METABOLISM SUBSTRATE WITH NEGATIVE MYOCARDIAL UPTAKE OF IODINE-123-BMIPP

Iodine-123-BMIPP is an iodinated methyl-branched-chain fatty acid. Low uptake of BMIPP relative to thallium or other perfusion tracer indica tes metabolically damaged but viable myocardium (for example, ischemic but viable myocardium). In some cases, however, negative myocardial u ptake of BMIPP is observed. The main purposes of this study were to as sess the frequency of such BMIPP findings and to clarify metabolism of such cases by using PET, Methods: Among the 1258 patients who underwe nt BMIPP scintigraphy, 11 patients(0.9%) showed negative myocardial up take of BMIPP, Under fasting condition, PET using [C-11]palmitate, 2-[ F-18]fluoro-2-deoxy-D-glucose ([F-18]FDG) and [C-11]acetate was perfor med in nine of these 11 patients. Results: Global myocardial uptake of [C-11]palmitate, expressed as the standardized uptake value, was sign ificantly lower in the patients than in control (3.62 +/- 0.44 versus 5.49 +/- 1.62; p < 0.01). However, the early phase clearance rate of [ C-11]palmitate and oxidative metabolism was not significantly differen t, In the fasting state, PET studies showed increased FDG accumulation in seven of nine patients (high group) and decreased accumulation in two patients (low group). In the high group patients, glucose metaboli sm in the fasting state was similar to that in the normal volunteers a fter glucose loading (K-complex: 0.050 +/- 0.016 versus 0.038 +/- 0.01 5; p = ns). However, low glucose metabolism was noted in the low group patients (K-complex: 0.007 and 0.005). Conclusion: Negative myocardia l uptake of BMIPP is occasionally, but not often, observed. Global upt ake of [C-11]palmitate was decreased in these patient. The majority of these patients showed ''metabolic switching'' from normal free fatty acid metabolism to abnormally enhanced glucose metabolism in the fasti ng state. However, some patients showed decreases in both exogenous gl ucose utilization and free fatty acid uptake in the fasting state.