EKG Artifact and Technical Quality
Flashcards on recognizing wandering baseline, muscle tremor, AC interference, and lead reversal before interpreting an EKG.
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Questions Covered in This Set
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What is the first question to ask before interpreting any EKG?
Is this tracing trustworthy? Check technical quality first — voltages are tiny (QRS ≈ 1 mV) and easily corrupted by artifact.
Wandering baseline: appearance and causes
The isoelectric line slowly rolls up and down while waveforms stay crisp. Causes: respiration, poor electrode contact, dried gel, patient movement, diaphoretic skin.
Why does a wandering baseline matter clinically?
You cannot reliably judge ST elevation or depression, because ST measurement requires comparison to a stable reference (TP or PR segment).
Muscle tremor (somatic) artifact: appearance and typical causes
Irregular fast spiky fuzz, often in only some leads. Caused by Parkinsonian tremor, shivering, anxiety, or an arm resting on a rail.
How do you distinguish Parkinsonian tremor artifact from true VT?
March out the QRS complexes — in tremor you can find underlying regular narrow QRS marching through the fuzz, artifact spares some leads, and the patient looks well. True VT has no narrow QRS and affects all leads.
AC (60 Hz) interference: appearance and how to confirm it
A perfectly regular, uniform, high-frequency thick fuzzy band. At 25 mm/s, 60 Hz gives ~2.4 cycles per small box; its metronomic evenness distinguishes it from irregular tremor fuzz.
Causes and fixes for AC interference
Causes: nearby electrical equipment, tangled/unshielded cables, loose electrode acting as antenna, ungrounded bed. Fixes: unplug equipment, separate lead wires, check ground, replace electrodes; the 60 Hz notch filter is only a bandage.
Classic pattern of LA/RA (arm lead) reversal
Lead I fully inverted (negative P, QRS, T); leads II and III swap; aVR and aVL swap. Precordial leads look normal.
How do you tell arm lead reversal from dextrocardia?
Both invert lead I, but dextrocardia also shows reverse R-wave progression (tall R in V1 fading to tiny R in V6); in arm reversal V1–V6 look normal.
What do LA/LL reversal and a right-leg (ground) electrode swap look like?
LA/LL reversal is subtle — mostly swaps leads I and II, creating or erasing inferior Q waves. A ground-electrode swap produces a nearly flat line in one or two leads.
