Oct. 13, 1999 DALLAS, Oct. 12 -- A new type of stress test may soon offer doctors a safer and easier way to diagnose heart disease, researchers report today in Circulation: Journal of the American Heart Association.
The new stress test, called fast cine magnetic resonance imaging or MRI, offers physicians an alternative for diagnosing coronary artery disease in patients who are not good candidates for standard stress tests, such as stress echocardiography.
"The technique will open a lot of doors," says W. Gregory Hundley, M.D., assistant professor of medicine in cardiology and radiology at Wake Forest University School of Medicine and lead author of the study. "With this information doctors will be better able to determine the severity of a patient's heart disease, and decide on the most appropriate medical management."
In an accompanying editorial, Gerald M. Pohost, M.D., the Mary Gertrude Waters professor of cardiovascular medicine at the University of Alabama at Birmingham, said that until now, MRI technology was geared toward organs that move very little, such as brains and bones. "In order to image the heart, it was necessary to synchronize the imaging with the heart's cycle so that images were required over numerous heartbeats in a 5-10 minute interval. The newest, most modern technology allows imaging of the heart in 'real time.' This is a major step in the evolution of MRI applications to the heart," he says.
"Perhaps the most important potential of MRI is that it could provide a very comprehensive evaluation of the heart, displaying the function, structure, blood flow, and coronary arteries," says Pohost. "Ultimately it should provide everything you need in one package."
Standard stress tests, such as treadmill exercise tests, can indicate how well an individual's heart handles increased physical exertion, and can help physicians find a blockage or other problem in the blood vessels of the heart. A thallium stress test uses a radioactive substance that is injected into the bloodstream to show how well blood is flowing to the heart muscle. It is usually done in conjunction with an exercise stress test on a treadmill or bicycle.
The fast cine MRI stress test uses a new form of high-speed MRI to view the wall of the heart as it beats. The fast cine MRI is able to capture the heart's movement at almost the same time the heart is contracting and relaxing, or close to 'real time.'
Patients receive a drug called dobutamine and are placed in the MRI machine. Dobutamine works like adrenaline and mimics the effects of exercise on the heart by increasing the heart rate and the speed at which it contracts and relaxes. It also induces cardiac ischemia, a reduction in the blood being supplied to the heart.
With the high-speed imaging, the physician can evaluate the ability of the left ventricular wall to move during physical stress. The fast cine MRI uses the highest speed available to visualize the rapid movements of the heart and obtain a nearly immediate image of the heart in motion.
The test is an alternative for patients who aren't well suited for standard stress echocardiograms, such as obese patients, individuals who have undergone previous cardiothoracic surgery, or who have lung disease. However, the fast cine MRI stress test should not be used in patients with pacemakers, cochlear implants, metal clips, or defibrillators.
The fast cine MRI stress test has advantages over other forms of stress testing, according to Hundley. "Since the test doesn't require the use of ionizing radiation, there is no radioactive waste to dispose of," he says. Because it is 3-dimensional, fast cine MRI also offers physicians a better view of what's happening inside the heart wall compared to standard stress tests.
The MRI stress test takes approximately 35 minutes, says Hundley, who adds that patients he studied tolerated the procedure very well, despite the well-known fears of MRI procedures, which include claustrophobia. The test proved to be an accurate predictor of heart disease. Among patients who had a negative MRI stress test, 97 percent were free of heart disease within the first year of testing.
Co-authors were Craig A. Hamilton, Ph.D.; Mark S. Thomas, R.N.; David M. Herrington, M.D., M.H.S.; Tiffany B. Salido, B.E|.; Dalane W. Kitzman, M.D.; William C. Little, M.D. Kerry M. Link, M.D. and Robert W. W. Biederman, M.D. co-authored the editorial.
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