The problem appears to me to be a design problem of the implanted devices, not the iPhone.

Unless I'm mistaken this is what's happening:

1. ICDs want/need to communicate with the outside (at least one way).

2.However, this is not trivial since a human body is a bag of salt water. Therefore low frequencies are needed.

3. Low frequencies are very difficult at the necessary length scales with electric fields, so they used the magnetic field instead.

So far, so good. But then they assumed that the person would never be next to a magnet? That's a design flaw on their end, not the iPhone's. There's magnets, and low moving large currents, everywhere!

The should have implemented a primitive type of port knocking.