Background: Enhanced uptake of the glucose analogue 18F-fluorodeoxyglucose (FDG) in relation to flow has been proposed as an accurate method of identifying viable myocardium. The evaluation of myocardial oxidative metabolism could be an alternate way to identify reversible injury. The aim of the present study was to investigate in patients with reperfused anterior infarction whether differences in regional oxidative metabolism exist among regions with and without flow-metabolism mismatch.
Methods and results: Fifteen patients with reperfused anterior myocardial infarction were studied between 2 weeks and 3 months after the acute event. Regional myocardial blood flow (13N-ammonia; three-compartment model), oxidative metabolism (11C-acetate; monoexponential clearance), and glucose uptake (FDG, linear graphic analysis) were evaluated with dynamic positron emission tomography. Flow-metabolism patterns were used to differentiate reversibly (FDG/flow greater than 1.2) from irreversibly injured myocardium (FDG/flow less than 1.2) using circumferential profile technique. Relative 13N-ammonia uptake was reduced in 71 of 90 anterior and/or septal segments, including 24 with (seven patients) and 38 without (eight patients) flow-metabolism mismatch. Acetate clearance (k), reflecting oxidative metabolism, was reduced by 51% in the center of the infarct area versus remote segments (27 +/- 12 versus 55 +/- 13 min-1.10(-3), p less than 0.001). Compared with infarct segments without flow-metabolism mismatch, segments exhibiting increased glucose uptake relative to flow had faster acetate clearance (35 +/- 14 versus 23 +/- 9 min-1.10(-3), p less than 0.01). Similarly, myocardial blood flow was better preserved in segments with flow-metabolism mismatch (54 +/- 13 versus 45 +/- 8 ml/min/100 g, p less than 0.01) compared with segments without mismatch. However, at similar levels of hypoperfusion, there was no significant difference in acetate clearance among segments with and those without flow-metabolism mismatch: 37 +/- 14 versus 41 +/- 15 min-1.10(-3), respectively. A positive correlation (r = 0.89, p less than 0.001) was found between absolute myocardial blood flow and acetate clearance, regardless of the flow-metabolism pattern.
Conclusions: In patients with reperfused myocardial infarction studied between 2 weeks and 3 months after the acute event, regional oxidative metabolism is reduced in proportion to residual myocardial blood flow and does not differ significantly among similarly hypoperfused segments with and without flow-metabolism mismatch.