The Footprints of Electrocardiographic Interference: Fact or Artefact
Corporeal and particularly extra-corporeal interference is a very common problem encountered with both resting electrocardiograph (ECG) tracings and ambulatory recordings. The interference may be either electrical or mechanical and if severe, may affect the interpretation of the tracings. The interference, seen as artefact, can be divided into obvious, subtle or complicated. Obvious artefact may result from poor electrode attachment or body motion, whereas electrical interference is predominantly 50 or 60 Hz alternating current or radiofrequency waves from power lines, electrical equipment, mobile phones, fluorescent lights and electrical diathermy. Careful attention to the application of electrodes and finding the best environment for performing a 12-lead ECG will eradicate most interference. When subtle, the artefact can mimic cardiac arrhythmias, leading to incorrect interpretation of the tracings. There is also a complicated interference group, usually due to implanted cardiac electronic pacing devices and neurostimulators. These create persistent artefact, which may result in repeated unsuccessful attempts at procuring an artefact free tracing. This manuscript will describe the genesis of interference, how an ECG machine or monitor deals with interference and will discuss the common causes of interference. The characteristic patterns will be described and clues provided on how to differentiate subtle artefact from cardiac arrhythmias.
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Atrial ectopics can be generated from irritable foci anywhere in the atria, although most arise from charactristic sites of anatomic heterogeneity. They increase frequency with age and are generally innocent, unless there us an underlying cause. The ECG footprints of atrial ectopy are prematurity and a non-sinus P wave morphology. Additionally, variable AV conduction, post-ectopic compensatory (or otherwise) pauses and QRS widening due to aberrant conduction may all be observed and all should be considered, when interpreting this common electrophysiology phenomenon.