Quality of the ECG Trace
Overview
A poor quality ECG trace can be incredibly difficult to interpret and, more dangerously, may be misinterpreted.
Baseline Wander
This type of interference originates from the interface of the skin and the electrode, and makes interpretation of high amplitude waves (e.g. the T wave or ST segment) difficult. In certain circumstances, baseline wander may mimic life-threatening arrhythmias.
Look For
- Low-frequency variation of the isoelectric line.
Causes of Baseline Wander
- Patient movement - especially respiration
- Inadequate contact between electrodes and body surface
- Improper skin preparation
- Patient sweating
Electrical Interference
This type of interference originates from the power cable, ECG machine, leads or the patient; it makes interpretation of low amplitude waves (e.g. the P wave) difficult or impossible.
Look For
- High-frequency variation of the isolelectric line.
Causes of Electrical Interference
- Incorrect earthing
- Other electrical equipment plugged into the same circuit
- The patient’s muscle activity
Incorrect ECG Lead Placement
Reversal of arm leads (RA and LA)- inversion of lead I (negative P waves and QRS complexes)
Reversal of RA and LL - inversion of lead II (negative P waves and QRS complexes)
Reversal of LA and LL - inversion of lead III (negative P waves and QRS complexes)
Reversal of LA and LL + RA and RL - flattening of lead I (very low frequency waves)
Reversal of RA and RL - flattening of lead II (very low frequency waves)
Reversal of LA and RL - flattening of lead III (very low frequency waves)
Superior misplacement of V1 / V2 - poor R wave progression
No changes will be seen with reversal of LL and RL.
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