Induced hypothermia in dogs with acute myocardial infarction and shock

Acute myocardial infarction with shock (AMI/S) was produced in 46 anesthetized "closed-chest" dogs by catheter injection of metallic mercury into the circumflex coronary artery. Twenty-four dogs were kept normothermic and 22 were maintained at 32 degrees C. Nine of the latter were rewarmed to 37 degrees C. and the experiments then were terminated, so that true survival time was arbitrarily shortened. Including these dogs, the survival time was three times longer than in the normothermic series (p less than 0.001). Hypothermia reduced heart rate (HR) by 34 percent, oxygen consumption by 38 percent, and myocardial oxygen consumption by an estimated 30 to 40 percent, while cardiac output (CO), stroke volume, and stroke work were unchanged. Left ventricular end-diastolic pressure (LVEDP) was reduced by 40 percent during hypothermia (p less than 0.05) and increased by 60 percent on rewarming. HR during rewarming increased substantially more than CO and thereby significantly reduced stroke volume.