DIFFERENCES IN REPERFUSION LENGTH FOLLOWING 30 MINUTES OF ISCHEMIA INTHE RABBIT INFLUENCE INFARCT SIZE, AS MEASURED BY TRIPHENYLTETRAZOLIUM CHLORIDE STAINING

Assessment of myocardial infarct size in acute experimental models is usually done by triphenyltetrazolium-chloride (TTC) staining. A certai n period of reperfusion is mandatory for discrimination of the infarct zone, especially after relatively short ischemic periods. However, it is unclear what the optimal reperfusion time is for full delineation of the infarct following 30 min of myocardial ischemia in the rabbit. This study compares infarct size, assessed by TTC, in anesthetized ope n-chest rabbits subjected to 30 min of coronary artery occlusion follo wed by either 2 (n=14) v 4 (n=14) (protocol 1), or 3 (n=8) v 6 (n=7) h of reperfusion (protocol 2). Area at risk was assessed by blue dye an d necrotic zone by TTC staining. Protocol 1: heart rate and mean blood pressure were comparable in both groups throughout the protocol. Regi onal myocardial blood flows in both the ischemic and non-ischemic zone s during ischemia and after 2 h of reperfusion were comparable between the groups. Regional myocardial blood now in the post-ischemic zone d eteriorated between 2 and 4 h (1.11+/-0.15 v 0.58+/-0.09 ml/min/g, res pectively; P=0.0004) of reperfusion. The size of the area at risk was comparable (0.31+/-0.03 v 0.33+/-0.03 of the LV weight in the 2 and 4 h reperfusion groups). However, the ratio of the necrotic zone to the ischemic zone at risk was 63% larger in the 4 compared to the 2h of re perfusion group (0.31+/-0.04 v 0.19+/-0.03, respectively, P=0.02). Ana lysis of covariance performed on the weight of tissue that developed n ecrosis and the weight of ischemic zone at risk revealed a significant effect of the reperfusion time (P=0.014), Protocol 2: there was no di fference in infarct size between rabbits subjected to three (0.38+/-0. 05 of the area at risk) v 6h (0.41+/-0.07) of reperfusion (P=0.72). An alysis of covariance performed on the weight of tissue that developed necrosis and the weight of ischemic zone at risk did not reveal a sign ificant effect of the reperfusion time. Infarct size as assessed by TT C following 30 min of myocardial ischemia, is smaller when measured 2 h after reperfusion than after 4 h of reperfusion. At least 3 h of rep erfusion is needed to delineate infarct size by tetrazolium staining f ollowing 30 min of ischemia. (C) 1997 Academic Press Limited.