Abstracts

Rationale:
Epilepsy is a serious neurologic condition, affecting about 1-2% of people worldwide. While 65-70% of patients with epilepsy are able to manage their seizures with antiepileptic medication, 30-35% of patients are unable to completely control seizures with medication alone and have to consider alternatives. Vagus Nerve Stimulation (VNS) is an effective nonpharmacologic option for treatment resistant epilepsy. AutoStim technology is a relatively new VNS feature that provides extra stimulations in response to ictal tachycardia, as 82 percent of patients experience increases in heart rate associated with epileptic activity. However, while older VNS models operated on standard on/off periods (duty cycles) with predictable amounts of firing per day, the addition of Autostim adds an unknown number of extra stimulations per day, particularly when stimulations can be administered at specific increases in heart rate (tachycardia thresholds). This study aims to evaluate actual stimulations patients receive per day as a function of varying duty cycles and tachycardia thresholds in VNS stimulators with Autostim technology.
Method:
This project was a retrospective chart review of patients with VNS followed in the outpatient epilepsy program at Northwestern Memorial Hospital. All patients with implanted VNS devices with Autostim technology managed at our epilepsy clinic were included in the study. Data was extracted from eight encrypted and HIPAA compliant programming tablets on which VNS patient data was stored after every patient programming session. Data was collected on duty cycle, tachycardia threshold, expected number of stimulations per day, normal mode stimulations per day, and AutoStims per day. Associations between all variables were evaluated. Patients with less than three values for a given duty cycle at a specific threshold were not included in final analysis. Results67 patients with VNS stimulators met inclusion criteria, and for each patient, the initial interrogation of the VNS device at each patient visit was evaluated, yielding 305 unique interrogation results. When assessed for extra stimulations per day, this study demonstrated the smallest number of extra stimulations between tachycardia thresholds of 40 and 60 (see figure 1). When evaluating extra stimulations per day as a function of duty cycle for a given tachycardia threshold, this study found a trend of decreasing extra stimulations per day with increased duty cycle at thresholds of 20, 30, 40, and 50 (see figure 2).
Conclusion:
These data demonstrate for the first time the effect of duty cycle and frequency threshold on extra stimulations per day and demonstrated the optimal settings for reducing extra stimulations. This research provides reassurance about the actual number of stimulations patients receive with AutoStim technology and allows for providers to have a more accurate understanding of the number of stimulations their patients receive.
Funding:
:None