Efficacy and Tolerability of Ultra Rapid Duty Cycling Vagus Nerve Stimulation for Medically Refractory Absence Seizures

Abstract

Background: Significant knowledge gap exists on vagus nerve stimulation (VNS) efficacy and tolerability in medically refractory absence seizures (MRAS). This retrospective review of patients with MRAS aims to narrow this knowledge gap by comparing ultra rapid duty cycling ([URDC] ON time seven seconds, OFF time 0.2 minutes) with less frequent stimulations of rapid duty cycling (RDC, OFF time <1.1 minutes) and normal duty cycling (NDC, OFF time ≥1.1 minutes).

Methods: Patients with MRAS aged less than 21 years who underwent VNS implantation were identified. Patient demographics, antiepileptic medications, seizure types, frequency, VNS parameters, outcomes of seizure reduction rate (SRR), and seizure freedom were extracted and compared among NDC, RDC, and URDC patient cohorts.

Results: Thirty-six patients with MRAS were identified. After a mean follow-up of 32.6 months, responder rate ([RR], SRR ≥50%) for URDC was 80% for absence seizures and 80% for all seizure types versus 66.67% and 66.77% for NDC and 78.57% and 57.14% for RDC, respectively. Six of 10 patients (60%) on URDC achieved complete seizure freedom. A higher rate of subjective improvement in academic performance, attention, and developmental gain was noted in the URDC group. Patients on URDC tolerated higher output current (mean 3.025 mA) with minimal side effects but required a battery change sooner.

Conclusions: VNS is a safe and effective nonpharmacologic management choice in patients with MRAS. The data presented demonstrate that the combination of URDC and high output current provides better RR and seizure freedom. Apart from a reduced battery life, this parameter modality seems to be well-tolerated.

Keywords: Absence seizures; Rapid duty cycling; Ultra rapid duty cycling; VNS.