Ineffective or inappropriate ICD shocks – Part 3

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.

Boston Scientific

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:

  1. Locate the patient’s Medtronic ICD.
  2. 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.*
  3. In this magnet mode, tachyarrhythmia detection and therapy is suspended and the ICD will not interpret EMI, e.g. from cautery, as an arrhythmia.
  4. 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.
  5. 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.
  6. 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).
  7. Magnet removal returns the device to permanently programmed operation. Keep the magnet at least two feet (61cm) away from the implanted ICD device.
  8. 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.


See also:

Inappropriate or ineffective ICD shocks Part 1

Inappropriate or ineffective ICD shocks Part 2

Inappropriate or ineffective ICD shocks Part 3

Updated 12/13/2015


  • Wow — that is some great info Tom. Thanks for following up!

  • Tom B says:

    My pleasue, MIFL. I’m glad you brought it up! Tom

  • Tom, this information MUST be included in the ICD protocol. Great work as always!

  • Tom B says:

    You read my mind, Pete.Tom

  • Great information. Thanks. Wondering if the manufacturers provide the patients with ring magnets to use for misfiring ICDs? The reason being that though our protocols may not include use of the ring magnets but we may run on a pt who has self-applied the device.

  • Tom B says:

    Metro Medic FF – I’m sure they don’t supply patients with ring magnets.Without continuous ECG monitoring, there’s no way for a patient to know whether or not the ICD is delivering appropriate therapy!Thanks for the comment.Tom

  • That’s what I figured. But I thought the question should be asked/answered anyway. Funny thing here. I spoke with a friend of mine who works in an ER in a rural area. He told me that he has seen two patients who self-transported with a magnet taped to their chest. Complaints were misfiring AICD. One guy told his wife “if I pass out, take this thing off me.” Rural engineering at its best! Both patients were lucky that they indeed had a malfunctioning device rather than a lethal arrhythmia.

  • And I asked how they obtained the magnets. Physician friend couldn’t recall the details.

  • Tom B says:

    “If I pass out, take this thing off of me.” Sure thing, honey! If I’m not in the other room getting another beer…Thanks for sharing, Metro Medic FF! :)Tom

  • Shaggy says:

    Two questions. 1.Yes, you stated you got one free from your Medtronic rep, but what about the rest of us? Should we contact one of the big three about obtaining one? 2. I am assuming the magnests differ by manufacturer? Can they be interchanged?I apologize for asking for such stupid questions, but my limited cranial capacity still has me scratching my head.

  • Tom B says:

    Shaggy – As far as I know, they all work exactly the same. Next time you’re in the ED, ask if they know where they got theirs. You could also ask one of the cardiologists when they have their pacemaker clinic and talk to one of the reps. Or, just give one of the device companies a call! Tom

  • Shaggy says:

    That is now on my agenda. Thanks.

  • Anonymous says:

    I have heard in England they give every ICD patient a magnet ring and tell them how to use it. I have one and my sister does too – we keep them on top of the frig. Instructions from ICD nurse – hold it over device – do not let someone else hold it on you – they do not know how you feel (dizzy or faint). Do not tape it on – because if you faint you want it to fall off. Got magnet free from Medtronic – must sign off that you understand what magnet does & how to use it. After 8 shocks in 30 min I really wanted a big magnet!

  • Shocking says:

    Great information! I am a Home Hospice RN researching these same types of issues. For ICD magnets, the big 3 will all mail free magnets upon phone request; Boston Scientific-1.800.227.3422; Medtronic-1.800.222.0331; St. Jude Medical-1.800.681.9293. All companies except Medtronic claim any ICD magnet can be used; per a Medtronic representative, it is recommended that only a “Model 9466 Patient Magnet” be used. Thanks again for sharing- I have been having trouble finding step-by-step published information for many ICD issues.

  • Tom B. says:

    Thanks for the comment, “Shocking”! Good info.


  • Device Tech says:

    As a device tech..I work with all 3 manufacturers checking/programming devices in clinic.. Just a couple other points..   From experience .. one ring magnet, regardless of where it came from will work on all the 'big 3'.   They get their magnets pretty much from the same places, so the "medtronic 9466 patient magnet" has no signficant difference than any one elses.  I have a Boston Scientific magnet on my device cart & it works just fine..  Also from experience, in 8 years, I have never had 1 device that was programmed to have the magnet feature turned off – it's a valuable safety feature, and most implanters/reps make sure its on.
    We have never given a magnet to a patient – the chance of them turning it off during actual episodes would be too big of a liability. (gets a couple shocks… they or the family member doesn't want them to get shocked so they whip out the magnet). We tell our patients – if it goes off more than 1 time in a short period of time call 911. If it goes off multiple times it needs to be treated regardless.

  • Rep says:

    Put the ring magnet over the device and leave it. Removing the magnet returns the device to therapy. Magnets are not company specific. Placing a magnet over an ICD disables Tachy tx, does not affect pacing. Placing a magnet over a pacemaker forces pacing- changes it to async, returns to demand when magnet removed.

  • Rep – You only "leave it" for Medtronic and St. Jude Medical. You do, in fact, remove it for Boston Scientific after disabling tachy therapy as per their reply to my inquiry.

  • hck12 says:

    Patients randomized to ICD therapy in the early primary and secondary prevention ICD trials were found to have substantially higher rates of appropriate ICD shocks when compared to the rate of sudden cardiac death experienced by patients randomized to medical therapy.

  • kurioso says:

    Such an inappropriate event in a patient with an implanted Riata lead should prompt detailed fluoroscopic evaluation of the lead especially in the region around the tricuspid valve to avoid subsequent inappropriate ICD shocks.

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