Critical collateral bloodflow level for salvage of ischemic myocardium

Twenty-three dogs with occluded coronary arteries were retrospectively analyzed in an attempt to estimate the critical collateral bloodflow for salvaging ischemic myocardium. Under pentobarbital anesthesia a coronary branch was occluded by an embolus. The field of the occluded artery (ischemic zone) was determined by subsequent autoradiography of 141cerium (141Ce) labelled microspheres injected into the left ventricle, 2 to 8 mins after embolization. The regional myocardial bloodflow was also measured by microspheres. Dogs were sacrificed after 24 h (n = 9) or 48 h (n = 14) of coronary occlusion and the data pooled. Size of the necrotic myocardium, determined by tetrazolium staining, was expressed as a percentage of the ischemic zone (percentage necrosis). Percentage necrosis (%N) was negatively correlated with the collateral flow as a percentage of the flow of the corresponding nonischemic layer (%CF) whether the subendocardial, midmyocardial or subepicardial collateral flow was considered. For subendocardium, %N = 81.15 - 3.96%CF and r = -0.77; for midmyocardium, %N = 80.60 - 1.98%CF and r = -0.71; and for subepicardium, %N = 90.23 - 1.03%CF and r = -0.90, all P less than 0.01. Because there is a transmural gradient of the collateral flow in the ischemic zone, the zero necrosis intercept of the regression line of percentage necrosis-subendocardial percentage collateral flow plot would represent the minimal flow level for myocardial survival. This intercept was calculated to be 20.5% normal with a 95% confidence interval between 10.4% and 37.5% (df = 21).(ABSTRACT TRUNCATED AT 250 WORDS)