Vagus Nerve Stimulation for Chronic or Treatment-Resistant
Depression
About Vagus Nerve Stimulation
VNS is not related to 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.
On July 15, 2005, the FDA approved vagus nerve stimulation as a
treatment for chronic depression.
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.
What Happens After the Vagus Nerve Stimulation Surgery? Most
Vagus Nerve Stimulation patients go home the same day or the
next day. You will feel some minor stiffness/soreness around the
area of the implant for a few days. Your doctor may prescribe a
minor pain medication such as Tylenol with codeine. A week later
your surgeon will probably want to check the scars and a nurse
can program/change the settings on the stimulator in the
doctor's office.
Is the Vagus Nerve Stimulation Surgery Final?
The Vagus Nerve Stimulator can be turned off or removed
(explanted) at any time if the patient feels that it is not
helping, or in the unlikely event that the patient can't
tolerate the stimulation. The device can be completely turned
off in less than 30 seconds in the doctor's office, all it takes
is for a nurse to hold a programmable wand over the skin above
the Pulse Generator. Explantation (removal) of the Vagus Nerve
Stimulation device is also possible, however, less than one half
of one percent of the 22,000 patients have elected to have the
device removed. As for implantation, the surgery to remove the
device is a very simple procedure. Only the Pulse Generator is
taken out of the body; attempting to remove the electrode from
around the vagus nerve could cause damage, and is not
recommended.
References 1. Pharmacoresistant Epilepsy and VNS Therapy.
September 24, 2003 presentation by J.W. Wheless, MD. The
University of Texas Health Science Center, Houston TX, USA. 2.
Form 10-Q for Cyberonics Inc, September 4, 2003. 3. Vagus Nerve
Stimulation Therapy Mechanisms of Action. September 24, 2003
presentation by M.S. George, MD. Medical University of South
Carolina, Charleston, SC, USA. 4. The Investigation of Vagus
Nerve Stimulation Therapy in Treatment-Resistant Depression.
September 24, 2003 presentation by R.L. Rudolph, MD. Cyberonics,
Inc.