Researchers at Wake Forest University Baptist Medical Center are the first in the world to report the successful use of magnetic resonance imaging (MRI) to diagnose significant blockages in blood vessels leading to the heart. This is the first "non-invasive" test to visualize blockages and determine if they require treatment.
MRI is just as accurate at diagnosing blocked arteries as heart catheterization, the current standard test, reported researchers from the Medical Center and the University of Texas Southwestern Medical Center in this week''s issue of Circulation, a scientific journal of the American Heart Association.
"MRI allows us not only to locate a blockage, but to determine whether it limits blood flow enough to warrant treatment," said Greg Hundley, M.D., assistant professor of cardiology and radiology, and a member of the research team. "There is no other non-invasive test that can do this. With further development, many patients may benefit from this approach to assessing coronary blockages."
MRI uses magnetic fields and radio waves, so there is no exposure to ionizing radiation. Patients spend less than an hour in a scanner and can then go home. Cardiac catheterization, a procedure to thread a small, flexible tube called a catheter through the blood vessels into the heart, requires a six- to eight-hour wait afterwards and can have complications. These include allergic reactions to the dye released into the vessels that enables X-ray equipment to track blood flow, bleeding from the vessel where the catheter is inserted and, in rare cases, a heart attack.
In a study of 30 patients who had both MRI scanning and cardiac catheterization, the
MRI was just as effective as cardiac catheterization at diagnosing significant blockages in two
main arteries supplying the heart (the distal left main and the left anterior descending). It is important to diagnose blockages in these areas because they often require bypass surgery or artery-opening procedures. The research team is now working to measure flow with MRI in the right coronary artery, another common site of blockages.
The researchers achieved two breakthroughs in MRI imaging to develop the new test. They created computer software to control the scanner and analyze data that made it possible – for the first time – to measure blood flow in the small vessels leading to the heart.
Second, they used this imaging technique to measure flow while the heart is stressed, or beating close to capacity. This is the ideal time to assess whether a blockage requires treatment. Patients take a drug to temporarily speed up their heart rate for the test. As the heart rate increases, blood flow should also increase. When the results show that flow isn''t increasing to meet the heart''s demands, the patient''s physician may recommend heart bypass surgery or artery-opening procedures such as angioplasty.
"If the patient holds his breath for 8 to 15 seconds, we get clear pictures of the beating heart," said Kerry Link, M.D., associate professor of radiology and cardiology and a member of the research team. "We can tell not only what percentage he artery is blocked, but can measure how the blockage affects flow."
The MRI test cannot currently replace the cardiac catheterization as a "roadmap" to performing angioplasty or bypass surgery, but the researchers believe it has promise in the future to provide the detail necessary for these procedures.
Other members of the research team are Robert J. Applegate, M.D., associate professor of cardiology; Steve Darty, radiation technologist; Craig Hamilton, Ph.D., assistant professor of radiology; David M. Herrington, M.D., associate professor of cardiology; Kim Lane, sonographer; Tiffany Salido, engineer, and, Mark Thomas, R.N.
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