Asymptomatic Carotid Stenosis: Medical Therapy Best Option

May 22, 2013

There is not enough evidence from contemporary clinical trials to make firm recommendations for interventional approaches, such as stenting and endarterectomy, in asymptomatic carotid stenosis, a new review and meta-analysis has concluded.

The review, published in the May 7 issue of the Annals of Internal Medicine, was conducted by a group led by Gowri Raman, MD, MS, from Tufts Medical Center, Boston, Massachusetts.

"The medical management of patients with asymptomatic carotid stenosis has improved significantly over the past 20 years, with stroke rates having come down markedly," coauthor David E. Thaler, MD, PhD, commented to Medscape Medical News. "While there may be a role for invasive approaches such as stenting and endarterectomy in high-risk patients, it is not clear if these interventions are superior to medical therapy in the modern era; more work is needed to better identify high-risk patients and to test the interventional approaches in this group."

Dr. Thaler explained that asymptomatic carotid stenosis can be detected with a stethoscope. "Turbulent flow can be heard in a narrowed vessel. Then an ultrasound scan can be performed to confirm atherosclerotic narrowing."

While carotid stenosis is a known risk factor for stroke, Dr. Thaler noted that routine screening is not part of recommended clinical practice in the United States at present. However, carotid artery imaging of asymptomatic individuals is on the rise.

Medical treatment entails emphasizing good primary prevention measures, such as control of cholesterol, blood pressure, diabetes, smoking cessation, exercise, and diet. In addition, therapy with an antiplatelet drug and a statin is recommended, or in some cases an interventional approach with stenting or endarterectomy can be pursued.

Risk for Periprocedural Stroke

Dr. Thaler noted that interventional approaches do run the risk for periprocedural strokes due to emboli breaking off and causing a blockage downstream.

"We must ensure that the procedural related stroke is less than the overall expected stroke risk. There are guidelines on this. There probably are symptomatic patients who are at higher risk of stroke in whom intervention may be a better option than medical therapy but they have not been clearly identified as yet."

He continued: "Strokes generally occur from carotid stenosis caused by an embolus. They are not normally related to reduced flow. The degree of narrowing of the carotid is therefore not the main measurement of interest. It is more a proxy of the degree of plaque which could break off and form a blockage downstream. Some people may have high grades of narrowing but a low risk of stroke. The risk of stroke is more to do with the morphology of the plaque. Is it ulcerated, thin capped or calcified? We need to be more able to quantify these things and understand how they relate to risk in order to define a population of patients who may benefit from stenting or endarterectomy."

In the various studies that have compared the treatment options, Dr. Thaler noted that there are no good data on stenting vs medical therapy. However, some data from 2 trials suggest that endarterectomy is superior to medical therapy in patients with a high-grade asymptomatic stenosis, with stroke rates reduced from about 2% to 1%.

"The problem is these data come from trials done many years ago. And if you just look at medical therapy alone, stroke rates have come down over time, probably because of better treatments and primary prevention efforts. So with this improvement, medical therapy may now be associated with a stroke risk of around 1%, and we don't know if intervention with surgery or stenting will give a further improvement," he concluded. "We need modern trials to look at this."

Tempting Target

Asked to comment on these conclusions, Philip B. Gorelick, MD, MPH, professor of translational science and molecular medicine, Michigan State University College of Human Medicine, and medical director, Hauenstein Neuroscience Center, Saint Mary's Health Care at Mercy Health in Grand Rapids, Michigan, called asymptomatic carotid stenosis a "tempting target for surgical or endovascular intervention, as we have a number of readily available noninvasive diagnostic tests to determine the degree of stenosis, well-tested interventions, and public fear of having a stroke."

Lessons from the past, however, have questioned the value of screening for carotid bruits or stenosis, and observational studies have suggested that although carotid stenosis is associated with the risk for stroke and myocardial infarction, the mechanism of the stroke may not be directly related to ipsilateral carotid artery stenosis because lacunar infarcts, cardioembolic strokes, contralateral ischemic strokes, and brain hemorrhages may occur, Dr. Gorelick points out.

"In fact, current guidelines do not recommend routine screening for asymptomatic carotid artery stenosis," he said. "Furthermore, our modern medical therapy armamentarium has advanced substantially in relation to blood pressure lowering drugs (eg, RAAS [renin-angiotensin-aldosterone system] blockers) and statin agents with potential pleiotropic effects, and newer-generation antithrombotic agents are now available. A real attention-grabber was the results of the SAMMPRIS trial, which compared medical therapy to stenting for symptomatic intracranial occlusive disease, where medical therapy won out by a fairly substantial margin, based on the early results."

This systematic review and meta-analysis by Raman and colleagues reports an incidence of ipsilateral stroke across 26 cohorts receiving  medical therapy alone at 1.68% per year and more recently at 1.13% per year, and it discusses the need for randomized controlled trials of patients with asymptomatic carotid stenosis comparing revascularization interventions with best-available medical management.

"The question is spot on in relation to whether surgeries and endovascular interventions really provide incremental benefit over carefully administered medical therapy alone," Dr. Gorelick said. "Many in practice are betting on modern medical management, and we need to know if these modern medical therapies coupled with more meticulous lifestyle management are at least noninferior.

"For most patients, I recommend waiting until there is about 80% asymptomatic carotid artery stenosis before considering carotid endarterectomy or angioplasty and stenting of the extracranial carotid artery," Dr. Gorelick concludes. "Medical management according to evidence-based guidelines such as those of the American Heart Association and American Stroke Association should be followed."

The study was supported by the Agency for Healthcare Research and Quality. Financial disclosures are available with the original article.

Ann Intern Med. 2013;158:676-685. Abstract


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