On behalf of a fish biologist who wishes to remain anonymous, we are publishing this blog. The biologist has an implanted heart pacemaker and faced concerns about participation in electrofishing operations. The text has been authored in first person and lightly edited by us with approval by the author. We believe that this factual investigation will provide useful information to employees and supervisors alike.
~Colleen Caldwell, New Mexico Cooperative Fish and Wildlife Research Unit and Jim Reynolds, Alaska Cooperative Fish and Wildlife Research Unit (retired)
I talked to several medical professionals and none of them seemed concerned with the possibility of me getting shocked since, apparently, pacemakers have built-in insulation and are protected against electric shock. One cardiac nurse told me she had a man come in who had been hit with a Taser right on his chest above his pacemaker, and that he had not been affected.
My cardiologist told me he did not think it would be safe for me to electrofish. He was not worried about possible shock, but rather the possibility of electromagnetic interference. My pacemaker is in my abdomen instead of my chest as it is in most adults, and because of this, my setup is a little different than normal. I have a unipolar lead rather than a bipolar lead (a lead is an electrical cable that connects the heart to the pacemaker device). Unipolar leads are more susceptible to picking up external electrical signals, and the concern was that interference could cause the pacemaker to “over-sense” and think that my heart didn’t need assistance anymore. He seemed very confident that a bipolar lead setup (which, again, is far more common among pacemaker wearers) would eliminate this possible issue. He even offered to operate and to change out my pacemaker, but of course I could not justify to myself going to such drastic measures. He told me another option was to use an EMF (electromagnetic force) meter to measure interference around electrofishers. I explained the situation to my supervisor as soon as I heard back from my cardiologist, and he very graciously purchased an EMF meter for me to make sure my environment was going to be safe for me. I then also made an appointment to see the surgeon who had implanted my pacemaker and I gave him all the information I had. He was not worried at all, even about the interference.
I also tracked down my records and discovered that when I boat shocked for my seasonal job in 2012, I also had a unipolar lead (I had my pacemaker replaced in 2013). And the medical device technicians I spoke with thought that since I had electrofished before and had been fine, it should be safe. One of them just recommended I don’t wear a backpack shocker to eliminate any possible danger from interference there.
I am happy to say that I’ve helped on many backpack shocking trips and everything has been fine. I even went in for a routine check-up after having backpack shocked twice and my cardiologist told me that the pacemaker hadn’t reported any abnormal activity and that everything looked great. I finally got to electrofish from a boat this month and everything still seems fine on my end. Before my first time backpack shocking and boat shocking this season, I measured EMF while the units were running and both methods checked out. The only real danger would be if I were to lay down next to the boat generator while it is running for some reason, which should never realistically happen. The interference a few inches from the generator was just above the upper limit that my device can tolerate, according to a chart provided to me by the manufacturer (Medtronic). Based on the advisement of a technician and an engineer, I determined that the maximum allowable field strength for my pacemaker is 1 gauss. The chart reads: “1 gauss (or <0.1 millitesla or <80 amps per meter) for frequencies up to 10 kilohertz (kHz)”. However, I would definitely recommend that others check with their own medical support. The interference even an inch from the backpack shocker was minimal, but my supervisors still agreed that it was safer for me not to wear the unit because of what the technician said about keeping an arm’s length away from the shocking units.