Myocardial Blood Flow During Low Dose Dobutamine Infusion: Relation to Thallium Uptake in Asynergic Regions- Different patterns of thallium (TL) uptake are used to detect the presence of scarred or viable myocardium. We sought to examine if these different patterns reflect the magnitude of myocardial blood flow (MBF) during low dose dobutamine (LDD) infusion in asynergic regions. We studied 17 pts with chronic CAD and LV dysfunction (mean LVEF=29+/-8%) who underwent quantitative SPECT stress-redistribution-reinjection TL, PET with N-13 ammonia and FDG, and cardiac cine MRI. Two to five PET, TL and MRI short-axis were matched and analyzed per patient. For each slice, absolute MBF (ml/min/g) at rest and during LDD (5 mcg/kg/min)infusion, using N-13 ammonia and a two-compartment model, and regional TL and FDG uptake were computed, in 8 regions per slice. A total of 208 asynergic regions were studied. MBF during LDD increased significantly in all categories of TL patterns; however, the magnitude of MBF differed among TL categories. Regions with normal TL uptake (0.64+/-0.22) and mild irreversible TL defects (0.57+/-0.25)exhibited significantly higher mean MBF values at rest when compared to regions with moderate (0.48+/-0.24) and severe (0.43+/-0.22) irreversible TL defects (p<0.01). Similarly, during LDD, regions with normal TL uptake (0.93+/-0.32) and mild irreversible TL defects (0.83+/-0.43) exhibited significantly higher mean MBF values when compared to regions with moderate (0.64+/-0.26) and severe (0.56+/-0.29) irreversible TL defects (p<0.01). This implies that the myocardial tissue composition, reflected by regional TL uptake, plays an important role in the magnitude of MBF at rest and during LDD infusion.
