Background Limited study disclosed atrial heterogeneous sympathetic innervation in atrial fibrillation recently. But the changes of vagal nerve and the effect of medicine on neural remodelling are not clear.
Methods and Results Twelve dogs underwent atrial pacing at 600 bpm. Six of them were given propranolol (1 mg/kg tid po, propranolol group), while the other six took placebo only. (AF group) All paced dogs developed sustained AF by 5 weeks of pacing. Tissues from six healthy dogs were used as controls. Immunohistochemistry staining of cardiac nerves was performed using anti-tyrosine hydroxylase (TH) and anti-acetylcholine (Ach) antibodies. In AF group, the density of TH-positive in the right atrium (RA), atrial septum (AS) and left atrium (LA) was 2156.66±677.57 μm2 per mm2, 3679.92±1951.41 and 18961.8±10274.15 μm2 per mm2 respectively, which was significantly (p<0.01) higher than the nerve density in control tissues (608.8±414.60, 660.62±273.29 and 792.46±326.33 μm2 per mm2, respectively). In propranolol group, the density of TH-positive nerve in RA, AS, LA was 879.96±755.13 μm2 per mm2, 960.48±919.92 and 1151.98±678.43 μm2 per mm2 respectively, which was lower than the AF group.(p<0.01) In AF group, the density of ACh-positive nerve in the RA, AS and LA was 721.94±341.07 μm2 per mm2, 279.86±110.25 and 109.22±29.86 μm2 per mm2 respectively, which was significantly (p<0.001) lower than the nerve density in control tissues (7102.32±2058.67, 6093.20±2512.27, and 5285.54±1982.96 μm2 per mm2, respectively). In propranolol group, the density of ACh-positive nerve in RA, AS, LA was 5356.86±1733.25 μm2 per mm2, 4774.86±1069.30 and 3550.76±1399.55 μm2 per mm2 respectively, which was higher than the AF group. (p<0.01) It proved the truth that higher density of TH-positive nerve (10899.84±6365.15 μm2 per mm2, p<0.001) and lower density of Ach-positive nerve (127.94±88.98 μm2 per mm2, P2/mm2 (p<0.01) and 4223.22±1188.23 μm2/mm2 respectively (p<0.01).
Conclusion Sympathetic hyperinnervation and vagal denervation are associated with canine model of sustained AF produced by prolonged left atrial pacing. Propranolol can prevent autonomic remodel to some extent.