Imaging Technique Predicts Success Of Bypass Surgery Or Angioplasty

CHICAGO, IL — November 16, 2000 — An advance in magnetic resonance imaging (MRI) developed by researchers at Northwestern University Medical School and Siemens Medical Systems has radically improved the ability to determine which patients with coronary artery disease will benefit from bypass surgery or angioplasty.

The investigators, led by Northwestern cardiologist Raymond J. Kim, MD, and basic scientist Robert M. Judd, used an improved version of a technique known as contrast-enhanced MRI in 50 patients with heart disease who were scheduled to have bypass surgery or coronary angioplasty.

As reported in an article in the Nov. 16 issue of The New England Journal of Medicine, the scientists found that contrast-enhanced MRI boosted image intensity by tenfold over previous methods and enabled the researchers – without stress testing or use of radioactive tracers-to distinguish between reversible and irreversible heart injury.

Drs. Kim and Judd explained that with this technique, heart regions damaged by heart attack or other coronary artery disease appear on MRI as hyperenhanced, or “bright.”

The researchers found that areas of the heart that were “dark” on the MRI recovered following bypass surgery or angioplasty, whereas “bright” areas did not recover after surgery.

The research group, which consisted of cardiologists, basic scientists and physicists, also reported that contrast-enhanced MRI is the first technique to allow physicians to view the extent of damage within the heart wall following a heart attack.

The wall of the heart is approximately 10 millimeters thick. In a heart attack, the cells in the inner part of the heart wall die first and the damage progresses outward.

“We found that heart muscle function at the injury site was more and more likely not to improve as the extent of ‘bright’ areas increased through the wall of the heart,” Dr. Kim said.

The ability to look at damage within the wall of the heart is possible because of the high spatial resolution of MRI and the capability of the new technique to contrast alive and dead areas of the heart in such a striking manner as ‘dark’ and ‘bright’ spots,” he said.

“We found that when most of the thickness of the heart wall was ‘bright,’ there was only a 2 percent chance of improvement following bypass surgery or angioplasty,” Dr. Judd said.

“This indicates that MRI performed before surgery can identify patients who are unlikely to benefit from the intervention and an unnecessary procedure can be avoided,” Dr. Judd explained.

Contrast-enhanced MRI is completely non-invasive; the contrast agents that are used in the studies are naturally flushed out of healthy heart tissue in about 15 minutes, while lasting in the dead tissue for approximately one hour.

Other methods for assessing heart damage include positron emission tomography, single-photon emission computed tomography and dobutamine echocardiography. These techniques have proven clinical utility, but each requires stress testing or the use of radioactive tracers, and since they cannot discern the extent of damage across the heart wall may have reduced diagnostic accuracy.

Kim is assistant professor of medicine at the Medical School, a cardiologist at Northwestern Memorial Hospital and a researcher at the Feinberg Cardiovascular Research Institute at Northwestern University Medical School. Dr. Judd is assistant professor of medicine and biomedical engineering and a researcher at the Feinberg Cardiovascular Research Institute.

Their co-authors on the study were Edwin Wu, MD, cardiology fellow; Allen Rafael, MD, cardiology fellow; Enn-Ling Chen, physicist, Feinberg Cardiovascular Research Institute; Michele A. Parker, statistician, Feinberg Cardiovascular Research Institute; Francis J. Klocke, MD, professor of medicine and director, Feinberg Cardiovascular Institute; Robert O. Bonow, MD, Max and Lilly Goldberg Distinguished Professor of Cardiology and chief of cardiology at the Medical School and Northwestern Memorial Hospital; and Orlando Simonetti, a physicist with Siemens Medical Systems.

This study was supported in part by an American Heart Association Scientist Development Grant and grants from the National Institutes of Health.