Qi themselves mention that their technology is related to inductive coupling used to charge early pacemakers. Given that, I'd stay well away from these until I heard an opinion from a doctor.
The prime concern is that oscillating fields could interfere with the low-voltage low-current stimulus leads, inducing convulsions or worse. Secondary concern is overloading & frying the device.
I knew there was something I was going to ask my cardio doc a few days ago...we discussed potential problems with electric cars instead (user's manual is filled with "Warning! Pacemaker users stay away so we don't have to get this car medically certified!"-type notices).