Negative chronotropic effect of beta-blockade therapy reduces myocardial oxygen expenditure for nonmechanical work

Abstract

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.