Dynamics of wavelets and their role in atrial fibrillation in the isolatedsheep heart

Background: The multiple wavelet hypothesis is the most commonly accepted m echanism underlying atrial fibrillation (AF). However, high frequency perio dic activity has recently been suggested to underlie atrial fibrillation in the: isolated sheep heart. We hypothesized that in this model, multiple wa velets during AF are generated by fibrillatory conduction away from periodi c sources and by themselves may not be essential for AF maintenance, Method s and results: We have used a new method of phase mapping that enables iden tification of phase singularities (PSs), which flank individual wavelets du ring sustained AF. The approach enabled characterization of the initiation, termination, and lifespan of wavelets formed as a result of wavebreaks, wh ich are created by the interaction of wave fronts with functional and anato mical obstacles in their path. AF was induced in six Langendorff-perfused s heep hearts in the presence of acetylcholine. High resolution video imaging was utilized in the presence of a voltage sensitive dye; two-dimensional p hase maps were constructed from optical recordings. The major results were as follows: (1) the critical inter-PS/wavelet distance for the formation of rotors was 4 mm, (2) the spatial distribution of wavelets/PSs was non-rand om (3) the lifespan of PSs/wavelets was short; 98% of PSs/wavelets existed for <1 rotation, and (4) the mean number of waves that entered our mapping field (15.7+/-1.6) exceeded the mean number of waves that exited it (9.7+/- 1.5: P<0.001). Conclusions: Our results strongly suggest that multiple wave lets may result from breakup of high frequency organized waves in the isola ted Langendorff-perfused sheep heart, and as such are not a robust mechanis m for the maintenance of AF in our model. (C) 2000 Elsevier Science B.V. Al l rights reserved.