AJP - Heart and Circulatory Physiology, Vol 257, Issue 3 935-H941, Copyright © 1989 by American Physiological Society
Brief vagal bursts can induce Wenckebach arrhythmia
D. W. Wallick and P. J. Martin
Mount Sinai Medical Center, Cleveland, Ohio 44106.
We hypothesized that a brief burst of vagal stimulation applied in each
cardiac cycle could elicit an atrioventricular (AV) nodal Wenckebach
arrhythmia. Twenty-six dogs were anesthetized with pentobarbital sodium (30
mg/kg iv) and were given propranolol (1 mg/kg iv). We varied the timing of
a vagal stimulus burst in steps of 25-50 ms relative to the onset of atrial
or ventricular depolarization. In four of nine experiments, a Wenckebach
arrhythmia occurred despite changing the timing of stimuli. By prolonging
the effects of vagal stimulation on AV conduction with physostigmine, the
timing of the stimuli no longer influenced the severity of the arrhythmia.
We did experiments to open one of the feedback control loops; these results
indicated that this arrhythmia has elements of a positive feedback control
system. We also studied the effects of vagal stimulation on the arrhythmia
during retrograde conduction. We found that the timing of vagal stimulation
was critical in eliciting the arrhythmia in only 4 of the 10 dogs.
