Monday, January 5, 2015

Irregularly irregular supraventricular very fast rhythm: what is it?

A young woman presented to the ED with a complaint unrelated to any cardiac condition.

The pulse was fast.  The physican noted it was irregular.  The woman stated that this happens frequently for years, but she had never sought medical attention for it.

Here is the 12-lead:
The rhythm is very fast and irregularly irregular.  Usually that means either atrial fibrillation or multifocal atrial tachycardia.

----Is it atrial fibrillation?  There are clearly waves that look like P-waves, so probably not.
----Is it MAT?  No, the P-waves are unifocal (of one morphology)
----Is it atrial flutter?  They look like P-waves, not like flutter waves, which should have a continuously undulating baseline.  

----Moreover, with atrial fluter, the QRS should land on the same part of the atrial wave every time.   In this tracing, the QRS sometimes lands in the middle of atrial activity, and sometimes after it.
             ----Accordingly, if it is flutter, t
he R-R interval should be some integral multiple of the flutter interval (hence: it would be regularly irregular; here it is irregularly irregular.
----The atrial activity looks like P-waves, not flutter or fibrillation waves.

I sent this one to K. Wang and also showed it to the members of the Facebook EKG club.  The consensus opinion corresponded to K. Wang's interpretation, which I paraphrase below:

There is an atrial tachycardia at a rate ranging from ~250 to 300 per minute with primarily 2:1 AV conduction but occasionally 3:1 or even 4:1 AV conduction which converts to NSR at the end of the 1st tracing.  The baseline does not continuously undulate in any of the 12 leads, indicating there is no continuous circus movement of the electrical front, so it is not atrial flutter.

So it has to be called atrial tachycardia.  EKGs at this rate are often atrial flutter, and that is why it is confusing, but in this case it is a fast atrial tachycardia.  In young people, especially children but also young adults, atrial tachycardia can be very fast.  It is also unusual for the atrial rate to not be consistent (here it varies, so this is unusual).

This is another important observation: It is not the P-wave directly before the QRS that is conducting, but rather the previous one.  

See this ladder diagram drawn by Dr. Wang:

Acute treatment options include AV node blockade with Diltiazem or, better yet, beta blockade to attempt to slow the atrial tachycardia AND conduction through the AV node.  

Metoprolol was given. Electrolytes were normal.

What else do you think is going on?  Answer below.


The patient was found to have an undetectable TSH, and a T3 and T4 above the lab measurement capabilities.  She was noted to have some thyroid "fullness," but no proptosis.  She did have thyroid antibodies (which activate the TSH receptor) and was diagnosed with Graves' disease.

Here is a one slide summary of assessment and management of atrial tachycardia, from my lecture on SVT:

Etiologies: Lytes, acid-base, drug toxicity, fever, hypoxia, thyroid
Digitalis toxicity
lCorrect hypokalemiaDigibind
Correct underlying disturbance
Beta blocker or Ca channel blocker
Mg (2-4 g IV)
Adenosine occasionally terminates (only if the atrial rhythm is regular)
lSinus node re-entry or triggered activity
Electrical treatment rarely needed
l50-100 J if unstable
Overdrive transvenous atrial pacing

Learning Point:

Any very fast supraventricular atrial rhythm should lead to suspicion of hyperthyroidism.

Here are some rhythm strips for anyone interested:


  1. Thank you for this HYPER-interesting case. Really good learning points!

  2. If this is atrial flutter,2 to 1,3 to 1 conduction not block. If atral tachhycardia like this, is it also condution not block? Is there any
    difference a.tachycardia and flutter in
    the point of treatment?

    1. It is atrial tach with less than 1:1 block. It is too fast for the AV node to conduct every beat, so in that sense it is similar to atrial flutter. Flutter is a circus rhythm that goes around a relatively larger area of atrial myocardium, where atrial tach is either a fast automatic rhythm (like sinus) or has a smaller area of re-entry. If re-entrant, it may convert just as flutter does. But if automatic, as most are, and as this one is (you can tell because it is slightly irregular, where re-entrant rhythms are very regular), then electrical cardioversion does not work and you need medications that slow the automatic rhythm, like a beta blocker.

  3. GREAT case! - which I'm just seeing now. To me - the KEY reason why despite the very rapid atrial rate that this is NOT atrial flutter- is that the ATRIAL activity is NOT regular. Calipers are needed to assess this. In parts of the tracing - the P-to-P interval is regular - but in other parts, the P waves just do NOT march out. There are atypical atrial flutter rhythms (about 15% of AFlutter does not produce the typical sawtooth pattern in the inferior leads) - but atrial flutter waves should still be regular - and they are not regular here. GREAT case! - with excellent additional teaching points about faster-than-usual atrial rates for ATach in some patients (esp. younger individuals) - and need to consider hyperthyroidism with excessively fast SVT rhythms (with of course a young female being a high-likelihood demographic for hyperthyroidism). THANKS for presenting.

  4. Thank You. Very useful. Have you available some records with transmitral flux in SVT?


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