The oxygen cost of contractility in patients with severe LV dysfunction was significantly greater than in those without LV dysfunction (0.022 vs 0.005 mL O2 x mL x mm Hg-1 per beat, P<.05).
Observational (n=30)
Does the oxygen cost of contractility differ among patients with varying degrees of left ventricular dysfunction after myocardial infarction during dobutamine infusion?
Patients with severe LV dysfunction after myocardial infarction exhibit an increased oxygen cost of excitation-contraction coupling, which may explain the lack of long-term mortality benefit with inotropic agents.
Absolute Event Rate: 0.022% vs 0.005%
p-value: p=<.05
BACKGROUND: Although the use of inotropic agents to treat congestive heart failure (CHF) in patients with coronary artery disease has yielded short-term hemodynamic improvement, long-term mortality has shown less improvement. The loss of cardiac muscle as a result of infarction not only decreases the pumping ability of the heart but also leads to some dramatic changes in myocardial energetics. However, little is known about the mechanoenergetics of the heart in patients with left ventricular (LV) dysfunction after myocardial infarction. METHODS AND RESULTS: The present study was designed to compare by means of the Vo2-pressure-volume area relation (PVA, a measure of total mechanical energy) and Emax (LV contractility index), the incremental oxygen cost of contractility measured as nonmechanical energy per unit increment in contractility in patients with various kinds of LV dysfunction. We assessed Emax, Vo2, and PVA using conductance and Webster catheters under control conditions and during different rates of dobutamine infusion (3 and 6 micrograms x kg-1 x min-1) in 30 patients with coronary artery disease. Patients were divided into three groups according to LV ejection fraction (EF): 10 without LV dysfunction (EF>/= 60%), 10 with mild LV dysfunction (40% </= EF < 60%), and 10 with severe LV dysfunction (EF < 40%). Under control conditions, the Vo2-PVA relation was linear in each group. Contractile efficiency, the reciprocal of the slope of this relation, was comparable among the three groups. The oxygen cost of contractility in the severe LV dysfunction group was significantly greater than in the groups without and with mild LV dysfunction (0.022 +/- 0.014 versus 0.005 +/- 0.002 and 0.0012 +/- 0.005 mL O2 x mL x mm Hg-1 per beat, P <.05). CONCLUSIONS: These findings suggest that the alteration in mechanoenergetics in patients with severe LV dysfunction after myocardial infarction may result from the increased oxygen cost of excitation-contraction coupling rather than from a reduction in the efficiency of chemomechanical energy transduction.
Hayashi et al. (Fri,) conducted a observational in Coronary artery disease with left ventricular dysfunction after myocardial infarction (n=30). Dobutamine infusion vs. Control conditions (baseline) and comparison across LV dysfunction severity groups was evaluated on Oxygen cost of contractility (p=<.05). The oxygen cost of contractility in patients with severe LV dysfunction was significantly greater than in those without LV dysfunction (0.022 vs 0.005 mL O2 x mL x mm Hg-1 per beat, P<.05).