Carotid Conundrum: Role of Ultrasound Screening

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 - Roper St. Francis Healthcare Heart & Vascular Center
A technologist at Roper St. Francis Healthcare Heart & Vascular Center in Charleston, S.C., checks an image while performing an ultrasound screening test.

The U.S. Preventive Services Task Force (USPSTF) reversed its rating on ultrasound screening for carotid artery stenosis in 2007, and after careful analysis, USPSTF labeled the test grade D, recommending against screening for asymptomatic stenosis in the general population. However, a mere recommendation may not suffice to change practice patterns. More than 11 million exams were performed by specialists between 2000 and 2007, and screening remains a widespread problem.

Carotid artery ultrasound screening emerged roughly 25 years ago, and vascular labs quickly embraced the exam. It significantly adds to the business model, and remains the second most common vascular lab test in most labs, says John Hallett, Jr., MD, medical director of Roper St. Francis Healthcare Heart & Vascular Center in Charleston, S.C. Reimbursement is relatively favorable, with a technical fee in the $150 range and professional fee in the $35 to $45 range.

While utilization skyrocketed, evidence trickled in. The USPSTF was unable to provide a definitive recommendation in 1996. By 2007, more data about the screening and treatment of carotid artery stenosis were available and the task force recommended against the exam.

As many as 90 percent of patients are asymptomatic and most undergo ultrasound screening prior to revascularization. The risk of stroke for asymptomatic patients depends on the degree of stenosis, ranging from 1.6 to 3.2 percent annually (N Engl J Med 2000;342[23]:1693-1700).

But, carotid endartarectomy (CEA), the primary surgical intervention for carotid stenosis, is a problematic procedure. Although the intent is to open the artery and reduce the risk of stroke, the surgery actually causes stroke in 2 to 3 percent of patients.

“A few randomized trials suggested that high-risk participants operated on by selected surgeons showed a net reduction in stroke,” says Michael L. LeFevre, MD, MSPH, medical director of family medicine at the University of Missouri School of Medicine in Columbia and co-vice chair of USPSTF. “The problem with that statement is that there are a few too many ‘selecteds’ in it.” The Asymptomatic Carotid Atherosclerosis Study demonstrated a 5 percent, five-year risk of ipsilateral stroke among asymptomatic patients who undergo CEA, compared with 11 percent in medically managed patients. Prevention of stroke hinged closely on patient characteristics, risk factors and surgical expertise.

Screening’s shortcomings

Carotid artery ultrasound screening also is plagued by less than stellar accuracy. “When screening ultrasound is applied to millions of people over the age of 60, the exam will identify at least as many false positives as true positives,” says Timothy P. Murphy, MD, of Warren Alpert Medical School at Brown University in Providence, R.I.  And some of these patients may head down a slippery slope toward revascularization. Although stenting may be a viable treatment for carotid artery stenosis, for most patients, CEA is the only option, as Medicare and most private payers do not currently reimburse for stenting of asymptomatic disease.

In 2011, a slew of professional societies, including the American Stroke Association, the Society for Cardiovascular Angiography and Interventions and the Society for Vascular Medicine, concurred with the USPSTF recommendations against routine screening of asymptomatic patients without clinical symptoms or risk factors for atherosclerosis (J Am Coll Cardiol 2011;57[8]:e16-e94).

Carotid artery ultrasound screening still remains common practice. Screening is actively marketed, primarily by two groups: private companies that offer screening in churches, malls and senior centers; and specialists, many of whom perform revascularization procedures.

To examine whether providers who perform revascularizations are incentivized to perform carotid artery ultrasound screening, Murphy and colleagues analyzed Medicare claims from 2000 to 2007 among three specialties that perform revascularization for carotid stenosis and one that does not (AJR 2012;198[4]:866-868). Cardiology topped the chart, increasing at a compound annual growth rate (CAGR) of 11 percent from 2000 to 2007. Another potential self-referrer, vascular surgery, saw a 6 percent CAGR, followed by interventional radiology at 3 percent. The three were benchmarked against diagnostic radiology, the lone specialty that does not provide revascularization. Diagnostic radiology had the largest volume but the least growth, with