This study assesses regional differences in myocardial blood flow and 18F-fluorodeoxyglucose (FDG) retention in acutely stunned porcine myocardium.
Methods: Two groups of swine were used for these studies. In Group 1, 15 animals underwent stunning induced by 20 min of myocardial ischemia followed by reperfusion. Regional function was measured with ultrasonic crystals and myocardial blood flows were quantitated with radiolabeled microspheres. Within 2 hr postischemia, myocardial blood flow images were obtained with 15O-water, and FDG uptake was estimated with dynamic scanning. In a second group of five animals, PET scanning was performed 2 hr poststunning and repeated 24 hr later.
Results: In Group 1 animals, postischemic reductions were noted in both regional shortening and myocardial oxygen consumption. Myocardial blood flows at baseline were 0.72 +/- 0.05 ml/min/g in the LAD region and 0.83 +/- 0.07 ml/min/g in the non-LAD region; following reperfusion they were 0.70 +/- 0.07 ml/min/g and 0.89 +/- 0.08 ml/min/g, respectively. Within 2 hr of reperfusion, FDG retention was significantly lower in the LAD region compared with remote myocardium. As with Group 1, Group 2 also showed a reduction in FDG uptake in acutely reperfused myocardium relative to remote regions. Twenty-four hours later, FDG uptake within reperfused regions increased to 0.31 +/- 0.04 mumole/min/g and did not differ from remote myocardium.
Conclusion: FDG uptake in acutely stunned swine myocardium is lower than remote regions at a time when regional myocardial blood flows are not dissimilar. This differs from 24 hr following reperfusion in which enhanced FDG uptake may be observed relative to perfusion. Therefore, the time course of metabolic changes following reperfusion needs to be considered in patients undergoing viability studies with PET.