Strip Tease 13: Answer

This was an AVB example provided by my training captain in a class that he taught.

Most people will call this a 3:1 2nd degree type 2, or Mobitz 2.

Lets have a look:

First measure your PP interval, and make sure they "march out"

Okay, seems like the PP is pretty consistent. There are 3 p-waves for every R -wave; this favors third degree AV block. Now lets check the RR-interval.

As expected the RR-interval is consistent. This is also highly favorable of third degree AVB, but isn't conclusive. We have to prove complete atrioventricular(AV) disassociation. We do this by measuring our PR-intervals.
If you measure the first PR-interval against the last PR-interval you will see that they do not match. This leads to a couple conclusions.

Either this is a 3rd degree AVB and the atrial rate just happened to be almost exactly 3 times as much as the ventricular rate. If this is true, further monitoring will show the AV disassociation clearer, since the PR-interval is varying.

Or, this is a high grade transient AVB. Meaning this is the end of a Mobitz 2, as it becomes a 3rd degree AVB. I call these Mobitz 3s.

I personally think this is a simple 3rd degree AVB and coincidence confused the masses. If all else fails, and the pattern continues, call it a 3:1 AVB.

ps. If you don't have a fancy set of calipers, a piece of paper works fine. Just draw lines on the pice of paper to measure out your intervals and see if they match.


C. Watford said...

It seems odd that it would be narrow and disassociated, especially with how isochronic they appear to be. I guess I'm wondering why I wouldn't be seeing a wider QRSd or at least a faster junctional rhythm if narrow (40-60)?

Also some slurring of the S-wave, right bundle problems too?

Adam Thompson, EMT-P said...


That is a great observation. The QRSd actually is about 120 ms from my calculations. It appears quite narrower on the computer.

It isn't that wide though and this may be due to a few factors.

- It may be that this is a degenerating Mobitz 2 as stated.

- Or, the block may be just just above the bundle of his. With a block proximal the bundle branches you may have less obvious aberrancy. Those trifascicular CHBs are pretty wide.

There are many examples of seemingly narrow CHBs on the web. It is less common.

Rogue Medic said...

I disagree with the approach as you present it. The PR interval is the important measurement, as you point out.

Suppose that the P-P interval is irregular, does that tell us anything? Many ECGs have P-P variability, but what does it mean? It is normal and healthy for the heart rate to vary with respirations. This does not happen without P-P variability.

Regardless of whether there is R-R variability, the PR interval is what matters.

I confess that I did not pay close enough attention to the PR interval to pick up on the variation. It is there, but superficially appears to be a regular, for the conducted P waves, PR interval. Excellent example of an easy mistake to make.

Regardless of the different intervals and regardless of the final diagnosis of the rhythm, we should base our treatment on the condition of the patient. Bradycardia is an important algorithm to be familiar with.

These patients tend to be closer to death than the tachycardia patients. The more normal response to stress, the more healthy response to stress, is tachycardia - not bradycardia. We should be prepared to become very aggressive very quickly, if indicated. Bradycardia seems to be mistreated much more often than tachycardia.

Adam Thompson, EMT-P said...


That is a good point to make. I can't believe I didn't mention this. Whatever the rhythm is, the treatment for the high grade AVB is the same. The argument is just semantics.

Anonymous said...

I am afraid, that I do not know.

Adam Thompson, EMT-P said...

Don't know what?

Tom B said...

Adam -

I am convinced that stupid little ambiguous comments from anonymous bloggers like "I am afraid I do not know" or "Good point" or "Thank you this is useful" are "pings" from SPAM robots to see if they can target your blog.