Inverse relationship between heart rate and myocardial oxygen consumption per beat

Relationship between heart rate and myocardial oxygen consumption per beat was studied in anesthetized open-chest dogs. Myocardial oxygen consumption per minute (MVO(2)) was calculated as the product of the left coronary artery blood flow and coronary arterio-venous oxygen difference. Myocardial oxygen consumption per beat (MVO(2)-Beat) was the quotient of MVO(2) divided by heart rate (HR). HR was varied in 78-210 beats/min with left atrial pacing. Systemic arterial and left ventricular enddiastolic pressure were kept constant, and arterial blood gases were within physiological ranges. Although MVO(2) correlated significantly with HR (r=0.71), MVO(2)-Beat decreased in association with an increase in heart rate. Closer relationship was observed between MVO(2)-Beat and HR; MVO(2)-Beat (ml/100g LV muscle)= -0.00036 + 0.13, r= -0.86, P<0.001. As the results, MVO(2) was represented as a quadratic equation of HR; MVO(2) (ml/min/100g LV muscle)= -0.00036HR(2) + 0.13HR. There was a good correlation (r=0.88) between MVO(2)-Beat and the area under a stroke left ventricular pressure curve. This finding and constant systemic arterial and left ventricular pressure suggest that the inverse relationship between MVO(2)-Beat and HR is mainly due to a reduction in duration of systolic left ventricular wall tension.