Aug. 17, 2011 -- Two noninvasive imaging tests may help determine which people with a narrowing of arteries in the neck will need surgery to reduce their future risk of stroke, a study suggests.
A narrowing of the carotid arteries in the neck is known as asymptomatic carotid stenosis (ACS). "Asymptomatic" means the patient does not experience any symptoms.
Carotid arteries in the neck deliver blood to the brain. They typically become narrowed when plaques build up in the inner lining of the arteries.
There is some uncertainty within the medical community on how to best identify people with ACS who are at high risk for stroke and need surgery or stenting to open their carotid arteries as opposed to treatment with medication.
In a two-year study of 435 people with severe ACS, researchers used ultrasound to assess the quality and composition of the plaque in the carotid arteries and a Doppler ultrasound test to look for the presence of tiny blood clots or particles called microemboli that may break off from the arteries and travel to the brain, causing stroke.
The study is published in Neurology.
Determining Stroke Risk
During the study, 10 people had strokes and 20 people had transient ischemic attacks or mini-strokes.
People with fatty plaque in their carotid artery were more than six times more likely to have a stroke than those people without this type of plaque. Plaques that are rich in fat are considered more dangerous.
People with both fatty plaque and signs of microemboli were more than 10 times more likely to have a stroke than those without these two markers, the study shows.
According to the new study, the risk of future stroke is 8% per year for people who test positive on both screening tests. By contrast, future risk of stroke is lower than 1% per year for those with negative results on both imaging tests. The findings held regardless of other stroke risk factors such as high blood pressure, diabetes, smoking, and vascular disease.
"Most patients will stay asymptomatic [without symptoms] and not suffer a stroke, but it's hard to identify the patients who are at highest risk and should undergo surgery," says study researcher Raffi Topakian, MD, a neurologist at Academic Teaching Hospital Wagner-Jauregg in Linz, Austria. "If you are at high risk for future stroke, medication is not enough for you."
If these findings are reproduced by other researchers, they could change the way ACS is evaluated and treated, he says. As it stands, using ultrasound to look at plaque composition is common. The Doppler ultrasound test, however, is time consuming and the results can vary based on the technician performing the test.
Tatjana Rundek, MD, professor of neurology at the University of Miami Miller School of Medicine in Florida, routinely evaluates ACS patients using these two screening tools.
"These individuals have a disease but don't have symptoms yet, so this field is sort of divided," she says. "We would love to select patients at the highest risk for stroke for surgery."
"It is not enough to know the percent of [narrowing]. We need to know the composition of the plaque and what it looks like and the potential for embolization," she says.
Itzhak Kronzon, a cardiologist at Lenox Hill Hospital in New York, says evaluation for patients with ACS starts with taking a thorough medical history including neurological exam. "If you have ACS, the likelihood of a stroke is small, but if you do have a stroke, it is devastating."
The Doppler test is not a standard part of assessing stroke risk in people with ACS, and Kronzon doesn't think it should be widely recommended based on these study results. More study is needed before this becomes common practice, he says.
In an accompanying editorial, Lars Marquardt, MD, the University of Erlangen-Nuremberg in Germany, writes that overall risk of stroke among people with ACS is relatively low and has decreased due to better management through cholesterol and high blood pressure drugs in recent years.
"If techniques like the one presented by [study researcher] Topekian are confirmed to be able to detect patients that have a higher than normal risk of stroke, screening of patients with this technique seems necessary," he writes in an email to WebMD.