COMPARISON OF LOW-DOSE DOBUTAMINE GRADIENT-ECHO MAGNETIC-RESONANCE-IMAGING AND POSITRON EMISSION TOMOGRAPHY WITH [F-18] FLUORODEOXYGLUCOSE IN PATIENTS WITH CHRONIC CORONARY-ARTERY DISEASE - A FUNCTIONAL AND MORPHOLOGICAL APPROACH TO THE DETECTION OF RESIDUAL MYOCARDIAL VIABILITY

Background There have been conflicting reports of whether substantial myocardial thinning alone as an indirect sign of myocardial scarring i s sufficient evidence to exclude the presence of viable myocardium in patients with previous myocardial infarction and persisting regional l eft ventricular akinesia. Demonstration of a dobutamine-induced contra ction reserve in postischemic viable but akinetic myocardium may serve as a direct indicator of myocardial viability. In the present study, end-diastolic wall thickness at rest and dobutamine-induced systolic w all thickening assessed by magnetic resonance imaging (MRI) were compa red with corresponding [F-18]fluorodeoxyglucose uptake as assessed by positron emission tomography (FDG-PET). Methods and Results Thirty-fiv e patients with myocardial infarction (infarct age, >4 months) and reg ional akinesia or dyskinesia assessed by left ventriculography underwe nt rest and dobutamine MRI studies (10 mu g dobutamine . min(-1) . kg( -1)) and FDG-PET followed by segmental analyses of end-diastolic wall thickness, systolic wall thickening, and FDG uptake in corresponding s hort-axis tomograms. Two definitions of viability, as assessed by MRI, of a segment akinetic at baseline were used: (1) end-diastolic wall t hickness of greater than or equal to 5.5 mm (the mean minus 2.5 SD of a healthy control group [n=21]) and (2) evidence of dobutamine-induced systolic wall thickening greater than or equal to 1 mm. Segments were graded as viable by FDG-PET if FDG uptake was greater than or equal t o 50% of the maximum uptake in a region with normal wall motion as ass essed by left ventriculography. Preserved end-diastolic wall thickness in akinetic regions was found in 17 of 35 (48%) patients at rest, and functional recovery within the infarct region was found in 19 of 35 ( 54%) patients during dobutamine infusion. Viability of the infarct reg ion was indicated by FDG-PET in 23 of 35 patients (66%), yielding a di agnostic agreement between FDG uptake and myocardial morphology in 29 of 35 (83%) and between dobutamine-induced contraction reserve and FDG -PET in 31 of 35 (89%). Of 2200 segments, 482 (22%) were akinetic at r est. Of these akinetic segments, 234 (48%) had preserved end-diastolic wall thickness, 251 (52%) had a dobutamine-induced contraction reserv e, and 299 (62%) were graded as viable by FDG-PET. Correlations of FDG uptake with end-diastolic wall thickness at rest (r=.48) and with dob utamine-induced wall thickening (r=.42) were similar. Comparison of se gmental MRI and FDG-PET gradings indicated that dobutamine-induced wal l thickening was a better predictor of residual metabolic activity (se nsitivity, 81%; specificity, 95%; positive predictive accuracy, 96%) t han was end-diastolic wall thickness (sensitivity, 72%; specificity, 8 9%; positive predictive accuracy, 91%). However, grading a segment as viable if at least one of both MRI parameters fulfilled viability crit eria improved the sensitivity (88%) of MRI for FDG-PET-assessed metabo lic activity without a major decrease in specificity (87%) or positive predictive accuracy (92%). Conclusions Viable myocardium is character ized by preserved end-diastolic wall thickness and a dobutamine-induci ble contraction reserve. Both parameters should be taken into account to maximize the sensitivity of MRI in the detection of regions with si gns of viability on FDG-PET images.