Validity of myocardial oxygen consumption parameters.

The purpose of this study was to examine any reported indices for estimating myocardial oxygen consumption (MVO2) under uniform experimental conditions at maximal variation of hemodynamics and MVO2. One hundred sixty-two steady states were analyzed in 10 closed-chest dog experiments. Myocardial blood flow was directly measured by a different pressure catheter in the coronary sinus. The indirect values of MVO2 calculated from 24 indices were compared with directly measured MVO2. Throughout a wide range of hemodynamic states, the best correlate with MVO2 was found to be the additive parameter Et (r = 0.96). Any indices that do not incorporate potentially important changes of MVO2 related to both myocardial contractility and ventricular dimensions show unsatisfactory correlations with MVO2 at extreme changes of hemodynamics. Tension-time index (TTI) correlates poorly with MVO2 (r = 0.63). This result is due to the neglect of contractility. Pressure-heart rate product (P X HR) correlates with MVO2 with r = 0.86. Better results for TTI and P X 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 X 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 E1 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 MVO2. Results are discussed with regard to the clinical application of MVO2 indices.