Comparison of fluorine-18-fluorodeoxyglucose and tritiated fluoromisonidazole uptake during low-flow ischemia

Fluorine-18-fluoromisonidazole (FMISO) is trapped in hypoxic but viable canine myocardium. Because of the potential for its use as a marker of myocardial viability, we compared FMISO activity to [18F]fluorodeoxyglucose (FDG) activity in the same myocardial samples from eight dogs subjected to 3 hr of moderate regional myocardial ischemia.

Tritiated FMISO was injected 15-30 min after onset of regional ischemia (40%-70% reduction in systolic wall thickening) which was maintained for 3 hr. FDG was injected after 2 hr of ischemia. Myocardial blood flow (MBF) was measured by the radiolabeled microsphere technique at the time of each radiotracer injection. At 3 hr of ischemia, the heart was excised and cut into short-axis slices. One slice encompassing both ischemic and normal tissue was cut into 64 samples. FMISO and FDG activity in each sample were normalized to the mean normal zone activity and further expressed as a function of regional MBF.

FMISO uptake was consistently greater than FDG uptake, although this was significantly different only for MBF, between 40%-60% of normal. When analyzed relative to endocardial-epicardial location, endocardial FMISO uptake was significantly greater in all hypoperfused samples.

These results suggest that FMISO is as sensitive as FDG for detecting myocardial ischemia and could be used for identification of viable myocardium.