Influence of ventricular pacing on myocardial oxygen tension

The influence of heart rate on cardiac output, oxygen consumption, and myocardial activity has been widely investigated. However, the influence of heart rate on myocardial oxygen tension ( pO 2) remains unclear. Since the introduction of flexible pO 2 micro catheters to measure partial oxygen tension in a working muscle, it is possible to investigate the influence of heart rate on myocardial oxygen tension. Intraoperatively, a flexible pO 2 micro catheter was positioned in the mid-myocardium of 8 male farm pigs. The heart rate was varied via an external pacer from base rate up to fibrillation and the corresponding myocardial pO 2 was measured. Within 2 min, the myocardial pO 2 adjusted to a change in heart rate. In this animal model, an optimal myocardial pO 2 was observed at 109 bpm. A further increase in heart rate led to a decrease in myocardial pO 2. When the heart rate was reaching the level of a fibrillation, pO 2 dropped to zero. In young healthy pigs – with a normal blood vessel regulation and the pharmacologic and experimental conditions used in this study – a significant relation between myocardial pO 2 and heart rate was observed. Myocardial oxygen tension increased during cardiac pacing until a heart rate of 109 bpm. Thereafter a decline of pO 2 occurred. Each change in heart rate resulted in a corresponding change of pO 2 within roughly 2 min.