ECG of the Week – 12th March 2018 – Interpretation

The following ECG is from a 76 yr old male who presented with a 3 week history of progressive shortness of breath and occasional chest heaviness.

 
 
Click to enlarge

Rate:

  • Mean ventricular rate 36 bpm
  • Mean atrial rate 72 bpm

Rhythm:

  • Irregular ventricular rate
    • R-R varies between 1520 – 1680 ms (~36 – 39 bpm)
  • Variability in P-P interval
  • PR prolonged before QRS ~260ms 
  • Apparent 2:1 conduction

Axis:

  • LAD

Intervals:

  • QRS – Prolonged (180ms)

Additional:

  • Voltage criteria for LVH – aVL >11mm
 

Interpretation:

  • 2:1 AV block
    • This is what this ECG appears to show at initial review
    • There is P-P and R-R variability
    • Could represent ventriculophasic sinus arrhythmia although pattern is not entirely predictable
  • Possible CHB
    • QRS Morphology unusual
    • May represent multi-level conduction system pathology
    • ? Isorhythmic dissociation – apparent temporal relationship between P & QRS
  What is Ventriculophasic Sinus Arrhythmia

 This phenomenon can be seen in up 40% of case of complete AV block and, as in this case, can be seen with 2nd degree AV block also.

You get a shorter P-P interval when there is an associate QRS complex with a longer P-P when there is no QRS between the P waves. Several mechanisms have been proposed including  alterations in sinus node perfusion related to ventricular contraction and the mechanical effects of atrial stretch.

To make things more confusing there is a much rarer paradoxical phenomenon when the P-P is longer when a QRS is contained between them.

It is important to recognized as the P-P variability may be mistaken for other ECG features such as U waves for example.

You can read more about ventriculophasic sinus arrhythmia in this nice case report of the paradoxical version here: 

What happened ?
There was no reversible cause identified for the AV block.
The patient was admitted under cardiology and underwent an uneventful PPM insertion.
  

References / Further Reading
 
 

Textbook

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

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