Unusual response of demand pacemakers to magnets.

Most contemporary demand pacemakers contain a magnetic reed switch easily actuated by the application of an external magnet over the pulse generator. This report describes the unusual response of two implanted pulse generators to the testing magnet. The magnetic reed switch of one pulse generator was found to 'stick' in the open position making it impossible to revert the pulse generator to its fixed-rate mode with the magnet. The other pulse generator exhibited erratic pacing while the magnet was being held completely still over it, probably because the additionalforces imposed by the magnet upon the already swollen batteries unmasked imminent pacemaker failure. These observations constitute new additions to the growing list of demand pacemaker problems.