American Society of Regional Anesthesia and Pain Medicine May 2017 - 30
Review of Advances in Spinal Cord Stimulation Waveform Technology:
A Neuromodulation Special Interest Group Article
INTRODUCTION
Advances in spinal cord
stimulation (SCS) have resulted
in new stimulation platforms.
Historically, creation of
electrical fields resulting in
paresthesia was fundamental
to SCS analgesia.1 However,
paresthesia-free therapy is
now available, as are other
platforms. This article will
provide a brief overview of
neuromodulation platforms.
from pleasant to noxious.5 The difference between perception
and discomfort threshold comprises the therapeutic window of
stimulation amplitude for an individual patient.
Because pulse width is adjustable to widen or narrow the electrical
field, amplitude and pulse width have been the primary parameters
adjusted during trialing and maintenance of SCS. Frequency is
adjusted to alter the "smoothness" of perceived stimulation.
Alexios Carayannopoulos, DO, MPH
Comprehensive Spine Center, Pain and
Rehabilitation Medicine
Rhode Island Hospital,
Providence, Rhode Island
Warren Alpert Medical School of
Brown University
Providence, Rhode Island
CURRENT VERSUS VOLTAGE
The internal pulse generator
(IPG) uses either a constant
current (CC) or a constant
voltage (CV) power source. A
CC source supplies current
to tissue by adjusting voltage
Section Editor: David Provenzano, MD
in response to impedance,
resulting from lead positioning,
fibrous encapsulation, and scar tissue.2 A CV source adjusts current
in response to impedance, maintaining constant voltage. Changes
in impedance affect strength of stimulation during a stimulus pulse
and efficacy of stimulation over time.3
Although both systems produce paresthesia and effectively treat
chronic pain, limited studies reveal that some patients prefer CC
stimulation, describing more comfortable and better pain relief.4
Why patients prefer CC over CV stimulation is unknown but may
reflect differences in pulse shape. CV generates spike-shaped
pulses, which steepen with rise
of impedance at the beginning
of each pulse. CC generates
rectangular-shaped smooth
pulses, created in response to
increased impedance, which
may be perceived as more
comfortable.
HIGH-FREQUENCY STIMULATION
Low frequencies (20-120 Hz) result in patients feeling individual
pulses. At higher frequencies, pulses start to blend, resulting in a
tingling sensation without detection of individual pulses.6 Recently,
investigators examined the effect of altering the frequency rate. In
preliminary work, application of higher frequency rates in SCS has
shown promise for low back pain, while maintaining efficacy for
neuropathic pain syndromes. Two-year data shows maintenance of
such effect.7
Because of these advances, neuromodulation nomenclature has
changed.8-11 Traditional methods of tonic SCS programming are
called "conventional" stimulation, whereas platforms between
500 to 10,000 Hz-platforms with higher frequency bursts of
stimulation-are now called "high-frequency" (HF) stimulation.8-11
The 10 kHz setting is an energy-demanding form of stimulation,
requiring frequent charging of the device.
BURST STIMULATION
Pulse shape is one factor determining nerve fiber response to
SCS. Another factor is the frequency of pulses used to activate
large fibers in dorsal column. Frequencies of SCS impulses vary
between 30 and 120 Hz but are usually in the range of 50 Hz. Burst
stimulation is an alternative paradigm created to combine elements
of high-frequency stimulation
with less energy-demanding
requirements of tonic
stimulation. As such, it offers
concise signal transmission,
allowing for passive discharge
during the recovery phase
between each pulse within
the burst pulse train and
between each group of burst
pulse trains. This differs from cycling, as cycling requires an active
discharge in the recovery phase. The de Ridder12 burst waveform
uses pulse trains of five high-frequency spike pulses at 500 Hz,
occurring 40 times per second.
"Pain specialists should stay informed
of advances in neuromodulation to
help more patients and to enhance
generalizability of therapy."
TONIC STIMULATION
Paresthesia is created by manipulating three basic elements of
SCS: frequency, amplitude, and pulse width. Frequency is how
often the device delivers charge and depolarization. Amplitude
is the relative strength of charge delivered. Pulse width is the
duration of charge delivery.5 Traditionally, tonic stimulation involves
low frequencies, typically in the 20-120 Hz range. Amplitude is
adjusted until the patient feels stimulation. Perception threshold is
the amplitude first detected by the patient. Discomfort threshold
is the amplitude when the patient feels paresthesia transitioning
30
2
Burst stimulation mirrors neuronal firing patterns in the spinal
cord. These neurons fire in groups of action potentials, followed by
periods of quiescence, akin to the burst program generated by the
IPG. Other neurons, at the same stage of sensory processing, fire in
American Society of Regional Anesthesia and Pain Medicine
2017
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