EFFECTS OF DOBUTAMINE ON MYOCARDIAL BLOOD-FLOW, CONTRACTILE FUNCTION,AND BIOENERGETIC RESPONSES DISTAL TO CORONARY STENOSIS - IMPLICATIONSWITH REGARD TO DOBUTAMINE STRESS-TESTING

To determine the effects of dobutamine stimulation on myocardium dista l to a coronary stenosis, transmural spatially localized phosphorus 31 nuclear magnetic resonance measurements of myocardial high-energy pho sphate compounds (adenosine triphosphate and phosphocreatine), inorgan ic phosphate, and blood flow and systolic wall thickening were made in 8 open-chested dogs. Data were collected under (1) control conditions , (2) after the application of a moderate coronary stenosis, (3) durin g infusion of dobutamine with continuing stenosis, and (4) after the r elease of the stenosis with continuing dobutamine. Stenosis was associ ated with concordant reductions of subendocardial blood flow, wall thi ckening, and high-energy phosphate, and mild elevation of inorganic ph osphate; subepicardial measurements were essentially unchanged. During dobutamine infusion, blood flow increased in all myocardial layers. W all thickening returned to control values in the subendocardium and in creased nonsignificantly in the subepicardium. Additional loss of high -energy phosphate occured only in the subepicardium. The data suggest that improved contractile function associated with dobutamine infusion resulted from the inotropic effects of dobutamine and was made possib le by the improved blood flow it produced. The data indicate that meas urements of blood flow and contractile function do not reliably predic t the transmural myocardial metabolic responses to inotropic perturbat ions in the hypoperfused heart. Taken together, the present findings y ield insights with regard to the interpretation of diagnostic dobutami ne stimulation testing with single photon emission tomography, radionu clide angiography, and echocardiography.