2.4 ECG Artifact Recognition, Signal Interference & Technical Troubleshooting

ECG Artifact Recognition & Technical Troubleshooting

Producing a clean, diagnostic-quality ECG is the primary responsibility of the Certified Cardiographic Technician. Even with perfect electrode placement, various sources of interference—collectively known as artifact—can obscure the cardiac signal. In worst-case scenarios, artifact can mimic lethal arrhythmias like ventricular fibrillation or ventricular tachycardia, leading to unnecessary and potentially dangerous medical interventions. Identifying the source of an artifact and employing rapid troubleshooting techniques is an essential competency.

Types of Artifact

Artifacts generally fall into three main categories based on their origin and appearance on the tracing: Somatic Tremor, Wandering Baseline, and Alternating Current (AC) Interference.

1. Somatic Tremor (Muscle Artifact)

Somatic tremor occurs when the patient's skeletal muscles contract. Because muscles generate electricity when they work, the ECG machine picks up these signals alongside the heart's electrical activity.

Appearance:

• Chaotic, high-frequency, jagged noise superimposed on the baseline.
• Can completely obscure P waves and distort the QRS complex.
• If severe, it can look alarmingly similar to coarse Ventricular Fibrillation.

Common Causes:

• The patient is cold and shivering.
• The patient is tense or anxious.
• The patient has a neurological condition causing tremors (e.g., Parkinson's disease).

Troubleshooting & Solutions:

• Ensure the patient is warm (provide blankets) and comfortable.
• Calm the patient and ask them to relax their shoulders and let their arms fall flat.
• For patients with Parkinson's, placing the patient's hands under their buttocks can sometimes minimize arm tremors.
• Ensure limb electrodes are on fleshy areas, avoiding bone.
• As a last resort, utilize the ECG machine's muscle tremor filter (usually a low-pass filter set around 40 Hz), though this can slightly distort the true QRS morphology.

2. Wandering Baseline

A wandering baseline occurs when the isoelectric line of the ECG slowly drifts upward and downward across the paper, making it difficult to assess ST segments accurately.

Appearance:

• The entire tracing undulates in a slow, rolling wave pattern.
• The complexes remain intact, but they ride up and down the page.

Common Causes:

• Exaggerated respiratory movements (breathing heavily).
• Poor electrode-to-skin contact (the most common technical failure).
• Dried out conductive gel on expired electrodes.
• Tension on the lead wires pulling on the electrodes.

Troubleshooting & Solutions:

• Skin Preparation: This is the most crucial step. Use an alcohol prep pad to aggressively wipe away skin oils, dead skin cells, and lotions. For hairy chests, shaving the exact electrode site is mandatory; placing an electrode over hair guarantees poor contact. After cleaning, the skin must be completely dry before applying the electrode.
• Ask the patient to breathe normally, or in severe cases, ask them to hold their breath for a few seconds during the recording.
• Ensure the lead wires are draped loosely across the patient and are not pulling on the adhesive patches.
• Never use expired electrodes, as the hydrogel dries out and loses conductivity.

3. AC Interference (60-Cycle Noise)

AC interference is caused by electrical power from the surrounding environment leaking into the ECG system. In North America, the power grid operates at 60 Hertz, meaning the interference will cycle 60 times per second.

Appearance:

• The baseline becomes thick, fuzzy, and uniform.
• If you look closely or increase the paper speed, you will see a continuous series of fine, even spikes exactly 60 times per second.

Common Causes:

• The ECG machine's power cord is draped across the patient.
• Other electrical equipment is in use nearby (e.g., IV pumps, mechanical ventilators, electric beds).
• Poor electrical grounding of the room or the machine.

Troubleshooting & Solutions:

• Ensure the ECG machine is plugged into a properly grounded wall outlet.
• Move the patient's bed away from the wall and ensure no power cords are touching the patient or the ECG cables.
• Turn off or unplug non-essential electrical equipment in the immediate vicinity.
• Activate the ECG machine's 60 Hz notch filter. A notch filter specifically targets and removes the 60 Hz frequency while leaving the rest of the cardiac signal intact. (Note: In Europe, this would be a 50 Hz filter due to their power grid standards).

Differentiating Artifact from Arrhythmia

The most dangerous consequence of artifact is when it mimics a lethal rhythm. Somatic tremor can look like Ventricular Fibrillation, and rhythmic tapping on an electrode can look like Ventricular Tachycardia.

The "March Through" Rule: The key to differentiating artifact from a real arrhythmia is finding the normal QRS complexes. Even amidst terrible artifact, if you can identify distinct, regular QRS complexes "marching through" the noise at a normal rate, the underlying rhythm is not Ventricular Fibrillation. The heart cannot be in Ventricular Fibrillation and produce normal QRS complexes simultaneously. If you suspect artifact, immediately check a different lead (e.g., look at V1 instead of Lead II) to see if the noise is isolated to one area or one bad electrode.

ECG Artifact Recognition & Troubleshooting