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


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
H
H
First Department of Internal Medicine, Kobe University School of Medicine, Japan.
Takeuchi
M
M
Takaoka
H
H
Hata
K
K
Mori
M
M
Yokoyama
M
M
D000319:Adrenergic beta-Antagonists / Q000494:pharmacology*; D000328:Adult; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D001810:Blood Volume / Q000187:drug effects; D002303:Cardiac Output, Low / Q000503:physiopathology; D002304:Cardiac Pacing, Artificial; D004734:Energy Metabolism / Q000187:drug effects; D005260:Female; D006339:Heart Rate / Q000187:drug effects*; D006439:Hemodynamics / Q000187:drug effects; D006801:Humans; D008297:Male; D009206:Myocardium / Q000378:metabolism*; D010101:Oxygen Consumption / Q000187:drug effects*
D000319:Adrenergic beta-Antagonists