Differences in organization between acute and chronic atrial fibrillation in dogs

OBJECTIVES The purpose of this study was to determine differences in acute and chronic atrial fibrillation (AF) “organization” in canine models. BACKGROUND Electrophysiologic changes occur during atrial remodeling, but little is known about how remodeling affects AF organization. We hypothesized that atrial remodeling induced by long-term rapid atrial rates heterogeneously decreases AF organization. METHODS In seven dogs, acute AF was induced by atrial burst pacing, and in eight dogs chronic AF was created by six weeks of continuous rapid atrial pacing. Atrial fibrillation was epicardially mapped from the right atria (RA) and left atria (LA). Atrial cycle length (CL), spatial organization and activation maps were compared. Spatial organization was quantified by an objective signal processing measure between multiple electrograms. RESULTS In acute AF, mean CL was slightly shorter in the LA (124 ± 16 ms) than it was in the RA (131 ± 14 ms) (p < 0.0001). In chronic AF, LA CL (96 ± 14 ms) averaged 24 ms shorter than RA CL (121 ± 18 ms) (p < 0.0001). Right atria and LA in acute AF had similar levels of organization. In chronic AF, the LA became ∼25% more disorganized (p < 0.0001) while the RA did not change. In acute AF, a single broad wave front originating from the posterior and medial atrium dominated LA activation. In chronic AF, LA activation was more complex, sustaining multiple reentrant wavelets in the free wall and lateral appendage. CONCLUSIONS Acute and chronic AF exhibit heterogeneous differences in CL, organization and activation patterns. The LA in chronic AF is faster and more disorganized than it is in acute AF. Differences in the models may be due to heterogeneous electrophysiologic remodeling and anatomic constraints. The design of future AF therapies may benefit by addressing the patient specific degree of atrial remodeling.