Myocardial Blood Flow Changes During Low Dose Dobutamine Infusion: Relation to F-18 deoxyglucose uptake In asynergic myocardial regions rendered dysfunctional by chronic hypoperfusion, F-18 deoxyglucose (FDG) is useful in differentiating viable from scarred myocardium. In this study, we determined whether regional myocardial blood flow (MBF) responce during low dose dobutamine (LDD) infusion also differentiates hypoperfused but viable from scarred myocardium when compared to FDG uptake. To this end, 11 pts (mean age 65+/-9 years) with chronic CAD and LV dysfunction (mean LVEF = 32+/-6%) underwent positron emission tomography (PET) with N-13 ammonia (NH3) and FDG. Absolute MBF was computed at rest and during LDD (5microg/kg/min) infusion, using a two compartment NH3 model. Four to five NH3 and FDG PET slices (8 regions per slice) were matched and analyzed for each patient. Rest and LDD N-13 ammonia data were then analyzed according to the magnitude of FDG uptake. FDG (% uptake) N-13 Ammonia (ml/min/g) Rest Low-dose Dobutamine Normal (greater than 80%) 0.64+/-0.18 0.98+/-0.32 Moderate (50-79%) 0.47+/-0.22 * 0.82+/-0.38** Severe (<50%) 0.37+/-0.21 * 0.57+/-0.25** * p=NS, **p<0.001 At rest, MBF was similar in regions with moderately and severely reduced FDG uptake. During LDD infusion, although mean MBF increased in all three categories, the extent of MBF increase was significantly greater in regions with moderately than in regions with severely reduced FDG uptake (0.35+/-0.26 vs 0.20+/-0.30 ml/min/g, p<0.05). Furthermore, 85% of regions with moderately reduced FDG uptake showed mismatch pattern (FDG:MBF greater than or equal to 110). These data suggest that an assessment of MBF responce during LDD infusion may differentiate hypoperfused but viable from nonviable myocardial regions.