Cardiac function and myocardial metabolism during tachycardia induced by atrial and ventricular pacing

We studied atrial and ventricular pacing-elicited tachycardia in mongrel adult dogs to evaluate ensuing changes in cardiac function and myocardial metabolism. The aortic pressure, left ventricular pressure, and left ventricular end diastolic pressure were measured under anesthesia. Using an electromagnetic flow-meter, coronary blood flow and aortic blood flow were recorded simultaneously with the recording of ECG. Atrial and ventricular pacing (1.5 times the basic heart beat) were performed using a catheter introduced via the jugular vein and positioned in the coronary venous sinus. Aortic blood and coronary venous blood were sampled for determination of blood oxygen concentrations and lactic acid concentrations. The results showed that oxygen extraction changed little compared with the control study on atrial pacing (AP) and ventricular pacing (VP) whereas the lactate uptake showed little change in the AP control study but decreased slightly in the VP study. It appears that aerobic metabolism occurs during both AP and VP when the pacing rate is not more than 1.5 times the basic heart beat.