Validity of myocardial oxygen consumption parameters

The purpose of this study was to examine any reported indices for estimating myocardial oxygen consumption (MV̇O 2 ) under uniform experimental conditions at maximal variation of hemodynamics and MV̇O 2 . One hundred sixty‐two steady states were analyzed in 10 closed‐chest dog experiments. Myocardial blood flow was directly measured by a differential pressure catheter in the coronary sinus. The indirect values of MV̇O 2 calculated from 24 indices were compared with directly measured MV̇O 2 . Throughout a wide range of hemodynamic states, the best correlate with MV̇O 2 was found to be the additive parameter E t (r = 0.96). Any indices that do not incorporate potentially important changes of MV̇O 2 related to both myocardial contractility and ventricular dimensions show unsatisfactory correlations with MV̇O 2 at extreme changes of hemodynamics. Tension‐time index (TTI) correlates poorly with MV̇O 2 (r = 0.63). This result is due to the neglect of contractility. Pressure‐heart rate product (P × HR) correlates with MV̇O 2 with r = 0.86. Better results for TTI and P × HR, as reported in previous works, are reproducible by dividing our data into two groups of different inotropic states. At normal and moderate inotropic stimulation the correlation for TTI rises to r = 0.96, and for P × HR to r = 0.91. This augmentation is to be referred to the close relationship (r = 0.92) of peak ventricular pressure to maximum rate of pressure rise in this group. The additive parameter E t is the best, both at moderate (r = 0.97) and at maximal inotropic stimulation (r = 0.87), and is to be preferred for indirect estimation of MV̇O 2 . Results are discussed with regard to the clinical application of MV̇O 2 indices.