvedi S, et al; American Heart Association Stroke Council; Council on Cardiovascular Nursing; Council on Epidemiology and Prevention; Council for High Blood Pressure Research; Council on Peripheral Vascular Disease; and Interdisciplinary Council on Quality of Care and Outcomes Research. Guidelines for the primary prevention of stroke: a guideline for healthcare professionals from the American Heart Association/American Stroke Association. Stroke. 2011;42:517-84.
24.Brott TG, Halperin JL, Abbara S, Bacharach JM, Barr JD, Bush RL, et al. 2011 ASA/ACCF/AHA/AANN/AANS/ACR/ASNR/CNS/SAIP/SCAI/SIR/SNIS/SVM/SVS guideline on the management of patients with extracranial carotid and vertebral artery disease: executive summary. Catheter Cardiovasc Interv. 2013;81(1):e76-123.
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AHRQ Publication No. 13-05178-EF-2
Current as of February 2014
U.S. Preventive Services Task Force. Screening for Carotid Artery Stenosis: Draft Recommendation Statement. AHRQ Publication No. 13-05178-EF-2. http://www.uspreventiveservicestaskforce.org/draftrec3.htm