Regional and functional factors determining the induction and
maintenance of atrial fibrillation in dogs.
Wang, J., L. Liu_, J. Feng, and S. Nattel.
Department of Medicine*, Montreal Heart Institute and University of
Montreal and the Department of Pharmacology and Therapeutics, McGill
University, Montreal, Quebec, Canada, HIT IC8
APStracts 2:0541H, 1995.
Atrial fibrillation (AF) can be initiated in experimental animals and
patients by premature or rapid atrial activation, and is then
sustained for a variable period of time. The present study was
designed to determine the factors governing the ability of premature
beats at various atrial sites to initiate AF, and the determinants of
the duration of AF, in morphine/chloralose-anesthetized dogs. Various
levels of constant vagal tone were produced by bilateral cervical
vagal nerve stimulation at frequencies between 1 and 10 Hz. There
were important differences in the ability of extrasystoles at
different atrial sites to induce AF, although once AF was induced at
a given site its duration was independent of the site of induction.
Regional differences in the ability to induce AF were due to
differences in local refractoriness. AF was always initiated by a
premature beat which blocked in regions of greater refractoriness,
causing a macroreentrant activation with subsequent disorganization
of activation producing fibrillation. Atrial burst pacing induced AF
of relatively consistent duration that depended strongly on vagal
stimulation frequency. The atrial refractory period and wavelength
for reentry during rapid 1:1 atrial pacing were weak predictors of AF
duration (r= 0.24, 0.23 respectively), which was found to depend more
strongly on variability in regional refractoriness as measured by the
standard deviation in local refractory periods (r = 0.80,
P?<0.001) and on the heterogeneity of activation during AF as
determined by a quantitative index (r = 0.74, P <0.001). These
results show that premature beats cause AF by initiating a single
macroreentrant cycle that degenerates into multiple wavefronts, that
regional refractoriness is the primary determinant of AF induction by
premature beats, and that variability in refractoriness may be an
important determinant of the ability of AF to sustain itself.
Received 22 March 1995; accepted in final form 16 November 1995.
APS Manuscript Number H277-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 8 December 95