Vagus Nerve Stimulation (VNS)

VNS was introduced in the 1990’s to treat treatment resistant epilepsy and scientists noticed there was a favourable effect on depressive symptoms. Since 2005 it has been approved to treat chronic recurrent depression. The patient must be >18years and have been ill for longer than 2 years, failing to respond to at least 4 adequate drug treatments. Such patients may be described as having difficult-to-treat depression. More than 4000 patients with DTD have been treated with VNS and more than 100,000 patients with drug-resistant epilepsy.

It is an invasive technique. With local or general anaesthesia, a pulse generator or ‘stimulator’ (a bit like a pacemaker) is implanted under the skin in the upper left hand chest wall. A lead is passed from the stimulator under the skin and attached to the left vagus nerve in the neck. Electrical signals are transmitted from the stimulator to the vagus nerve via the lead and these signals are transmitted to the brain. The stimulator can be adjusted using a “wand” connected to a computer. This is not done by the patient themselves but can be carried out in a clinic by a specially trained doctor or mental health nurse.

Usually, 2 weeks following implantation, the device is turned on. Most commonly, the stimulator is on for 30 secs every 5 mins [1]. The device is programmed to the patient comfort and tolerability. The device can be turned off using a special magnet by the patient if needs be. Depending on its settings, the battery life of the stimulator is 6-10 years. Once the battery has failed, surgery is required to replace the stimulator. This is a minor surgical procedure.

Generally, VNS is well tolerated. It does not cause a seizure and is free from memory problems. Surgical side effects that can occur include: painful scar, wound infection, paralysis of left vocal cord, a loose device or device malfunction. Stimulation side effects decline over time and include: voice alterations (60%), cough (38%), breathlessness (21%), paraesthesia (21%). If the side effects are going to be problematic eg public speaking, exercising- the patient can switch the stimulation off using a hand held magnet.

VNS increases neurotransmitters and neurotrophic factors. It affects various regions of the brain and alters the functional activity of brain areas that are dysregulated (not working as they should be) in depression.

The response to VNS can take 6-12 months to start happening - so it is not an acute treatment. Although responses take longer than ECT, it is a more sustained response. Patients who respond best are those who have a shorter duration of their current episode of depression, who have failed to respond to fewer antidepressants and who have responded to ECT. VNS with treatment as usual is more effective than TAU alone- with up to 68% of patients responding over 5 years [2] Approximately 20% of patients are in remission from depression at 2 years.

Key efficacy outcomes include:

• Reduced depressive symptoms
• Improved quality of life
• Reduction in other treatments and in the need to be hospitalised

Safety outcomes

• Device failure
• Infection (the rate is only 1.7%)
• Worsening of mood including feeling suicidal
• There are some contraindications to VNS which include
  • A bilateral or left cervical vagotomy (vagus nerve has been removed)
  • Pre-existing cardiac, swallowing or breathing difficulties

It is important to note diathermy should be avoided. If a female requires a mammogram and they have a VNS device- then they must be specially positioned. Also, defibrillation of the heart or MRI scans can damage the VNS device.

If a patient’s depression does not respond to VNS, then the device can be switched off. It can also be surgically removed, though it is usually recommended to leave the wire in place since removing this could damage the vagus nerve.

A non-invasive form of VNS referred to as transcutaneous VNS (tVNS), requires further research. It is a non-surgical technique using an ear clip to stimulate a branch of the vagus nerve in the ear [3, 4].

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