Diathermy Interactions with Implanted Leads and Implanted Systems with Leads

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Diathermy Interactions with Implanted Leads and
Implanted Systems with Leads

• Marian Kroen
• Office of Surveillance and Biometrics
• Issues Management Staff
• May 29, 2003

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Adverse Events

• Interactions of diathermy therapy in patients
  with Deep Brain Stimulators
• Two patients treated with shortwave diathermy
• One pt. treated after oral surgery
• One pt. treated at thoracolumbar region
• Both patients went into a coma and subsequently
  died

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What is Deep Brain Stimulation?
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What is Diathermy?

• Diathermy can be thought of as an
  electro-magnetic heating pad. While a heating
  pad only heats the skin, this heats inside the
  body.
• Diathermy means deep heat, but can be used in
  both heating and non-heating modes.
• Used for relief of pain, sprains, strains,
  bursitis, muscle spasms.

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Diathermy
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Who Uses This?

• Diathermy is used by
• physical therapists
• occupational therapists
• sports trainers
• others..

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Three Kinds of Diathermy

• Shortwave (radio-frequency)
• 13 to 27.12 MHz
• Newer models use 27.12 MHz
• Microwave
• Ultrasound

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Medtronic Testing

• Medtronic performed in vitro testing to assess
  the effect of diathermy on DBS systems and
  provided the results to FDA
• Results
• Temperature rise of 55º C at DBS lead electrode
  during 15 minute diathermy exposure (max.
  diathermy settings)
• Temperature rise of 27º at pulse rate of 8 and
  amplitude of 10 (setting for adverse event)

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What Information Do We Need?
?
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What is the Scope of The Problem?

• Expert committee determined need for more testing
  to determine scope of interaction problem
• Are all implants affected?
• Are all metal implants affected?
• Does the shape of metal implants matter?
• Is the problem only with active implants?

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OST Tested Active Implants

• Temperature rise at the lead electrode is high.
• Temperature rise occurs whether or not a
  pacemaker is connected.
• Cardiac lead and pacemaker system showed the
  highest temperature rise of 48.8 degrees C
• Spinal Cord Stimulator system and lead had 2nd
  highest temperature rise of 27.6 degrees C.
• The temperature rise with leads was highest where
  a shallowly implanted lead was simulated.

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OST Tested Non-Active Implants

• Minimal heating (1 to 3.6 degrees C) for
• 4 inch long screw
• Fracture Plate
• Fracture plate screws
• Titanium rod
• Stainless Steel rod

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Conclusions

• Diathermy Interactions with dangerously high
  temperatures limited to
• Implantable systems with metallic (conductive)
  leads
• implanted metallic leads themselves

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Theory

• Implanted lead acts like an antenna to receive
  energy.
• Power is dissipated in the tissue where there is
  no insulation (electrodes).
• The current density, and thus the temperature, at
  the lead electrodes can be very high, due to the
  small surface area of the electrodes.

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Can All Types of Diathermy Cause this Interaction?

• Both Shortwave and Microwave diathermy produce an
  electro-magnetic field which can interact with
  implanted leads.
• Ultrasound diathermy would have a different mode
  of interaction with implants (mechanical rather
  than electro-magnetic).

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Taking Action
Alerts
Recalls
Education
Labeling
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FDA Actions

• Labeling on Metallic Leads and Lead Systems
• Labeling on Diathermy Equipment
• FDA issued a Public Health Notification
• Journal Articles
• Patient Safety News

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Hmm, Why No Injuries from Pacers?

?
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Why are There No Reported Injuries for
Interactions of Diathermy with Cardiac Pacemakers
and Leads?

• Testing shows high pacing lead electrode
  temperatures
• Pacemakers and leads have long history.
• Two reports of damage to the pacemaker (but not
  to the heart) with diathermy use.

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Possible Reasons for Lack of Pacing/Diathermy
Injuries

• Warnings adequate?
• Blood flow in heart carries away heat
• Distance, diathermy to heart
• Damage, but nobody put 2 2 together
• Brain has no pain receptors, heart does

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Thoughts?

?