On Sun, 22 Sep 2013 00:38:29 -0500, Jon Elson
wrote:

Don Foreman wrote:


He looked at me oddly. He said that if the ICD were erroniously
tripped it would feel like being kicked in the chest by a mule.

I think most of this is a bunch of bull, because the makers of the
ICD have no idea what it will do in this case. The electric field
of the HF will not penetrate the body, although the leads are
usually buried pretty shallowly from the unit across the chest.
But, the unit has very strong filters to remove non-heart
frequencies from the input that it is processing, to extract only
the muscle pulse. However, it is definitely programmed to
detect big electrical pulses as the use of an external defibrillator in
the hands of a trained expert, and just shut off completely for
a few minutes to allow medical personnel to perform what they need
to do without any automated interference.

Paramedics know that a strong magnet will shut down an ICD by design.
They carry big white toroidal magnets specifically for that purpose,
and that's why we who have ICD's don't walk under the big
electromagnets that pick up cars.

I know that skin effect would theoretically limit penetration of HF
(high-frequency, about 8 MHz) electric fields into the body -- that's
why it's HF! If it weren't HF, that several kilovolts of arc-starter
would eventually provide an unpleasantly shocking experience rather
than just a little burn. But understanding the theory is one thing,
being the potential kickee is quite another.

So, my guess is that the only way to interfere with the ICD is
possibly to allow the HF to zap to your arm on the side where the
ICD unit was placed.

I agree -- and my ICD is on my left while I wield my TIG torch with my
right hand. My concurring opinion was based on considerably more
rigor than a guess.

Well, that COULD happen, I've done it
myself. The HF arc sure looks mean, but through clothing, it
really doesn't feel that impressive. The HF just doesn't have
anywhere near the signature of fibrillating heart muscle.
The arc currents when welding with AC might, but that would be
mostly magnetic field, not electric. And, you said your
tests showed the magnetic field was not a problem.

Right. I've been MIG welding routinely since my implant in January of
2010, sometimes at current levels considerably higher than I usually
use with TIG. My measurements indicated that H field strength was
within bounds even at the highest current my TIG machine can deliver,
and I never need that much current.

Lead dress is very important as I'm sure you know.


Anyway, If I'd been in the same situation, I would have had
somebody with me the first time, and showed them how to turn
the machine off, and be ready to call 911 if I did get the
ICD to trigger.


Yeah, Jon, you're not the first to have mentioned that! I was
actually pretty sure I knew what I was doing, or I wouldn't have been
doing it. Your recommended procedure would certainly have been more
prudent.