The Electrocardiogram (ECG) is a diagnostic test that creates a graphic representation of the heart’s electrical activity. This recording is a sequence of waves and segments that reflect the cardiac cycle, allowing healthcare professionals to assess heart rhythm and function. An ECG artifact is any electrical activity or interference recorded by the machine that does not originate from the heart itself. Recognizing these false signals is a necessary skill, as they can obscure the true cardiac rhythm and potentially lead to misinterpretation. This article aims to help the reader visually identify and understand the origins of this non-cardiac interference.
Sources of ECG Signal Interference
ECG artifact can be categorized into three primary sources: patient factors, equipment issues, and environmental electrical noise. Patient movement is a frequent cause of interference, which can include involuntary actions like shivering, coughing, or even deep breathing. Muscle contractions, referred to as electromyogram (EMG) noise, are generated by the skeletal muscles and can contaminate the delicate cardiac signal.
Equipment-related problems are often caused by a poor interface between the patient’s skin and the recording device. Loose electrode patches, dry conductive gel, or inadequate skin preparation create high electrical resistance that distorts the tracing. Patient cables and lead wires that are broken, tangled, or improperly connected to the machine also introduce significant interference.
The environment contributes to artifact primarily through alternating current (AC) interference, which is electrical noise. Sources include nearby power cords, fluorescent lighting fixtures, and other electronic devices like cell phones. Because the heart’s signal is measured in millivolts, it is highly susceptible to this external electromagnetic field interference.
Visual Identification of Common Artifacts
One of the most frequently encountered patterns is Baseline Wander, which presents as a slow, undulating, or wave-like movement of the entire tracing. This slow drift makes the isoelectric line—the flat line between heartbeats—appear to roll up and down across the paper. It is typically caused by the patient’s respiration or subtle shifts in position that affect the electrode contact.
Another highly recognizable pattern is Somatic Tremor, or muscle artifact, which results from muscle activity. This appears as rapid, jagged, and uneven spikes that densely obscure the underlying rhythm, making the entire tracing look thick and fuzzy. Shivering, anxiety-induced muscle tension, or neurological tremors are common mechanical causes of this visual distortion.
The third major type is AC Interference, also known as 60-Hz artifact in North America. This electrical noise creates a dense, regular, and uniform “picket-fence” pattern superimposed over the true cardiac waves. It is characterized by small, extremely fast oscillations that occur precisely 60 times per second.
Differentiating Artifact from Arrhythmias
Artifact is typically a transient event, meaning it often starts and stops abruptly or changes immediately if the patient moves or the source of interference is removed. A true arrhythmia, by contrast, is a sustained biological electrical event originating from the heart.
A patient’s clinical status provides the most powerful clue for differentiation. An arrhythmia like Ventricular Fibrillation (V-fib) causes the patient to be pulseless and unresponsive, as the heart is unable to pump blood effectively. However, a patient whose ECG shows a somatic tremor that mimics V-fib remains hemodynamically stable, talking, or moving normally.
Artifact often affects multiple leads simultaneously, sometimes disrupting the entire 12-lead tracing in a non-anatomical fashion. An underlying regular rhythm may sometimes be visible in the small, clean segments between the artifact, confirming the heart’s normal function.
Practical Steps for Artifact Reduction
The first step in minimizing artifact is proper patient preparation to ensure a clean electrical connection. This involves vigorously rubbing the skin at the electrode sites with a gauze pad to remove dead skin cells and oils, and clipping or shaving any excessive hair. This crucial skin preparation significantly lowers the electrical resistance between the skin and the electrode.
Ensuring the patient is physically comfortable and warm is necessary to prevent muscle artifact. Shivering, a common cause of somatic tremor, can often be stopped by simply providing a blanket. The technician should also check that the lead wires are securely snapped onto the electrodes and are not tangled or pulling on the patches.
Equipment checks involve ensuring that the electrodes themselves are fresh, moist, and securely adhered to the skin, avoiding placement over large muscles or bony areas. If AC interference is suspected, the ECG machine should be physically moved away from electrical outlets, power cords, and other medical devices. Maximizing the distance between the recording equipment and environmental electrical noise is a quick way to reduce this form of interference.