Saturday, 27 September 2014

ECG of the Week - 22nd September 2014 - Interpretation

Sorry but I don't have any clinical information on this ECG at all but that hasn't stopped us before.

So what's going on here ?

Check out the great discussion on this ECG in the comments section from our original post.

Click to enlarge

Numbered Ventricular Complexes
Click to enlarge



Rate:
  • Mean ventricular rate 54 bpm
Rhythm:
  • Interesting !
  • P waves
    • Precede all ventricular complexes
    • P waves occur regularly every 760 ms
    • EXCEPT between complexes #2/3, 4/5, 7/8 where the P waves is dropped
    • The gap between the P waves either side of the pause is 1520 ms 
      • i.e. double the normal P-P interval
  • QRS Complexes
    • Progressive PR lengthening
    • Progressive R-R shortening
    • Grouped beatings
    • The dropped QRS is not preceded by a P wave
      • Not just 2nd Degree AV Wenckebach
Axis:
  • Normal
Intervals:
  • PR - Initially normal (180ms) then progressive lengthening
  • QRS - Normal (100ms)
  • QT - 440ms 
Segments:

  • ST Depression leads II, III, aVF, V2-6

Additional:

  • T wave inversion Leads III, aVR, V1-3
  • rSR' Pattern V1
  • Deep inferior Q waves with smaller lateral Q waves
  • Baseline irregularity
  • Lead I rhythm strip makes P waves more difficult to identify

Interpretation

So we have clear evidence of a AV Wenckebach but where do the P waves go ?

Frequent ECG of the Week commenter / ECG author / blogger / legend Ken Grauer shares his thoughts on our missing P waves:

I strongly suspect that there is a blocked PAC that causes the pause (and terminates the Wenckebach cycles) - but unfortunately in the long lead I it is very difficult to be certain of this ... I do think I see tiny-but-real differences in the T wave of the beats that initiate the pause (in lead II for beat #2; in aVF for beat #4; and in V2 for beat #7)

My other theory:

Presence of a 2nd Degree Type II SA exit block in addition to our 2nd Degree Type I AV block !
There is a regular P-P interval with the interval including the dropped P wave being twice that of the normal P-P interval. The causative factors for both types of block are virtually identical - ischaemia, drugs, electrolyte abnormality, cardiomyopathy, myocarditis etc.

Do I have a definitive answer ? No

I don't have any other ECG's or clinical information on this case. A longer rhythm strip, serial ECG's, old ECG's, more clinical information, and ideally lead II as the rhythm strip may shed more light on the likely rhythm disturbance and causative factors.

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.