DALLAS, July 25, 2000 -- EBCT, a non-invasive test that measures calcium in the blood vessels, may, in some groups of patients, be about 70 percent specific for detecting blocked arteries, according to a new study reported in today's Circulation, A Journal of the American Heart Association.
The American Heart Association and the American College of Cardiology recently issued an expert consensus document (July 4) on the use of EBCT for the diagnosis and prognosis of coronary artery disease. Used along with standard approaches to assessing risk, EBCT, by detecting calcium deposits in the coronary arteries, may help guide appropriate treatment for patients with coronary artery disease.
"This study, which includes people without symptoms of heart disease, establishes that EBCT is more specific than previously thought," says study co-author Patricia A. Peyser, Ph.D., a professor of epidemiology and director of the Public Health Genetics Program at the University of Michigan, Ann Arbor. However, researchers involved in this study say that EBCT still should not be used as a stand-alone method for diagnosing coronary artery disease, but rather as a complement to other diagnostic information.
"Our results show that EBCT can aid in the detection of coronary artery disease," Sheedy says. "But doctors have to use this information in addition to everything else they know about their patients."
Although the specificity of the test in this study was higher than previously reported in other research, the study authors do not advocate using the test for mass screening at this time. Specificity is the likelihood that the test result will be negative in a patient without narrowed coronary arteries.
Atherosclerosis is the buildup of plaque ñ cellular debris, blood fats, cholesterol and cholesterol, and other substances ñ in the walls of the blood vessels and begins early in life. When the coronary arteries, blood vessels that supply blood to the heart, are narrowed by plaque they can become blocked, causing a heart attack. Chest pain is one symptom of atherosclerosis. As atherosclerosis progresses, the plaque begins to contain measurable levels of calcium, a mineral that can be "seen" with EBCT. In general, the higher the number and density of these calcium deposits, the more extensive the atherosclerosis. However, the study explained that there is not a one to one relationship between calcium deposits and coronary artery disease.
"Prior studies examined the accuracy of EBCT mostly in patients suspected to have heart disease because of chest pain or other symptoms of heart disease," Peyser says. "Those studies estimated that the specificity of any calcium on EBCT was less than 50 percent. This study found the specificity to be about 70 percent."
Researchers from the Mayo Clinic examined the results of EBCT scans from 213 individuals who complained of chest pain or tightness, and 765 individuals who did not have symptoms of atherosclerosis. The subjects without symptoms are part of the on-going Rochester (Minn.) Family Heart Study, which began in 1983. The researchers used computer software to assign a calcium score indicating the amount of detectable calcification in each subject's arteries. They then divided the subjects into several groups based on their calcium score and their age.
They found that for patients under age 50, a calcium score of 100 or greater provided a strong likelihood that their coronary arteries were narrowed by more than 50 percent. In those over age 50, a calcium score of 200 or more suggested that narrowed coronary arteries were very likely. In addition, a calcium score of 0 suggested that subjects over age 50 did not have obstructed, or narrowed coronary arteries.
However, one patient with symptoms who scored 0 did have coronary artery blockage and three patients with symptoms with calcium scores above 500 had blockages of less than 50 percent in their coronary arteries. Researchers say this is evidence of why EBCT should not be used by itself to diagnose heart disease.
The researchers agree that EBCT testing can help physicians by giving them a better idea of how quickly a patient's atherosclerosis is advancing. It can also help identify which patients need exceptionally aggressive treatment to lower risk factors such as high cholesterol levels or high blood pressure to delay the development of heart disease, Peyser says.
Media advisory: Dr. Peyser can be reached by phone at (734) 763-4077, or by Email at ppeyser@umich.edu . Dr. Sheedy can be reached at (507) 538-0348, or by Email at psheedy@mayo.edu . (Please do not publish telephone numbers.)
For journal copies only, please call: (214) 706-1173
For other information, call:
Carole Bullock: (214) 706-1279
Maggie Francis: (214) 706-1397