ECG Recording Technique, Artefacts, and Machine Operation
ECG Recording Technique, Artefacts, and Machine Operation
This domain tests safe, clean and technically valid recordings. Correct skin preparation and electrode placement prevent many artefacts before they appear.
Technique and machine checks
- Identify the patient, explain the procedure and ensure privacy. Expose only the needed chest area.
- Clean skin, apply electrodes firmly and place limb leads correctly; the right leg electrode is the neutral/ground. Place V1 at the fourth intercostal space right sternal edge, V2 left sternal edge, and V4-V6 along the left chest.
- Set standard gain 10 mm/mV and speed 25 mm/s unless a clinician requests otherwise. Confirm calibration and paper supply.
- Common artefacts: baseline wander from movement or breathing; somatic tremor from shivering; AC interference from poor contact or cables; loose electrodes causing sudden spikes.
Worked example
A tracing shows a thick, fuzzy baseline at 50 Hz. The likely cause is AC interference, not atrial fibrillation. Reasoning: AF produces irregular QRS complexes with absent P waves, whereas mains interference is a continuous high-frequency oscillation. Check electrode contact, cable routing and grounding, then use the machine's filter if appropriate.
Traps that cost marks
Arm lead reversal changes lead I and aVR/aVL patterns and can mimic pathology. Chest lead misplacement distorts R-wave progression. Do not treat somatic tremor as ventricular fibrillation. Never adjust filters to hide a real arrhythmia without documenting the setting.