there is so much misinformation, or partial information out here on this topic. there are some posts in this thread which help, and many which repeat false assumptions or keep asking questions which imply false assumptions.
i’m not a doctor, but i have an ICD, and have received “therapy” (a powerful and very unpleasant defibrillating shock) from it a dozen or so times over a period of a few years.
some facts:
1) the response to a strong, local magnetic field of these devices is by design. as noted by the doctor a page or so back, it is a feature designed in to allow a very crude level of universal control. ANY suitably strong magnet held close enough will do it. like many ICD patients, i have several such magnets purchased for the purpose.
2) what exactly the device does in the presence of this field is selectable for most modern devices. they’re all slightly different. as an example, mine was originally programmed to pace my heart at a certain rate and NOT deliver any other therapy, like a major defibrillating shock. that’s a fairly typical configuration for an ICD, i believe, but i had a discussion with my doctor (cardiac electrophysiologist) about changing it to not pace, and not deliver a shock, for reasons which are too obscure to discuss here. it is literally a drop down setting on the programming device, which uses RF, not magnetism, to reprogram the ICD.
3) the most common setting for a pacemaker in the presence of a strong magnet seems to be to switch to asynchronous pacing - not to just shut off completely.
4) again, all these devices vary, and many patients are different, but for my st jude (now abbot) ICD, the magnet has to be very, very close. like, physically in contact with my skin and in pretty much the exact spot. my
phone (12 pro max currently) has never triggered it. the pockets on my suit jackets are not in the right spot for it to do so, once we all go back to going to work and wearing suits...
so, in the case of my device, here is the only
scenario in which this “issue” would be an issue: my heart is in a dangerous abnornal
rhythm (ventricular tachycardia) and i require a potentially lifesaving shock (defibrillation) to reboot the heart rhythm. i pass out (perhaps due to said arrhythmia!) and my phone falls onto my chest in exactly the spot needed to switch the ICD into “do not shock” mode and stays there while i lie completely still until i’m dead. all other scenarios, in which i am conscious, simply won’t occur because for me it’s quite obvious when a magnet is in exactly the right spot and the ICD has switched into “do not shock mode.”
now, speculating: a higher risk would be for those who have a pacemaker, not an ICD, and the switching of the pacemaker into asynchronous mode potentially generates other arrhythmia risks, which the device is not capable of resolving with the magnet in place and the owner is not aware of the change. not everyone can feel their device doing something “different” and there are certainly many kinds of harmful heart rhythm problems. still speculating: the VERY highest risk would be if there are in fact pacemakers which are currently programmed to completely shut off in the presence of a magnetic field, implanted in patients who are completely dependent on pacing. this would be an insanely risky setting in my opinion, given that ANY strong enough magnetic field would trigger it. i have never heard of such a thing: remember that this response to magnetism is by design, not because the devices are being “interfered” with.
again, those last two points are speculation, hopefully there’s an EP in the room who can add some detail.