Modulation of vagal activity to atria electrical remodeling resulted from rapid atrial pacing

Background Atrial electrical remodeling(AER) plays an important role in the pathogenesis and maintenance of atrial fibrillation. However, little is known about modulation of vagal activity to AER. This study aimed to investigate the relationship between vagal moduation and AER. Methods Twenty four adult mongrel dogs under general anesthesia were randomized into 3 groups. Sympathetic activity was blocked by administration of metoprolol in 3 groups. The changes in vagal modulation to atria after AER were observed in 10 dogs without vagal interruption in group A. The effects of vagal intervention on AER were investigated in 8 dogs with administration of atropine in group B. The impact of aggressively vagal activity on AER was studied in 6 dogs with bilateral cervical vag sympathetic trunks stimulation during AER in group C. Bilateral cervical vagosympathetic trunks were decentralized. Multipolar catheters were placed into high right atria (RA), coronary sinus (CS) and right ventricle (RV). AER was induced by 600 bpm pacing through RA catheter for 30 minutes. Atrial effective refractory period (ERP) and vulnerability window (VW) of atrial fibrillation were measured with and without vagal stimulation before and after AER. Results In group A, ERP decreased significantly at baseline and during vagal stimulation after AER compared with that before AER (all P <0.05). In group B, ERP remained unchanged at baseline and vagal stimulation after AER compared with that before AER (all P >0.05). In group C, ERP shortened significantly at baseline and vagal stimulation after AER compared with that before AER (all P <0.05). ERP shortening after AER in Groups A and C increased significantly than that in group B (all P <0.05). Atrial fibrillation could not be induced at baseline (VW close to 0) before and after AER in three groups. VW became widen significantly during vagal stimulation after AER compared with that before AER in Groups A and C (all P<0.05), while VW remained unchanged in group B (VW close to 0). Conclusions Short-term AER results in the decrease in ERP. AER is accompanied by the increases in atrial vagal modulation. The increased vagal activity and vagal stimulation promote AER, thereby increase the susceptibility to atrial fibrillation. The interrupted vagal activity attenuates AER, thereby suppresses the atrial fibrillation mediated by vagal stimulation. (J Geriatr Cardiol 2008; 5:159-163)