Imaging Tracer Shows Cause of Chest Pain

These findings may help clinicians 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 is something else, such as indigestion. The findings of the study are published in the October 4, 2005, issue of the journal Circulation and are now available on the online edition of the journal.

Researchers at the University of Maryland Medical Center (College Park, US) assessed the radioactive tracer for this study, known by the brand name Zemiva (iodofiltic acid I 123) and developed by Molecular Insight Pharmaceuticals, (Cambridge, MA, USA). Zemiva binds a fatty acid to a radioisotope that is injected in the patient. The researchers used single photon emission computed tomography (SPECT) imaging to assess the tracer in this study.

The heart typically utilizes fatty acid as its main fuel source for energy. Decreased blood flow to the heart, caused either by blocked or narrowed arteries or increased demand on the heart during strenuous exercise, triggers a metabolic disturbance that slows down or stops the way fatty acid is normally utilized. This condition is known as myocardial ischemia. The disturbance causes the heart to switch from fatty acid as its primary fuel to glucose. The new tracer test hones in on this metabolic disturbance and apparently remembers the imprint of an episode of reduced blood flow long after the episode, a process that is called "ischemic memory.”

Thirty-two patients were enrolled in the study. To determine the accuracy of images acquired by Zemiva, the researchers first identified patients who had evidence of myocardial ischemia on a treadmill using a standard tracer, thalium, to produce SPECT images. Later on, SPECT images of the same patients were captured with the new tracer injected at rest (without repeating the treadmill exercise), but no more that 30 hours after the exercise thalium test. The exercise-induced thalium-based images were compared with the rest-injected Zimeva images. The comparison showed the two tracers pointed to the same abnormality in the heart in over 90% of the cases. This suggests that disturbances in fatty acid metabolism can persist up to 30 hours after an ischemic episode, which can be imaged with the new tracer Zemiva.



Related Links:
University of Maryland Medical Center
Molecular Insight Pharmaceuticals