The relationship between duty cycle, tachycardia threshold and autostimulation delivery in cardio-responsive vagus nerve stimulation

Purpose: Many patients with epilepsy are unable to completely control seizures with medication alone. Vagus nerve stimulation is an effective nonpharmacologic option for treatment-resistant epilepsy. AutoStim technology is a relatively new VNS feature that provides extra stimulations in response to tachycardia, which often precedes seizures. This feature adds a currently unknown number of extra stimulations per day. This study aims to evaluate that actual stimulations’ patients receive per day as a function of varying VNS settings. Methods: This project was a retrospective chart review. All patients with implanted VNS devices with AutoStim technology managed at Northwestern's epilepsy clinic were included in the study. Data were 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. Results: Sixty-seven patients with VNS stimulators met inclusion criteria leading to 305 unique VNS interrogation results. This study demonstrated the smallest number of extra stimulations between tachycardia thresholds of 40 and 60 with absolute minimums at 35 and 45. Our results also demonstrate a trend of decreasing extra stimulations per day with increased duty cycle at each tachycardia threshold evaluated. Conclusions: These data demonstrate the effect of duty cycle and tachycardia threshold on extra stimulations per day and demonstrated the optimal settings for reducing extra stimulations. This research provides reassurance and information to patients and providers about the actual number of stimulations patients receive with AutoStim technology.