Effects of dobutamine and arbutamine on regional myocardial function in a porcine model of myocardial ischemia

Veterans Affairs Medical Center-San Diego, California 92161.

OBJECTIVES. The present study was performed to determine the mechanisms for catecholamine-induced wall motion abnormalities and to compare the diagnostic efficacy of two catecholamines: arbutamine and dobutamine. BACKGROUND. Catecholamine stress echocardiography is used to induce regional wall motion abnormalities for the detection of coronary artery disease, but the mechanism by which these abnormalities occur is unknown. METHODS. Ten pigs were instrumented with left circumflex coronary artery ameroid constrictors, sonomicrometers to measure transmural wall thickening in the left circumflex (ischemic) and left anterior descending (control) coronary artery beds and a pressure gauge to measure left ventricular pressure and its first derivative (dP/dt). Myocardial blood flow was measured by microspheres. RESULTS. At 38 +/- 6 days (mean +/- SEM) after surgery, percent wall thickening was normal at rest in both beds but abnormal in the left circumflex coronary artery bed during atrial pacing. These findings were associated with reduced myocardial blood flow in the ischemic bed during atrial pacing. Dobutamine infusion increased percent wall thickening, with no differences between the two beds (p = 0.63). In contrast, arbutamine infusion increased percent wall thickening only in the nonischemic bed, with no effect on percent wall thickening in the ischemic bed (p = 0.03). Although the endocardial/epicardial blood flow ratio tended to be reduced in the left circumflex artery bed during catecholamine infusion (p = 0.07), both agents were similar in this effect. Despite differences in function between the beds, there was no difference in transmural myocardial blood flow between the two beds during catecholamine infusion. When examined at matched metabolic demands, arbutamine elicited greater differences in percent wall thickening than dobutamine between the two beds (p < 0.01). CONCLUSIONS. Arbutamine was able to provoke regional differences in function in a manner superior to dobutamine. This occurred independently of altered transmural myocardial blood flow or differences in hemodynamic effects between the agents. Differences in their inotropic properties may be important in explaining their different effects on ischemic myocardium.

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