Washout of ⁸²Rb as a marker of impaired tissue integrity, obtained by list-mode cardiac PET/CT: Relationship with perfusion/metabolism patterns of myocardial viability

Purpose Myocardial washout of the potassium analogue ⁸²Rb may indicate tissue impairment. Few studies have evaluated its usefulness for viability assessment, and controversial results were reported. We revisited this topic using list-mode positron emission tomography (PET)/CT. Methods A total of 22 patients with chronic ischemic cardiomyopathy (ICM) and 11 control subjects with normal CT coronary angiogram were studied. Rest ⁸²Rb PET/CT studies were acquired in list mode and resampled to static, gated, and dynamic images. Using a 17-segment model, ⁸²Rb washout was determined by monoexponential fitting of myocardial time-activity curves. In ICM patients, 18Ffluorodeoxyglucose (FDG) studies were obtained in the same session and segments were classified as normally perfused, mismatch, or matched defect. Results ⁸²Rb washout was minimal and homogeneous in control subjects. Normally perfused segments of ICM did not differ (p=0.33). ICM patients had a left ventricular ejection fraction (LVEF) of 25±12%, 25/353 mismatched, and 46/353 matched defect segments. ⁸²Rb washout was higher in hypoperfused vs normal segments (p<0.05), but not different between mismatch and matched defect (p= 0.18). Intraindividual analysis in nine patients showing both FDG mismatch and matched defect confirmed absence of differences. Overall, segmental ⁸²Rb washout correlated inversely with ⁸²Rb uptake (r=-0.70; p<0.05) and less well with FDG uptake (r=-0.31; p<0.05). Conclusion Using state-of-the-art PET/CT technology for myocardial viability assessment, ⁸²Rb washout does not distinguish between perfusion/metabolism patterns of hibernating myocardium and scar. Tissue integrity may be at least partially impaired in hibernation.