Electromagnetic interference (EMI) refers to electrical or magnetic signals from external sources that can potentially interfere with the sensing and function of an implanted cardiac device such as an ICD or pacemaker. Devices continuously sense the heart’s electrical activity to detect arrhythmias; if an external electrical signal is misinterpreted as cardiac activity, the device may respond inappropriately.
Potential consequences of EMI include inappropriate shocks, where an ICD misinterprets EMI as ventricular fibrillation and delivers an unnecessary shock; inhibition of pacing, where a pacemaker misinterprets EMI as cardiac activity and withholds a pacing impulse in a pacemaker-dependent patient; and reprogramming, where in rare cases very strong electromagnetic fields can alter device settings.
In practice, most everyday electrical appliances pose little or no risk to cardiac devices. Modern ICDs and pacemakers are well shielded and designed to be resistant to most common sources of EMI. Sources that patients are commonly and unnecessarily concerned about include mobile phones, household appliances, and airport security scanners.
Sources that may pose a genuine risk include medical diathermy (surgical electrosurgery), the most clinically significant EMI risk, which requires the clinical team to be informed of any implanted device before surgical or dental procedures. MRI scanners carry risk depending on device classification (see MR Conditional/Unsafe). Large industrial motors, welding equipment, and high-voltage power lines can cause EMI in some circumstances, and theft-detection (EAS) systems can cause brief interference; the recommendation is to walk through, not linger.
Patients should carry their device card at all times and inform healthcare professionals before any procedure. Their cardiac device clinic can advise on specific activities or environments relevant to their device model.
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