Vagus Nerve Stimulation for Chronic or Treatment-Resistant Depression
About Vagus Nerve Stimulation(VNS)
VNS is not brain surgery, although it is a treatment that affects the function of the brain. Vagus Nerve Stimulation uses specific stimulation of the vagus nerve to send stimulation to specific parts of the brain that are involved in mood. It is not like Electro-Convulsive Therapy (ECT), a treatment that involves stimulation of the entire brain and induces convulsions in patients. In fact, patients may not even feel the stimulation from VNS since the vagus nerve does not have the type of nerves that carry pain signals. Nor does VNS interfere with drugs, and patients having Vagus Nerve Stimulation can continue taking their other drugs without worrying about side effects or interactions between drugs.
What is the Vagus Nerve ?
Vagus means "wandering" in Latin, and is the perfect description for the vagus nerve, the longest nerve in the body. It averages almost two feet in length and "wanders" throughout the upper body. The vagus nerve starts in the brain, goes down the neck and into the body where if affects the vocal cords, the acid content of the stomach, the heart, the lungs, and other organs. In the brain it projects to areas believed to be responsible for seizures, mood, appetite, memory and anxiety (note 3). However, the vagus nerve cord does not have many pain nerves, so stimulation of the vagus nerve is not painful, although some patients may feel some sensation when electrical pulses are generated.
The History of Vagus Nerve Stimulation
Vagus Nerve Stimulation has been used to treat epilepsy patients for years; the first human clinical trial was in 1988,(note 1) and the FDA approved VNS therapy for epilepsy in 1997 (note 2). So far over 22,000 people worldwide have had VNS therapy (note 3), and it has proven to be a safe and effective treatment for epilepsy. These patients have reported minimal side effects, which have tended to decrease over time. The efficacy of the treatment has also been shown to increase with longer treatment time (note 1).
When Vagus Nerve Stimulation was first approved for epilepsy, some patients reported an improvement in mood. Researchers decided to design a study specifically to measure changes in a patient's mood and depression due to stimulation of the vagus nerve. In 1999, scientists began the first open label (no placebo group) study for depression with 60 patients. This first study found that there was indeed an improvement in mood for depressed patients. Based on this study, a more detailed and thorough study was designed to determine if Vagus Nerve Stimulation would be a safe, tolerable and effective treatment for chronic depression.
The recently completed one-year, double blind, placebo controlled trial had 235 patients from 21 participating hospitals in the United States, and showed clinically significant improvements due to treatment compared to baseline (note 2). The acute (short-term) phase lasted three months, during which half of the patients received stimulation (treatment group) and half did not (control group). The long-term phase of the study lasted an additional 9 months (for one year total treatment) of stimulation. The HRSD-24 (24 item clinician-rated Hamilton Rating Scale for Depression) improvements observed over the first year were highly significant. The results of this long-term, pivotal study were submitted to FDA in October 2003; the FDA's decision on the use of Vagus Nerve Stimulation for depression is not anticipated before October 2004 (note 2). Of note, Vagus Nerve Stimulation therapy was approved for use in patients with treatment resistant depression in the European Union in March 2001, and in Canada in April 2001 (note 2) .
How Does Vagus Nerve Stimulation Therapy work ?
The Pulse Generator (battery) delivers a small amount of electrical current to the vagus nerve intermittently (30 seconds on and five minutes off ) (note 3) 24 hours a day, 7 days a week for up to 10 years. The stimulation is delivered automatically, so the patient does not have to do anything. Because there is nothing to remember, compliance is assured. The stimulation is not supposed to be uncomfortable, and some patients do not even feel the stimulation. A nurse at the doctor's office can adjust the level of stimulation (amount of electricity delivered) if the patient ever feels uncomfortable. In the study currently being reviewed by the FDA, researchers noted several similarities between epileptic and depressed patients (note 4).
One of the most important similarities is that Vagus Nerve Stimulation treatment efficacy improves over time. The longer the patient receives stimulation, the better the results. In addition, both populations of patients share the following:
Assured adherence to treatment regimen
Safety of the procedure
Safety of the therapy
High continuation rates
No drug interactions
What is the surgery like?
Vagus Nerve Stimulation is NOT brain surgery, even though it is an invasive surgical procedure that changes the function of the brain. The stimulator is a pacemaker-like device that generates electrical pulses (Pulse Generator); it is implanted under the skin in the left chest through a small incision. While this may sound like a serious or dangerous procedure, it is not. The FDA has approved the use, and confirmed the safety of this procedure, and 22,000 patients have received the implant to treat epilepsy. The Vagus Nerve Stimulation surgery involves two small incisions, one in the chest and one at the lowest part of the neck. At no time is the brain physically manipulated by the surgeon.
The surgery to implant the NCP System takes 45 minutes to two hours. Local, regional or general anesthesia (putting the patient to sleep) is used during the surgery; the doctor and anesthetist determine which type of anesthesia is best for each patient. Most Vagus Nerve Stimulation patients will have outpatient surgery, (note 3) but some patients may need to stay in the hospital overnight, and in that case they will need a family member or companion to take them home from the hospital.