Interactions between atrial electrical remodeling and autonomic remodeling: how to break the vicious cycle.

Background: The mechanism(s) underlying the maintenance of atrial fibrillation (AF) during the first few hours after AF was initiated remains poorly understood.

Objective: To investigate the roles of the intrinsic cardiac autonomic nervous system in the maintenance of AF at the early stage.

Methods: In 10 anesthetized dogs, we attached multielectrode catheters on atria and pulmonary veins. Microelectrodes inserted into the anterior right ganglionated plexi recorded neural activity. At baseline, programmed stimulation determined the effective refractory period (ERP) and window of vulnerability (WOV), a measure of AF inducibility. For the next 6 hours, AF was simulated by rapid atrial pacing (RAP) and the same parameters were measured hourly during sinus rhythm. A circular catheter was positioned in the superior vena cava for high-frequency stimulation (20 Hz) of the adjacent vagal preganglionics. During 4-6 hours of RAP, we delivered low-level vagal stimulation in the superior vena cava (LL-SVCS), 50% below that which induced slowing of the sinus rate.

Results: During the 6-hour RAP, there was a progressive decrease in the ERP and an increase in ERP dispersion, WOV, and neural activity. With LL-SVCS during 4-6-hour RAP, ERP, WOV, and neural activity returned toward baseline levels (all P <.05, compared with the third-hour RAP values).

Conclusions: RAP not only induces atrial electrical remodeling but also promotes autonomic remodeling. These 2 remodeling processes may form a vicious cycle and each may perpetuate the other. These findings may help to explain how AF maintains itself in its very early stage. LL-SVCS both reversed remodeling processes and can potentially break the vicious cycle of "AF begets AF" in the first few hours of AF.