Maintenance of atrial fibrillation by reciprocal triggering of competitive focal sources: a hypothesis.

The primary mechanism of atrial fibrillation (AF) maintenance remains debatable. However, contemporary atrial surface AF mapping studies readily detect multifocal activity, less readily "incomplete reentries" (defining them as reentries or false reentries) and never or rarely full-circuit reentries. Most of the surface multifocal waves during AF are short-lasting (1-3 waves) and they appear to be largely breakthroughs. Some of the multifocal activities during AF, particularly repetitive/sustained, can be explained with reciprocal triggering of delayed afterdepolarization (DAD) activities. Indeed, the condition that causes DAD activity (i.e., intracellular calcium abnormalities plus rapid activation) is continuously present during AF throughout the atria, that may provide a sufficient "arrhythmogenic reserve" for the generation of multiple competitive focal sources sustaining AF. In such scenario, there should be commonly one dominant source at a time along with subsidiary active and/or latent/overridden sources (the currently fastest sustained source acts to override all the others, covering all, most, or a large part of the atrium at a time). This may account for a spatiotemporal periodicity usually recorded during AF. Sustained focal sources should self-terminate/decelerate sooner or later and/or be overridden by currently faster sources, entailing a periodical switching of dominant sources (the currently "fittest" dominates). Anti-AF success of the Cox-Maze and pulmonary vein isolation procedures, separating the main atrial arrhythmogenic regions, can be generally explained with the interruption of mutual triggering of multiple DAD sources. Thus, reciprocal triggering of competitive DAD sources may broadly account for the maintenance and spatiotemporal periodicity of AF as well as for the anti-AF success of the Cox-Maze and pulmonary vein isolation procedures.