Shun-ichiro Sakamoto, Richard B. Schuessler, Anson Lee, Abdulhameed Aziz, Ralph J. Damiano, Jr..
Division of Cardiothoracic Surgery, Washington University School of Medicine, Saint Louis, MO, USA.
OBJECTIVE: Increased vagal tone plays an important role in the initiation and maintenance of atrial fibrillation. Focal ablation of the ganglionated plexus (GP) has been proposed to reduce vulnerability to AF. However, little is known about the extent of vagal denervation and the distribution of reinnervation after GP ablation. The purpose of this study was to examine the electrophysiological changes in vagal tone in the canine atrium acutely and chronically after epicardial GP fat pad ablation.
METHODS: Adult mongrel canines (N=6) were used in this study. After propranolol was given, high frequency stimulation was applied to 4 epicardial GP fat pads in each animal. Every fat pad was ablated using a pen-type bipolar radiofrequency ablation device (Atricure Inc.). Sinus interval and atrioventricular (AV) interval changes during bilateral vagosympathetic trunk (VST) stimulation were examined before, after GP ablation, and at four weeks. Vagally induced ERP changes and mean QRST area changes relative to an isoelectric baseline (index of local innervation) were examined in 5 atrial regions using epicardial templates with 250 unipolar electrodes.
RESULTS: A vagal reflex was observed in 29% (7/24) of GP fat pads during stimulation. The right pulmonary vein fat pad was the most responsive fat pad (sinus slowing rate of 32-49% in 4 animals). In 2 animals, AF was induced by GP stimulation. All vagal reflexes were eliminated after focal GP ablation. Sinus and AV interval change during vagal stimulation decreased immediately after the ablation, however the vagal effect on the sinus node was restored from 0.8±0.4 % to 8.5±1.7 % for 4 weeks (p<0.05). ERP changes were attenuated after the ablation in every region and remained so 4 weeks after the ablation. Mean QRST area changes were heterogeneous, showing a significant decrease in the left superior and inferior atrium and an increase in the right inferior atrium after GP ablation. Chronically, QRST area changes with VST stimulation increased more than control values in all regions (p<0.001)
CONCLUSIONS: Focal epicardial GP fat pad ablation acutely decreased vagal tone and increased atrial repolarization heterogeneously. Increased vagal resposes in the chronic stage suggested early reinnervation of the atria.
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