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
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