In the early days of artificial hearts a huge problem was the mechanical damage done to blood cells. IIRC, that was the motivation to go to membrane style pumps - they were gentler. Now we have a 2000 rpm centrifugal pump? I guess that I'm missing something.
The article asserts that the spinning disk doesn't create large enough shea r forces to damage red and while blood cells.
The actual shear forces aren't predictable just from the speed of rotation. You'd need the actual speed of the disk, and it's spacing from the static supporting structure. Note that the disk is magnetically levitated, so you haven't got any tight clearances.
That's not the problem. There are permanent magnets in the rotor disc, and the large magnetic field inside a magnetic resonance scanner is going to influence them in ways which may not be compatible with the job the rotor is designed to do.
Primarily the lack of magnetic materials in the device and lead(s) and a means to disable feedback (shuts off sensing and enters an open-loop mode with default operation). The device is signaled to go into this "safe mode" by placing a rare earth magnet over the device (opens a reed switch).
The magnet doesn't turn it off, rather puts it in a known, hardware defined, state (60bpm, AOO or, less often, VOO mode). Turning off a pacemaker isn't usually a wise move. The response to the magnet isn't programmed. It's a hardware function. The point is to bring the pacemaker down to its most basic operation.
The unit is downloaded before the procedure and completely reprogrammed after, in case the MRI upset the firmware.
That's malpractice by your hospital/cardiologist/electrophysiologist and staff. I can't count the number of times I was warned, and that was _before_ I left the hospital. It does take a strong magnet, placed very close to the device but the magnets in high-end headphones are enough to do it. They're not likely to cause a problem, in use, because of the distance from your ear to chest but hanging them around your neck can cause problems. I also was warned to not put my cell phone in my shirt pocket. In addition to the transmitter being very close to the device, the magnet in the speaker is pretty strong (to make it small). Or, as one of the tech suggested, a spouse listening to music while resting their head on my chest may be enough. Well, that's not likely to happen for a few reasons. ;-)
Magnetic fields in general are badness but not only because it might trigger the safe mode. Large AC magnetic fields can confuse sensing causing abnormal and unpredictable device operation (really not goodness).