DOBUTAMINE ECHOCARDIOGRAPHY FOR DETERMINING THE EXTENT OF MYOCARDIAL SALVAGE AFTER REPERFUSION - AN EXPERIMENTAL EVALUATION

Background Although dobutamine echocardiography is being increasingly used to determine the presence of viable myocardium in patients who ha ve undergone successful reperfusion therapy, the physiological basis f or such a use has not been clearly defined. Because postischemic myoca rdium has contractile reserve, we hypothesized that the absolute degre e of wall thickening induced by dobutamine during reflow would be dire ctly related to the amount of myocardium that has escaped necrosis. Me thods and Results Three groups of 12 dogs each were studied at baselin e and during 2 to 6 hours of coronary artery occlusion and 15 minutes of reperfusion. In group 1 dogs, which did not receive dobutamine duri ng any of these stages, percent wall thickening at these stages was 32 +/-6%, -2+/-6%, and 5+/-6%, respectively, and there was no relation be tween infarct size and percent wall thickening during reflow (r=.20, P =.51). In group 2 dogs, which received 15 mu g/kg per minute of dobuta mine at all stages, wall thickening at these stages was 40+/-8%, 0+/-8 %, and 19+/-10%, respectively, and a good inverse correlation was note d between infarct size and percent wall thickening during reflow (r=-. 81, P=.001). In group 3 dogs, in which wall thickening during reflow w as measured both before and during infusion of 15 mu g/kg per minute o f dobutamine, it was 5+/-8% and 18+/-14%, respectively, at these stage s. Although the correlation between infarct size and percent wall thic kening was poor in the absence of dobutamine (r=.36, P=.26), an excell ent inverse correlation was noted between the two in the presence of d obutamine (r=-.93, P<.001). A fair inverse correlation was also noted between infarct size and the absolute change in wall thickening induce d by dobutamine (r=-.72, P<.01). Maximal wall thickening was noted at a dobutamine dose of 15 mu g/kg per minute, and lower doses did not el icit thickening in the presence of larger infarcts despite the presenc e of viable myocardium. Conclusions When myocardial necrosis coexists with postischemic myocardial dysfunction and no residual coronary sten osis, 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 post ischemic myocardium is related to the amount of myocardial necrosis.