Wednesday, 16 January 2013

ECG of the Week - 14th January 2013 - Interpretation

Another week of mystery. 
 
This ECG is from a male, and that's all I've got.


 
Click to enlarge
 
 
Rate:
  • Ventricular Rate 60 bpm
  • Atrial rate 90 bpm
Rhythm:
  • Regular rhythm
  • Regular atrial activity
  • Pattern
    • P wave -> QRS -> P wave -> Pause -> Paced Complex + Buried P wave
Axis :
  • Sinus Complexes - LAD (-37 deg)
  • Paced Complexes - LAD (-80 deg)
Intervals - Sinus Complexes:
  • PR - Normal (~180ms)
  • QRS - Prolonged (120ms)
  • QT - 440ms
Intervals - Paced Complexes:
  • QRS - Prolonged (160ms)
  • QT - 520ms 
Segments:
  • Appropriate ST segment & T wave discordant changes in both Sinus & Paced Complexes
Additional:
  • LBBB Morphology of Sinus Complexes
  • Right Ventricle Pacing
    • Paced Complexes have LBBB Morphology
  • Pacing Interval 60 bpm from Conducted QRS
    • If no QRS sensed 1000ms after last QRS PM will pace
    • Unknown if P wave following sinus QRS would have conducted with long PR or would have blocked
  • P waves hidden in ST segment of Paced Complexes
    • Unlikely to be retrograde conduction
    • Likely Atrial Rate is Isorhythmic to Pacing in 3:1 Pattern
Interpretation:
  • High Grade AV Block with Escape Ventricular Pacing
  • LBBB
This is an interesting ECG and I would encourage our readers to go back and read both Jason's & Christopher's comments on this ECG, they can be found here 

Question Time

VVI vs DDD ?

Christopher raised the question if you can tell whether this PPM is DDD or VVI from this ECG.
Dr Arieh Keren, has kindly come to the rescue. and gives us a brief explanation of pacing modes and their ECG morphology.
"The PM is VVI.  A DDD pacemaker will be pacing the atrium if the sinus rate is below the lower rate limit only. Usually if the sinus rate is normal or above the lower rate, the way you know it's a DDD, is that you have every P wave followed by a  paced QRS (A sense V pace) or a conducted QRS with a max set PR interval. (not common).  
If there is a pattern to the P wave association with the QRS and it is not timing off a conducted beat like in this case, it must be dual chamber otherwise the PM can not coordinate an association."

Why is the PR Interval Normal for Sinus Complexes ?

We know we have significant conduction system disease present in this case, and yet the PR segment is normal for the conducted QRS complexes, why ?

There are essentially two non-conducted P waves preceding every conducted QRS, this allows time for AVN & HIS systems to recover

Many thanks to all our commenter's for sharing their thoughts and raising some interesting questions. Also thanks to Dr Arieh Keren, from our blogging team, for his thoughts and explanations on this ECG.

 
References / Further Reading
 
Life in the Fast Lane
 
  • 2nd Degree AV Block
  • Paced Rhythms here
Textbook
  • Chan TC, Brady WJ, Harrigan RA, Ornato JP, Rosen P. ECG in Emergency Medicine and Acute Care. Elsevier Mosby 2005.