From the Guidelines
Vagus nerve stimulators have been shown to be effective in reducing seizure frequency in patients with epilepsy, with a significant reduction in seizure frequency observed in the HIGH stimulation group compared to the LOW stimulation group. The study published in 2019 in the journal Cold Spring Harbor Perspectives in Medicine 1 found that the HIGH stimulation group had a significantly greater reduction in frequency of all seizures than the LOW stimulation group, with a reduction of 24.5% vs. 6.1% (p = 0.01). This suggests that VNS can be an effective treatment option for patients with epilepsy who do not respond adequately to medications.
Some key points to consider when using VNS for epilepsy include:
- The device consists of a pulse generator implanted in the chest that sends electrical impulses through a wire to the vagus nerve in the neck
- The stimulation is typically delivered at regular intervals, such as 30 seconds on, 5 minutes off, with parameters adjusted by a neurologist
- The HIGH stimulation group received 0.25–3.5 mA (set to patient tolerance), 30 sec ON + 5 min OFF, 30 Hz, and 500–750 µsec pulse duration, which was found to be more effective than the LOW stimulation group
- Side effects are generally mild and include hoarseness, cough, voice changes during stimulation, and throat discomfort
The exact mechanism of how VNS works is not fully understood, but it is thought to modulate brain activity through the vagus nerve's extensive connections to key brain regions involved in mood regulation and seizure generation 1. Overall, the evidence suggests that VNS can be a useful treatment option for patients with epilepsy, particularly those who do not respond adequately to medications. The HIGH stimulation parameters, as described in the study, should be used to optimize therapeutic benefit.
From the Research
Vagus Nerve Stimulators Efficacy
- 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 2.
- The efficacy of VNS becomes optimal around the sixth month of treatment, with a 50-100% seizure frequency reduction achieved in approximately 45-65% of patients 3.
- VNS can lead to an improvement of about 25-35% in depression scores, 35% in anxiety scores, and 25% in mood assessment scores 3.
- Responder rate, defined as >50% seizure improvement from baseline, was observed in 43%, 48%, 41%, and 50% of patients after 6,12,24, and 36 months of follow-up, respectively 4.
Therapeutic Parameters and Safety
- Programmable pulse parameters for VNS therapy include output current, frequency, pulse width, and ON/OFF times, which must be individualized for each patient 2.
- Output current is gradually increased from 0.25 mA to the maximum tolerable level, with typical therapeutic settings ranging from 1.0 to 1.5 mA 2.
- Greater output current is associated with increased side effects, including voice alteration, cough, a feeling of throat tightening, and dyspnea 2.
- Active VNS demonstrated significantly more percent time in response on the Clinical Global Inventory-Impression and Quick Inventory of Depressive Symptomology-Self Report, and significantly more percent time in partial response on the Clinical Global Inventory-Impression and Quick Inventory of Depressive Symptomology-Clinician, versus sham VNS 5.
Clinical Trials and Studies
- Several clinical trials have examined the effect of VNS in treatment-resistant depression, with promising evidence of antidepressant efficacy and durability 6.
- A one-year, randomized, sham-controlled trial found that active VNS demonstrated significantly more percent time in response and partial response on multiple instruments, versus sham VNS, in patients with marked treatment-resistant depression 5.
- VNS was found to be safe and effective in participants with marked treatment-resistant depression, with no new adverse events identified 5.