Cardiac pacemaker induced ventricular fibrillation during surgical diathermy

Two demand pacemakers were observed to repeatedly fibrillate the heart during clinical surgery employing diathermy. Marked hypotension associated with a rapid, irregular venticular action was observed in another patient who had a fixed rate pacemaker implanted. Pacemakers were tested with function generators over a range of frequencies and some increased their rate to between 200-600 impulse/min. Animal experiments confirmed that, contrary to manufacturers advice, surgical diathermy produces myocardial fibrillation in the presence of some pacemakers. Mechanisms of these effects and their clinical significance are discussed.