Hemodynamic and metabolic effects of skin and blood-stream cooling in experimental myocardial infarction with shock

The hemodynamic and metabolic effects of moderate hypothermia (28-30 °C.) induced by skin or blood cooling were studied in dogs with acute myocardial infarction and shock produced by plastic sphere coronary embolization. There was no increase in ventricular fibrillation, asystole or congestive heart failure in the hypothermic animals, whether cooled by skin or blood stream, as compared to animals with acute infarction remaining normothermic for similar periods. All cooled animals demonstrated, upon rewarming, more adequate return of cardiac output, aortic pressure and systemic vascular resistance than did animals remaining normothermic, although skin cooling was associated with metabolic acidosis, slower cooling and less decline in left ventricular work during hypothermia than blood-stream cooling. Chlorpromazine, which diminished shivering, resulted in postrewarming depression of cardiac output and aortic pressure. Skin cooling resulted in apparently favorable hemodynamic alterations in the postrewarming period despite shivering and maintenance of relatively high left ventricular work during hypothermia. It is suggested that benefit may be derived from hypothermia in acute myocardial infarction through physiologic mechanisms in addition to reduction of the oxygen requirement of the left ventricle.