Objective: : Autonomic ganglionated plexi (GP) in fat pads near the pulmonary veins may contribute to initiation and maintenance atrial fibrillation (AF). We attempted to localize these plexi in a canine model, and evaluate the efficacy of microwave ablation in eliminating their vagal reflexes.
Methods: : 8 Mongrel dogs (25-31 kg), underwent cervical vagal trunk stimulation to produce AV nodal block and sustained AF. Sternotomy was performed and the epicardial fat on the posterior left atrium and pulmonary veins was locally stimulated at high-frequency (20 Hz, 3-5 mA). Locations that produced a vagal response were identified and in 7 dogs ablated using the Flex 4 epicardial microwave ablation probe (Guidant Corp) at 65 watts/90 sec. One animal was a control and not ablated. Vagal responses were retested with local stimulation as well as stimulation of the cervical vagal trunks. The presence of AV block and duration of sustained AF was recorded.
Results: : Baseline cervical vagal stimulation produced AV block and AF in all the animals. Local high-frequency stimulation (HFS) elicited vagal responses at the junction of the inferior vena cava and the middle pulmonary vein (IVC-MPV) in 8 animals, the base of the left pulmonary veins/ligament of Marshall (LoM) in 5 animals, and between the upper and lower right pulmonary veins (RPV) in 2 animals. Microwave ablation at the IVC-MPV eliminated the vagal response upon local fat pad HFS. Cervical vagal trunk stimulation yielded less AV block (n = 2) or no AV block (n = 5) after microwave ablation of the IVC-MPV alone (n = 4) or in conjunction with LoM area ablation (n = 3). The average duration of AF during cervical vagal stimulation decreased significantly from baseline (52.7 ± 27.0 sec) versus after fat pad ablation (13.8 ± 20.3 sec, p = 0.004).
Conclusions: : In a canine model we found the primary epicardial autonomic ganglionated plexi to be at the junction of the IVC-MPV. Epicardial microwave ablation of this GP eliminated the vagal response during local fat pad stimulation; and attenuated or eliminated AV block and induction of sustained AF during cervical vagal trunk stimulation. Epicardial microwave ablation of the ganglionated plexi in epicardial fat pads is feasible and can eliminate vagal reflexes that maybe important in atrial fibrillation.