Comparison of hemodynamic determinants for myocardial oxygen consumption under different contractile states in human ventricle

Abstract

Background. Recently, several indexes such as tension-time index (TTI), tension-time or force-time integral (FTI), rate-pressure product (RPP), pressure-work index (PWI), and systolic pressure-volume area (PVA) have been developed as predictors of myocardial oxygen consumption in experimental and clinical studies. However, it is still unclear whether these indexes are reliable predictors of myocardial oxygen consumption under various contractile states in human hearts. Methods and Results. We assessed the relation between TTI, FTI, RPP, PWI, and PVA and myocardial oxygen consumption per beat (V̇o2) in 13 patients with heart disease during volume loading. Left ventricular (LV) volume and pressure were measured simultaneously by the conductance catheter with the tipped micromanometer technique. V̇o2 was calculated from arterial coronary sinus oxygen content difference, and coronary sinus blood flow was measured by the thermodilution method. After z transformation of the correlation coefficients, mean z value for the V̇o2-PVA relation (1.83±0.60) was greater than those for the V̇o2-TTI relation (1.22±0.66; p<0.005), V̇o2-FTI relation (1.18±0.61; p<0.05), V̇o2-RPP relation (0.95±0.65; p<0.05), and V̇o2-PWI relation (1.24±0.58; p<0.05). During dobutamine infusion (5 μg · kg-1 · min-1) in five of the 13 patients, V̇o2 also correlated best with PVA (z=1.70±0.89) compared with TTI (z=1.43±0.86), FTI (z=1.48±0.95), RPP (z=1.00±0.53), and PWI (z=0.88±0.80). The contractile efficiency (38±14% to 38±20%), the reciprocal of the slope of the V̇o2-PVA relation, remained unchanged, whereas the V̇o2,PVA 0.8 (V̇o2 at PVA=0.8 J per beat/100 g LV) increased from 1.48±1.16 to 2.06±1.13 J per beat/100 g LV (p<0.05). These results show the parallel upward shift of the V̇o2-PVA relation during dobutamine infusion. Because increases in the V̇o2-intercept represent the V̇o2 for the increased excitation-contraction (E-C) coupling associated with the augmented contractile state, the parallelism of the V̇o2-PVA relation could discriminate between V̇o2 for mechanical work (PVA-dependent V̇o2) and V̇o2 for E-C coupling (PVA-independent V̇o2). Conclusions. The results of the present study indicate that PVA is a reliable and valuable predictor of myocardial oxygen consumption under different contractile states in human hearts. The V̇o2-PVA relation could provide useful information about mechanoenergetics in diseased human hearts.