# Presentation: 504262

## Diathermy Interactions with Implanted Leads and Implanted Systems with Leads

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

##  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

## What is Deep Brain Stimulation?

## 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.

## Diathermy

## Who Uses This?

-  Diathermy is used by:
- 	             physical therapists
-                occupational therapists
-                sports trainers
- 			  others.....

## Three Kinds of Diathermy

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

## 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)

## What Information Do We Need?

- ?

## 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?

## 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.

## 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

## Conclusions

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

## 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.

## 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).

- Taking Action

- Alerts

- Recalls

- Education

- Labeling

- FDA Actions

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

## Hmm, Why No Injuries from Pacers?

- ?

## 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.

## 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

## Thoughts?

- ?