Purpose: Positron emission tomography (PET) with (18)F-fluorodeoxyglucose (FDG) has been reported to be unreliable for identifying viable myocardium in acute myocardial infarction (AMI), especially in areas with discordance in myocardial blood flow (MBF) and glucose metabolism. In myocardium with decreased FDG uptake but preserved MBF, referred to as exhibiting reverse mismatch, myocardial viability remains controversial and little is known about the metabolic state. The aims of this study were to clarify substrate use and to estimate myocardial viability in infarct areas exhibiting reverse mismatch.
Methods: Eighteen AMI patients with successful revascularisation were included in this study. Two weeks after onset, (11)C-acetate and (18)F-FDG PET were performed to evaluate regional oxygen consumption (k mono), MBF and glucose metabolism. Free fatty acid (FFA) metabolism was evaluated with (123)I-15-(p-iodophenyl)-3-(R, S)-methylpentadecanoic acid (BMIPP) single photon emission computed tomography (SPECT). To assess wall motion, movement in left ventricular endocardial surface was calculated using ECG-gated (99m)Tc-tetrofosmin SPECT.
Results: The %k mono values in reverse mismatch segments (52.6 ± 13.6%) were not significantly different from those in non-infarct segments (60.4 ± 12.8%, p = 0.071) and normal match segments (preserved MBF and FDG uptake) (58.6 ± 11.6%, p = 0.396), although regional wall motion was more severely impaired (3.06 ± 2.52 mm vs 6.78 ± 3.17 mm, p < 0.0001, and vs 5.30 ± 2.33 mm, p = 0.042, respectively). Compared to segments with reduced match (reduced MBF and FDG uptake), %k mono and %BMIPP uptake were significantly higher in reverse mismatch segments (52.6 ± 13.6% vs 37.4 ± 8.9%, p = 0.0002, and 58.8 ± 10.6% vs 40.2 ± 10.7%, p < 0.0001).
Conclusion: Reverse mismatch in reperfused AMI patients, high oxygen consumption and FFA metabolism were observed despite decreased glucose metabolism. We conclude that reverse mismatch indicated the myocardium with early restoration of MBF and aerobic FFA metabolism.