Diathermy Interactions with Implanted Leads and Implanted Systems with Leads

1. Diathermy Interactions with Implanted Leads and Implanted Systems with Leads Marian Kroen Office of Surveillance and Biometrics Issues Management Staff May 29, 2003

2. 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

3. What is Deep Brain Stimulation?

4. 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.

5. Diathermy

6. Who Uses This? Diathermy is used by: physical therapists occupational therapists sports trainers others…..

7. Three Kinds of Diathermy • Shortwave (radio-frequency) 13 to 27.12 MHz Newer models use 27.12 MHz • Microwave • Ultrasound

8. 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)

9. What Information Do We Need? ?

10. 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?

11. 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.

12. 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

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

14. 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.

15. 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).

16. Taking Action Alerts Recalls Education Labeling

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

18. Hmm, Why No Injuries from Pacers? ?

19. 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.

20. 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

21. Thoughts? ?