Regional oxygen consumption and supply in the dog heart: Effect of atrial pacing

The effects of atrial pacing on the relationship of O₂ supply to demand were studied on a regional basis in the dog heart. Experiments were conducted on fourteen hearts, seven in control pentobarbital-anesthetized, open-chest dogs and seven in dogs paced at 225 beats/min. Regional O₂ extraction was determined by a microspectrophotometric method, and coronary blood flow was measured with radioactive microspheres. There was an 89% increase in coronary blood flow, a small but significant decrease in O₂ extraction, and an increase in O₂ consumption with atrial pacing. With pacing the increase in blood flow and the decrease in O₂ extraction were uniform throughout the heart. In control hearts, right ventricular blood flow and O₂ consumption were lower than the mean in the septal or left ventricular free wall. In the left ventricular free wall in control, the subepicardial region had a lower O₂ consumption and O₂ extraction than the subendocardial region. These differences were also preserved during pacing. Due to the large increase in coronary blood flow, the relationship of oxygen supply to demand was improved by atrial pacing.