Protective effect of body mild hypothermia for acute myocardial infarction in rabbits

Objective:To study the effect of body mild hypothermia for acute myocardial infarction in coronary artery occluded rabbits. Methods: thirty-six rabbits were randomly divided into 2 groups according to the duration of left anterior descending coronary artery occlusion: continuous coronary artery occluded group （CCAO group, n=22） and transient coronary artery occluded group （TCAO group, n=14）. Each group was divided into two sub-groups: mild hypothermia group and the control. Core temperatures were measured with thermistor. The mild hypothermia group received ice cooling around the body and the core temperature was dropped to 32-35℃ after occluded for 30 minutes, while the control group's body temperature were kept 38-40℃. Myocardial area at risk and infarct size were determined with Evans blue dye and triphenyl tetrazolium chloride（TTC）. Results: （1） The total elevated amplitude of ST segment in chest leads V 1, V 3 and V 5 in the mild hypothermia group were lower than that in the control CCAO group （22.8±18.7）mV vs （34.7±19.3）mV, P=0.090; TCAO group （25.8 ±8.5）mV vs （37.7±6.5）mV, P=0.021. （2）The changes of serum CK-MB activities after coronary occlusion in mild hypothermia group were significantly lower than the control groupCCAO group （2672.1±909.1）vs（4192.7±1960.9）U/L,P=0.047; TCAO group（2646.9±1227.3）U/L vs （4787.8±1934.2）U/L,P=0.045. （3） Myocardial infarct size as a percentage of the area at risk（CCAO group 31.3%±7.6% vs 47.9%±6.6%,P＜0.001; TCAO group 21.4%±4.4% vs 35.7%±6.6%,P=0.001）and of the left ventricle size （CCAO group 6.5%±1.3% vs. 11.3%±3.7 %, P＜0.001; TCAO group 4.1%±1.0% vs 7.1%± 2.7%, P=0.029）of CCAO and TCAO groups were smaller than control groups. Conclusions: Mild hypothermia may have the protective effect for acute myocardial infarction and reduce infarct size in rabbits.