A surface electrode adjacent to vagal nerve stimulator lead can aid in characterizing vagal nerve stimulator-mediated pediatric sleep-disordered breathing: a case series of 7 patients

Study Objectives: The vagal nerve stimulator (VNS) is a nonpharmacological treatment for refractory epilepsy. A side effect of the VNS is sleep-disordered breathing. The purpose of this study was to demonstrate how a surface electrode placed over the VNS lead can help distinguish whether sleep-disordered breathing is due to VNS discharge. Methods: Seven pediatric patients (aged 7.7 +/- 2.2 years) with a VNS underwent a polysomnogram with an additional surface electrode on the left anterolateral neck to detect VNS discharge. The VNS-associated apnea-hypopnea index was calculated by determining the number of hypopneas and apneas occurring during VNS discharge. We evaluated the veracity of the VNS electrode by comparing signal duration and total number to those expected by programmed settings. We compared these findings to chin electromyogram signal change. Results: Three patients had an obstructive pattern with VNS discharge, and 3 had an increase in respiratory rate without gas exchange abnormalities, including 1 with both patterns; 1 patient experienced no respiratory abnormalities. The mean obstructive apnea-hypopnea index was 8.2 +/- 8.3 events/h. The mean VNS-associated apnea-hypopnea index was 4.8 +/- 6.2 events/h and accounted for 46.9 +/- 30.2% of the total obstructive apnea-hypopnea index. The additional electrode captured a statistically high percentage of expected discharges (94.7 +/- 6.5%) compared to chin electromyogram (36.1 +/- 35.8%; P <.05). Conclusions: We demonstrated that a surface electrode on the VNS lead can temporally coregister VNS discharges and enabled us to attribute sleep-disordered breathing to VNS stimulation in 4 patients. We propose that this sensor be standard procedure in patients with VNS undergoing polysomnogram.