Wednesday, 28 June 2017

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
  • Ventricular rate ~54 bpm
    • Based on QRS R-R interval best seen in left precordial leads
    • Unable to accurately visualise atrial activity
  • Regular ventricular rate
  • Rhythm indeterminate
  • Unable to assess
  • Unable to assess
  • High frequency high amplitude interference
    • Relative sparring of lead aVR
    • Frequency ~30 Hz
  • Baseline wander
  • 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
  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.

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