Comparison of low-dose dobutamine-gradient-echo magnetic resonance imaging and positron emission tomography with [18F]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 is sufficient evidence to exclude the presence of viable myocardium in patients with previous myocardial infarction and persisting regional left ventricular akinesia. Demonstration of a dobutamine-induced contraction 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 wall thickening assessed by magnetic resonance imaging (MRI) were compared with corresponding [18F]fluorodeoxyglucose uptake as assessed by positron emission tomography (FDG-PET).

METHODS AND RESULTS

Thirty-five patients with myocardial infarction (infarct age, > 4 months) and regional akinesia or dyskinesia assessed by left ventriculography underwent rest and dobutamine MRI studies (10 micrograms 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 short-axis tomograms. Two definitions of viability, as assessed by MRI, of a segment akinetic at baseline were used: (1) end-diastolic wall thickness of > or = 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 > or = 1 mm. Segments were graded as viable by FDG-PET if FDG uptake was > or = 50% of the maximum uptake in a region with normal wall motion as assessed 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 region was indicated by FDG-PET in 23 of 35 patients (66%), yielding a diagnostic 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 rest. Of these akinetic segments, 234 (48%) had preserved end-diastolic wall thickness, 251 (52%) had a dobutamine-induced contraction reserve, 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 dobutamine-induced wall thickening (r = .42) were similar. Comparison of segmental MRI and FDG-PET gradings indicated that dobutamine-induced wall thickening was a better predictor of residual metabolic activity (sensitivity, 81%; specificity, 95%; positive predictive accuracy, 96% than was end-diastolic wall thickness (sensitivity, 72%; specificity, 89%; positive predictive accuracy, 91%). However, grading a segment as viable if at least one of both MRI parameters fulfilled viability criteria improved the sensitivity (88%) of MRI for FDG-PET-assessed metabolic activity without a major decrease in specificity (87%) or positive predictive accuracy (92%).

CONCLUSIONS

Viable myocardium is characterized by preserved end-diastolic wall thickness and a dobutamine-inducible contraction reserve. Both parameters should be taken into account to maximize the sensitivity of MRI in the detection of regions with signs of viability on FDG-PET images.