Saturday, 24 October 2015

ECG of the Week - 19th October 2015 - Interpretation

This ECG is from an 80 yr old male, unfortunately I don't have any further clinical information on this case.


Click to enlarge

Rate:
  • Mean ventricular rate 60 bpm
  • Mean atrial rate ~78-84 bpm
Rhythm:
  • Irregular narrow complex ventricular rhythm 
  • Single PVC (QRS Complex #8)
  • Atrial activity with variable rate 
    • Number of P waves are buried within the terminal QRS / T waves
P waves labelled
Click to enlarge
Axis:
  • Normal
Intervals:
  • QRS - Normal (80-100 ms)
  • QT - 440 ms
Segments:

  • ST segment variability due to baseline wander and P wave super-imposition

Additional:

  • P-P variability likely due to ventriculophasic arrhythmia


Interpretation:


  • Complete heart block
    • It could be 2:1 block but I think the P waves being buried before the T wave suggest complete heart block to be absolutely certain you'd need a longer rhythm strip
  • Ventriculophasic Arrhythmia


What is ventriculophasic 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.

We've had a few case examples on our blog the best of which can be found here:


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


References / Further Reading

Life in the Fast Lane

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