Vagus nerve stimulation therapy in depression and epilepsy: therapeutic parameter settings

Vagus nerve stimulation (VNS) therapy is an effective adjunctive treatment for chronic or recurrent treatment-resistant depression in adults, and for pharmacoresistant epilepsy in adults and adolescents. VNS therapy is administered through an implanted pulse generator that delivers programmed electrical pulses through an implanted lead to the left vagus nerve. Programmable pulse parameters include output current, frequency, pulse width, and ON/OFF times. Within a range of typical values, individual patients respond best to different combinations of parameter settings. The physician must identify the optimum settings for each patient while balancing the goals of maximizing efficacy, minimizing side effects, and preserving battery life. Output current is gradually increased from 0.25 mA to the maximum tolerable level (maximum, 3.5 mA); typical therapeutic settings range from 1.0 to 1.5 mA. Greater output current is associated with increased side effects, including voice alteration, cough, a feeling of throat tightening, and dyspnea. Frequency is typically programmed at 20 Hz in depression and 30 Hz in epilepsy. Pulse width is typically 250 or 500 mu s. The recommended initial ON time is 30 s, followed by 5 min OFF; OFF time > ON time is recommended. As with pharmacotherapy, VNS therapy must be adjusted in a gradual, systematic fashion to individualize therapy for each patient.