4.4 Common Traps in EKG Analysis and Interpretation

Artifact Versus True Arrhythmia

The most common trap is calling an artifact an arrhythmia. Artifact is unwanted electrical noise that distorts the tracing but does not come from the heart. Recognize and fix the source rather than reporting a false rhythm:

The key test: a true arrhythmia changes the organized complexes (P, QRS, T), while artifact distorts the baseline between or around them. If the patient is alert with a normal pulse but the monitor shows V-fib, suspect artifact and check the leads before raising an alarm.

Ischemia, Injury, and Infarction

The ST segment and T wave reflect myocardial oxygen supply, and these changes appear in a recognizable progression:

• Ischemia (reduced blood flow): ST-segment depression and/or T-wave inversion. The tissue is starved but not yet dying.
• Injury (acute, ongoing): ST-segment elevation, the urgent finding that, with symptoms, signals an evolving ST-elevation myocardial infarction (STEMI).
• Infarction (completed death of tissue): pathologic Q waves that are at least 0.04 second wide (one small box) or greater than one-third the height of the QRS. These persist and indicate an old, completed MI.

The CET does not diagnose a heart attack, but recognizing new ST elevation as a high-priority finding and escalating it promptly is squarely within scope. Always confirm the tracing is artifact-free and the leads are placed correctly before reporting ST changes, because reversed limb leads or poor placement can mimic injury patterns.

Avoiding the Classic Interpretation Errors

Beyond mistaking artifact for arrhythmia, a handful of recurring errors cost points and, in practice, cause false alarms or missed findings:

• Calling absent P waves before checking the lead. Low-amplitude P waves can hide in a noisy or poorly chosen lead. Switch to lead II before declaring a junctional or fibrillatory rhythm.
• Naming a rhythm from rate alone. A regular rate of 45 is not automatically sinus bradycardia; confirm an upright P before every QRS, or it may be a junctional or idioventricular escape rhythm.
• Ignoring the QRS width. A fast regular wide-complex tachycardia is treated as V-tach until proven otherwise, not assumed to be SVT.
• Misreading reversed limb leads. Swapped arm electrodes can invert P waves and QRS in lead I, mimicking dextrocardia or an injury pattern; verify electrode placement.
• Confusing a pacemaker spike with artifact. A regular sharp vertical spike tied to each complex is a paced beat, not noise.

The defense against all of these is the disciplined 5-step method plus a habit of confirming lead placement and signal quality before reporting any abnormal finding.

Bundle Branch Blocks and Pacemaker Rhythms

A bundle branch block (BBB) delays conduction down one bundle, widening the QRS to 0.12 second or more while the rhythm remains supraventricular in origin (a P wave still precedes each QRS). A right BBB classically shows an RSR-prime (rabbit-ear) pattern in the right precordial leads; a left BBB shows a broad, notched QRS. The technician's job is to recognize the wide QRS and note it, not to localize the block.

Pacemaker rhythms are identified by a sharp, narrow vertical pacing spike:

• A spike before the P wave indicates atrial pacing.
• A spike before the QRS indicates ventricular pacing (the QRS is usually wide).
• Spikes before both indicate a dual-chamber (AV sequential) pacemaker.

Failure to capture is a spike not followed by the expected complex; failure to sense is a spike that fires inappropriately on top of the patient's own beats. Do not mistake a pacing spike for artifact, and do not mistake the wide paced QRS for a primary ventricular arrhythmia.

One more recognition pitfall ties these topics together: a wide QRS has several possible explanations, and the surrounding features tell them apart. If a normal upright P precedes each wide QRS, suspect a bundle branch block; if a sharp spike precedes each wide QRS, suspect a paced rhythm; if the wide QRS is early with no P, it is a PVC; and if wide complexes run fast with no P waves, it is V-tach. Reading only the QRS width and skipping the P-wave and spike check is exactly how look-alikes get mislabeled.

As always, confirm clean signal and correct lead placement first, because a single noisy lead can blur a narrow QRS into something that looks wide.

To prevent artifact in the first place rather than chasing it later, the technician controls the common sources during acquisition: prepare the skin (clean, dry, and lightly abrade oily or lotioned sites; clip excess hair), ensure firm electrode contact with fresh gel, keep the patient still and warm to limit muscle tremor, route cables away from power cords and unplug nonessential equipment to reduce 60-cycle interference, and verify each lead is seated. A tracing acquired this way rarely needs to be repeated and far less often produces a false-alarm rhythm.

When an abnormal pattern does appear on a clean strip, that is the signal worth reporting.