AJP - Heart and Circulatory Physiology, Vol 248, Issue 5 674-H677, Copyright © 1985 by American Physiological Society
Beta-adrenergic modulation of direct defibrillation energy in anesthetized dog heart
R. Ruffy, K. Schechtman and E. Monje
Catecholamines facilitate ventricular defibrillation in animals. We
examined the effects of beta-adrenergic stimulation and blockade on
ventricular defibrillation threshold in anesthetized dogs. Calibrated
shocks were delivered between epicardial and superior vena caval
electrodes, and defibrillation threshold was measured before and after
administration of isoproterenol and propranolol. Eight dogs (group 1)
received isoproterenol before propranolol. Nine dogs (group 2) received
propranolol before isoproterenol. In group 1, the minimum energy required
to defibrillate before isoproterenol was 10.6 +/- 1.7 (SE) J and decreased
to 5.9 +/- 1.3 with isoproterenol (P less than 0.001). In group 2, the
minimum energy required to defibrillate was 8.3 +/- 2.4 J before
propranolol and increased to 10.7 +/- 2.2 after propranolol (P less than
0.001). In group 1, propranolol after isoproterenol increased
defibrillation threshold (P less than 0.07), whereas in group 2
isoproterenol after propranolol produced no significant change in
defibrillation threshold. Thus beta-stimulation decreased defibrillation
threshold significantly in the anesthetized dog heart, an effect that was
blocked by propranolol. Conversely, propranolol increased defibrillation
threshold, an effect that occurred despite prior beta-stimulation, probably
because of the short half-life of isoproterenol.
