Help for Those with Movement Disorders

Activa System implant and other technologies offer help for those suffering
from uncontrollable shaking in diseases like Parkinson's 

From: Design News, Lifesavers: The Components behind Today's Medical
Breakthroughs - May 5, 2003 - page 9

By: Amy Castor

The uncontrollable and sometimes violent shaking that accompanies Parkinson's
and another movement disorder called "essential tremor" can rob its victims
of the ability to do simple tasks. 

In 1997, new hope arrived when the Food and Drug Administration (FDA)
approved Medtronic's Activa system, a device that blocks the errant brain
signals responsible for the symptoms. Since Design News first reported on
Activa four years ago, the device has evolved, gained new FDA approvals for
its use, and gathered momentum for use in treating other movement disorders,
along with obsessive compulsive disorder and epilepsy. 

Today, 10,000 people throughout Europe, Canada, and Australia have an Activa
system implant. For the nearly 650,000 people in the U.S. who suffer from
Parkinson's, the device brought a welcome option to drug treatments that lose
their effectiveness over time and surgeries that permanently destroy brain
tissue. A reversible procedure, the Activa works by delivering mild
electrical pulses to targeted areas of the brain to block the signals that
cause the symptoms. 


Caption 1: A new device called Kenatra (not shown), up for FDA approval, will
eliminate the need for two pulse generators to stimulate both sides of the
brain in patients who require tremor control on both sides of the body. 


Through its upgrades, the inner workings of Activa remain the same: An
insulated electrical lead is surgically implanted in a targeted area of the
brains thalamus. From it, an insulated extension wire threads out under the
skin of the head, neck, and shoulder to an implanted pulse generator just
below the collar bone. The pulse generator sends a constant stream of tiny
electrical pulses to thalamus. Once the system is implanted, the user can
turn the device on and off at will or change the setting from low to high
stimulation by moving a hand-held magnet over the pulse generator. An
external computer allows doctors to make minor adjustments to the system
noninvasively. 

Hardware Updates 

Some of the advancements in Activa are minor, but worthy of mention. They
include an 25% thinner extension wire, which makes it less noticeable and
more comfortable for the patient. Spacing between the four electrodes in the
lead is reduced from 1.5 to 1.0 mm, allowing it to reach smaller brain
targets. And replacing the briefcase-sized computer used to program Activa is
an N'Vision programmer that resembles a supersized PDA. Using telemetry to
communicate to Activa, the device allows clinicians to alter various settings
of the pulse generator by touching the screen with a stylus. 

More Updates Are Pending 

Medtronic is crossing its fingers in hopes that by this summer the FDA will
approve use of a bidirectional implanted pulse generator. The new device,
called Kinetra, replaces the need for two pulse generators in patients who
want two Activa systems to reduce tremors on both sides of the body. Kinetra
accepts two leads and two extensions. For the patient, this means less cost,
fewer implants, and less time on the operating table. The device also leaves
room on the right side of the chest for cardiac assist devices, should the
patient ever need one. 

"Kinetra has been selling for three years in Europe," says Lynn Otten, senior
principal design engineer for Activa. "But releasing products in Europe is
substantially easier then in the U.S."  

Further out on the Activa timeline is Restore, a rechargeable battery for the
implanted pulse generator that would eliminate the need for battery
replacement surgery. The 9V battery in Activa lasts about five years.
Currently, Restore is undergoing clinical testing in cadavers. 

"We're looking at bioacceptability and doing testing to determine where on
the skull to place these things that would be the least traumatic if a person
were in a car accident or got hit in the head," says Otten. "All these
questions need to be answered before we even go to fixed prototypes." She
expects the device to hit the market in five to six years. 

Otten gets excited in talking about a new technology currently in testing at
three U.S. clinics called "active MRI," which allows the surgeon to place the
lead into the brain a real time without the use of a head frame. Normally,
heavy stereotactic titanium frames are screwed onto the patient's skull prior
to taking the MRI. Extremely uncomfortably, these frames provide a coordinate
system for localizing targets. Not only are active MRIs a blessing to the
patient, but they open a door to understanding how Activa works. 


Caption 2: Replacing the briefcasesized computer used to program Activa is an
N'Vision programmer. 

Caption 3: The implantable impulse generator, shown here, is similar to a
cardiac pacemaker. It generates electrical signals that are delivered to the
brain via a thin, implanted coiled wire with electrodes attached at the tip.


In Parkinson's, cells die in the substantia nigra, a corner of the brain that
produces dopamine, a neurotransmitter that allows communication between brain
cells involved in the control of movement. The reduced levels of dopamine
lead to the symptoms of Parkinson's. Some theories suggest that Activa works
by enhancing dopamine receptor cells to better absorb dopamine, but no one is
sure. 

"Right now nobody knows how Activa works,", says Otten. "All we know is that
it works, and when we shut it off, it doesnt work."  

Other Benefits 

Patients suffering from other types of movement disorders also may soon be
finding relief in Activa. Right now there are 250 patients in Europe using
Activa to treat Dystonia, the third most common movement disorder outside of
Parkinson's and essential tremor. Often occurring in children, Dystonia is a
syndrome of sustained muscle contractions that cause twisting, repetitive
movements, or abnormal postures. 

"The results are phenomenal," says Otten. "You go from a contorted, screaming
child who drags himself along the floor to one who is running marathons."  

There's also a pocket of studies going on with Activa and obsessive
compulsive disorder with "interesting to good results." And Activa is now
being tested on epilepsy patients, using a combination of blocking and
sensing technologies. 

Shrinking Technology 

The future for Active looks bright, but tiny. "Were looking for total
miniaturization of the system," says Otten. 

Although tight-lipped about the technical details, she says that as soon as
five years we may be seeing a system that is entirely implantable and fits
completely inside the patient's head. 

"You won't have to do anything with the chest walls anymore, and no more
wires dangling through the neck," she says. 

Prototypes exist, she says, and are currently being tested on cadavers. 


Caption 4: Medtronic developed a new extension, which threads under the skin
of the head, neck, and shoulders. The thin, implanted coiled wire is 25%
thinner than its predecessor, giving it a lower profile and making it more
comfortable for patients.

