ISCHEMIC EVENT CHARACTERISTICS DETERMINE THE EXTENT OF MYOCARDIAL STUNNING IN CONSCIOUS DOGS

Both the severity and duration of postischemic myocardial dysfunction (''stunned'' myocardium) are unpredictable and may vary considerably b etween subjects that underwent apparently similar ischemic insults. To explain this heterogeneous response of the heart to ischemia and repe rfusion, we investigated the determinants of stunning in conscious dog s. Twenty-five dogs were chronically instrumented for measurement of g lobal and regional myocardial performance (wall thickening) and myocar dial perfusion (coloured microspheres). A hydraulic occluder was posit ioned around the LAD coronary artery. Conscious dogs were subjected to acute coronary artery occlusions of predetermined duration (2, 5 and 10 min), followed by complete reperfusion. Multiple regression analysi s identified the following variables as determinants of postischemic c ontractile recovery: 1) the duration of ischemia (p < 0.01), 2) the am ount of collateral perfusion (p = 0.01) and 3) left ventricular end-di astolic pressure during ischemia (p < 0.01). Neither the severity of r egional dyskinesia during ischemia nor indices of global systolic hemo dynamic performance correlated with the rate of recovery. Our data con firm that myocardial stunning relates primarily to the intensity of pr eceding ischemia. Variations in the preexisting level of collateral pe rfusion may result in markedly different recovery profiles. Except for LV end-diastolic pressure during ischemia, indices of global and regi onal cardiac performance fail to predict the severity of postischemic contractile failure.