"Normothermic range" temperature affects myocardial infarct size.
OBJECTIVE
This study tested the hypothesis that small changes in temperature above the hypothermic range may alter myocardial infarct size after acute coronary occlusion-reperfusion. A secondary hypothesis, that a correlation between temperature and infarct size may be independent of an associated change of heart rate, was also evaluated.


METHODS
Eighteen pentobarbitone-anaesthetised, open chest rabbits underwent 30 min coronary artery occlusion and 3 h reperfusion at blood temperatures ranging from 35-42 degrees C, achieved and maintained using surface methods (not paced, group NP). In a second group of 11 animals, heart rate was held constant across the same range of temperatures (paced, group P), before and throughout coronary artery occlusion-reperfusion. Infarct sizes were assessed by the tetrazolium method.


RESULTS
Target temperature was effectively controlled over the duration of the experimental protocol to within +/- 0.25 degrees C. Area at risk did not vary with temperature. Infarct size, normalised to area at risk, was correlated with temperature in both groups (infarct size = 7.9 x temp-250.0, r = 0.75, p = 0.0003, group NP; infarct size = 11.7 x temp-404.5, r = 0.88, p = 0.0004, group P). There was no significant difference between the slopes of these two lines (p = 0.18), indicating that the positive correlation between infarct size and temperature is not related to changes of heart rate.


CONCLUSIONS
Temperatures in the range of 35-42 degrees C affect myocardial infarct size significantly, independent of heart rate.
Chien
G L
GL
Department of Anesthesiology, Oregon Health Sciences University, Portland.
Wolff
R A
RA
Davis
R F
RF
van Winkle
D M
DM
D000818:Animals; D001831:Body Temperature; D008297:Male; D009203:Myocardial Infarction / Q000473:pathology*; D015428:Myocardial Reperfusion Injury / Q000473:pathology*; D009206:Myocardium / Q000473:pathology*; D011817:Rabbits