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Radiofrequency
Dr.Moallemy
Lesioning
Radiofrequency (RF) current is used in pain medicine to make discrete
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therapeutic lesions in various targets throughout the nervous system.
The technique is most frequently used to block nociceptive signals from
reaching the central nervous system and thereby anesthetize the
source of the pain.
RF is implemented percutaneously by means of an insulated needle
with a metal active tip that is placed in the appropriate nerve pathway.
Before the introduction of modern RF equipment, various techniques
(e.g.,cryosurgery and chemical neurolysis) were used in an attempt to
produce localized nervous system lesions; however, none have been as
widely used or are as effective as RF.
Dr.Moallemy
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The use of electricity to treat pain was first described in 1931, when
direct current was applied to the gasserian ganglion for the treatment of
trigeminal neuralgia.
Because the frequencies used (350 to 500 kHz) were also used in radio
transmitters, the procedure was termed radiofrequency.
An RF lesion generator is a device used to produce lesions in nervous
system or other tissue by the direct application of high-frequency
current to selected sites.
A typical RF lesion generator has the following systems: continuous
impedance monitoring; nerve stimulation; monitoring of voltage,
current,
and
temperature;
and
pulsed
current
delivery
mode.
Dr.Moallemy
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Image of a radiofrequency
generator.
Dr.Moallemy
The energy is focused around the active tip of the electrode and
activates charged molecules(mainly proteins) to oscillate with the rapid
changes in alternating current . This produces friction in the tissue that
causes heat formation directly around the active tip.
The grounding electrode serves to complete the circuit and to
disperse heat buildup, thereby preventing a burn of the skin.
RF energy can be applied as either continuous or pulsed current.
Continuous RF current heats the tissue surrounding the electrode and
lyses the targeted nerve. On a pathologic level, continuous RF current
heats nerve fibers and results in wallerian degeneration. On a
physiologic level, continuous RF current destroys all fiber types within
a nerve and is not selective for any one fiber
type.
Pulsed RF (PRF) delivers RF current in small bursts and thus prevents
the accumulation of heat around the electrode...
Dr.Moallemy
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Radiofrequency Lesion Generator:
Continuous Impedance Monitoring:impedance monitoring is
primarily used to confirm continuity of the electrical circuit.
However, in the pulsed mode, impedance monitoring is more
crucial because the strength of the electrical field is decreased
when impedance is high.
Nerve Stimulation: the two types of stimulation are sensory
and motor. Sensory stimulation occurs at 50 Hz and is used to
determine the distance between the electrode and the targeted
nerve fiber. Motor stimulation occurs at 2 Hz and is used to
determine whether a needle is placed too close to motor fibers ,
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Monitoring
Temperature:
Monitoring
Voltage:
Monitoring
Current:
Dr.Moallemy
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Continuous
Lesioning
The heat generated in the continuous mode causes tissue coagulation in
a small, discrete oval surrounding the active tip of the electrode.
to coagulate the largest area of nerve fibers reliably, the electrode must
be positioned parallel to the nerve.
The size of the lesion depends on several factors:
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Tissue temperature
Duration of coagulation,
Gauge of electrode and length and gauge of active electrode tip:
efficacy is maximized when needle placements anatomically precise,
when larger (e.g., 18- to 20-gauge) needles are used, and when
multiple parallel lesions are generated (within one needle width from
each other) to account for the variable nerve topography.
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Dr.Moallemy
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Dr.Moallemy
Pulsed
Lesioning
The therapeutic effect of PRF lesioning is thought to be the result of the
electrical field, rather than of the thermal effects.
The aim of PRF is done by delivering short bursts of energy (20
milliseconds) twice per second, followed by a quiet phase (lasting
480 milliseconds) during which no current is applied. This approach
allows for heat dissipation, thus keeping the tissue temperature
lower than the neurodestructive threshold of 45°C.
Voltage in the continuous mode is 15 to 25 V, compared with 45
V in the pulsed mode.
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Because the electric field is strongest at the tip of the electrode, it
is recommended that electrodes be placed perpendicular, rather
than parallel, to the targeted nerve during creation of a PRF lesion
PRF current appears to have both thermal and nonthermal effects
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Pulsed
Lesioning (continued)
The nonthermal effects may be attributed to an effect on the function
of
voltage-gated ion channels.
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It would appear that the best use for this modality is in the treatment
of radiculopathies and painful peripheral neuropathies.
it is recommended that electrodes be placed perpendicular, rather
than
parallel, to the targeted nerve during creation of a PRF lesion.
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PRF lesioning is traditionally considered safer than continuous RF because
it has no reported neurologic side effects.
Dr.Moallemy
Dr.Moallemy