Most Carotid Ultrasounds Performed for Uncertain or Inappropriate Indications

The vast majority of imaging tests that result in carotid revascularization of asymptomatic patients are performed for “uncertain” indications, with as many as one in nine carotid ultrasounds performed for “inappropriate” indications, according to the results of new analysis. 

Among 4,063 asymptomatic patients who underwent carotid revascularization following an ultrasound in the analysis, just 5.4% of those had an appropriate indication for the imaging test, the most common appropriate reason being follow-up after a previous carotid revascularization procedure.

Overall, the most common reason patients underwent carotid ultrasound was the detection of turbulent carotid blood flow during a physical examination. Carotid bruit, which is classified as an uncertain indication given the mixed recommendations from various guidelines, accounted for approximately one-third of all indications for carotid imaging. 

“Given that carotid imaging is a fairly commonly ordered test, targeting carotid imaging using decision support tools to reduce inappropriate use may be a good approach to improve the value of healthcare without compromising quality,” write lead researcher Salomeh Keyhani, MD (University of California, San Francisco), and colleagues in their paper published online April 18, 2016, in JAMA: Internal Medicine.

In 2012, the American Board of Internal Medicine (ABIM) Foundation launched the Choosing Wisely campaign, an initiative designed to reduce wasteful or unnecessary medical tests or procedures. Number eight on the list of “Fifteen Things Physicians and Patients Should Question,” advises against screening for carotid artery stenosis in asymptomatic adult patients because there is “good evidence” the harms outweigh the risks. Screening in asymptomatic patients could lead to unnecessary surgeries that could result in serious harm, such as death, stroke, or MI, according to the American Academy of Family Physicians who made the recommendations to the ABIM.

Conflicting Guidelines

Part of the reason for large degree of uncertainty regarding the use of carotid ultrasound may stem from the conflicting national guideline recommendations on carotid imaging in asymptomatic patients without a history of stroke or transient ischemic attack.

The American Stroke Association/American Heart Association (ASA/AHA) state that there is no benefit of routine screening in patients with no clinical manifestations of disease or risk factors for atherosclerosis. Likewise, the United States Preventive Services Task Force (USPSTF) does not recommend carotid imaging in such patients, nor does the USPSTF recommend screening for asymptomatic carotid artery stenosis in asymptomatic adults.

However, some uncertainty sets in for other types of patients. For example, the USPSTF does not recommend carotid ultrasound for the asymptomatic patient with carotid bruit, whereas the ASA/AHA state that duplex ultrasonography is reasonable in such a patient but the recommendation is based on diverging expert opinion, case studies, or standard of care (class IIa, level of evidence C). The American Institute of Ultrasound Medicine, on the other hand, states that carotid imaging is indicated in asymptomatic patients with carotid bruit. There is also mixed recommendations when it comes to using carotid ultrasound as a follow-up imaging test in patients with carotid stenosis.   

In this retrospective cohort study, the researchers identified 4,063 patients 65 years of age and older who underwent carotid revascularization with either carotid endarterectomy (CEA) or carotid artery stenting (CAS) for asymptomatic stenosis in the Veterans Health Administration between 2005 and 2009.

In total, there were 5,226 indications for the 4,063 carotid ultrasounds, with approximately 25% of patients having multiple indications. Overall, the large majority of indications for ultrasonography were vascular-based (74.2%), including carotid bruit and stenosis/history of carotid disease. Near-syncope/syncope (10.8%), eye-related issues (6.7%), preoperative evaluation (4.5%), and neurological/psychological reasons (2.2%) comprised the other clinical indications.

In reviewing the indications for carotid ultrasound—a process done by three internists, two vascular neurologists, one vascular surgeon, and two ophthalmologists—just 5.4% of the indications were considered appropriate. Most of the appropriate indications assigned to the imaging tests by the reviewers were related to ocular disease. Follow-up after carotid revascularization was the most common appropriate vascular indication. More than 83% of the indications for the ultrasound were considered “uncertain,” the two most common reasons being for carotid bruit (30.2%) and follow-up in patients with carotid disease (20.8%). In total, 11.3% of the indications were inappropriate, including referring patients with dizziness, vertigo, syncope, and blurred vision for ultrasound.

Larry Goldstein, MD (University of Kentucky, Lexington, KY), who wrote an editorial accompany the study, said physicians are often forced to work in the absence of solid information. “It is often hard to cover every medical issue in randomized trials, and clinicians often make decisions based on incomplete data and extrapolations,” he told TCTMD in an email. “It needs to be recognized that these decisions may be incorrect.”

When investigators analyzed survival rates after the carotid endarterectomy/stenting procedure, overall survival was 71.4% at 5 years, suggesting “many patients do not live long enough to benefit from revascularization,” according to Keyhani and colleagues.

In their view, the results suggest that reducing inappropriate carotid imaging “may stem a ‘pipeline’ of low-value care, because many patients who were subsequently revascularized received initial imaging for reasons considered inappropriate by our expert panel.” Reducing “low-value imaging” can reduce “low-value carotid interventions” in patients who will not live long enough to benefit (> 5 years),” they advise.

Importantly, the analysis only examined the appropriateness of the imaging test and not the revascularization procedure. As the researchers point out, a patient might be screened with ultrasound for an inappropriate indication, but this could lead to an entirely appropriate CEA or CAS procedure. This tension between the individual perspective—which does not include a consideration of the societal harms of false-positive test results—and the societal perspective “is at the root of many of the current national debates on screening,” write Keyhani and colleagues.

Is There a Meaningful Effect on Patient Care?

In his editorial, Goldstein states that screening for a disease or clinical conditional makes sense only if identifying the disease/condition has a “meaningful effect on patient management.” Previous epidemiological studies have shown that an anterior cervical bruit is a marker of general atherosclerosis and tends to be a greater risk factor for death due to coronary artery disease than stroke. In one epidemiological study, among strokes that did occur in patients with a carotid bruit, the type and location did not correlate with the bruit.

“Therefore, the detection of a cervical bruit might reasonably prompt aggressive identification and treatment of other vascular risk factors,” he writes.

To TCTMD, Goldstein said the “use of carotid ultrasound to screen general populations without established risk factors is a concern, as there is no evidence that it is of value,” noting that only a small percentage of carotid ultrasound studies were done in patients with appropriate indications for the test. He added that the analysis includes a biased sample in that all of the patients had a revascularization procedure. In a larger group of asymptomatic patients who undergo carotid imaging, but do not undergo revascularization, the percentage of tests done for inappropriate or uncertain reasons could be even higher.

As for the benefits of revascularization, he notes that the clinical trials comparing CEA plus best medical therapy versus medical therapy alone were conducted one to three decades ago, and while current guidelines recommend revascularization for selected patients with asymptomatic carotid stenosis on the basis of those trials, optimal medical therapy has evolved since then, making the results from such trials questionable. The Carotid Revascularization Endarterectomy versus Stent Trial-2 (CREST-2) is currently ongoing, and investigators are reevaluating the benefit of CEA and CAS in addition to optimal medical therapy compared with best medical therapy alone, he said.

“The ongoing trials should help us understand whether there is currently, under the most optimal circumstances, benefit from revascularization of patients with an asymptomatic carotid artery narrowing,” said Goldstein.

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