Transient Atrial Fibrillation after the Implantation of a Vagus Nerve Stimulator (2004)

To the Editor: Paroxysmal atrial fibrillation is a common dysrhythmia that can be initiated by sympathetic or parasympathetic stimulation (1). We describe a patient who developed this arrhythmia shortly after the placement of a vagus nerve stimulator (VNS). A 40-year-old woman, with partial seizures refractory to medical treatment, underwent implantation of a VNS. The day after the procedure, she appeared in the emergency department with nausea, vomiting, lightheadedness, and palpitations. Telemetry showed intermittent runs of atrial fibrillation (A-fib), atrial flutter, and frequent premature atrial complexes. A 12-lead electrocardiogram (ECG) between these episodes was unremarkable. She was hemodynamically stable during the arrhythmia. No history of dysrhythmia or other cardiovascular disease was noted. Troponin-I level, thyroid-function tests, and echocardiogram were normal. Given the temporal association, the VNS was identified as a potential etiology for the patient's arrhythmia, and the device was turned off. She continued to have paroxysmal runs of atrial flutter and fibrillation for 24 h, but thereafter remained in sinus rhythm. The device was turned on at a later date, and the arrhythmia did not recur. Paroxysmal atrial fibrillation may be provoked by either vagal or sympathetic stimulation. Vagally mediated A-fib usually occurs in young people with no underlying structural heart disease. The typical history is of paroxysmal episodes of the A-fib alternating with atrial flutter occurring at night, and conversion to sinus rhythm occurs in the morning when the sympathetic drive is higher (1). In contrast, adrenergically mediated paroxysmal A-fib occurs more commonly in older patients during the daytime and is usually triggered by emotional stress or physical exertion (1). Several studies have confirmed the safety and efficacy of intermittent VNS for the treatment of intractable seizures (2-4). In human trials using VNS at stimulation parameters for seizure control, no effect on heart rate was seen (2-4). This presumably relates to the location of the stimulating electrode in the neck distal to most of the cardiac branches of the left vagus nerve (5). However, in one study, in four patients, transient ventricular asystole developed intraoperatively, after VNS (6). Atrial fibrillation has been induced in experimental animals by the electrical stimulation of the cervical vagus nerve. Stimulation of the right vagus produces the arrhythmia at a lower intensity of stimulus when compared with the left (7). However, this is the first reported case of atrial fibrillation temporally associated with the implantation of a VNS in humans. The patient's arrhythmia was transient and occurred in the immediate postoperative period. The device was turned on at a later date, and she did not have a recurrence of the arrhythmia at the same stimulation parameters as initially used at the time of implantation. Thus we speculate that initial mechanical stimulation and postoperative inflammation hypersensitized the vagus nerve to VNS stimulation, leading to a transient increased vagal efferent activity, which in turn contributed to the arrhythmia. However, temporal association does not imply cause and effect, and short-term rhythm monitoring after implantation may be warranted. This would allow us to evaluate the incidence and study the causality of the arrhythmia.