How to disable tachy therapy with a ring magnet
In an effort to make sure I was giving accurate information, I contacted the Big 3 implantable medical device companies (Boston Scientific, Medtronic, St. Jude Medical) and asked each of them how their ICDs would react to ring magnet application.
So what did I find out?
Ring magnet application works for devices from all three companies.
When you apply a ring magnet to a Boston Scientific ICD, in most cases you will hear tones (or beeps) that correspond with the R waves on the ECG. In some cases the device may beep once per second. This lets you know that you are in the right spot.
After about 30 seconds, you will hear a longer tone that indicates that tachy therapies are disabled.
At this point you remove the ring magnet.
To turn tachy therapy back on, you reverse the procedure.
If no tones are heard after you apply the ring magnet to a Boston Scientific ICD, you are either in the wrong spot, or the magnet feature has been disabled.
(Note: This feature was disabled on certain models of Boston Scientific ICDs due to an FDA Advisory.)
For ICDs made by Medtronic, you simply apply the ring magnet and tachy therapies are disabled as long as the ring magnet is applied. When the ring magnet is removed, tachy therapies will resume.
A technical consultant from Medtronic emailed me a document entitled Magnet Use for Suspending Medtronic ICD Detection (Rev B, 18-DEC-2007).
The document offers these instructions for magnet use:
- Locate the patient’s Medtronic ICD.
- Place the magnet directly over the Medtronic ICD (secure magnet to patient to prevent dislodgement from device). Leave the magnet in place for the duration of the procedure.*
- In this magnet mode, tachyarrhythmia detection and therapy is suspended and the ICD will not interpret EMI, e.g. from cautery, as an arrhythmia.
- If the device has Patient Alert/ Care Alert Self-monitoring, you may hear a constant tone for 10-30 seconds when the magnet is first applied. If a pulsing tone or high/low alternating tone is heard with magnet application, contact the patient’s cardiologist or electrophysiologist.
- If a tachyarrhythmia occurs during the procedure and intervention is required, remove the magnet to restore permanently programmed detections and therapy or use external rescue. Removal of the magnet by at least two feet (61 cm) returns the device to permanently programmed operation.
- Magnet application does not affect the programmed bradycardia pacing mode. EMI from cautery could cause inhibition of pacing due to oversensing. If inhibition is noted on the ECG monitors, use short, intermittent and irregular bursts of cautery (e.g. less than one second in duration).
- Magnet removal returns the device to permanently programmed operation. Keep the magnet at least two feet (61cm) away from the implanted ICD device.
- Perform the following steps to ensure an electrical reset has not occurred. This can be performed on all Medtronic ICDs, except Jewel AF 7250, Micro Jewel II 7223Cx, Micro Jewel 7221 and Gem III AT 7276.a. After 10 seconds of magnet removal, re-apply the magnet to the ICD and verify that no tone or a 10-30 second constant tone results. This indicates no electrical reset has taken place. If a pulsing tone or high/low alternating tone is heard with magnet application, an electrical reset may have occurred, then call Medtronic. b. Removal of the magnet returns the device to permanently programmed operation. Call Medtronic for sterilization instructions.* These instructions are used to disable ICDs during certain surgical procedures where EMI (electromagnetic interference) could cause the ICD to oversense and trigger inappropriate therapy.
St. Jude Medical
For ICDs made by St. Jude Medical, you simply apply the ring magnet and tachy therapies are disabled as long as the ring magnet is applied. When the ring magnet is removed, tachy therapies will resume.
A representative from St. Jude Medical emailed me a document entitled Magnet Use for SJM Implanted Cardioverter-Defibrillators (August 2008).
Interestingly, this document states:
The magnet should be positioned off-center so that the curve of the donut magnet is over the top or bottom end of the device as shown below. Improper magnet placement may hinder magnet activation and could lead to undesired delivered therapy.
This image appears in the document:
St. Jude Medical appears to be the only manufacturer who specifically recommends applying the ring magnet off-center.
Ask to see the patient’s ID card
As a final thought, it’s a good idea to ask to see the patient’s ID card to clarify exactly how the device will respond to ring magnet application.
Inappropriate or ineffective ICD shocks Part 3