Thursday, May 24, 2012

Wide Complex Tachycardia: what is it?

I'm going to show you this one without history.

Rate is 133.  There are no definite p-waves.  The QRS is only 126 ms.  See answer below

When the QRS duration is less than 140 ms, it is more likely SVT. Furthermore, there is a left bundle branch block morphology, supporting SVT.   A rate of 130 - 170 should make you think of atrial flutter with 2:1 block and prompt a search for flutter waves, best seen of course in leads II and V1.   Of course PSVT is also possible.

In this case, the flutter waves are best seen in lead aVR (usually leads II and V1 are easiest.  I have annotated this with lines below.  I found the waves in aVR and drew red lines down to the lead II rhythm strip across the bottom.  Then I can find the same bumps on lead II across the entire ECG and draw black lines up. 

Wide complex?  Left bundle branch block (LBBB), possibly rate related

Here is the obvious atrial flutter rhythm after AV nodal blocking with Diltiazem.

Atrial flutter with variable (3, 4, and 5) to 1 block.  LBBB persists, so it is NOT rate related


  1. I'm just trying to clarify my understanding. I was always under the impression that if there is a "return to baseline" then it is EAT with block whereas if it is a continuous undulating waveform then it is A-flutter. Could you perhaps elaborate on how to differentiate between the two?

  2. 1) EAT is far less common
    2) EAT is automatic, not re-entrant, and therefore its rate is not always constant
    3) EAT is from an automatic focus (as if it is a different sinus node) and will have distinct p-waves, rather than a continuous waveform
    4) flutter has an inferior-superior axis as this one does up-down-up-down. This is seen easily in II and V1.


  3. Dr. Smith,

    What is your opinion of the Lewis lead?

    Do you think it has a role in the differentiation of regular, wide complex tachycardias in a stable patient when the atrial activity is as subtle as in the presenting ECG of this case?

  4. Good point. It would probably be very useful here. On the other hand, it would be easy to just give adenosine and see the response.