Effect of Atrial and Ventricular Tachycardia on Cardiac Oxygen Consumption

Atrial tachycardia and ventricular tachycardia were induced by electric stimuli applied to the heart in the modified dog heart-lung preparation. Cardiac oxygen consumption was measured by the direct Fick method. Left ventricular output was kept constant at about 900 ml/min and arterial pressure at 100 mm Hg during both atrial and ventricular pacing. An increase of heart rate from 130 to 157 beats per minute in atrial tachycardia, and from 130 to 158 beats per minute in ventricular tachycardia, increased cardiac oxygen uptake by 11.5% and 50% respectively (mean of seven experiments). The greater energy expenditure of the heart in ventricular tachycardia, when compared with atrial tachycardia at equivalent heart rates, was attributed to the asynchrony of fractionate contractions of the ventricular muscle when stimuli are applied to the ventricular surface. Total coronary flow increased in both types of tachycardia, but more in ventricular tachycardia.