EVALUATION OF PATTERNS OF PERFUSION AND METABOLISM IN DOBUTAMINE-RESPONSIVE MYOCARDIUM

Objectives. We investigated the patterns of perfusion and metabolism i n dysfunctional myocardium whose contractility improved with dobutamin e. Background. Clinical studies have suggested that dobutamine echocar diography can identify hibernating myocardium, but laboratory studies suggest that reduced perfusion limits the response to dobutamine. Meth ods. Twenty five patients with coronary disease and ventricular dysfun ction underwent low (5 and 10 mu g/kg body weight per min) and high do se (maximum of 50 mu g/kg per min) dobutamine echocardiography and pos itron emission tomography (PET) using nitrogen-13 (N-13) ammonia and f luorine-18 fluorodeoxyglucose (FDG) for imaging of perfusion and metab olism. Wall motion and tracer uptake were scored in 16 left ventricula r segments. Results. Perfusion and metabolism were normal in 56.4%, mi ldly reduced in 29.1% and mismatched (reduced perfusion, preserved FDG uptake) in 14.5% of dysfunctional segments viable on PET. Wall motion improved with dobutamine in 89 dysfunctional segments (62 at low dose , 27 only at peak dose), and 86 of these (97%) were viable on PET. Imp rovement in wall motion with dobutamine was more common in segments wi th normal perfusion and metabolism (56.5%) than in those with mildly r educed tracer uptake (28.5%, p < 0.001) and those with mismatch (32%, p = 0.03). All the segments with a biphasic response were supplied by vessels with greater than or equal to 70% stenosis, and 88% had normal perfusion and metabolism. Conclusions. The majority of viable segment s dth rest dysfunction had normal perfusion and metabolism, suggesting that myocardial stunning was common. Improvement of wall motion at lo w and high doses of dobutamine was highly correlated,vith myocardial v iability on PET and was more common in myocardium with normal perfusio n. A biphasic response to dobutamine identified segments with normal p erfusion and metabolism supplied by severely diseased vessels.