Negative Chronotropic Effect of β-Blockade Therapy Reduces Myocardial Oxygen Expenditure for Nonmechanical Work

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Abstract
Background The negative chronotropic effect of β-blocking agents is likely to provide hemodynamic and energetic advantages. However, the negative chronotropic effect on cardiac energetics observed on the initiation of β-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 V̇o2), mechanical efficiency (EW/total V̇o2), and V̇o2 for nonmechanical work (total V̇o2−2·EW) were measured with the use of conductance catheter and Webster catheter at the following three states: under control conditions and after β-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 β-blockade with pacing and returned to the control level after pacing was stopped. Total V̇o2 did not change during β-blockade with or without pacing, whereas V̇o2 for ...