Re: Jacob's Ladder

["Donald E. Simanek" <dsimanek@eagle.lhup.edu>]

Someone asked about the safety of using high voltage physics demos near
students (and profs) with pacemakers. I passed this on to a friend who
does technical writing for a pacemaker company. He supplied some
interesting information, which I forward below:

	-- Donald

......................................................................
Dr. Donald E. Simanek                            Office: 717-893-2079
Prof. of Physics                    Internet: dsimanek@eagle.lhup.edu
Lock Haven University, Lock Haven, PA. 17745          CIS: 73147,2166 
Home page: http://www.lhup.edu/~dsimanek            FAX: 717-893-2047
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> From Robert.Schadewald-1@tc.umn.edu Fri Aug 22 10:40:58 1997
Date: Thu, 21 Aug 1997 22:27:00
From: Robert Schadewald <Robert.Schadewald-1@tc.umn.edu>
To: "Donald E. Simanek" <dsimanek@eagle.lhup.edu>
Subject: Re: Jacob's Ladder (fwd)

Don,

You are right; I do some contract technical writing work for Medtronic.
That hardly makes me an expert on pacemakers, but here is my understanding
of the matter.

In the early days of pacing, there was real potential for powerful magnetic
fields to disrupt a pacemaker.  Needless to say, pacemaker engineers are
conscious of the potential problems, study them in great depth, and build
substantial defenses into the devices.  A modern pacemaker is enclosed in a
laser-welded, hermetically sealed titanium can, and the human body itself
must provide some shielding.  My guess is that the pacing leads, which run
from the device into a vein and then down into the heart, provide antennas
that could be a problem if you induced substantial currents into them.
Again, the designers are quite conscious of this and build their defenses
accordingly.  Several pacemakers on the market today are guaranteed to
coexist with an implantable defibrillator, which means that they can
withstand a jolt of tens of joules delivered to tissue an inch or so away
from their own lead electrodes.

On the extremely rare occasions when a modern pacemaker does get "zapped"
despite its defenses, the usual result is an electrical reset.  This
typically means that it "forgets" how it was programmed to pace and goes
into a basic, relatively brainless pacing mode -- essentially, what *all*
pacemakers did 20 years ago.  This will keep a pacemaker-dependent patient
alive and functional but with none of the extra benefits modern pacemakers
can provide.  The patient probably will notice that something happened and
go into the clinic, where they slap the programming head over the device,
interrogate it by telemetry, figure out what happened, and reprogram it.
If the patient doesn't even notice the reset (a real possibility for some
patient conditions), the problem will be discovered and corrected at the
next scheduled follow-up.

Whatever, Medtronic has a 24-hour hotline for pacing-related questions.  I
don't know the 800 number, but the regular switchboard is 612-514-4000, and
you can ask for the hotline.  If the hotline people don't know the answer
offhand, they will get it.  They're damned good.

Bob