Monday, April 29, 2013

Another Guest post from K. Wang: What is the rhythm/conduction problem?

What does this rhythm strip of lead V1 show?

















How about choosing from multiple choice?



a) Acceleration AV junctional rhythm with occasional premature atrial beats
b) NSR and AV junctional acceleration with AV dissociation and occasional capture beats
c) Extreme sinus bradycardia (34/m) and AV junctional acceleration and occasional capture beats
d) Extreme sinus bradycardia and complete AV block with AV junctional escape rhythm



Here is a ladder diagram of the rhythm:



Answer: b) NSR and AV junctional acceleration with AV dissociation and occasional capture beats.
Discussion. As diagrammed, P waves from the sinus impulse occur regularly at a rate of 65/m (P1,2,3...etc). The blips pointed by the arrows are not r' of rSr', but sinus P waves, judging from the timing.  If it were an r', then all QRSs would have it.   The primary problem in this patient is AV junctional acceleration. P1 is conducted to R1. P2 was going to be conducted but accelerated junctional beat (R2) occurred sooner than that. P2 and R2 are dissociated because they occur close together during the physiologic refractory periods of each other. R3 is the accelerated junctional beat which failed to conduct to the atria and next sinus P wave is uninterrupted and occurs on time and conducts to the ventricle (R4). And the cycle repeats. 

Thus, there is AV dissociation without any AV block.

The primary problem is junctional acceleration. What is the clinical significance of junctional acceleration? One has to consider digitalis intoxication, myocardial ischemia or infarction, or excess amount of catecholamines circulating which means any stressful condition. Again, a given ECG tracing can be dissected into primary disorder and secondary manifestations and ask what is causing the primary disorder, so that the patient can be treated appropriately, promoting quality patient care.

6 comments:

  1. thanks dr smith for this interesting ecg ,can we say that it is a 2/1 AV BLOCK with an accelerated jonctional rythm like the case shown previously http://hqmeded-ecg.blogspot.com/2013/04/what-kind-of-av-block-is-this-guest.html

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    1. No, because there is no AV block at all! There is only AV dissociation because the AV nodal automatic rhythm is faster than the sinus and its retrograde conduction blocks the anterograde conduction originating from the sinus node.

      AV Dissociation without AV block

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  2. Very interesting rhythm! I couldn't connect the AV-dissociation with an accelerating rhythm, because I hadn't heard from an accelerated junctional rhythm before.
    I do have a question. Is the blockage of the retrograde conduction part of the primary disorder? I understand R2 is probably blocked due to the refractory period, but R3 is also blocked.

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  3. Thank you for posting Steve - and I LOVE Dr. Wang tracings. That said - I forced myself to draw my own laddergram before looking at his answer - and I see that mine is different. Please GO TO: https://www.dropbox.com/s/1gpgfhyccwthlfa/Dr.%20Wang-S.Smith-AV-Laddergram-%284-30-2013%29.png

    What bothered me about this being an accelerated junctional rhythm (interrupted each 3rd beat by sinus capture) - was that the R-R interval for the 1st junctional beat in each sequence (= the R-R between beats #3-4; 6-7; 9-10; and 12-13) is slightly different (shorter) than the R-R interval of the subsequent beat (= the R-R between beats #4-5; 7-8; 10-11; and 13-14) - whereas if this was AV dissociation by usurpation with junctional acceleration I would have expected them to be the same ....

    Why couldn't the mechanism be the one I drew - whereby there are PJCs (beats #4,7, 10, 13) that conduct retrograde enough to slow down forward conduction of the next sinus impulse. Admittedly - that next sinus impulse is slowed down to a greater extent than usually occurs with such concealed conduction (perhaps due to switching to some alternate slow conduction pathway ... ).

    Just wondering if Dr. Wang might consider my alternate mechanism plausible. In any case - GREAT TRACING - and what IS agreed is that there is AV dissociation from some junctional intervention and no evidence of any AV block.

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  4. It is only blocked because of the descending depolarization from above.

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