Work place electromagnetic interference - Medtronic

Hi all

I am back at work today (working from home still). 

I normally work in an industrial environment, with large transformers, lots of EMF signalling and 25,000 V uninsulated power lines.

Have any of you managed to get a more detailed document from the pacemaker manufacturers on how my employer can conduct a risk assessment on my safety at work?

In addition, if for whatever reason my pacemaker did go into a safe mode or worse - other than symptoms would the pacemaker alert me in some way?

Kind regards







industrial environment

by Tracey_E - 2020-11-27 09:57:14

It's possible for the employer to have an EMI analysis to figure out exactly what's safe for you. I don't know much about it but a few people have posted before that their employers had this done.

In order to cause problems, a magnet has to be very large and very close, less than 6" is the rule of thumb. Rare earth magnets are stronger but still have to be 8-10 inches away. I found a chart with size of the magnet/distance for a pacer. It's in a post somewhere from 3-4 months ago when I got a rare earth magnet knife holder for my kitchen. I wasn't worried about having it in the house, but wasn't sure if I should be installing it myself or have my husband do it. 

The pacer will never turn off. The worst that can happen is it switches to test mode and paces at a steady rate, probably 60. It won't alert you but if you pace a lot you will feel it. This is what they do every time they interrogate the pacer. That puck they place over it is a magnet. As soon as you get away from the interference, it will go back to normal. 

If you ever suspect you switched modes, ask when you have your next interrogation. It will show up on the report. 


by AgentX86 - 2020-11-27 13:15:47

The minor problem is switching to "safe mode" .  This happens if there is a very strong DC magnetic field.  This falls off as the cube of the distance so it's unlikely that a DC (e.g. a permanent) magnet will be strong enough to trip the sensor at a distance of over 6", give or take.  All this would do is put your pacemaker into a safe mode, set to a constant rate (usually 60bpm) and with all feedback turned off (set to AOO or VOO, probably).  You might feel this but it's unlikely to be dangerous.

The magor problem can be "oversensing".  This occurs when and AC (changing) magnetic field induces a current into the pacemaker leads, fooling the PM to think the heart is being paced when it's not, or there's something wrong and an ICD may deliver a shock.

How maor this is depends on your particular situation.  If you're pacing a low perentage of the time, it may not be important. You'll probably feel any changes and be capable of moving to a sfe distance.  If you're dependent, it could get serious.  You may not be able to get away from the problem because your heart isn't beating.


by quikjraw - 2020-11-28 06:01:45

Thank you both.

I'm generally not worried outside of work but my work site is full of EMF sources. We don't even have metal fences as a current is induced in them.

I've managed to get some numbers from Medtronic and passed them to my employer. I suspect that they will end up having to get someone in to actually measure the different fields.

"Power Frequency (50/60 Hz)

10 000 V/m (6 000 V/m; outside nominal)

High Frequency (150 KHz & up) 141 V/m

Static Magnetic Fields (DC) 10 gauss

Modulated Magnetic Fields

80 A/m up to 10 KHz and 1 amp/meter for greater than 10 KHz

*Limits may vary for other device settings refer to device labeling for further device-specific guidance. "

I sit about 3m from a large transformer and about 10m from 25000V AC uninsulated power line.


by AgentX86 - 2020-11-28 12:59:49

The reason I focus on magnetic fields rather than electric feilds is that e-feilds are easy and cost-effective to shield. Even tin-foil will shield most.  Magnetic fields are not so easy and require heavy and expensive material.  Your pacemaker is fairly well shielded from e-fields but it would be impossile to shield agains b-fields and still fit it in the body.

It doesn't matter one bit how high the voltage is in the transformer.  Current and the windings (number and size) matters create the magnetic fields.

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