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Jason's Blog: ECG Challenge of the Week for Feb. 10th - 17th.

jer5150's picture

Patient's clinical data:  84-year-old black man

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Submitted by jhwan on

1. Atrial rate: 96 bpm, ventricular rate: 78 bpm

2. Sinus rhythm, irregular, in 'clusters' of beats

3. Axis normal

4. PR interval prolongation with subsequent non-conducting p waves (4th, 10th, 14th beat) = second degree heart block, Mobitz type 1 (wenkebach type)

5. 'Camel hump' T wave as a result of PR prolongation causing p to fuse with T waves.

6. QRS interval normal

7. QTc = 0.465ms = ?long QT for a man

8. No high voltage to suggest ventricular hypertrophy, no ischemic ST-T changes, no evidence of past MI

My impression: Sinus rhythm (sinus rate of 96bpm) and ventricular rate of 78bpm complicated by second degree Mobitz type 1 AV block with prolonged QTc

would want to check for:




drugs eg antiarrythmics, TCA, antipsychotics


Hope to learn his clinical condition from you. Thank you for sharing!


Submitted by Cristian on

Nice, detailed description by jhwan. I would add one thing: the cause for the irregularity of the rhythm seems to be both the 2nd deg AVB type I (beat 10) and the non conducted atrial echo beats (beats 4 & 14 with their inverted P' waves). The Wenckebach is actualy the reason for the appeareance of these echo beats (when the AV conduction is prolonged enough, the VA conduction becomes possible and manifest; with a normal AV conduction duration, the VA conduction would probably remain concealed). A nice laddergram would nicely illustrate what happens in this beautiful ecg Smile

Submitted by jhwan on

Thank you so much for your input. Learnt something interesting from you :)'s picture


First - GORGEOUS tracing by Jason!

  • I agree entirely with succinct explanation by Cristian. There is both 2nd Degree AV Block Mobitz I (AV Wenckebach - in the middle of the rhythm strip) - as well as termination of progressive Wenckbach PR prolongation by blocked Atrial Echo Beats at the beginning and end of the tracing.
  • CALIPERS are the key to recognizing neat conduction blocks such as this one. Pure AV blocks manifest a constant P-P interval. Clearly - there can be slight P-P variation (underlying sinus arrhythmia; ventriculophasic sinus arrhythmia) - but it is usually easy to see that there is an underlying at-least-fairly-regular atrial rhythm when you have a pure AV block. Hard to miss the earlier-than-expected negative (retrograde) P wave deflection that occurs after the 3rd and 11th QRS complexes if you are using calipers ...
  • Alternative (and much less likely) Explanation - is that a blocked PAC ends the Wenckebach cycles after the 3rd and 11th QRS complexes. I don't know how you can rule blocked PACs out from this surface ECG - but I like blocked atrial echoes much more as the probable explanation.

THANKS for presenting Jason!

Ken Grauer, MD   [email protected] 

jer5150's picture
Submitted by jer5150 on

(1.)  Sinus rhythm (rate about 98/min) with . . .
(2.)  . . . Type I A-V block manifest as a . . .
(3.)  . . . 6:5 Wenckebach period.
(4.)  Two probable reversed reciprocal beats (i.e., atrial "echos" - see laddergram).

It's important to remember that delayed conduction favors reentry.  While this is certainly true, it is also important to realize that the conditions need to be just right.  Twice we see a potential for Wenckebach periodicity as evidenced by the progressively lengthening P-R intervals and twice this progression is interrupted by retrograde P'-waves (downward arrow) in lead II.  I would postulate that these represent atrial "echos" because they both follow identically prolonged P-R intervals of 0.28s.  Then why isn't an atrial "echo" responsible for the pause in the middle of the tracing?  Again, I would postulate that if the P-R interval is 0.27s, it is too short for reentry to take place.  Conversely, if the P-R interval is 0.30s, it is too long for reentry to take place.  In other words, there is a very narrow "window of opportunity" or one could say the "Goldilocks zone" required for reentry to take place is exactly 0.28s.  If the prolonged P-R interval is any shorter, reentry doesn't occur.  If the P-R interval is 0.30, it won't occur either.  Any longer than 0.30s, and the next descending sinus impulse arrives at the A-V node during it's absolute refractory period and results in a "dropped" beat (upward arrow in lead V1).  If all I saw in this ECG were pauses generated by atrial "echos" and the absence of any "dropped" beats, then I would not call this pure Type I A-V block.  I would simply state that there was a "potential" for Type I A-V block.  Case and point, if you refer to this ECG of a "Floating P-R interval", you will notice the the length of the P-R interval is waxing and waning.  There are times when the P-R interval is progressively lengthening but does not result in the "dropped" beat.  Instead the P-R interval retreats back to a shorter duration.  As is, one can't assume that the patient's rhythm will ever progress to "dropping" beats until there is direct evidence that it does so.   

Nonconducted APBs can't be completely ruled out, but as Ken pointed out, atrial "echos" are for more likely given the "company that it keeps" - that being, the 6:5 Wenckebach period.

Jason E. Roediger - Certified Cardiographic Technician (CCT)
[email protected]

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