Role of atrial remodeling in patients with atrial fibrillation.

Atrial fibrillation (AF) maintenance is promoted by an atrial substrate that is suitable for the initiation and continuation of the re-entering wavelets. During the first week of AF, the atrial substrate is modified by electrical remodeling, with shortening of the atrial refractoriness and slowing of the conduction velocity. Structural remodeling is the so-called "second factor" that facilitates the maintenance of AF in the following months. The ultrastructural changes result in an inhomogeneous conduction and electrical uncoupling, and the enlarged atrium is able to accommodate more circulating wave fronts that stabilize the AF. Reversal of the electrical remodeling develops within 1 week after the restoration of AF to sinus rhythm. However, reverse structural remodeling develops more slowly and may be just partially reversible. The substrate properties during AF recurrences after undergoing catheter ablation are more complex and need to be clarified in future studies.