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.
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
