Abstracts

Rationale: This case series reports the efficacy of a new parameter programming strategy for vagus nerve stimulation (VNS). The benefits of 60 second ON-time plus 1.1 minute-OFF time (duty cycle of 51%) when combined with a reduction in output current were studied in three consecutive adult patients with medically intractable epilepsy of differing etiologies.Methods: Seizure frequencies of 3 patients with refractory epilepsy that had not adequately responded to VNS for 27-83 months were studied. Patient 1, a male aged 25 years, had tuberous sclerosis and developmental regression. Patient 2, a female aged 50 years, had idiopathic partial seizures and remote history of temporal lobectomy. Patient 3, a female aged 53 years, had mental retardation/developmental delay and Lennox-Gastaut Syndrome. Patients 1 and 3 had epilepsy for their entire lives and patient 2 for her entire adult life. The nursing staff (patients 1 and 3) or the family (patient 2) kept a diary of seizures, seizure clusters (defined as 2 or more seizures without return to baseline consciousness), for a baseline of 14 to 20 weeks. During baseline, the VNS duty cycle was 30 seconds ON and 1.1-1.8 minutes-OFF. Each patient’s VNS generator was reprogrammed to 60 seconds ON-time and 1.1 minutes OFF-time with simultaneous 0.25-0.50 mA reduction in output current, and seizure diaries were kept for 14 to 34 weeks follow up. Concomitant antiepileptic drugs (AEDs) remained unchanged except for patient 3 who required an additional AED during a hospitalization. Results: Seizure frequency was reduced for all 3 patients. Patient 1 experienced a 44% seizure reduction, and seizure-free days increased from 2% to 15%. Seizures decreased by 89% for patient 2, and seizure-free weeks increased from 79% to 93%. Seizure reduction was 83% for patient 3, seizure clusters were reduced by 70%, and seizure-free weeks increased from 0% to 44%. No adverse side effects were noted by the patients or caregivers.Conclusions: The benefits of implementing a 60-second ON-time plus 1.1 minute-OFF time combined with a reduction in output current were apparent. All patients experienced a robust reduction in seizure frequency and increases in seizure-free days or weeks. The number of seizure clusters was greatly reduced in the patient afflicted with this pattern. Reducing the output current had the dual advantage of reducing the potential for side effects that might occur with the longer ON-time of 60 seconds while simultaneously lowering usage of the VNS battery. This new programming paradigm may be useful for some epilepsy patients whose seizures remain refractory at more traditional VNS settings.