The real-life experience is that power lines do not interfere with implanted heart devices.  But it is theoretically possible for interference to occur, so it is important to ask what the consequences would be.  But we stress this is theoretical: there is no known instance of power lines causing interference with a correctly fitted modern heart device in the UK.

Consequences for pacemakers

A pacemaker, when it detects interference, normally reverts to asynchronous pacing mode (that is, instead of sensing what the heart is trying to do and reinforcing it, it makes the heart beat at a fixed constant rate).  This is not the best mode of operation for the patient, but is very unlikely to be harmful.

Consequences for defibrillators (ICDs)

An ICD could be inhibited from delivering a defibrillating pulse when it is needed.  This would clearly present a serious hazard for the patient (though the probability of the heart needing defibrillating at the exact moment the device was inhibited would normally be very low). There is mixed evidence on whether this can actually happen or not.  Some sources list it as a possibility, but other, more detailed, sources suggest inhibition can be produced by high static magnetic fields, but not from alternating fields such as produced by power lines.

An ICD could be falsely triggered to deliver a defibrillating pulse when one is not needed.  This carries some hazard to the patient, though it would not necessarily be fatal.

Are any effects permanent?

In all cases, manufacturers advise that any interference should be only temporary.  The device should not be damaged in any way and should work correctly again as soon as the interference is removed.

Advice to patients

Any interference with an implanted heart device must be treated as a potentially serious hazard.  However, in the case of pacemakers, it is unlikely to harm the patient, and in the case of ICDs, the potentially really serious consequence, inhibition when a shock is required, may not be caused by alternating fields, only by static fields.  In practice, interference with implanted heart devices from power lines does not appear to occur.  But the likelihood of interference may vary from individual to individual, for example depending on the installation of the leads and the sensitivity settings of the device.  Patients with concerns should consult their cardiologists.