• Ling Zhang, Sunny S Po, Huan Wang, Benjamin J Scherlag, Hongliang Li, Juan Sun, Yanmei Lu, Yitong Ma, and Yuemei Hou.
• *Cardiovascular Center, First Affiliated Hospital of Xinjiang Medical University, Urumqi, China; †Heart Rhythm Institute, University of Oklahoma Health Sciences Center, Oklahoma City, OK; and ‡Department of Cardiovascular Diseases, The 6th People's Hospital, Shanghai Jiaotong University, Shanghai, China.
• J. Cardiovasc. Pharmacol. 2015 Sep 1; 66 (3): 307-15.

BackgroundThe mechanism(s) of how atrial fibrillation (AF) sustains itself in the first 24 hours is not well understood.ObjectiveWe sought to investigate the role of autonomic remodeling in the first 24 hours of AF simulated by rapid atrial pacing (RAP).MethodsForty-eight rabbits were divided into 6 groups. One group (n = 8) was euthanized after baseline recordings. Another group (n = 8) did not receive RAP during the 24-hour period to serve as controls. In the other 4 groups, rabbits were euthanized after RAP for 4, 8, 12, or 24 hours (n = 8 for each). Before and after designated hours of RAP, atrial effective refractory period, heart rate variability, and left vagal and sympathetic nerve activity (VNA and SNA, respectively) were determined. The right and left atrial tissues were obtained for immunocytochemical analysis for growth-associated protein 43 (GAP43), tyrosine hydroxylase (TH), and choline acetyltransferase (ChAT).ResultsRAP resulted in progressively shortened atrial effective refractory period and slower heart rate. In the first 12 hours of RAP, both SNA and VNA progressively increased. Then, VNA remained stably elevated but SNA began to attenuate. The high-frequency component and low-frequency/high-frequency ratio of heart rate variability followed the trend of VNA and SNA, respectively. The density of GAP43-positive, ChAT-positive, and TH-positive neural elements in the right and left atria was progressively higher with RAP.ConclusionsAF resulted in progressive autonomic remodeling, manifesting as nerve sprouting, sympathetic and vagal hyperinnervation. Autonomic remodeling may play an important role in sustaining AF in the first 24 hours.

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