Vagal Nerve Stimulator (VNS) is used in refractory epilepsy. Arrythmias have been rarely reported. We are reporting a case of delayed onset Mobitz type II AV nodal block caused by VNS. 

A 41-year-old male, with history of pre-term birth, intellectual disability and refractory epilepsy, on multiple antiseizure medications and VNS presented for progressive lethargy. First VNS placed in 2004-2013 complicated by infection, replaced in 2019. VNS set at output of 3.25mA. His seizure medications were not associated with heart block.

Information obtained via retrospective review of electronic medical records 

Telemetry showed multiple sinus pauses 2-8.5 seconds, Electrocardiogram demonstrated second degree Mobitz type II AV block. Transthoracic echocardiogram showed EF of 65% without valvular abnormalities. Sleep study showed mild sleep apnea. Previous TTE and 30-day cardiac monitor had shown only normal sinus rhythm. Sinus pauses resolved completely after VNS was turned off. His lethargy improved after turning off VNS. 

Vagal stimulation is thought to modulate GABA receptors which ultimately helps control the seizure frequency in refractory cases. Rare cardiac arrythmias have been reported perioperatively including bradycardia, complete heart block, paroxysmal atrial fibrillation, and asystole. Delayed onset arrythmias and sinus arrest are extremely rare complications. Proposed explanations for this effect are that VNS stimulation of vagal afferent pathway leads to decreased SA node, AV nodal and purkinji system conduction or that there is an anatomical variation allowing a hypersensitive baroreceptor reflex. Additionally, autonomic changes in hypothalamus and insular cortex via VNS-induced changes in the nucleus tractus solitaries have been seen through functional MRI. While rare, VNS can cause new-onset cardiac arrhythmias in epilepsy patients.