BackgroundAlthough dobutamine echocardiography is being increasingly used to determine the presence of viable myocardium in patients who have undergone successful reper-fusion therapy, the physiological basis for such a use has not been clearly defined. Because postischemic myocardium has contractile reserve, we hypothesized that the absolute degree of wall thickening induced by dobutamine during reflow would be directly related to the amount of myocardium that has escaped necrosis.Methods and ResultsThree groups of 12 dogs each were studied at baseline and during 2 to 6 hours of coronary artery occlusion and 15 minutes of reperfusion. In group 1 dogs, which did not receive dobutamine during any of these stages, percent wall thickening at these stages was 32±6%, −2±6%, and 5 ±6%, respectively, and there was no relation between infarct size and percent wall thickening during reflow (r=.20,P=.51). In group 2 dogs, which received 15 μg/kg per minute of dobutamine at all stages, wall thickening at these stages was 40±8%, 0±8%, and 19±10%, respectively, and a good inverse correlation was noted between infarct size and percent wall thickening during reflow (r= −.81,P=.001). In group 3 dogs, in which wall thickening during reflow was measured both before and during infusion of 15 μg/kg per minute of dobutamine, it was 5±8% and 18±14%, respectively, at these stages. Although the correlation between infarct size and percent wall thickening was poor in the absence of dobutamine (r=.36,P=.26), an excellent inverse correlation was noted between the two in the presence of dobutamine (r= −.93,P<.001). A fair inverse correlation was also noted between infarct size and the absolute change in wall thickening induced by dobutamine (r= −.72,P<.01). Maximal wall thickening was noted at a dobutamine dose of 15 μg/kg per minute, and lower doses did not elicit thickening in the presence of larger infarcts despite the presence of viable myocardium.ConclusionsWhen myocardial necrosis coexists with post-ischemic myocardial dysfunction and no residual coronary stenosis, the absolute degree of wall thickening during dobutamine can be used to determine the extent of myocardium that has escaped necrosis. The dose of dobutamine needed to elicit maximal thickening of the postischemic myocardium is related to the amount of myocardial necrosis.