Patient with ischemic cardiomyopathy implanted with a dual-chamber ICD Evera XT DR; recording of an episode classified as VF in the device memory in conjunction with interference generated by a poorly insulated household appliance.
The graph shows an initially slow rhythm in the atrium and ventricle (1:1 ratio) followed by a sudden acceleration in both channels with very short intervals and a spontaneous return to the initial rate.
- The graph shows a characteristic feature of oversensing of electromagnetic interference with non-physiological signals detected in both channels, saturating the baseline;
- an initial mode switch on suspicion of atrial arrhythmia (MS marker) can be observed followed by the detection of a VF episode after 30 intervals classified as FS (programming 30/40); this is hence interpreted by the device as a dual tachycardia; beginning of the charging of the capacitors;
- charging of the capacitors abandoned after interruption of the oversensing.
The potential risk of electromagnetic interference with an implantable defibrillator has been frequently described in various settings, including within the hospital environment, in the patient's home or during his or her professional activities. Interference may occur by conduction if the patient is in direct contact with the emitting source or by radiation if the patient is within an electromagnetic field. The most recent ICDs are protected against the vast majority of sources of interference that the patient may encounter in his or her daily life. The parasitic signals are typically filtered, the analysis being restricted to a narrow bandpass corresponding to the physiological signals (high-pass and low-pass filters). However, the high adaptive sensitivity levels required in ICDs for correct signal detection during ventricular fibrillation can promote the sensing of non-physiological signals corresponding to the same bandpass as cardiac signals. The signals corresponding to electromagnetic interference may not be appropriately filtered and lead to more or less severe consequences, ranging from the occurrence of inappropriate therapies to pacing inhibition in dependent patients, inappropriate mode switching due to false diagnosis of supraventricular arrhythmia, rapid ventricular pacing synchronized to atrial oversensing, suspension of detection, or reversion to asynchronous pacing. Exceptionally, interference with a high intensity electromagnetic field can cause permanent damage to the circuitry.
The diagnosis of electromagnetic interference is based on the concordance between a history of exposure to a source at the time of the episode and oversensing of characteristic signals (fast, regular and spanning the baseline). Electromagnetic interference at the "mains" frequencies (60 Hz in the USA and 50 Hz in Europe) occurs when the patient is in physical contact with poorly insulated electrical equipment. If oversensing is prolonged, a single electrical shock is most often curative of the oversensing since the patient generally interrupts his activity immediately. Electromagnetic interference is more frequent for an integrated bipolar lead than for a "true" bipolar sensing, the sensing antenna being wider. The characteristic high frequency, non-physiological signals are sensed on all available channels (possible diagnosis of dual tachycardia, AF + VF) and are typically of higher amplitude on the far-field channel than on the near-field channel.
The main preventive measures consist in identifying the emitting source and avoiding the use of poorly insulated instrumentation. This patient being monitored remotely, we received an alert the next day and were able to link the sensed event to the use of a poorly insulated household appliance.