Validity of myocardial oxygen consumption parameters

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Abstract
The purpose of this study was to examine any reported indices for estimating myocardial oxygen consumption (MV̇O2) under uniform experimental conditions at maximal variation of hemodynamics and MV̇O2. 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 MV̇O2 calculated from 24 indices were compared with directly measured MV̇O2. Throughout a wide range of hemodynamic states, the best correlate with MV̇O2 was found to be the additive parameter Et (r = 0.96). Any indices that do not incorporate potentially important changes of MV̇O2 related to both myocardial contractility and ventricular dimensions show unsatisfactory correlations with MV̇O2 at extreme changes of hemodynamics. Tension-time index (TTI) correlates poorly with MV̇O2 (r = 0.63). This result is due to the neglect of contractility. Pressure-heart rate product (P × HR) correlates with MV̇O2 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 Et 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 MV̇O2. Results are discussed with regard to the clinical application of MV̇O2 indices.