Vagus Nerve Stimulation (VNS)

Overview

Vagus Nerve Stimulation (VNS) is a form of neuromodulation that alters nerve activity through the implantation of a device. This device delivers regular, mild electrical pulses to the brainstem via the vagus nerve located in the neck. Once these pulses reach the brainstem, they are transmitted to various brain regions, effectively modifying the function of brain cells.

Often likened to a “pacemaker for the brain,” VNS helps regulate brain activity much like a pacemaker does for heart function. It is typically considered for individuals who have not found relief from other conventional therapies. VNS is primarily used for patients with treatment-resistant epilepsy or depression, and it has recently been approved as a rehabilitation aid for certain stroke survivors.

Reasons for undergoing the procedure

The vagus nerve is one of the twelve pairs of cranial nerves that transmit electrical signals between the brain and various regions of the neck, head, and torso, playing a crucial role in regulating many bodily functions. Identified as cranial nerve X (10), it is the longest of the cranial nerves. Each person has a vagus nerve on both sides of the body, with both originating from the brainstem and extending through the neck into the chest and abdomen.

This nerve is vital for connecting the neck, heart, lungs, and abdomen to the brain. The U.S. Food and Drug Administration (FDA) has approved VNS for the treatment of three specific medical conditions.

Epilepsy

When traditional medications have been ineffective in controlling a patient’s seizures, VNS is approved as an adjunct therapy for adults and children aged four and older who are experiencing focal (partial) seizures.

Depression

Adults who are 18 years of age or older with persistent or recurrent serious depression who have not improved after four or more antidepressant therapies are eligible to use VNS.

Stroke rehabilitation

For patients with moderate to severe ischemic stroke (blocked blood flow)-related loss of arm and hand function, VNS is approved as an adjunct to rehabilitation therapy.

The exact mechanism of VNS remains unknown to researchers.

VNS is believed to help regulate seizures by:

• Increase blood flow to vital brain regions.
• Modify the erratic electrical rhythm that occurs during a convulsion.
• Raise the concentration of neurotransmitters in your brain that may regulate the onset of seizures, namely norepinephrine and serotonin.

VNS is believed to help treat depression by:

• Modify the concentration of particular neurotransmitters in your brain that are involved in mood regulation.

VNS is believed to help with stroke rehabilitation by:

• In order to regulate your arm and hand movements, you should activate the motor cortex part of your brain.

Before the procedure

Before your surgery, your doctor will perform a physical examination. To ensure there are no underlying health concerns, you may need to have some blood drawn.

The device implantation surgery is typically conducted as an outpatient procedure, but some surgeons may recommend that you stay overnight for monitoring.

During the procedure

Prep for surgery

You will take an antibiotic the day of the procedure to reduce the possibility of an infection from the incision.

Before surgery, your chest and neck are cleaned. In order to numb the surgical sites, you might be given local anesthesia throughout the procedure. Usually, general anesthesia is administered to keep you unconscious during the process.

Vagus nerve stimulation device

The components of the vagus nerve stimulation device are an insulated wire lead with electrodes at the end and a vagus nerve stimulator (pulse generator).

Device implantation

To access your vagus nerve, your surgeon will first make two incisions (cuts); the first will be on the left side of your neck, and the second will be on your upper left chest. Through the incision created in your neck, the coil electrodes at the end of the lead wire are gently wrapped around your left vagus nerve. The insulated lead line that runs from the electrodes in your neck to your chest at the incision in your chest is then guided by your surgeon. After that, they attach the electrode’s end to a battery. A little larger than a silver dollar is the battery. It passes through the opening created above your muscle in your chest.

Device initial testing

The system is tested once the electrodes, lead wire, and device are implanted. Normally, the gadget is set to the lowest level and left on for 30 to 90 seconds to ensure that your vagus nerve is being stimulated. Next, the system is tested by your surgeon. Lastly, permanent stitches (sutures) are used to attach the device to your pectoralis fascia, which is the thin layer of collagen covering your pectoralis major muscle.

Typically, the surgery takes 45 to 90 minutes to complete.

