Long-term changes in sequence of atrial activation and refractory periods: no evidence for "atrial memory".
OBJECTIVE
The purpose of this study was to test whether the spatial distribution of the atrial refractory period (AERP) and the vulnerability to atrial fibrillation (AF) are altered by long-term changes in the sequence of atrial activation.


BACKGROUND
The spatial distribution of the AERP plays an important role in AF. Changes in the activation sequence have been postulated to modulate atrial repolarization ("atrial memory").


METHODS
Six goats were chronically instrumented with epicardial atrial electrodes to determine activation time and AERP at 11 different areas of the right (RA) and left (LA) atrium and the Bachmann bundle. Activation time and AERP were measured during sinus rhythm and during prolonged RA and LA pacing (1 week RA pacing, 2 weeks LA pacing, 1 week RA pacing; 150 bpm). Inducibility of AF was determined by the number of atrial sites where single premature stimuli induced AF paroxysms >1 second.


RESULTS
During sinus rhythm (106 +/- 4 bpm), AERP was longest at the Bachmann bundle and shortest at the LA free wall (185 +/- 6 ms and 141 +/- 5 ms, P < .001). In five of six goats, an inverse correlation between local activation time and AERP was found during sinus rhythm (r = -0.53 +/- 0.05; P < .05). The increase in atrial rate during RA and LA pacing caused an overall shortening of AERP from 167 +/- 6 ms to 140 +/- 6 ms (P < .001). However, a switch between long-term RA and LA pacing did not significantly change AERP at any of the 11 atrial regions and had no significant effect on AF inducibility.


CONCLUSIONS
During sinus rhythm, an inverse relationship exists between the sequence of atrial activation and the local refractory period. However, long-term changes in the sequence of atrial activation do not alter the spatial distribution of AERP or the inducibility of AF.
Vollmann
Dirk
D
Department of Physiology, Cardiovascular Research Institute Maastricht, University of Maastricht, The Netherlands. DirkVollmann@aol.com
Blaauw
Yuri
Y
Neuberger
Hans-Ruprecht
HR
Schotten
Ulrich
U
Allessie
Maurits
M
D000200:Action Potentials; D000818:Animals; D016275:Atrial Function; D004594:Electrophysiology; D006041:Goats; D006325:Heart Atria / Q000033:anatomy & histology; D006339:Heart Rate / Q000502:physiology; D012032:Refractory Period, Electrophysiological / Q000502:physiology*