EMI : Electromagnetic interference

Basic concepts

The potential risk of interaction between electronic systems and implantable cardioverter-defibrillator has been frequently reported. Electromagnetic interference (EMI) can occur in a variety of settings,  within and outside the hospital environment, at home, work, and other everyday environments. EMI may occur by conduction if the patient is in direct contact with the source or by radiation if the patient is positioned within an electromagnetic field. Contemporary, ICDs are protected from most sources of interference a patient may encounter in daily routine life. Signals are typically filtered by narrow bandpass filters to exclude noncardiac signals. However, very-high-sensitivity levels required in ICDs can promote oversensing of extracardiac non physiological signals corresponding to the same bandpass of cardiac signals. Electromagnetic interference may not be filtered and may result in consequences ranging from inappropriate shocks to pacing inhibition, automatic mode switching, triggering of rapid ventricular pacing from oversensing by the atrial channel, closure of the reed switch with temporary suspension of arrhythmia therapies and reversion to asynchronous pacing. Infrequently, interference within a high-intensity electromagnetic field can cause permanent damage to the circuitry.

The diagnosis of electromagnetic interference is based on an history of exposure to a source at the time of event and oversensing of characteristic rapid, regular signals spanning the entire cardiac cycle. Electromagnetic interference at power frequencies (60 Hz for Europe and 50 Hz for Europe) occurs when the patient is in physical contact with poorly grounded electrical equipment. If oversensing is prolonged, a single shock is most of the time curative since the patient stops immediately the provoking activity and thus stopping the interference. Electromagnetic interference is more likely for integrated-bipolar sensing than for true-bipolar sensing since the antenna is larger. The non-physiological, high frequencies signals oversensed by the device are typically of higher amplitude in the near versus far-field channel and are sensed on all the channels with possible diagnosis of double tachycardia (atrial fibrillation and ventricular fibrillation). These artifacts may be consistent with 50 or 60-Hz alternating current and a change in sweep speed allows the display of the characteristic sinusoidal aspect with a 20 or 16-ms interval in-between each signal.

The main preventive measures consist of finding the emitting source and avoiding the use of poorly insulated instrumentation. Different companies (Boston Scientific, Sorin, and Abbott) provide noise reversion algorithm based on rejection of high frequency repetitive non-physiological signals, designed to overcome electromagnetic interference and lower the risk of inappropriate therapy.


Use of electrocautery

When an ICD recipient undergoes a surgical intervention, the surgeon must be advised to use electrical scalpels in bipolar mode, to use it for very brief durations, and to place the grounding plates of the scalpel away from the pulse generator keeping the system outside of the current flow. The device must be temporarily deactivated in order to completely eliminate the risk of interference. During periods of therapy deactivation, the patient must be monitored with external defibrillation equipment immediately available. Two options can be chosen to deactivate the device: application of an external magnet and device reprogramming. The application of the magnet is usually preferred because 1) in case of occurrence of a true arrhythmias during the procedure, the medical team can immediately reactivate the device, the magnet effect being reversible, both the detection and therapies are immediately available after the magnet is removed 2) absence or delay in reactivation of the therapies is not infrequent in case of device reprogramming.

The magnet effect also has some specificities according to the device company: no effect on pacing except for Sorin devices, interruption of the effect after 8 hours of application in Biotronik devices, programmable magnet response in Abbott devices (normal or ignore) and Boston Scientific devices (on versus off); before chosing the magnet strategy for the devices of these 2 companies, the magnet response must be checked and eventually reprogrammed to normal or on.