The negative chronotropic effect of beta-blockade therapy offsets mechanoenergetical deterioration from its negative inotropic effect by reducing oxygen expenditure for nonmechanical work.
Does propranolol IV alter myocardial oxygen expenditure and mechanical efficiency in patients with heart failure?
The negative chronotropic effect of beta-blockers offsets their negative inotropic effect by reducing oxygen expenditure for nonmechanical work in heart failure patients.
BACKGROUND: The negative chronotropic effect of beta-blocking agents is likely to provide hemodynamic and energetic advantages. However, the negative chronotropic effect on cardiac energetics observed on the initiation of beta-blockade therapy has not been fully elucidated. METHODS AND RESULTS: In 18 patients with heart failure, left ventricular pressure and volume, external work (EW), myocardial oxygen consumption per beat (total Vo2), mechanical efficiency (EW/total Vo2), and Vo2 for nonmechanical work (total Vo2-2.EW) were measured with the use of conductance catheter and Webster catheter at the following three states: under control conditions and after beta-blockade (0.15 +/- 0.07 mg/kg propranolol IV) with and without atrial pacing to keep the heart rate at control levels. Heart rate decreased after atrial pacing was stopped. EW decreased during beta-blockade with pacing and returned to the control level after pacing was stopped. Total Vo2 did not change during beta-blockade with or without pacing, whereas Vo2 for nonmechanical work increased with pacing and returned to the control level after pacing was stopped. As a result, mechanical efficiency decreased during beta-blockade with pacing and returned to the control level after pacing was stopped. CONCLUSIONS: The negative chronotropic effect of a beta-blocking agent may offset the mechanoenergetical deterioration resulting from its negative inotropic effect through a reduction in oxygen expenditure for nonmechanical work. These findings suggest that the negative chronotropic effect is an important aspect of beta-blockade therapy.
Yamakawa et al. (Thu,) conducted a other in heart failure (n=18). propranolol vs. control conditions was evaluated on left ventricular pressure and volume, external work, myocardial oxygen consumption, mechanical efficiency, and Vo2 for nonmechanical work. The negative chronotropic effect of beta-blockade therapy offsets mechanoenergetical deterioration from its negative inotropic effect by reducing oxygen expenditure for nonmechanical work.