March 2, 1998

EMBARGOED FOR RELEASE UNTIL THURSDAY, MARCH 5, 1998 AT 6:30 P.M. EST

NEW IMAGING TECHNIQUE PINPOINTS DEAD HEART MUSCLE

Scientists at Johns Hopkins have developed the first precise, noninvasive means of measuring a chemical in the heart tied to the extent of muscle damage from a heart attack.

The test pinpoints in injured heart tissue depleted concentrations of creatine, a molecule that provides energy to the muscle. The new test works using commonly available magnetic resonance imaging scanners, which will make the technique potentially widely available.

"Until now, there were no methods for noninvasively assessing local creatine levels in the normal and diseased human heart. Now we can observe and measure total creatine throughout the human heart and its reduction in infarcted, or dead heart tissue," says Robert G. Weiss, M.D., associate professor of medicine and cardiology and an author of the report on the development published in the March 7 Lancet .

The new test, developed with funding from the National Institutes of Health and the American Heart Association, identifies and measures creatine concentrations using magnetic resonance spectroscopy (MRS) in different regions of the heart. The image of each region to be examined with MRS is first obtained by MRI during the same examination.

"MRI allows us to see only the structure of the heart," says Paul A. Bottomley, Ph.D., professor of radiology and co-author of the paper. "But in combination with MRS, we can investigate specific regions on the MRI images and measure the concentration of creatine there with pinpoint accuracy. We can even see heart muscle damage in the back of the heart wall, a difficult area to observe with prior imaging techniques."

In clinical studies of the new "creatine depletion" test, Bottomley and Weiss, evaluated 10 healthy volunteers and 10 patients with prior heart attacks, checking for the amount of creatine in tissues of the septum, the wall separating the right and left ventricles or main pumping chambers of the heart; and in the front and back walls of the left ventricle, from which blood is pumped to the rest of the body. In every case of prior heart attack, significant depletion of creatine was directly observed.

Creatine has an energy-rich form, creatine phosphate, that is metabolized, or used up to feed the heart's endless appetite for fuel. A drop in creatine concentration has long been known to signal injury and heart muscle death, but at present, the only way to use it to measure heart damage is indirectly, by looking for the amount of creatine kinase, a heart enzyme released into the blood that breaks down creatine. Moreover, currently available creatine kinase tests on blood samples can't identify the location or reliably measure the extent of heart muscle damage.

In the new metabolic test, MRS, guided by MRI, measures creatine level in any selected areas of the heart muscle.

Weiss and Bottomley say studies of larger numbers of patients are needed to show if the new test will prove better than other imaging studies at predicting which patients will respond most favorably to treatments like surgery or balloon angioplasty. But already, they say, the advantages of the new development are that it does not require exposure to ionizing radiation and can be done in any of the large number of hospitals with MRI scanners.

MRI scanners are quite numerous and therefore accessible to large numbers of patients, they say. And MRI performed during the same study can provide high resolution anatomic and functional information about the heart muscle and blood vessels to complement the localized metabolic findings.

--JHMI--

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