Epicardial Temperature is a Major Predictor of Myocardial Infarct Size in Dogs

To determine whether epicardial temperature varies among anesthetised, open-chest dogs,and, if so, whether such variation has a measurable effect on myocardial infarct size, 35 open-chest mongrel dogs underwent 60 min of circumflex coronary artery occlusion and 3 h of reperfusion. Infarct size was measured using triphenyl tetrazolium chloride (TTC) macrochemistry. Known predictors of infarct size including area-at-risk (AAR) and collateral blood flow (CBF) were measured. Epicardial temperature was monitored using a temperature probe placed in the pericardial space adjacent to the posterior surface of the heart. In each individual dog, epicardial temperature was nearly constant throughout the period of coronary occlusion. Amongst dogs, however, epicardial temperature ranged from 35.5–41.0°C. By multiple regression analysis, infarct size was better predicted by the combination of temperature and CBF than by CBF alone. “Low-T” (35.5–38.0°C,n=17) and “high-T” (38.1–41.0°C,n=18) subgroups were compared by analysis of covariance (ANCOVA), using infarct size as the dependent variable and CBF as the independent variable. Following adjustment of infarct size for CBF, infarct size in the low-T subgroup was only 53%vthat in the high-T subgroup (16.9±2.7%v31.9±5.0% of AAR,P<0.001). Thus, in open-chest dogs, relatively minor variation in epicardial temperature had major effects on myocardial infarct size. We conclude that myocardial temperature is an independent predictor of infarct size in dogs. Although such variation could confound studies of the therapeutic efficacy of proposed cardioprotective interventions, controlling for temperature variation in such studies should reduce the likelihood of false positive or negative results.