Pacemakers and internal defibrillators
Since a pacemaker only administers low-energy impulses, it is not designed for times when a person begins to experience ventricular fibrillation, a condition where the heart quivers rather than beats. It is also possible for a pacemaker to malfunction, failing to deliver the lifesaving intervention. However, every AED instruction kit will say not to use an AED on a person with a pacemaker.
External defibrillation may still be necessary for a person with a pacemaker. If the implanted pacemaker delivers a low-energy shock while you are attempting to use an AED or another defibrillator, you simply wait for 30 to 60 seconds for the pacemaker to complete its therapy cycle before administering the shock. While it is possible that the energy from an external defibrillator, AED or otherwise, may damage the pacemaker, these devices are designed to withstand external defibrillation.