After the procedure

Device adjustment and operation

You will return to your doctor’s office in two to four weeks to either activate the stimulator device or adjust its settings if it has already been turned on. The device is programmed using specialized software, a computer, and a programming wand. It will be set to deliver electrical impulses to your vagus nerve with specific parameters, including the strength of the current (measured in milliamps), pulse frequency (measured in Hertz), pulse duration (measured in microseconds to seconds), and an on/off cycle (measured in seconds to minutes). Initially, the settings are typically kept low to assess your response and monitor for any side effects.

Your doctor will determine the on/off cycle of the device, and you will also receive a handheld magnet. This magnet can be used to provide additional stimulation if you sense a seizure is approaching by swiping it over the device. During home rehabilitation exercises after a stroke, swiping the magnet will initiate 30 minutes of stimulation. Holding the magnet over the device will turn off the stimulator, while removing it will revert the device to its programmed stimulation cycle. In some cases, an increase in your heart rate may also activate the device, particularly in epilepsy treatments.

Regular follow-up visits with your healthcare provider are essential to ensure that the device remains properly positioned in your chest and is functioning correctly. Adjustments to the device settings can be made as necessary.

Battery life

The battery in your stimulator will need to be replaced approximately every six years, though some batteries may last as little as one year or as long as fifteen years. When the battery runs low, the entire stimulator will be replaced. This procedure is relatively brief and involves making a small incision in your chest wall.

Notifying more medical professionals

Before undergoing any medical procedures or imaging tests, such as Magnetic Resonance Imaging (MRI), disclose to all of your healthcare professionals that you are the owner of a vagus nerve stimulator device. This test may cause issues for your gadget.

Risks

When stimulating the vagus nerve, common dangers include:

• Infection.
• Soreness and swelling where cuts are made.
• Injury to the vagus nerve or nearby tissues.

Following vagus nerve stimulation, common side effects include:

• Coughing.
• Headache.
• Hoarseness.
• Modification of voice.
• Speak with difficulty (dysphonia).
• Tickling or pain in the neck or throat.
• Dyspnea, or shortness of breath or difficulty breathing.
• Having difficulty swallowing (dysphagia).

If you have these side effects, they might go away or you might stop being troubled by them eventually. In the event that the adverse effects become intolerable, the electrical impulses may be adjusted, or the device may be switched off either permanently or temporarily.

Among the harmful side effects are:

• Infection.
• Syndrome Horner.
• Paralysis of vocal cord.
• Cardiac arrest, or stopping of the heart, is possible.
• Facial muscle paresis, or weakness of the muscles in your lower face.
• Mechanical issues such as a malfunctioning gadget or a break in the lead wire.
• An abrupt, inexplicable death. This does not occur more frequently than is typical in the population of epileptics.

Outcome

Forty-eight hours after your device is implanted, you can return to your regular activities. There is no need to remove your sutures, as they are designed to absorb themselves.

Epilepsy

Vagus nerve stimulation (VNS) does not cure epilepsy, and it is unlikely to completely stop your seizures. As such, you will probably still need to continue taking anticonvulsant medication. The primary goal of VNS is to reduce the frequency, duration, and intensity of seizures.

In a study of 454 participants, 37% of patients experienced a reduction of 50% or more in their seizures after one year, 43% after two years, and 43% after three years.

Depression

The effectiveness of Vagus Nerve Stimulation (VNS) for treating depression remains uncertain in research. As a result, it is generally not recommended until after patients have tried medication alongside psychotherapy.

The FDA’s approval was based on studies involving over 200 patients with depression who had not responded to traditional treatments. After one year, 20% to 30% of these patients reported significant improvement. However, some individuals with depression either showed no improvement or experienced worsening symptoms.

Stroke rehabilitation

The outcomes of a study involving 108 patients provided the basis for the FDA’s approval. Over six weeks, participants were divided into two groups: a study group of 53 patients and a control group of 55 patients. Both groups were required to complete 300–400 physical therapy exercises for 90 minutes a day, three times a week. During these 90-minute sessions, the study group received Vagus Nerve Stimulation (VNS).

The treatment group experienced an average increase in limb mobility scores of five points, while the control group improved by only 2.4 points. Ninety days after starting therapy, 47% of the treatment group showed an improvement of six points or more in their limb mobility scores, compared to just 24% in the control group.

It may take a year or more to fully assess the benefits of VNS for all FDA-approved uses.