3.3 Scenario Practice for EKG Acquisition
Key Takeaways
Wandering baseline is a slow up-and-down drift fixed with fresh electrodes, skin prep, and drying the site.
Somatic (muscle) tremor appears as fine irregular fuzz; fix it by warming and relaxing the patient.
AC (60-cycle) interference is a thick, perfectly regular blur at exactly 60 Hz from ungrounded or nearby electrical equipment.
For tremor patients, warm, reassure, and support the limbs; limb electrodes may sit anywhere on the limbs distal to the shoulders and hips, and a tracing with torso limb electrodes must be labeled.
Match the artifact to its cause first; most artifacts trace back to electrodes, skin prep, patient movement, or electrical sources.
The Three Artifacts You Must Recognize
An artifact is any deflection on the EKG that is not generated by the heart. The CET must distinguish artifact from true pathology, find the cause, and re-run a clean strip. The three classically tested artifacts are:
| Artifact | Appearance | Most common causes |
|---|---|---|
| Wandering baseline | Slow, undulating up-and-down drift of the baseline | Dried/expired electrodes, poor skin prep, lotion/oil, respiration, loose leads |
| Somatic (muscle) tremor | Fine, irregular, fuzzy spikes overlying the tracing | Cold/shivering, anxiety, tense muscles, Parkinsonian or other tremor |
| AC (60-cycle) interference | Thick, perfectly regular, uniform blur — exactly 60 cycles/sec | Ungrounded equipment, nearby electrical devices, crossed/dangling cables, frayed wires |
The distinguishing clue for AC interference is its absolute regularity — 60 identical, evenly spaced spikes per second produce a thick, uniform band of constant height. Somatic tremor is irregular fuzz of varying height. Wandering baseline moves the whole tracing slowly up and down rather than thickening it.
Scenario 1: Wandering Baseline
Scenario: You run a 12-lead and the baseline slowly drifts up and down across the strip like gentle waves; P-QRS-T complexes are intact but ride the drift.
Diagnosis: Wandering baseline. First actions in order: (1) check that electrodes are fresh and not dried out — replace any expired ones; (2) re-prep the skin (clean, dry fully, abrade); (3) confirm electrodes adhere flat and lead wires are not pulling; (4) reassure the patient to breathe normally if respiration is the driver. Wandering baseline usually traces to electrode/skin contact or breathing, so fresh electrodes, good prep, and normal breathing fix most cases.
Scenario 2: Somatic (Muscle) Tremor
Scenario: A cold, anxious, or tremor-prone patient produces a tracing covered in fine, jittery fuzz that varies moment to moment.
Diagnosis: Somatic tremor. Fixes: warm the patient with a blanket, raise room temperature, and help them relax (explain the test, ensure limbs are supported and not dangling). For Parkinsonian or essential tremor, support the limbs and keep the limb electrodes on the limbs: anywhere distal to the shoulders and hips is acceptable for a standard 12-lead. If torso placement is ever used, the tracing is not equivalent to a standard ECG and must be labeled. Never tell a shivering patient to simply 'hold still' — address the cause.
Scenario 3: AC (60-Cycle) Interference
Scenario: The entire tracing is a thick, uniform, perfectly regular blur of identical small spikes, the same in every lead.
Diagnosis: AC / 60-cycle interference from electrical power (mains electricity in the US runs at 60 Hz). Troubleshooting steps: (1) unplug or move away nearby electrical equipment (IV pumps, warming devices, phones, fans); (2) verify the EKG machine is properly grounded and check for frayed or crossed cables; (3) ensure lead wires lie flat and are not crossing power cords; (4) confirm the patient is not touching metal bed rails; (5) confirm electrodes have good contact (high impedance worsens AC pickup).
Modern machines include a notch (AC) filter, but the filter masks the problem rather than curing it, so find and remove the electrical source first.
Decision rule for any artifact: identify the pattern (drift vs. irregular fuzz vs. regular blur) → infer the source (electrode/skin vs. patient/muscle vs. electrical) → apply the targeted fix → re-run and verify before handing off the tracing.
Scenario 4: A Single Bizarre Lead
Scenario: Eleven leads look clean, but one lead (say V3) shows wild, isolated noise or a flat line.
Diagnosis: A single noisy or flat lead points to that one electrode — a loose, dried, or disconnected electrode, or a broken lead wire — not a patient-wide problem. Fix: re-seat or replace that specific electrode and wire; if a single limb lead is dead, check that one cable connection. Because artifact in only one lead isolates the culprit, you rarely need to re-prep the whole patient.
Scenario 5: Distinguishing Artifact from True Pathology
Scenario: A jittery, irregular tracing could be ventricular tachycardia or could be muscle tremor.
Diagnosis approach: Look for 'marching' P waves or normal complexes hidden within the noise — if you can find regular underlying QRS complexes at a normal rate beneath the fuzz, the rhythm is sinus and the chaos is artifact, not a lethal arrhythmia. A true ventricular rhythm has no normal complexes peeking through. The CET's job is never to diagnose, but recognizing that artifact can mimic dangerous rhythms prevents a false alarm — always re-run a clean strip before the tracing reaches the physician, and report obvious emergencies immediately while you re-acquire.
A useful mental model is to treat every artifact as a clue pointing to one of four sources. Electrode and skin problems (dried gel, poor prep, oily or sweaty skin) cause wandering baseline and flat or noisy single leads. Patient and muscle sources (cold, anxiety, tremor, talking, movement) cause somatic-tremor fuzz. Electrical environment sources (ungrounded machine, nearby devices, crossed cables) cause regular 60-cycle interference. Equipment and cable faults (broken wire, loose connector) cause an isolated dead or wild lead.
Walking this short list in order — skin, patient, environment, equipment — lets you correct nearly any artifact methodically instead of guessing. Crucially, you fix the cause rather than hiding it with filters: turning on a muscle filter or AC notch filter can smooth the display, but an over-filtered tracing distorts the true waveform and can erase real findings, so filters are a last resort after the physical source has been addressed and the strip is still acceptable for the ordering provider.
A tracing shows a thick, perfectly regular blur that looks identical in every lead. What is the most likely cause?
Somatic muscle tremor from a cold patient
Wandering baseline from dried electrodes
AC (60-cycle) electrical interference
Normal sinus rhythm at fast paper speed
Which intervention BEST reduces somatic tremor artifact in a cold, shivering patient?
Provide a blanket and warm the patient to relax the muscles
Apply expired electrodes to dampen the signal
Switch the paper speed to 50 mm/sec
Reverse the RA and LA electrodes
A baseline slowly drifts up and down across the strip while the P-QRS-T complexes stay intact. What is the FIRST thing to check?
Whether the patient is touching a metal bed rail
Whether the room lighting is causing 60 Hz noise
Whether the AC notch filter is turned off
Whether the electrodes are fresh and the skin was properly prepped and dried
Sections you finish are checked off in the contents.