ECG Artefacts
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Direct answer
Not every strange-looking tracing is a strange heart rhythm: artefact imitates ventricular tachycardia, atrial flutter and ST-segment change so convincingly that patients have been cardioverted and admitted for their electrodes rather than their hearts. The big four are alternating-current (AC) interference — a fine, regular 50 Hz ripple in India (60 Hz where the mains supply is so) from earthing faults, nearby equipment or a dried electrode — baseline wander from movement, respiration and cable tension; muscle-tremor artefact from shivering, anxiety and Parkinson's disease; and electrode misplacement, classically limb lead reversal. The discipline that saves you: search the whole tracing for normal QRS complexes marching undisturbed between the "arrhythmia", and check the patient before the paper.
What you must remember
- AC interference: uniform fine serrations at mains frequency — 50 Hz in India — from loose or dried electrodes, poor skin prep, faulty earthing or cables near pumps and lights; fix electrodes first, then earthing, then move equipment.
- Baseline wander: slow undulation or drift from patient movement, talking, respiration, loose chest electrodes or cables under tension; support the cables, reattach electrodes, record during a quiet breath-hold if needed.
- Muscle tremor: irregular rapid oscillations from shivering, cold, anxiety, discomfort or a movement disorder; loudest in limb leads and notorious for mimicking atrial flutter or fibrillation.
- Parkinson's tremor artefact: a regular 4-6 per second oscillation often mistaken for flutter waves; moving the limb electrodes proximally (shoulders, upper thighs) reduces the amplitude — a favourite practical tip.
- RA-LA limb reversal: inverted P, QRS and T in lead I with a normal-looking lead II, aVR and aVL interchanged; unlike dextrocardia, the chest leads keep normal R-wave progression.
- Artefactual "ventricular tachycardia": hidden, regular, normal QRS complexes at the underlying rate within or between the wide complexes; the comfortable, talking patient is the clinical counterpart of the clue.
- ST-segment artefact from wander or poor contact has wrongly triggered thrombolysis; never report ST elevation from a single noisy lead — clean, repeat, compare.
A tracing that looks like ventricular tachycardia
A monitored ward patient with Parkinson's disease suddenly shows a run of wide complexes at 200 per minute on the central monitor. Walk the reasoning. First, the patient: he is sitting up, talking and brushing his teeth — a genuinely perfusing rhythm at 200 would not allow it. Second, the tracing: hunting through the "tachycardia" at fast sweep reveals a normal, narrow QRS appearing at regular intervals, marching through the artefact undisturbed at his sinus rate, because the heart has been firing normally all along while the tremulous arm generated the oscillations. Third, the source: the electrode sits loosely over a tremoring muscle belly; the tooth-brushing motion and the 4-6 per second Parkinsonian tremor together produced the wide-complex illusion.
Having named it, fix it: reattach the electrode firmly after skin prep, move the arm electrodes proximally where tremor amplitude is less, and re-record — the "ventricular tachycardia" vanishes. The same three-step habit — patient, hidden QRS hunt, electrode and cable check — resolves nearly every artefact puzzle, from the flutter-like baseline of a shivering elderly patient to the pseudo-asystole of a detached chest lead.
How the exam frames it
Questions test recognition with a picture and one discriminating feature. AC interference is "regular, fine, at mains frequency — 50 Hz in India": the frequency is the fact that separates the prepared answer. Atrial flutter versus Parkinsonian tremor is a classic: both show regular sawtooth-like activity, but flutter waves are identical across the tracing and unaffected by warming or repositioning, while tremor varies with the limbs and improves when electrodes move proximally. Limb lead reversal hinges on "inverted in lead I, normal in lead II" plus normal chest progression, contrasted with dextrocardia where chest progression reverses too. And the safety question — a monitor showing VT in a comfortable, talking patient — expects "look at the patient, find the underlying QRS complexes, check the leads" long before "prepare for cardioversion".
Frequently asked questions
What is the frequency of AC interference on an ECG in India?
Fifty hertz, matching the Indian mains supply (60 Hz in countries with that standard). It appears as fine, regular rippling of the baseline, usually from loose electrodes, poor earthing or nearby electrical equipment.
How is RA-LA limb lead reversal recognised on the tracing?
P, QRS and T waves are inverted in lead I, lead II looks normal, and aVR and aVL are interchanged, while chest leads keep normal R-wave progression. Swap the right and left arm electrodes and repeat.
How can artefact mimic ventricular tachycardia?
Rapid muscle tremor or a loose electrode generates wide-looking complexes, but searching the strip reveals normal QRS complexes marching regularly through the artefact, and the patient is haemodynamically well. Correcting the electrode abolishes the "arrhythmia".
Which tremor disorder commonly contaminates ECG recordings, and what is the trick?
Parkinson's disease, producing a regular 4-6 per second oscillation that mimics flutter waves. Moving the limb electrodes to proximal positions — shoulders, upper thighs — lessens the artefact without losing standard lead information.