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Atrial Flutter With 2:1 Conduction And Left Bundle Branch Block

Dawn's picture
Sun, 05/11/2014 - 22:10 -- Dawn

This ECG is a two-for-one teaching opportunity.  This elderly woman presents with a tachycardia at about 120/min.  We do not have any other information about her complaints or past medical history.

Her ECG shows a wide-complex tachycardia.  The QRS complexes are about 124 ms (.12 sec.) wide.  On the most basic level, we should teach our students to consider ALL wide-complex tachycardias to be ventricular tachycardia until proven otherwise.  This ECG has many clues that it is NOT ventricular tachycardia.  Tiny P waves can be seen in V1, V2, and V3.   But, these are not the only P waves.  The atrial rate in this case is twice the ventricular rate, making the rhythm ATRIAL FLUTTER with 2:1 conduction.  The flutter rate is about 240/minute, slightly on the slow side for AFL.  Atrial flutter with 2:1 conduction is often missed, as every other P wave is hidden.  Look at aVR and Lead II in this case for signs of the regular flutter waves.  It is important to look in all 12 leads for signs of flutter waves in any tachycardia over 120/min.  Occasionally, you will get lucky, and the patient will conduct at a different ratio, such as 3:1 or 4:1, making the flutter waves much more visable.  Sometimes, the atrial flutter becomes apparent during carotid sinus massage or a Valsalva maneuver.

The QRS width, in this case, is due to left bundle branch block.  The criteria for LBBB are:  Wide QRS, Supraventricular Rhythm (in this case, atrial flutter), and a negative QRS in V1 with a positive QRS deflection in Leads I and V6.  The ST changes seen here are typical of LBBB:  ST depression in leads with upright QRS complexes and ST elevation in leads with downward QRS complexes.


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Comments's picture
This tracing is an excellent one for teaching purposes. It is NOT at all obvious that the rhythm is AFlutter. Instead - we see exactly what Dawn describes = a regular WCT (Wide-Complex Tachycardia) at ~ 120/minute. Normal sinus P waves are absent (ie, no upright P in lead II). Therefore - one should contemplate VT until proven otherwise.
Clearly - “You have to be there” in order to know what best to do for this patient. As a teaching exercise - you can set whatever clinical scenario you desire. For example - IF a patient in this rhythm was hypotensive with mental status changes - then prompt cardioversion would be indicated regardless of what the rhythm turns out to be. But if the patient was hemodynamically stable (as we presume this patient was) - then you have some time to figure things out more. 
This tracing provides an excellent example in which lead aVR is the BEST lead for determining the rhythm. AVR is really the ONLY lead in which I clearly see flutter waves. Knowing this - I can then walk out 2:1 flutter conduction also in lead II - but this is only after lead aVR gave me the diagnosis of AFlutter. While possible to have simultaneous AFlutter with VT (I had a case once!) - that is rare - so diagnosis of AFlutter virtually determines for you that this rhythm is supraventricular - with 2:1 AV conduction. 
As to the LBBB morphology - it is important to realize that VT may produce very similar QRS morphology as is seen in lateral leads I,aVL and V6 with LBBB. The KEY in this tracing - is the remarkably steep downslope of the S waves in V2. While this steep downslope doesn’t prove this is supraventricular with LBBB - it does make this MUCH more likely. In conjunction with AFlutter as the rhythm - we have our answer.

Ken Grauer, MD   [email protected] 

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