Repeat examinations using ultrasound could help identify patients at high risk of having strokes or heart attacks, according to a new study.
Researchers from Austria performed ultrasound exams of the carotid arteries, the vessels in the neck that supply the brain with blood, and then repeated the exams six to nine months later to see if they could predict which patients were at high risk of a heart attack or stroke.
They zeroed in on changes in plaque -- the buildup of fat, cholesterol, and other substances that can narrow blood vessels. The researchers found that patients whose plaque appeared unstable were more likely to have a heart attack or stroke during the three-year follow-up.
About 600,000 Americans have a new or first stroke each year, according to American Heart Association estimates, and another 600,000 have a first heart attack. The attacks often come without apparent warning, as in the case of NBC newsman Tim Russert, who died June 13 of a heart attack after plaque ruptured in an artery, according to his doctor.
Tracking Plaque
For years, physicians have performed ultrasound exams of arteries in high-risk patients to determine how much the plaque has caused a narrowing in the blood vessels, called stenosis.
But "the determination of the degree of stenosis alone is insufficient to predict patients' risk," says Markus Reiter, MD, a physician at Medical University of Vienna, and the study's lead author. That is because a significant number of heart attacks and strokes occur in those whose blood vessels may not be extremely narrowed.
So Reiter's team zeroed in on patients who did not have symptoms of heart attack or stroke but were known to be at high risk for such problems. They gave them two ultrasound exams to analyze in detail the type of plaque they had, and then followed the plaque over time to see if they could predict which patients were more likely to have a cardiovascular crisis.
Repeat Ultrasounds to Predict Heart, Stroke Risk
Reiter's team first did ultrasound exams of the carotid arteries of 1,268 patients at high risk of cardiovascular disease because of multiple risk factors, such as smoking, diabetes, high blood pressure, high cholesterol, or known blockages in other blood vessels such as the coronary arteries.
Then they focused on the 574 patients with clearly demonstrable plaque buildup in the carotid arteries.
Six to nine months later, these patients all had repeat ultrasounds to measure changes in their plaque.
Reiter's team used the ultrasound images and a computer-assisted evaluation (called gray-scale median or GSM) to evaluate the darkness of the plaque and its density. If plaque appears darker, it has a low GSM and is thought to be unstable, more likely to rupture or burst.
"Our study is the first using repeat GSM testing for the assessment of an individual's cardiovascular risk," Reiter says.
Next, the researchers looked at whether the GSM levels had decreased -- considered a bad sign, reflecting unstable plaque -- or increased (a neutral to good sign) and whether the patient had had a cardiovascular event during the follow-up, for a median of three years.
Over a follow-up of slightly more than three years, the GSM levels decreased in 230 patients, or 40%, and increased in 344, or 60%. Those in the lowest GSM group, with the darkest plaque, were about 1.7 times more likely to have a cardiovascular event than those whose GSM went up the most, reflecting less dense plaque, during the follow-up.
Those whose GSM declined the most had a 68% survival rate at three years, compared to a 78% survival for those whose GSM increased.
The study is published in the September issue of the journal Radiology.
Ultrasound Predicts Stroke, Heart Attack: Second Opinions
Evaluating plaque at a single time point "is not as predictive an outcome as following it over time," says Nick Bryan, MD, a professor of radiology at the University of Pennsylvania, Philadelphia, and a spokesman for the American College of Radiology. That's a strength of the study, he says.
Another strength, he says: They used the ultrasound tests to predict cardiovascular events anywhere in the body, not just in the carotid artery.
So would a repeat ultrasound have helped Russert?
Too soon to say, Bryan says. "We don't know how well this [finding about repeat ultrasound] would apply to the general population," he says. In the study, the average age was 72. "This is not ready for clinical applications. It is a very interesting observation that will need a lot of follow-up."
"There is a bias," agrees Pablo Abbona, MD, a radiologist at Santa Monica-UCLA Medical Center & Orthopaedic Hospital in Santa Monica, Calif. "The patients are all in a high-risk population."
Another expert, Ravi Dave, MD, a cardiologist at Santa Monica-UCLA Medical Center & Orthopaedic Hospital and an associate professor of medicine at the University of California, Los Angeles, pointed out that although ultrasound is readily available, "not all labs have GSM."
Reiter agrees that more study is needed.
Lifestyle changes shouldn't be ignored, Dave says. "The current aggressive treatment of patients at high risk should be continued," he says. That means encouraging them to exercise if possible, eat a healthful diet, and control blood pressure, blood sugar levels, and cholesterol.
Labels: Medicine
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