Dobutam1ne increases regional myocardial efficiency in normal, but not in stunned myocardium

We tested the hypothesis that inotropic stimulation of postischemic reperfused myocardium would reduce efficiency by increasing regional myocardial 02 consumption more than regional segment work. In 9 open-chest anesthetized dogs, the effect of dobutamine (2.5 - 20 μg /kg/min IV) was investigated before and following a 15 min occlusion of the LAD coronary artery. Regional myocardial segment length and force were measured in the anterior (LAD) and posterior (CFX) regions of the LV myocardium. Work was calculated as the integrated products of force and shortening for each region. Regional myocardial O₂ consumption was obtained from LAD flow and arterial and local venous O₂ saturations. Efficiency was calculated as the ratio regional work / regional MVO₂. Before LAD occlusion, dobutamine elevated regional work by 191 % (from 703±117 to 2046±384 g*mm/min); work was only elevated by 57% in reperfused myocardium (1310±351 to 2058±537). MVO₂ increased from 8.27 ±0.6 to 12.3 ±1.05 ml Oz/min/100g before ischemia, and from 7.2±0.8 to 12.4±1.5 during reperfusion. Regional myocardia! efficiency was markedly increased by dobutamine in pre-ischemic myocardium. Although efficiency was elevated during untreated reperfusion, it was not significantly affected by dobutamine stimulation. It is concluded that functional improvement by dobutamine in stunned myocardium does not increase the oxygen cost of its local contraction.