Circulation, Vol 77, 289-297, Copyright © 1988 by American Heart Association
F Morady, WH Kou, SD Nelson, M de Buitleir, S Schmaltz, AH Kadish, LK Toivonen and JA Kushner
The purpose of this study was to determine whether there is accentuated
antagonism between sympathetic and vagal effects on ventricular refractory
periods (VRPs) in humans. The effects of 0.04 mg/kg of atropine on the
right ventricular effective and functional refractory periods were
determined in the setting of beta-adrenergic blockade by propranolol (0.15
mg/kg loading dose, then 0.1 mg/min continuous infusion, group 1) and in
the setting of beta-adrenergic stimulation by 25 or 50 ng/kg/min
isoproterenol (groups 2 and 3, respectively). Groups 4 to 6 served as
control groups. In group 4, VRPs were determined on three occasions
separated by 10 min each in the absence of drug. VRPs also were determined
on two occasions after infusion of propranolol (group 5) or 25 ng/kg/min of
isoproterenol (group 6). Groups 1 to 4 consisted of 10 subjects each, and
groups 5 and 6 consisted of five subjects each. VRPs were determined with
the use of basic drive cycle lengths of 600, 500, 400, and 350 msec.
Because of sinus tachycardia, sufficient data for comparison of groups 1 to
3 were available only at drive cycle lengths of 400 and 350 msec. Atropine
significantly shortened the VRPs in groups 1 to 3, but the magnitude of
atropine's effects in group 3 (5.3% to 5.8% shortening at drive cycle
length of 350 msec) was significantly greater than in group 1 (2.6% to 3.0%
shortening, p less than .05) Data from the control groups demonstrated that
there was no effect of time on measurement of VRPs either in the drug-free
state or in the presence of propranolol or isoproterenol. The results of
this study indicate that cholinergic tone lengthens VRPs in the absence of
background sympathetic activity and that this lengthening of VRPs may
become accentuated during beta-adrenergic stimulation.
ARTICLES
Accentuated antagonism between beta-adrenergic and vagal effects on ventricular refractoriness in humans
Department of Internal Medicine, University of Michigan Medical Center, Ann Arbor 48109-0022.
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