A national (USA) team of researchers, led by a cardiovascular nuclear medicine specialist at the University of Maryland Medical Center, has demonstrated for the first time that an experimental radioactive compound can show images of heart damage up to 30 hours after a brief interruption of blood flow and oxygen. The discovery may help physicians in emergency rooms and in their offices determine whether a patient's chest pain, which may have subsided hours earlier, is related to heart disease or something else, such as indigestion. The results of the study appear today in Circulation Online and will appear in the print version of Circulation on October 4, 2005.

"We are excited about this agent because it extends the time window for identifying myocardial ischemia, a common cause of chest pain, long after the pain stops and blood flow to the heart returns to normal," says lead investigator Vasken Dilsizian, M.D., professor of medicine and diagnostic radiology and nuclear medicine at the University of Maryland School of Medicine and director of Cardiovascular Nuclear Medicine at the University of Maryland Medical Center. "This probe provides a direct connection to the cause of the chest pain without requiring a treadmill stress test or use of a drug that produces stress to assess heart function," says Dr. Dilsizian.

Nuclear medicine combines computers, detectors and radioactive substances called radioisotopes to produce images of blood flow and biochemical functions in the heart and other organs. The radioactive tracer evaluated for this study, known by the brand name Zemiva, links a fatty acid to a radioisotope which is injected in the patient. The researchers used a technique called SPECT (Single Photon Emission Computed Tomography) to evaluate the tracer in this study.

The heart normally uses fatty acid as its primary fuel source for energy. Decreased blood flow to the heart, caused either by narrowed or clogged arteries or increased demand on the heart during strenuous exercise, sets off a metabolic disturbance that slows down or halts the way fatty acid is normally utilized. The condition is called myocardial ischemia. The disturbance causes the heart to switch from fatty acid as its primary fuel to glucose. The new tracer test keys in on this metabolic disturbance and seemingly remembers the imprint of an episode of reduced blood flow long after the episode, a process that is called "ischemic memory."