Peripheral nerve conduction stimulation: its effect on cardiac pacemakers.

External electromagnetic interference with cardiac pacemaker function is a recognized hazard of electronic instrumentation used for diagnosis or therapy. Although improved shielding and circuitry have made newer pacemakers less vulnerable to extraneous electronic artifact, their increasing use may expose more patients to the complications of electromagnetic interference. The effects of nerve conduction stimulation testing (NCST) on patients with cardiac pacemakers were evaluated both clinically and in the laboratory. Estimates of interference potentials likely to occur at a pacemaker input during NCST were made by making calculations from a theoretical model. For three different pacemakers, these estimates were compared to laboratory tests of sensitivity to interference. Some potential for pacemaker interference was shown to exist, although primarily with unipolar pacing leads. Twenty patients, five of whom were monitored electrocardiographically, underwent uneventful nerve conduction studies. Although pulse producing stimulators have the potential to affect demand type pacemakers, if current paths are confined within standard clinical parameters, untoward responses appear unlikely.