DALLAS, – High-resolution magnetic resonance angiography (MRA) may offer a risk-free way to identify narrowed vein grafts after bypass surgery, according to a report in today’s Circulation: Journal of the American Heart Association. High-resolution MRA provides clear 3-dimensional images of blood vessels. MRA accurately identifies blockage in vein grafts, as well as the extent of narrowing, researchers say.
“The high-resolution images were comparable to images obtained with X-ray angiography, which is the gold standard test for diagnosing blocked arteries and veins,” says Ernst E. van der Wall, M.D., an author of the study and professor of cardiology at Leiden University Medical Center, Leiden, the Netherlands.
In bypass surgery, surgeons take a blood vessel from another part of the body and create a detour around the blocked part of a coronary artery. In the procedure, an artery may be detached from the chest wall and the open end attached to the coronary artery below the blocked area. Or, a piece of a long vein in the leg may be used. One end is sewn onto the large artery leaving the heart – the aorta. The other end of the vein is attached or “grafted” to the coronary artery below the blocked area.
The MRA technique in this study was used to look only at bypasses that had used the patient’s leg vein.
“Recurrent chest pain after coronary artery bypass surgery is alarming for the patient and can pose a clinical dilemma for the physician: Should the patient undergo an invasive test, such as an angiography, to determine the cause of the pain, or is it better to follow a course of watchful waiting?” says van der Wall. MRA may provide the needed answers without the risk of invasive testing or the anxiety associated with waiting, he says.
Narrowed or blocked arteries and veins are caused by the buildup of a hard, fatty substance called plaque. This buildup of deposits on the inner surface of arteries and veins is called atherosclerosis. When blocked arteries are “bypassed,” the disease may progress to the new vein grafts and can cause recurrent chest pain called angina.
“The beauty of MRA is that it is a non-invasive test,” says van der Wall, whereas the traditional diagnostic test, coronary angiography, is invasive. He says coronary angiography is an excellent tool for diagnosing disease in coronary arteries and grafts, but it can be risky after surgery.
Patients who undergo coronary angiography have a thin catheter (tube) inserted in the groin, which is then carefully guided into the heart. Dye is released through this catheter and makes the arteries and grafts visible on an X-ray. While most patients undergo angiography with no ill effects, sometimes the catheter can tear a blood vessel or cause other complications.
With MRA there are no such risks, he says.
In the study, van der Wall’s team used high-resolution MRA to assess the condition of 56 vein grafts in 38 patients who complained of recurrent chest pain after bypass surgery. The patients, whose mean age was 67, were already scheduled for standard angiography to determine the cause of the pain, but agreed to have MRA in addition to the standard treatment. Nineteen of the patients had MRA before X-ray angiography and 19 patients underwent MRA following standard angiography.
Eighteen grafts were found to be narrowed by 50 percent or more, while 11 grafts were at least 70 percent narrowed and six were completely blocked. Two observers who were blinded to the findings of the standard angiogram or the report of the other observer assessed the MRA scans.
When the graft was at least 50 percent narrowed, the diagnostic accuracy of high-resolution MRA compared to traditional angiography was 65 percent to 88 percent. When the vessel was narrowed by 70 percent or more, accuracy was 73 percent to 87 percent, and when the vein graft was completely blocked, the accuracy was 83 percent to 100 percent.
Since MRA technology is still developing, van der Wall says it is too soon to suggest that it can replace standard angiography, but he says it could be considered as a useful diagnostic adjunct. “Also, the technique costs about $500, which is about half the cost of standard angiography.”
According to the American Heart Association’s latest statistics, about 12.6 million Americans have coronary heart disease. In 1999 more than 570,000 heart bypass surgeries were performed in the United States.
Co-authors of the study include: Susan E. Langerak, M.Sc.; Hubert W. Vliegen, M.D.; Albert de Roos, M.D.; Aeilko H. Zwinderman, Ph.D.; J. Wouter Jukema, M.D.; Patrik Kunz, Ph.D., and Hildo J. Lamb, Ph.D.
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