An electrocardiogram, or ECG (sometimes referred to as EKG), is a simple, non-invasive medical test that measures and records the electrical activity of the heart over a period of time. Electrodes placed on the skin detect the small voltage changes that occur as the heart muscle depolarizes and repolarizes with each beat. Analyzing the resulting wave patterns allows healthcare professionals to assess the heart’s rate, rhythm, and overall function. However, the accuracy of this recording can be compromised by unwanted signals that do not originate from the heart itself, which are commonly referred to as artifacts.
What Defines an ECG Artifact
An ECG artifact is any electrical activity recorded by the machine that does not represent the genuine electrical impulses produced by the heart muscle. These interferences disrupt the tracing and create “noise” that can obscure the true cardiac signal. Artifacts are not indicative of a heart problem, but their presence can significantly affect the interpretation of the reading.
Recognizing these disruptive signals is crucial because they frequently mimic serious cardiac conditions. For example, a severe artifact can produce a pattern similar to ventricular tachycardia, a dangerously fast heart rhythm. Other artifacts can appear like atrial fibrillation or atrial flutter. A misinterpretation can lead to an erroneous diagnosis, causing unnecessary patient anxiety, further testing, or inappropriate medical procedures.
Categorizing the Sources of Interference
Understanding the origin of the interference is the first step toward preventing it. ECG artifacts can be broadly categorized into three areas: patient, equipment, and environment. The first category involves the patient’s physical state or movement during the recording. Involuntary muscle contractions, such as shivering or a fine tremor, generate electrical signals that the machine records. Simple patient movements, including deep breathing or shifting position, can also change the electrical contact and introduce noise.
The second source of interference is the equipment used to perform the test. Issues often arise at the electrode-skin interface, a frequent source of poor signal quality. If the conductive gel is dry or the adhesive patch is loose, poor contact generates erratic waveforms. Similarly, a broken or frayed patient cable or a faulty lead wire can cause intermittent signal loss that appears as a disruptive artifact.
Finally, the environment surrounding the patient and the machine introduces the third type of interference. This often manifests as electromagnetic interference (EMI) from external electrical sources. In North America, power lines and nearby equipment introduce a characteristic 60-cycle interference (60 Hz pickup) onto the tracing. Ungrounded ECG machines, cell phones, or other medical equipment in close proximity can also introduce external electrical noise that corrupts the recording.
Visual Identification of Common Artifacts
The appearance of an artifact on the ECG tracing often provides direct clues about its origin, allowing for quick identification and correction. One common type is the Wandering Baseline, which presents as a slow, undulating curve rather than a flat, stable line between heartbeats. This shift in the isoelectric line is typically caused by patient movement, especially respiration, or by poor electrode contact due to dry gel or excessive oil on the skin.
Another frequently encountered disturbance is the Somatic Tremor artifact, which results from muscle activity. This appears as a fast, chaotic, and irregular series of spikes or jagged lines that thicken the baseline, often obscuring the underlying P waves and QRS complexes. Shivering or muscle tension from an anxious patient is a primary cause, and the resulting high-frequency noise can sometimes be mistaken for ventricular fibrillation or atrial flutter.
The 60-Cycle Interference artifact, which is electrical in nature, has a distinct appearance that looks like a thick, fuzzy baseline. This type of interference is characterized by rapid, symmetrical spikes that are superimposed uniformly across the entire tracing. The regular, high-frequency nature of this pattern reflects the alternating current frequency from the power source and indicates a problem with grounding or the proximity of other electrical devices.
Techniques for Preventing Artifacts
Minimizing artifacts begins with meticulous preparation of both the patient and the equipment before the recording starts. Proper skin preparation is a fundamental step, as the skin’s natural oils and dead cells create resistance that impedes the signal. This procedure involves cleaning the skin with an alcohol swab or soap and water, and sometimes lightly abrading the surface with gauze to improve electrical conductivity and electrode adhesion.
Securing the patient and the equipment is necessary to reduce movement-related artifacts. The patient should be lying flat, comfortable, and warm, which helps prevent the involuntary muscle contractions that cause somatic tremor. Lead wires should be secured with tape a few inches away from the electrode to prevent movement from pulling on the patch and causing intermittent contact issues.
Addressing equipment and environmental factors requires ensuring the ECG machine is properly maintained and grounded to avoid 60-cycle interference. Unnecessary electronic devices, such as cell phones, should be removed from the testing area, and power cables should not cross the patient’s lead wires. Using high-quality electrodes with fresh gel and periodically checking cables for wear also reduces the risk of equipment-related signal disruption.