Simultaneous multisite mapping studies during induced atrial fibrillation in the sterile pericarditis model. Insights into the mechanism of its maintenance.

Background: Chronic atrial fibrillation (AF) is thought to be due to multiple, simultaneously circulating wavelets. In the canine sterile pericarditis model, the mechanisms of maintenance of AF are not yet understood.
Methods and Results: During six induced AF episodes in six dogs with sterile pericarditis, 372 unipolar electrograms were recorded simultaneously from an electrode array placed around both atrial free walls, along with 10 to 24 electrodes from the atrial septum, by use of a multiplexing system. Activation maps during 12 consecutive 100-ms windows were analyzed from an episode of sustained AF in each dog (mean duration, 32 +/- 24 minutes). In two dogs, two such activation maps during the same episode of AF were analyzed. During AF, multiple unstable reentrant circuits (mean number, 1.4 +/- 0.1 per 100-ms analysis window) with very short cycle lengths (mean, 111 +/- 8 ms) present primarily in the atrial septum and right atrium were responsible for maintenance of AF. The unstable reentrant circuits frequently disappeared and re-formed. Wave fronts traveling from one atrium to the other and/or from the atrial septum play an important role in re-formation of unstable reentrant wave fronts.
Conclusions: In this model of paroxysmal AF, unstable reentrant circuits of very short cycle length principally involving the atrial septum appear to be critical for maintenance of AF. Some reentrant circuits disappear as others re-form, so that at least one reentrant circuit is always present. Because the atria cannot follow their very short cycle lengths in a 1:1 manner, AF is maintained.