An electrocardiogram, or ECG, is a test that records the electrical activity of the heart, providing a graphical representation of its rhythm. Sometimes, the recording picks up signals that do not originate from the heart itself. These disturbances, known as artifacts, are electrical noise that can obscure the true cardiac tracing. Because these false signals can mimic serious heart problems, understanding how to recognize them is a fundamental part of interpreting ECGs correctly.
Sources and Appearances of ECG Artifacts
One of the most frequent types is somatic artifact, also called muscle tremor, which is caused by electrical signals from skeletal muscles. It appears as a fuzzy or jagged baseline on the ECG and can be triggered by patient movement, shivering, or tense muscles from anxiety. Conditions like Parkinson’s disease can also produce these small, erratic spikes throughout the tracing.
Another source of distortion is alternating current (AC) interference. This artifact originates from external electrical equipment, like power lines or cell phones, near the ECG machine. It creates a very regular, fine line superimposed over the cardiac rhythm. In countries with a 60 Hz power supply, this is known as 60-cycle interference, which the ECG machine picks up.
A wandering baseline appears as a slow, undulating drift of the entire tracing up and down. This is caused by issues that affect the connection between the electrode and the skin. Common causes include patient breathing or other body movements that alter electrode contact. A poor skin-electrode interface from oily skin or insufficient conductive gel can also lead to this baseline drift.
Problems with the ECG equipment itself are a significant source of artifacts. Loose or disconnected electrode leads can result in a wildly erratic line or a flat line that could be mistaken for cardiac arrest. A poor connection can be caused by adhesive patches losing stickiness, improperly placed electrodes, or fractured cables, creating a nonsensical tracing.
Distinguishing Artifacts from True Cardiac Events
A primary step in ECG interpretation is determining if an unusual pattern is a genuine arrhythmia or an artifact by checking the patient. An individual with a life-threatening arrhythmia would show clinical signs, such as dizziness or loss of consciousness. If the patient is stable and comfortable but the monitor shows a chaotic rhythm, the cause is likely an artifact.
True cardiac events tend to follow physiological patterns, whereas artifacts are often more chaotic. A key technique is to look for underlying normal QRS complexes—the part of the ECG representing the main contraction of the ventricles—marching through the noise. If clear, normal beats can be seen at regular intervals, the interference is likely an artifact superimposed on a normal rhythm.
Another analytical method involves comparing signals across different ECG leads. A true cardiac event is a global phenomenon in the heart and should appear with logical consistency across multiple related leads. An artifact caused by a single faulty electrode or localized muscle movement may be confined to just one or two leads.
Sometimes, an artifact can mimic specific arrhythmias, which requires careful analysis. For instance, rhythmic muscle tremors can create a pattern that looks like atrial flutter or ventricular tachycardia. If the underlying rhythm is perfectly regular and the patient has a known tremor, the unusual waves are likely artifactual. A person cannot have a normal sinus rhythm and ventricular tachycardia simultaneously.
Strategies for a Clean ECG Tracing
Obtaining a high-quality ECG tracing begins with patient preparation. Ensuring the patient is comfortable, warm, and relaxed can reduce somatic artifacts from shivering or muscle tension. The patient should be instructed to lie still and breathe normally during the recording. Simple measures like providing a blanket can prevent shivering and lead to a cleaner signal.
Proper electrode application is fundamental to preventing wandering baseline and artifacts from poor connections. The skin should be clean, and hair may need to be shaved to ensure direct electrode adhesion. Using fresh electrodes with adequate conductive gel ensures a solid electrical interface. Confirming that each lead wire is securely attached also prevents signal interruptions.
The electrical environment can also be managed to minimize interference. Unplugging or moving non-essential electrical devices, such as fans and phones, away from the patient and the ECG machine reduces AC interference. Ensuring the ECG machine itself is properly grounded is another important step in preventing this artifact.
Finally, a routine check of the equipment can prevent artifacts caused by hardware faults. Before a recording, it is good practice to inspect lead wires and cables for signs of wear or damage. Ensuring that all connections from the electrodes to the machine are secure can prevent the sudden, erratic lines associated with a loose lead. These checks can save time and prevent misinterpretations.