"What Happened?"–Discussion

This is the discussion to "What Happened?" You may wish to review the case here.

Ok, let's review the initial 12 Lead:

Just about everyone picked up on the infero-posterior STEMI.

Where it got interesting for me, was determining what the rhythm was! At first glance, the rhythm was for the most part regular (note the computer interpretation of Atrial Fibrillation with RVR!) and narrow, with a rate just a touch faster than 100. I did not see P waves before most of the QRS complexes, and I initially thought it was a junctional tachycardia.

As the STEMI was most likely due to an RCA occlusion, it is not surprising to have conduction disturbances. The pause, followed by an apparent sinus beat (circled in red above), had me wondering if this was indeed junctional with a sinus "escape" after the pause, or some kind of sinus rhythm with AV block.

In keeping with our spirit of "Peer Sourcing", I ran this strip by electrophysiologist Dr. Nick Tullo, of the ECG Academy.com. A review done by Life in the Fast Lane of Dr. Tullo's excellent academy can be found here. This is the conversation I had with Dr. Nick about this rhythm:

Me: Thanks for the help Dr. Nick. Now, what the heck is this?? Junctional, or sinus/AV block?

Dr. Nick: I would call it "Atypical Wenckebach" –essentially 13:12. You can see a sinus P following the fourth beat, and then a similar pause just before the end of the tracing. The pause is less than two times the previous R-R, and the PR of the second beat following the pause is longer than the PR that interrupts the pause (what you are calling accelerated juntional is really sinus rhythm with a first degree AV block, but you can't see the P easily because it's buried in the previous T). In the setting of acute IWMI it's due to the same high-vagal-tone mechanism that would cause the usual 3:2 or 4:3 Wencheback (or even complete heart block in some patients) but the AV node is mostly keeping up.

Me: Wow… OK!  But, how do we know it's not a junctional rhythm with a sinus beat escaping from the pause?

Dr Nick: You have to look hard for the P waves. If it was a junctional rhythm you'd see consistent P's at the end of the QRS or maybe in the very early part of the ST segment. If I'm right, the P wave will be on the T-wave somewhere and not always in the same spot (since it's not directly connected to the previous QRS). Granted, the ST elevation makes it hard to see the Ps. But I see the answer clearly:

Look at V5…see how the first beat has a concave upslope of the T wave while the second beat looks like it has a bump on it? That bump is the P wave. Assuming that the R-R interval midway through the "junctional rhythm" is equal to the atrial rate (since the PR doesn't change midway through an Atypical Wencheback cycle) measure back from the visible P preceeding the third beat in V5…doesn't it land right at the bump? The reason the T looked concave the beat before that is because that P wave is on the peak of the T.

I've put together some graphics to help illustrate the important points. 

First is Lead V5, which Dr. Nick referenced, blown up. I've done the same with lead II. Note the subtle morphology changes in the two T waves. This is the last P wave  of the cycle, which does not conduct. the P wave following the pause is the first of the cycle, and has the shortest PR interval:

I know, you're thinking, "Really? Do those little blips/bumps really measure out?" Don't take my word for it. I've got one more illustration to show you. I took a mid cycle R-R interval (1), as Dr. Nick suggested, and used that to measure back and see where the P wave should be in leads II and V5 (2,3):

As you can see, right on cue, those blimps/bumps are right where the P wave should be. And there we have it: 13:12 Atypical Wenckebach, with a PVC at the very end of the strip.

My sincere thanks to Dr. Nick Tullo for his help with this case, and kudos to Jason, who expertly picked up on this in the comments section.

Now for the second 12 Lead:

The patient was treated with thrombolytics (TNK), and as many of you commented the resulting rhythm was an accelerated idioventricular rhythm (AIVR).  AIVR appears similar to VT, but slower (slower than 120). In the thrombolytics era, this transient rhythm was noted to be a marker of reperfusion, although not all patients with a reopened coronary artery have AIVR. When it appears it rarely causes hemodynamic instability, and usually requires no treatment. For more information about AIVR, see here.

Of course, you will notice that I have circled several leads in the 12 lead above. In keeping with this case, in which nothing seems to be typical, you will notice that in fact the ST segments have not resolved during the AIVR. The inferior ST elevations remain, as do the ST depressions in V1-V4, and aVL. 

When asked about this, Dr. Smith, of Dr. Smith's ECG Blog had this to say: "This is one of the few cases of AIVR I've seen that was not associated with reperfusion."

In this case, our patient failed thrombolytics. He was immediately sent for rescue PCI. Unfortunately, we don't have any additional information.

There was a lot of information in this discussion. I sure learned a lot! 

I look forward to your comments, and as always, thanks for reading!

2 Comments

  • Arnel C. says:

    Very interesting post. Nice to see another case of atypical Wenkebach. Even in the abcence of MI, I have seen supscious looking baseline first degree block then after a mile stretch a drop. It has been said that atypical is Webckebach is common but you need long strip. Thanks for sharing this interesting piece of art.

  • Jan Š. says:

    Great case. Dr. Tullo is a great teacher and I watch his weekly chalk-talk with awe..

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