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Wide Complex Tachycardia

Dawn's picture
Sat, 09/06/2014 - 15:03 -- Dawn

Wide-QRS rhythms can be difficult to diagnose from the ECG alone.  This difficulty is compounded when the rate is fast, as it can be hard to determine if P waves are present before the QRSs, or dissociated, or absent.

This ECG and rhythm strip were donated to the ECG Guru by Ryan Cihowiak.  We don't have clinical information on the patient, unfortunately.  It is a great example, however, of how difficult WCT can be to diagnose.

In the 12-Lead ECG, we see wide QRS complexes that are regular at a rate of 131 / minute. There are no obvious P waves before the QRS complexes, and no obvious distortion of the T waves, which would suggest a "hidden" P wave.  Unfortunately, there is significant artifact, which makes searching for P waves difficult.  The pattern overall suggests left bundle branch block, with the negative QRS in Lead V1 and positive QRS complexes in Leads I and V6.  However, one requirement for the diagnosis of LBBB is a supraventricular rhythm, and P waves are the best indicator of that.  An irregularly-irregular rhythm, indicating atrial fib, would also have made LBBB more likely.  In typical LBBB, the frontal plane axis is usually left-normal or left.  In this ECG, Lead III is taller than Lead I, putting the axis within normal range, but slightly rightward.

The rhythm strip uncovers something else.  Possible P waves are seen in some of the ST segments (arrows).  Are these dissociated?  Do they represent a first-degree AV block?  Are they actually artifact?  If this is a supraventricular rhythm, there is LBBB.   Then, notice beats #7,8,9.  If this rhythm is supraventricular (with LBBB), those must be a salvo of V Tach.  But, one of the possible P waves occurs in front of beat #7.

Another possibility is Right Ventricular Outflow Tract Tachycardia.  RVOT is a type of V Tach that typically has a LBBB pattern, with a slightly rightward axis.  If this is the case, beats #7,8,9 are probably "capture" beats or "fusion" beats.  Capture and fusion beats "prove" that the underlying tachycardia is ventricular, since, by definition, capture and fusion represent a return to supraventricular control of the rhythm.

What do you think about this ECG?  Remember, when WCT exists, it should be TREATED AS VENTRICULAR TACHYCARDIA until proven otherwise.  Emergency treatment of VT (and WCT) is chosen based on the patient's clinical condition.  The unstable patient should be immediately electrically cardioverted, as this is effective in VT and in SVT, provides immediate relief of the tachycardia, and has few side effects, if any. 

The ECG GURU website thanks Ed Burns of Life In the Fast Lane ( ) for providing a SUPERB reference source for all things ECG and more!

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Comments's picture
     I agree entirely with Dawn that some of the most interesting tracings are those in which you can't be certain of the diagnosis. These 2 tracings provide an excellent example of this. Unfortunately - patient information and follow-up are lacking - so I fear we'll never know for certain what is going on. 
As per Dawn - there is a regular WCT (Wide-Complex Tachycardia) in the top tracing at ~ 135/minute. Amidst the artifact in the top tracing - QRS morphology is of a LBBB pattern. In the absence of clear sign of atrial activity - we are left with a diagnosis of "WCT of Uncertain Etiology". If this was all we had - VT would have to figure prominently in our differential. If we had a history of underlying heart disease with this being a new rhythm (prior tracings showing sinus with normal QRS duration) - then VT becomes that much more likely. But while lead aVL in this tracing is atypical for LBBB - the remaining 11 leads to me look perfectly consistent with LBBB morphology - so our differential = VT until proven otherwise (and treat accordingly) - but could be supraventricular with either preexisting LBBB or aberrant conduction.
The simultaneously recorded 2-lead rhythm strip is VERY helpful. While I am not convinced that the blue arrows represent dissociated atrial activity (too much artifact going on for me to be confident these arrows mean anything ... ) - beats #7,8,9 show a decidedly different morphology. This suggests that either beats #7,8,9 are "capture" beats and that the rest of the tracing is VT - or - vice versa. 
IF beats #7,8,9 are supraventricular - then we have a QS pattern with marked ST elevation in lead III. What doesn't make sense - is that lead II in the rhythm strip should show a similar Q wave and ST elevation if these were the supraventricular beats in the setting of acute inferior MI - yet lead II is positive without any hint of ST elevation. This is why I think beats #7,8,9 are ventricular - and the rest of the complexes (which look identical to the QRS complexes in leads II and III on the 12-lead) are supraventricular with LBBB conduction.
The "good news" - is that the chances are that the clinical scenario (which we are not privileged to) would ALMOST CERTAINLY point us in the right direction as to the correct diagnosis. Lacking that - we are left to speculate .... but it makes for an interesting discussion along the way.

Ken Grauer, MD   [email protected] 

Dawn's picture
Submitted by Dawn on

Because the discussion thread about this ECG on FaceBook's EKG Club was so interesting, I am copying it heree for those who missed it:


·        Frank Ay the p waves after #4 and #11 make me want to say AV dissociation. #7,8, and 9 may be fusion beats. Which suggests the whole this is VT. Thoughts?


Ryan Tee Heng Seong Think those are conducted beats
Arrows showing P waves
Which makes this a VT complicated by inferior MI

September 3 at 6:22am · Edited · Like


Ken Grauer I'm not convinced from the 12-lead that this is VT ... Instead - I see a regular WCT (wide-complex tachycardia) with lots of baseline artifact and QRS morphology that may be consistent with complete LBBB. I'd interpret this one as "Regular WCT without sinus P waves of uncertain etiology"

On the other hand - the rhythm strip shows a CHANGE in QRS morphology for beats #7,8,9 in the middle of the tracing in lead III - so that suggests VT until proven otherwise. That said - this would make the NEGATIVE complexes in lead III the VT beats - as the upright complexes in the lead III rhythm strip look identical to what the QRS in the 12 lead looks like - which supports my suspicion that the 12-lead is supraventricuar with LBBB. I am not certain of this - but that would be my working assumption pending clinical circumstances ...

As to the blue arrows - maybe and maybe not. I am not a big advocate of AV dissociation UNLESS you can be certain you see it. When present - AV dissociation is GREAT, as it is diagnostic of VT. But in my experience - too many folks go searching for P waves when there are none. I see far too much baseline noise on this tracing to place much stock in the "bumps" under the blue arrows (just my 2 cents).

Any follow-up?

September 3 at 9:23am · Like


Dawn Altman Sorry, no followup as of yet. How about LBBB pattern with slightly rightward axis = RVOT tachycardia?

September 3 at 5:24pm · Like · 2


Ken Grauer @ Dawn - My thoughts (as mentioned above) = I wasn't certain what the regular wide tachycardia without normal P waves in the top ECG was ... It is only when I see the bottom strip - that we can say beats #7,8,9 are a salvo ( = VT). We are then able to deduce that the top ECG is probably supraventricular - since QRS morphology in this top 12-lead is similar to the non-VT beats in the lower rhythm strip ...

September 4 at 5:21am · Like


David Richley Just to play devil's advocate - is it possible that beats 7,8 & 9 are capture/fusion beats and that the rest of the ECG is RVOT VT? There is a possible p wave before beat 7 but I can't see one before beat 10. Not saying, just asking! It's a pity the tracing isn't of better quality.

September 4 at 5:55am · Like · 2


Ken Grauer Sure it is possible- but given the QRS in lead II, the QRS in lead III just didn't look supraventricular to me (esp with that ST segment) - but I admit to not knowing for sure ...


September 4 at 7:56am · Like

Dawn Altman, Admin

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