The irregularly irregular board question exception

There are some sure things in life.  Death.  Taxes.  The sun will rise tomorrow (see below).  Irregularly irregular tachycardias are A fib.  The boards love to test exceptions to the rule.  One of these is not like the others…


Roosevelt Gate at the NE entrance to Yellowstone

Let’s look again at last week’s EKG:

~65 y.o. woman with SOB

As always we start with the rate.  Given how irregular it is it’s hard to just count the big boxes so we’re better off counting the QRS’s and multiplying by 6.  By that standard it’s around 150.  We’ve already established it’s irregular, and clearly it’s irregularly irregular.  A fib.  Boom.  Done.  Or are we???  The vast majority of people said this was A fib, but you have to look everywhere.  Gestaulting an EKG is a ticket for disaster.  There’s 2 themes of the EKG section of this blog, the first is HAVE A SYSTEM.  The second is LOOK EVERYWHERE.  Let’s zoom in on V3:


There’s pretty clearly atrial complexes of some sort before virtually all of the QRS’s (and the one that doesn’t has a very short RR interval and a very peaky T wave, the P wave is likely buried in the T wave making it extra peaky).

The rhythm strip in II gives us even more information:


Not only are there P waves, there’s several different P wave morphologies.  This is Multifocal Atrial Tachycardia (MAT), a tachycardia most commonly seen in some COPD patients.  You treat it like a sinus tachycardia; treat the underlying problem.  The fact that it looks like A Fib but is not anticoagulated like A Fib, and not rate-controlled like A Fib, is what makes it a very common written board question.  I admit that this is one of the faster MAT’s that I’ve seen; usually they’re in the 120’s since it’s hard to have so many very excitable foci in the atria without actually having A Fib.

As always, we’ll round out our interpretation of the EKG.  QRS complexes are narrow, though she does meet criteria for LVH based on the size of the complexes in V2 + V5.  Note that she may not have LVH as she could simply have the body habitus of a small, frail COPD patient whose heart is very close to the electrodes.

She looks to have some mild flattening of her T waves in the lateral limb leads, review of an old EKG would show whether these are old or new.

The big take-home on this EKG is that irregularly irregular EKG’s aren’t always A fib (and the corollary is that if they show you an irregularly irregular EKG on boards it’s probably MAT!).

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