SIGNIFICANCE OF DEFECT SEVERITY IN TECHNETIUM-99M-MIBI SPECT AT REST TO ASSESS MYOCARDIAL VIABILITY - COMPARISON WITH FLUORINE-28-FDG PET

The pathophysiological significance of Tc-99m-MIBI uptake at rest for assessing myocardial viability in patients with coronary artery diseas e (CAD) is still controversial. Therefore, we studied the relationship of (TC)-T-99m-MIBI uptake at rest and preserved or absent uptake of ( 18)FDG as assessed with PET in 111 consecutive patients after overnigh t withdrawal of their antianginal medication. Methods: Each ventricle was evaluated in 13 segments derived from 25 regions of interest (ROIs ) in short-axis cuts and (18)FDG uptake was normalized to the intraind ividual normal reference ROI (ROI with maximal = 100% Tc-99m-MIBI upta ke). Segments with a normalized (18)FDG uptake >70% were defined as vi able while segments with a (18)FDG uptake <50% were defined as nonviab le. Results: Five to 11% of segments with Tc-99m-MIBI uptake at rest l ess than or equal to 30% of peak activity were viable and 80%-84% nonv iable. Of moderate to severe Tc-99m-MIBI defects at rest (31%-70% of p eak), 13%-61% were viable. Segmental Tc-99m-MIBI uptake and normalized (18)FDG uptake were linearly correlated (r = 0.61, n = 1443, p < 0.00 1). In segments revealing severely reduced Tc-99m-MIBI uptake (less th an or equal to 50% of peak) the correlation was considerably lower (r = 0.44, n = 295, p < 0.001). Conclusions: In patients with CAD, Tc-99m -MIBI uptake underestimates myocardial Viability in comparison to (18) FDG-PET, Myocardial Tc-99m-MIBI uptake therefore appears to reflect my ocardial blood flow rather than myocardial viability. Patients with mo derate and severe Tc-99m-MIBI defects at rest may benefit from additio nal metabolic PET imaging prior to final therapeutic decisions.