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Jason's Blog: ECG Challenge April and May, 2013.

jer5150's picture

Jason is taking a break (everyone needs one now and then).  April's ECG will appear through May, as well.  It's a good one!

These are 3 simultaneous rhythm tracings that were once part of a full 12-lead ECG.  Unfortunately, this ECG dates from a time period when our facility's computer database did not store complete 12-lead ECGs.  The technology at the time was known as "reduced data", so much of the entire 12-lead ECG was deleted and only leads II, V1, and V5 were preserved for review by the cardiologist.  This was in an attempt to reduce the amount of information that the computer would need to store over time.  I can only imagine that this method was eventually deemed to be an undesirable way of storing ECG data.  Later generations of computer storage would download the 12-lead ECG in its entirety. 

All of that being said, what is this showing?  Obviously, many things can not be determined without the remaining leads (e.g., QRS axis, chamber enlargement, etc) but the arrhythmic mechanism can still be determined. 

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My guess:

1st degree AV-block

Pauses due to non-conducted PAC's

retrograde P-waves at the end suggest AVRT???

Submitted by Jan Štros on

I think that there are atrial echoes + potential for Wenckebach involved - again.. 

Two cycles of wenckebach periods, both interupted by atrial echo.

And in the last cycle, the atrial echo starts run of AVNRT? Looking forward to the explanation :)!'s picture

Gorgeous tracing - and I'll look forward to Jason's laddergram! I see the following:

  • Underlying sinus rhythm with 1st degree AV block.
  • Blocked PAC in the T wave of beat #3.
  • Resumption of sinus rhythm with beat #4.
  • Another PAC in the T wave of beat #7 - but the coupling interval is a bit longer than for the PAC in the T wave of beat #3. This allows this PAC (in the T wave of beat #7) to conduct via the SLOW pathway (producing beat #8). There is a retrograde P following beat #8 with a very short RP'.
  • Resumption of sinus rhythm with beat #9.
  • Another PAC in the T wave of beat #11. The RP' is again longer than the RP' of the first PAC that was blocked. Therefore - there is again forward conduction down the SLOW pathway to produce beat #12.
  • Beat #12 again conducts retrograde - but since the RP' of this PAC is longer than the RP' of the PAC in the T wave of beat #8 - there is perpetuation of a tachycardia. It almost looks like the RP' of the last 3 beats on the tracing is prolonging (such that there probably will be retrograde Wenckebach).


Ken Grauer, MD   [email protected] 

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Submitted by jer5150 on


Not much to add to Ken’s interpretation.  As Ken points out, it’s the subtle changes of duration in the “coupling” interval that determines whether or not a PAC conducts.  The longer post-ectopic cycles end with sinus beats (4th and 9th beats) that conduct with somewhat shorter P-R intervals implying that there is undoubtedly a potential for Wenckebach conduction at a faster sinus rate.  The isolated retrograde P’-wave, following the 7th beat, can also be called an atrial “echo” or reversed reciprocal beat.  The two conducted PACs are labled “A”.  The upward-pointing arrows in V1 are marking the early ectopic atrial P’-waves whereas the downward-pointed arrows in lead II are marking the retrograde P’-waves.

I am a stark proponent of using the term “nonconducted PAC” in place of the all-too-often confusing term “blocked PAC”.  On more than one occasion, I have seen a patient get erroneously admitted for having a “new onset of A-V block” because the provider interpreting their ECG equated “blocked PAC” with being a type or form of A-V block.  Invariably, healthcare providers hear the word “block” and reflexively think of heart block.    

The reviewing cardiologist diagnosed this ECG simply as: 
Normal sinus rhythm 2nd degree AV block (Mobitz i, Wenckebach)

There are clearly no “dropped” beats.

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

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