Effect of mild hypothermia on cardiac function in rats with experimental cerebral infarction

Tao LI; Chengyan LI; Shaozu YU

ABSTRACT

BACKGROUND:

Mild hypothermia might in some degree affect the functions and metabolism of the vital organs, and its effects can be harmful sometimes but may also be favorable on some other occasions, which remained to be further studied.

OBJECTIVE:

To examine the effect of mild hypotherrnia on cardiac function of rats with experimental cerebral infarction by observing the changes in the cardiac energy reserve and electrocardiogram (ECG) manifestations,as well as the ultrastructural changes of the myocardium.

DESIGN:

Randomized controlled experiment.

SETTING:

Department of Neurology, Renmin Hospital of Wuhan University.MATERIALS This experiment was carried out in the Laboratory of Department of Neurology, Renmin Hospital of Wuhan University. Totally 58SD rats were randomized into sham operation group (n=10), cerebral infarction with normal temperature group (normal temperature group, n=24),cerebral infarction with mild hypothermia treatment group (mild hypothermia group, n=24).

METHODS:

Middle cerebral artery occlusion (MCAO) was induced in normal temperature group and mild hypothermia group with a suture intro duced into the middle cerebral artery of the rats. The rats in- sham opera tion group were only subjected to skin incision and vessel ligation without suture insertion into the middle cerebral artery. The rats in mild hypother mia group were kept at 4 ℃ with their anal temperature maintained at (34±1.0) ℃, while the rats in sham operation group and normal tempera ture group w ere kept at room temperature (20 ℃). Twelve hours later, the levels of myocardial ATP, DTP, adenosine phosphate and energy reserve were determined, and the changes in myocardial ultrastructure were ob served under electron microscope. MAIN OUTCOME

MEASURES:

① Changes of myocardial energy metabolism; ② Changes of cardiac electrophysiology; ③ Ultrastructural changes of the myocardium.

RESULTS:

All the 58 rats survived the operation and all enter the re sult analysis. The levels of myocardial ATP, DTP and energy reserve were significantly lowered in normal temperature group and mild hypothermia 12 hours after the ischemia in comparison with the sham operation group (P ＜ 0.01), but the level of ATP and energy reserve in mild hypothermia group was higher than those of normal temperature group (P ＜ 0.01). No significant difference was noted in ECG abnormality rate between normal temperature group and mild hypothermia group (P ＞ 0.05), but the heart rate was found obviously lower in mild hypothermia group [(290.92±44.18) vs (472.20±12.79) bpm, P ＜ 0.01], with 3 rats showing heart rate less than 150 bpm. Ultrastructural observation revealed the presence of my ocardial ischemic impairment in normal temperature group and mild hy pothermia group, but the impairment in mild hypothermia group was less severe.

CONCLUSION:

Heart rate can be markedly reduced during general mild hypothermia treatment for cerebral infarction to improve myocardial energy reserve and alleviate myocardial ischemia due to cerebral infarction without increasing the abnormality rate of ECG.