Abstracts

Rationale: The most common side effects of vagus nerve stimulation (VNS) are voice alteration, hoarseness, throat and neck pain, headache, cough, and dyspnea. Bradycardia and asystole are uncommon late-onset side effects of vagus nerve stimulation. Such complications are so rare, that these had only been previously reported in four cases. Our new case highlights late-onset cardiac syncope in VNS, which could potentially be life-threatening if unrecognized.Methods: This is a case report with chart review.Results: A 56-year-old male with medically refractory partial epilepsy, started having complex partial seizures at age nine. Partial seizure is associated with staring, lips turning blue, and hands wringing. He developed secondary convulsive seizures at 16. Later, epilepsy surgery therapy was ruled out, after failing numerous antiepilectic drugs. At 42, he received VNS therapy, which completely eliminated his secondary convulsion, and significantly lowered his partial seizure's frequency. He had pulse generator replacement with model 104 at 54, with unknown intraoperative lead testing result. After 1 year and 11 months, he experienced recurrent syncope, associated with lightheadedness, difficulty breathing, and complete loss of consciousness, lasting up to 10 s, without postictal confusion. His VNS parameters (21 s on-time, 3.2 min off-time, 2.75 mA output current, 25 Hz signal frequency, and 500 μ s pulse width) were stable for five months prior to syncope. He was on stable dose of levetiracetam, topiramate, and anxiolytic alprazolam for one year. His seizure frequency was unchanged for many years. During syncope, a family member, who was a nurse, noted heart rate in the 40s every 3-4 min. In the hospital, sinus bradycardia with heart rate of low 30s was noted on cardiac rhythm strip, which coincided with VNS stimulation felt by the patient, and resolved with VNS deactivation. Diagnostic testing was attempted, but he had immediate syncope with eight-second asystole after VNS reactivation. VNS was then deactivated. X-ray ruled out lead breakage. A 48-hour Holter monitor and transthoracic echocardiogram were normal after one month and four months, respectively. After 11 months, his seizure control had remained stable.Conclusions: The recurrent syncope of our case was likely related to VNS, but the ultimate cause remains unclear. Late-onset bradyarryhthmia after VNS implantation is rare, yet it could be life-threatening. Thus, clinicians should be aware of this complication, even a year or longer after implantation.