Activation patterns during atrial fibrillation in an experimental model

Introduction and objectives. In atrial fibrillation, along with the mechani sms of complete reentry and random activation focal activation patterns hav e been described which have been attributed both to propagation from the en docardium and to the existence of zones with automatic activity. The object ives of present study are to analyze and quantify the atrial activation pat terns in an experimental model of atrial fibrillation. Material and methods. In 11 Langendorff-perfused rabbit hearts atrial fibri llation was induced by atrial burst pacing after right atrial dilatation wi th an intra-atrial balloon. A multiple electrode consisting of 121 electrod es and positioned in the right atrial free wall was used to construct the a ctivation maps corresponding to 10 segments of 100 ms in 11 different episo des of sustained atrial fibrillation tone per experiment). Results. Of the 110 segments analyzed, 44 (40%) corresponded to random acti vation patterns. Fifteen segments (14%) corresponded to complete reentry, a nd in these cases the number of consecutive rotations ranged from 1 to 2.25 (mean 1.4 +/- 0.4). In 49 segments (44%) a single activation front was see n to pass through the recording area without block; alternatively, two simu ltaneous fronts were recorded that did not re-excite the zone activated by the other. In two segments (2%) there was a focal activation pattern withou t evidence of propagation from the epicardium surrounding the activated zon e. Conclusions. a) in the experimental atrial fibrillation model used, random activation patterns are more frequent than complete reentry patterns; b) co mplete reentry can occur in areas smaller than 1 cm(2), and c) focal activa tion during atrial fibrillation is rare.