Install shielding over your heart and electronics? Maybe something like a chain mail undershirt like the renfair reenactors wear under their armor? Grounded of course. Like a Faraday Cage. Or maybe make one out of brass screen, smaller holes for higher frequencies! You could attach it to the outside of a leather welding coat.
I do recall there are some precautions to take, like keeping the arc as far from your heart as possible, twisting the welding wires together to create a "twisted pair" that cancel each other out, use the full length of the leads to keep the welder as far away as possible and keep the wires far away too, and have someone there to watch for trouble and kill the power if you have an issue and can't do it yourself. As I understand it the interference from the welder doesn't damage the unit, it just confuses it so it may think the signal being picked up from the welding is a signal from your heart and it tries to "fix" it by changing your heart rate, zapping you, or whatever. Once the interference is removed the device no longer sees the bad info and reverts back to what it should be doing. Hopefully you recognize something is wrong, stop welding, and survive while it's adjusting!
Gas welding was used for everything before electricity became common enough to make arc welding practical. Heck, TIG is almost the same as gas, you're just using the arc to melt the puddle instead of a flame and the arc can be used to move the metal around a bit more than the gas jet can.
BTW, funny story about implanted defibs. A friend of mine had one installed. He was, ah, getting friendly with a ladyfriend when his went off. She apparently felt the jolt through her ladyparts and was always asking if he could do it again...