DALLAS, Nov. 16 -- A new imaging technique predicts the risk of a second heart attack or death among coronary patients better and sooner than the widely used exercise stress test, according to a study in today's Circulation: Journal of the American Heart Association.
The technique called vasodilator perfusion imaging -- can be used as early as two to four days after a heart attack with no complications, allowing treatment decisions to be made quickly and potentially preventing further heart attacks, shortening hospital stays and reducing costs, says lead author Kenneth A. Brown, M.D., professor of medicine and director of the nuclear cardiology and cardiac stress laboratories at the University of Vermont.
"I think this is something that should be much more widely applied," Brown says, adding that smaller hospitals are more likely to have the equipment necessary for this test than they are to have advanced cardiac care laboratories.
"Substantial cost savings can be realized in appropriate patient populations" if this technique is widely adopted, writes Frans J. Th. Wackers, M.D., director of the cardiovascular imaging and exercise laboratories at Yale University School of Medicine, in an accompanying editorial. It could be particularly useful for helping smaller hospitals quickly determine which patients should be transferred to larger medical centers.
The study compared patients who were given the new imaging test two to four days after their heart attacks and then also had an exercise stress test six to 12 days later, to a control group who had the exercise stress testing only in a total of 451 patients. The patients who underwent vasodilator perfusion imaging were first given a drug called dipyridamole, which increases blood flow through the heart by dilating blood vessels while the patient is lying down. After the drug is administered, a mildly radioactive drug is given to the patient to provide an image of blood flow using a technology called single photon emission computed tomography (SPECT).
The drug's effects cause less strain to the heart than exercise testing, which consists of walking briefly on a treadmill while an electrocardiogram provides readings, Brown says. During exercise the heart muscle works harder, causing increased heart rate and demand for oxygen and blood flow. This stress is the reason exercise testing is not generally performed until five to seven days after a heart attack, although further cardiac events may occur during that time.
Brown and his colleagues found that not only could the technique be used earlier than conventional exercise testing, but it was also better at identifying patients at greatest risk of future heart attacks.
For instance, patients whose images showed they had only small or intermediate areas of permanent heart damage and little or no additional heart muscle at risk had the lowest risk of death or another heart attack -- less than 1 percent over the year following their initial heart attack, Brown says. Those with more heart muscle at risk had second heart attack or death risks ranging from 6 to 17 percent.
By contrast, exercise stress testing, also known as ECG testing did not predict cardiac events in this study, Brown says. "This is another piece of evidence that stress ECG testing may not be adequate to predict future heart attacks or death," says Brown.
In his editorial, Wackers points out that this study confirms and surpasses a pilot study of 50 patients that Brown and his colleagues published in 1990, and it provides further evidence that patients who appear to recover well from a heart attack can be evaluated safely and effectively using this imaging technique.
Brown says that since this latest study focused only on heart patients who had no complications as a result of their heart attack, further study on different patient populations is needed.
Co-authors are Gary V. Heller, M.D., Ph.D.; Ronald S. Landin, M.D.; Leslee J. Shaw, Ph.D.; George A. Beller, M.D.; Michael J. Pasquale, M.D.; and Stephen B. Haber, Ph.D.
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