An interesting thought would be to have a nano-lead down the arterials to the wrist, where an external telemetry relay-watch could read the signals, and have the BLE device top dermal. (apple watch)
eliminating RF/BLE bullshit from talking to the pacemaker.
I don't think my particular pacemaker has the necessary circuitry to generate more than 5V, in pulses less than a few milliseconds. The voltage doesn't really matter much to the muscle.
If you got in you could probably put the leads into single-ended mode (so that there's more current path to cause mayhem) and pace my atrium and ventricles at 210bpm, and effectively give me a seizure. I can't imagine it would kill me before an EMS arrived with a magnet?
Perhaps a more nuanced attack would be to somehow use all the configuration parameters to intentionally bias the pulses so that there's net charge going into the muscle. Over a long time that would cause tissue damage.
If someone wanted to kill me overtly, a gun would be less work. A pacemaker malfunction that bad would be thoroughly investigated, and would be fixed in new devices within a year or two.
If they were able to cause the pacemaker to fire when they wanted they could time it during the repolarization, which could possibly cause a fatal arrhythmia even in a heart that doesn't need a pacemaker. It's called R-on-T phenomenon and it's usually caused by malfunctioning pacemakers.
I doubt you could do that through configuration changes alone, simply because of how defensive the firmware would be about that exact scenario. You'd probably have to resort to code exploits on top of simply gaining access. Even then, there's probably a rudimentary interlock at the silicon level.
The crazy thing was that this was when there was a lot of talk about Dick Cheney and how he was vuln to this attack -- and there was a lot of spec around if barnaby was silenced because it was the older, Cheney-esque politicians that could be taken out by this vector...
Perhaps, he got the 'reverse bounty' on this bug...
eliminating RF/BLE bullshit from talking to the pacemaker.