ECG of the Week - 26th June 2017 - Interpretation

The following ECG is from a patient who presented with atypical right sided chest pain.

Click to enlarge

Rate:

• Ventricular rate ~54 bpm
• Based on QRS R-R interval best seen in left precordial leads
• Unable to accurately visualise atrial activity

Rhythm:

• Regular ventricular rate
• Rhythm indeterminate

Axis:

• Unable to assess

Intervals:

• Unable to assess

Additional:

• High frequency high amplitude interference
• Relative sparring of lead aVR
• Frequency ~30 Hz
• Baseline wander

 Interpretation:

• Uninterpretable ECG due to significant interference and baseline wander

 Troubleshooting artefact

There are multiple factors that can generate artefact during the ECG recording / printing process including:

• Patient factors
• Implanted devices
• PPM - Pacing Spikes
• Nerve stimulators
• Movement disorders e.g. Parkinson's, essential tremor
• Rigors
• Muscle tremor / activity can be related to pain, hypothermia etc.
• CPR
• Habitus - very thin or obese patients, paediatric patients
• Poor pad contact due to hair
• Poor pad contact due to moisture - sweating, immersion etc.
• Lead factors
• Poor pad contact
• Pad misplacement
• Damaged lead or lead connection
• ECG Machine Factors
• Inappropriate settings of gain or filtering modes
• Electrical artifact from power supply
• Printing factors
• Low ink
• Print head tracking
• Paper alignment
• External factors
• Interference from surrounding electronic devices. Relatively rare using newer ECG machines and environmental interference is usually compounded by incorrect machine filter settings.

An awareness of these factors and a systemic approach to addressing each point in the recording process, from patient to printer, is important in addressing recording problems such as artifact and lead mal-positioning. 

What happened ?

 

Our patient had an implantable neuro-stimulator which was the source of the interference.

He was able to de-activate the device to allow an ECG to be recorded, below:

 

Click to enlarge

 Complete resolution of artefact with an interpretable ECG.

References / Further Reading

 

Textbook

• Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.