977-73 Observations During Induced Atrial Fibrillation and its Spontaneous Termination in the Sterile Pericarditis Model

Abstract

Atrial fibrillation (AF) is thought to be due to circulating multiple reentrant wavelets, but it is not known how interatrial activation acts to sustain AF. To test the hypothesis that the exchange of reentrant wave fronts between the right and left atria via the intercaval region, septum, and Bachmann's bundle plays a role in the self-sustaining mechanism of AF, we studied activation of both atria during induced AF and during its spontaneous termination. Three hundred seventy-two unipolar electrograms were recorded simultaneously from an electrode array placed on both atrial free walls by using a multiplexing system during 10 induced AF episodes lasting up to 7 minutes in 5 dogs with sterile pericarditis. Activation maps were analyzed during sustained AF and just before termination of AF for 5 consecutive beats, respectively. The mean number of the lines of functional block (LFB) par beat in each atrium, the mean AF cycle length, and the mean number of wave fronts passing between the atria per beat were compared in during sustained AF and before termination of AF in the same AF episode. Complete reentrant circuits were rarely detected in either atrium during AF. Wave fronts traveling in part around LFBs were observed, and the location and length of the LFBs changed from beat-to-beat. The mean number of LFBs detected in the right atrium did not change during sustained AF compared with AF termination (1.7 ± 0.5 vs. 1.8 ± 0.8, NS). However, the mean numberof LFBs in the left atrium significantly decreased from 1.4 ± 1.2 during sustained AF to 0.4 ± 0.6 before AF termination (p < 0.05). The mean AF cycle length significantly prolonged from 107 ± 19 ms during sustained AF to 151 ± 34 ms before AF termination (p < 0.0001). In the beats before AF termination, wave fronts going from left-to-right significantly decreased (1.4 ± 0.5 during AF to 0.4 ± 0.4 before AF termination, p < 0.05). so that the left atrium was activated by right atrial wave fronts. The presence of LFBs associated with partial reentrant circuits in the left atrium and exchange of wave fronts between the atria play an important role in sustaining AF. Spontaneous termination of AF is preceded by prolongation of AF cycle length, decreasing number of LFBs in the left atrium, and a marked decrease in left-to-right activation wave fronts.