Experimental study on "ischemic memory" of myocardium with different ischemic degrees by ¹⁸F-FDG PET/CT

Objective: Glucose metabolism and ranges of ischemic cardiomyocytes in model rats under fasting or feeding were compared by ¹⁸F-FDG PET/CT, respectively, to investigate the changes of glucose metabolism after myocardial reperfusion, and to determine time window of myocardial "ischemic memory" under feeding.

Methods: The ischemic-reperfusion model rats were established by ligating the left anterior descending coronary artery of rats. In fasting-feeding experiment, long-ischemia rats (n = 10) under fasting or feeding were subjected to ¹⁸F-FDG PET/CT at 24 h after modeling. Ischemic myocardium range and glucose metabolism were compared by calculating volume of interest (VOI), and mean standard uptake value (SUVmean). Under feeding, model rats in short, intermediate and long-ischemia groups were subjected to ¹⁸F-FDG PET/CT at 24, 48, and 72 h and long-ischemia rats were also subjected to ¹⁸F-FDG PET/CT at 96 h, and VOI and SUVmean were calculated and compared.

Results: (1) Under fasting, myocardial ischemic area of model rats showed "focal" ¹⁸F-FDG uptake, while "focal" ¹⁸F-FDG uptake defect appeared in the same area of myocardium under feeding and the difference was not statistically significant (P > 0.05). (2) Under feeding, PET myocardial images of model rats in three groups at 24 h and 48 h showed that there was an ¹⁸F-FDG uptake defect area near the apex of left ventricular wall. The images at 72 h showed that there was no abnormal ¹⁸F-FDG uptake defect area in short and intermediate-ischemia groups, while ¹⁸F-FDG uptake defect area in long-ischemia group disappeared at 96 h. Variance analysis of repeated measures was performed for data of three groups, which showed there was statistical significance between myocardial ischemia degree and "ischemic memory" time window (P < 0.05), and also between myocardial ischemia degree and difference of myocardial defect volume (P < 0.05).

Conclusions: Under feeding, recent myocardial ischemia could be diagnosed by ¹⁸F-FDG PET/CT. Under feeding, "ischemic memory" time window for short and intermediate-myocardial ischemia was at least 48 h and for long ischemia was at least 72 h. This study suggested that as the degree of myocardial ischemia increased, "ischemic memory" time window also extended.