Myocardial temperature reduction attenuates necrosis after prolonged ischemia in rabbits

Objective: Previously we observed that a large reduction in infarct size wa s attained by cooling the risk region of the: heart, either before or early after the onset of a 30-min coronary artery occlusion. While this is a sta ndard duration of ischemia used in the rabbit model of infarction, it may n ot reflect the situation of patients who are reperfused late. The effects o f regional hypothermia with a longer duration of ischemia, and when the int ervention is applied later, are unknown. This study tests the hypothesis th at a local reduction in cardiac temperature protects myocardium during prol onged ischemia (2 h) even if begun well after coronary artery occlusion. Me thods: Anesthetized rabbits received 2 h of coronary artery occlusion and 3 h of reperfusion. Rabbits were randomly assigned to a treated group: topic al myocardial cooling starting 30 min after coronary occlusion (n=14), or c ontrol group, no intervention (n =12), Myocardial temperature in the risk z one, hemodynamics and regional myocardial blood how were measured. Results: Ischemic zone temperature was similar in both groups at 30 min post occlus ion, but the cooling maneuver produced a reduction in temperature in the ri sk region of the treated group such that myocardial temperature was reduced an average of 10 degrees C between 30 and 60 min of coronary artery occlus ion. Myocardial temperature in the control group remained within 0.3 degree s C of baseline during coronary artery occlusion and into reperfusion. Core temperatures were similar in both groups. Hemodynamic parameters and colla teral blood flow during occlusion were also equivalent in both groups. Afte r 120 min of coronary occlusion, necrosis in the control group comprised 72 +/-38 of the ischemic risk region. However, in cooled hearts, infarct size, expressed as a fraction of the risk region was significantly lower. Infarc t size in this group averaged 59+/-3% of the risk region (p<0.004 vs. contr ols), and thus cooling resulted in a salvage of approximately 18% of the ri sk region. Conclusion: These results show that reducing myocardial temperat ure protects ischemic myocardium during a long duration of ischemia even if initiated after coronary artery occlusion. (C) 1998 Published by Elsevier Science B.V. All rights reserved.