Carotid Conundrum: Role of Ultrasound Screening
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 a CAGR of 1 percent.  

Next controversy & new model

The most recent controversy relates to medical management rather than screening, says Hallett. “It’s hard to find a patient with a family history of heart and vascular disease who is not on a statin.” In fact, many asymptomatic patients likely have been prescribed an antiplatelet agent as well to reduce the risk of stroke. Hence, some physicians have concluded that asymptomatic patients being treated for systemic cardiovascular disease can bypass carotid artery screening.

In 2009, Roper piloted a carotid artery ultrasound screening program. “Our primary care physicians approached us and asked if we would screen their asymptomatic patients for carotid disease,” says Hallett. When the vascular team questioned the motivation, the primary care physicians explained a common scenario. A young patient with a family history of heart attack or stroke would refuse to adhere with medication to reduce risk factors, citing good health. An image showing carotid intima-media thickening might encourage adherence.

Roper launched the program as a community service with vascular surgeons offering carotid artery ultrasound, abdominal aorta screening and ankle-brachial thickness screening at cost for a $125 out-of-pocket fee. “The program isn’t a money-maker, but it helps primary care providers convince patients to treat early disease,” says Hallett, asserting that screening for early disease may be more important than detecting advanced disease.

To date, Roper has screened 1,400 patients in their 40s and 50s who have a family history of heart and vascular disease. Six out of 10 showed signs of early carotid plaque, which may provide the tipping point to sway patients to take statins and aspirin, as well as control blood pressure and diabetes. Anecdotal feedback indicated the program has helped compliance, says Hallett. The organization plans to examine the effects of imaging on patient management in the next phase of the study.

Vascular surgeons have found asymptomatic carotid artery stenosis greater than 70 percent in fewer than five patients. All have been referred for further evaluation and possible CEA.

Several factors differentiate the health system’s model from private companies that offer screening, says Hallett. Mobile providers come to town periodically, while at Roper, tests can be performed and read by a vascular surgeon any day of the week. Private companies don’t offer the same sophisticated equipment as a vascular lab, and they do not tell about subtle early changes that inform the need for medication.

As screening tests are developed, the process may be a bit like opening Pandora’s box. Invariably, screening unleashes an array of potential troubles such as further testing and procedures. Can cardiovascular imagers responsibly repackage carotid artery ultrasound screening and offer an effective, efficacious service to patients and physicians? It remains to be seen.