Comparison of atrial fibrillation inducibility by electrical stimulation of either the extrinsic or the intrinsic autonomic nervous systems

To study the effects of bilateral vagosympathetic nerve stimulation (VNS) and ganglionated plexi stimulation (GPS) on atrial refractoriness and inducibility of atrial fibrillation (AF). Studies were performed in fourteen adult mongrel dogs anesthetized with Na-pentobarbital, 30 mg/kg. VNS was achieved by insertion of wires into the left and right VN trunks. An octapolar catheter was attached to contact the right superior pulmonary vein (RSPV) and other octapolar catheter electrodes were sutured to the right atrial (RA) free wall and appendage (RAA). GPS was performed via a plaque electrode sutured to the fat pad containing the anterior right (AR) GP. VNS and GPS were matched to decrease heart rate by 50%. Programmed stimulation delivered from the RSPV or RAA at 2x, 4x and 10x threshold (TH) allowed the determination of atrial refractory period (ARP) and the AF inducibility. The latter was quantitated by the cumulative window of vulnerability (WOV), i.e., the longest minus the shortest coupling interval during which AF was induced at 2x, 4x, 10x, TH combined. Programmed electrical stimulation at the RSPV showed that the ARP was significantly shorter for both VNS and GPS than baseline (baseline, 113 +/- 22 ms; VNS, 94 +/- 26 ms; GPS, 85 +/- 31 ms) but there was no significant difference in ARP between VNS and GPS. In contrast, the cumulative WOV was significantly wider with GPS (39 +/- 36 ms) than either the baseline state (1 +/- 1 ms) or with VNS (14 +/- 26 ms), p < 0.05. Moreover, pacing from RAA showed a significantly greater cumulative WOV for VNS (33 +/- 36 ms) vs both baseline and GPS (1 +/- 4 ms and 15 +/- 26 ms, respectively, p < 0.05). The heart rate slowing caused by GPS and VNS was not significantly different, 82 +/- 11/min vs 82 +/- 7/min. These data indicate a distinct functional separation of autonomic nerve innervation to the atria from the extrinsic and intrinsic nervous systems. AF is more liable to occur due to intrinsic nerve stimulation at the PVs whereas peripheral atrial sites are more readily inducible for AF due to the extrinsic neural input.