Interference in implanted cardiac devices, Part I.

Sensing intrinsic cardiac electrical activity is essential for the function of pacemakers and implantable cardioverter defibrillators (ICDs). Examples of undesired triggering or inhibition of pacemaker output by extraneous signals were identified early after the introduction of noncompetitive, “demand” pacemakers. Hermetic shielding in metal cases, filtering, and interference rejection circuits, together with a preference (much more marked in the United States than in Europe) for bipolar sensing, made contemporary pacemakers and ICDs relatively immune to electromagnetic energy sources in homes and workplaces. Sources of electromagnetic interference (EMI) remained ubiquitous in the medical environment. However, they were predictable and avoidable. New technologies that use more of the electromagnetic spectrum (i.e., wireless telephones, electronic article surveillance [EAS] devices) have rekindled interest in EMI risks for patients with implanted cardiac devices. Although these technologies do not constitute a major public health threat, adverse interactions can occur. The counterpart to EMI is electromagnetic compatibility, a science aimed at avoiding interference potential by adding shielding or redesigning circuits against specific EMI sources. There are three essential elements to any electromagnetic compatibility problem. There must be an electromagnetic source, a receptor or victim (in our case the implanted cardiac device) that cannot function properly due to the electromagnetic phenomenon, and a path between them that allows the source to interfere with the receptor. Each of these three elements must be present, although they may not be readily identified in every situation. Identifying at least two of these elements and eliminating (or attenuating) one of them generally solves electromagnetic compatibility problems. Collaboration among industry, physicians, regulatory agencies, and consumer groups will hopefully achieve full compatibility between implanted devices and other technologies. This will require adoption of international standards establishing the upper limit of permissible field intensities for the whole electromagnetic spectrum. Implanted devices should not react to fields below this limit; more intense fields will be prohibited. This two-part review discusses EMI with implanted cardiac devices. The first part of the review addresses general concepts and specific sources of EMI in everyday life and the workplace. The second part focuses on medical sources of EMI, highlighting preventive measures.