Atrial fibrillation: focal activity, re-entry, or both?

Abstract

Atrial fibrillation (AF) can be either paroxysmal or sustained. The latter can be further subdivided into persistent (convertible by shocks or drugs) or permanent forms. The exact mechanism by which some patients have paroxysmal AF while others develop persistent or permanent AF is unclear. One explanation is that there are multiple wandering wavelets and circulating re-entrant wavefronts that maintain AF. An alternative explanation is that there are rapidly firing foci that drive the atria into fibrillation. In the latter situation, re-entry and wandering wavelets are epiphenomena unrelated to the mechanisms of AF maintenance. A third possibility is that both re-entry and focal activity are important in maintaining AF. We1 recently reported that there are two types of ventricular fibrillation (VF). Type I is based on multiple wavelets, while type II VF is due to a focal discharge from a mother rotor. The type I VF can be converted to type II VF by flattening the action potential duration restitution and slowing down the conduction velocity. Based on these findings in VF, it is possible that more than one mechanism can be responsible for AF, depending on the underlying electrophysiologic substrates at the time of the arrhythmia.