Depressed contractile state and increased myocardial consumption for non-mechanical work in patients with heart failure due to old myocardial infarction.

OBJECTIVE

The aim was to characterise the impaired myocardial mechanoenergetics in patients with heart failure due to old myocardial infarction by using the oxygen consumption versus left ventricular pressure--volume area (PVA) relationship.

METHODS

The VO2-PVA relationship was assessed in 15 patients: group N consisted of seven patients with vasospastic angina pectoris whose left ventricular ejection fractions were normal [72 (SD 8)%], and group F consisted of eight patients with old myocardial infarction whose left ventricular ejection fractions were reduced [45(11)%]. Left ventricular volume and pressure were measured by the conductance catheter method. VO2 was measured by thermodilution.

RESULTS

Linear VO2-PVA relationships with dextran infusions were obtained in both groups (median r = 0.92 v 0.90). There was no difference in the slope between the two groups. There was a positive correlation between Emax and VO2 at median PVA (VO2,PVA0.8) in group N. Emax, an index of left ventricular contractility, was significantly smaller in group F than in group N, at 5.1(2.1) v 3.2(1.1) mm Hg.ml-1.m2; p < 0.05). On the other hand, the VO2 intercept in group F was comparable to that in group N, at 0.71(0.63) v 0.40(0.29) J x beat-1.100 g LV-1; NS). In addition, the ratio of VO2,PVA0.8 to Emax was significantly larger in group F than in group N: 0.55(0.14) v 0.89(0.37) J x beat-1.100 g LV-1.mm Hg-1.ml.m-2 (p < 0.05).

CONCLUSIONS

These results suggest that the VO2 for non-mechanical work in group F is disproportionately high relative to the reduced contractility. An abnormality of excitation-contraction coupling rather than of crossbridge cycling may be responsible for the impaired mechanoenergetics in patients with heart failure due to old myocardial infarction.