Roles of Autonomic Nerve System on the Evolution of PAF to PRAF

Abstract

Atrial fibrillation (AF) can be either paroxysmal or sustained. Not all patients with paroxysmal AF progress to sustained forms. The mechanisms by which paroxysmal AF progresses to sustained AF remain poorly understood. Intermittent rapid atrial pacing in large animals can initially induce paroxysmal AF followed by transition to persistent AF. Pacing-induced shortening of the effective refractory periods were thought to underlie the mechanisms of AF progression. However, the time course of changes in atrial refractoriness did not completely run parallel with the time course of development of sustained AF. We analyzed long-term recording of nerve activities in ambulatory dogs, and used an intermittent high rate atrial pacing protocol to determine the duration of pacing needed to induce sustained (>48 hrs) of AF. We found that differential patterns of interactions among cardiac autonomic structures naturally exist at baseline (before pacing). We also noted that dogs with good linear sympathovagal correlation and higher vagal tone at baseline have more paroxysmal atrial tachycardias at baseline and faster induction of sustained AF by rapid pacing, as compared to dogs with an L-shaped sympathovagal correlation and lower vagal tone at baseline. These findings suggest that simultaneous sympathovagal discharges, which simultaneously increase Ca2+ entry and shortens the action potential duration, are important in the development of persistent AF.