Abstract
Various types of induced cardiac arrest have been devised as an aiding measure facilitating open heart surgery. Electrical fibrillation (EF) and anoxic arrest (AA) and now most widely employed in clinical use. However, little work has been done to discuss the relative merits of the two methods due supposedly to discrepancy of the experimental method or of the parameters used by the investigators. The present study was designed to investigate comparatively the response of myocardial metabolism to the two methods under condition that the all variable factors but the method of induced cardiac arrest are maintained at the fixed levels. The effect of each method of induced cardiac arrest on intracellular metabolism of the myocardium was studied in respect of lactic and pyruvic acids metabolism expressed by myocardial "excess lactate" (XL) and changes in redox potential (ΔEh) across the heart. The dogs used in this study were divided into the following two groups : 1. EF-group (8 dogs), in which electrical fibrillation was induced for 45 minutes by applying an alternating current. 2. AA-group (7 dogs), in which intermittent anoxic arrest for 15 minutes was repeated 3 times with 2 intervals of a 5-minute's release. During induced cardiac arrest, the systemic circulation was maintained by means of total cardiopulmonary bypass using a SIGMAMOTOR Model TM-2 as a pump and one of several types of sheet oxygenator. The following special considerations were given in order to keep the experimental conditions settled : 1) In each experiment of the both groups, cardiac arrest was induced for the same duration of 45 minutes, which is the time used most generally in clinical application. 2) Mild hypothermia at the same temperature was applied to all dogs in the both groups, for minimizing the unfavorable effect of normal body temperature on metabolism. the mean rectal temperature was 33.0°C at control, while it was 30.5°C at the end of the experiment. 3) Perfusion rate in total cardiopulmonary bypass was 60-70 ml/min/kg. 4) To maintain appropriate systemic circulation, only donor blood primed in the extracorporeal circuit at the start was used with avoidance of any kinds of drugs except the anesthetics and of any additional blood transfusion which might disturb the measurements of lactate and pyruvate.
