Contractile versus microvascular reserve for the determination of the extent of myocardial salvage after reperfusion: The effect of residual coronary stenosis

Background: We hypothesized that microvascular reserve is a better indicator of the extent of viable myocardium postinfarction than contractile reserve, especially in the presence of the residual stenosis of the infarct- related artery. Methods and Results: Fifteen dogs with various infarct sizes were studied after reperfusion. Contractile reserve, studied by use of dobutamine echocardiography, and microvascular reserve, studied by use of myocardial echocardiography, were measured both before and after creation of a stenosis. In the absence of a stenosis, the relation between infarct size, expressed as percent of risk area, and wall thickening improved with increasing doses of dobutamine (r=.41, .71, and .90 for 5, 10, and 15 μg·kg^-1·min^-1, respectively; P<.01 for dobutamine 15 μg·kg^{- 1}·min^-1). In the presence of a stenosis, however, the relation was poor for all doses of dobutamine (r=.22, .57, and .32 for 5, 10, and 15 μg·kg^{- 1}·min^-1, respectively; P<.01 for 15 μg·kg^-1·min^-1 dobutamine in the absence of a stenosis). There was fair correlation between infarct size and perfusion defect size on myocardial contrast echocardiography after reperfusion (r=.82), with the defect size underestimating infarct size by approximately 20%. This relationship improved (P<.01) during infusions of both adenosine (r=.99) and dobutamine (r=.94) in the absence of a stenosis. The correlation between infarct size and perfusion defect on myocardial contrast echocardiography also remained good in the presence of a stenosis (r=.95 and .81 for adenosine and dobutamine, respectively; P=NS compared with stenosis). Conclusions: Microvascular reserve is superior to contractile reserve for definition of the spatial topography of necrosis and hence the extent of viable myocardium within the infarct bed after reperfusion, particularly when a residual stenosis is present in the infarct-related artery.