Magnetic resonance imaging (MRI) can accurately detect re-narrowed heart arteries in people who''ve had balloon angioplasty or other artery-clearing procedures, report researchers from Wake Forest University Baptist Medical Center (WFUBMC) and the University of Texas Southwestern Medical Center in this week''s Circulation.
MRI is the first non-invasive test to detect significant blockages as accurately as heart catheterization, the current standard test that requires a catheter and dye inside the arteries and uses X-rays to view narrowings.
"About a third of people''s vessels will re-narrow within six months of an artery-clearing procedure," said Greg Hundley, M.D., assistant professor of cardiology and radiology at WFUBMC. "Having a simple, non-invasive method to identify these patients would be extremely beneficial."
In the study, 17 patients who had recurrent chest pain at least three months after balloon angioplasty were tested with both MRI and heart catheterization. The two tests were found to be equally accurate (100 percent) at detecting vessel blockages of 70 percent or greater. At this level of blockage physicians normally recommend treatment.
"This puts us another step closer to a non-invasive screening test for heart disease," said Kerry Link, M.D., professor of radiology and cardiology. "In this study, we''ve applied the technology to patients with re-narrowed arteries. But it can also be used in seemingly healthy people to detect vessel disease in time to prevent heart attacks or angina."
With the MRI test, blood flow is first measured while the heart is at rest. Patients are then given a medicine to speed up their heart rates. Flow is measured again with the heart at stress, or beating close to capacity. As heart rate increases, blood flow should increase to meet the body''s needs. When it doesn''t, doctors know that the blockage is significant enough to affect heart function.
"The value of MRI, in addition to being non-invasive, is that it tells us how a narrowed artery affects the heart during activity," said Hundley. "It goes beyond measuring the size of the narrowing to tell us whether the body is getting enough oxygen-rich blood."
MRI uses magnetic fields and radio waves, so there is no exposure to ionizing radiation. Patients spend about an hour in the scanner and can then go home. The test for re-narrowed arteries can be used in patients who''ve had balloon angioplasty as well as other artery-opening procedures, including directional or rotational atherectomy or stenting. The test is not suitable for people who have pacemakers or defibrillators, or who''ve had previous coronary artery bypass surgery.
Heart catheterization, or angiography, is the current standard for evaluating the effect extent and severity of heart artery blockages. A small flexible tube is passed through blood vessels into the heart. Dye is released into the vessels and X-rays are used to evaluate blockages.
The number of people who require testing for re-narrowed arteries exceeds 150,000 a year. The American Heart Association reports that one-third of the 500,000 people who undergo balloon angioplasty each year will develop re-narrowed arteries within six months. Researchers are currently working on various strategies to prevent the problem, which occurs when fatty deposits either re-grow or expand within the artery. Symptoms can include chest pain or reduced exercise tolerance.
Balloon angioplasty - inflating a tiny balloon inside an artery to crush a bockage - is the most common nonsurgical treatment for blocked arteries.
The Medical Center researchers, in addition to Hundley and Link, were Craig Hamilton, Ph.D., medical engineer; Robert J. Applegate, M.D., cardiologist; David M. Herrington, M.D., M.H.S., cardiologist; Gregory A. Braden, M.D., cardiologist; and Mark Thomas, R.N., research nurse.
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