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 mu ltiple, simultaneously circulating wavelets. In the canine sterile per icarditis model, the mechanisms of maintenance of AF are not pet under stood. Methods and Results During six induced AF episodes in six dogs with sterile pericarditis, 372 unipolar electrograms were recorded sim ultaneously from an electrode array placed around both atrial free wal ls, along with 10 to 24 electrodes from the atrial septum, by use of a multiplexing system. Activation maps during 12 consecutive 100-ms win dows were analyzed from an episode of sustained AF in each dog (mean d uration, 32+/-24 minutes). In two dogs, two such activation maps durin g the same episode of AF were analyzed. During AF, multiple unstable r eentrant 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-for med. Wave fronts traveling from one atrium to the other and/or from th e atrial septum play an important role in re-formation of unstable ree ntrant wave fronts. Conclusions In this model of paroxysmal AF, unstab le reentrant circuits of very short cycle length principally involving the atrial septum appear to be critical for maintenance of AF. Some r eentrant circuits disappear as others re-form, so that at least one re entrant circuit is always present. Because the atria cannot follow the ir very short cycle lengths in a 1:1 manner, AF is maintained.