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ECG Basics: Atrial Flutter With 2:1 Conduction And An Aberrantly-conducted Beat

Sun, 08/23/2015 - 12:20 -- Dawn

This strip was taken from a patient at rest.  It shows a regular tachycardia with a slightly-widened QRS complex at about .10 seconds duration.  It is somewhat difficult to evaluate the baseline for P waves or flutter waves.  We ALWAYS recommend multi-lead assessment for such evaluation.  The P waves (or flutter waves) here have a sharp point, and can be easily "marched out", with a rate of about 300 per minute.

Whenever the ventricular rate is near 150/min., we should always consider the possibility of atrial flutter with 2:1 conduction.  Since atrial flutter results in atrial depolarization at around 250 - 350 per minute, conducting every other P wave results in a rate of about 150.  It can masquerade as sinus tach, but a patient with sinus tach at such a fast rate would probably have an obvious cause for a rapid heart rate, such as hypovolemia, drug overdose, or exertion.  This rhythm could also be mistaken for atrial tachycardia or other forms of supraventricular tachycardia (SVT, PSVT, AVNRT, etc.).   Multiple leads can more easily uncover the flutter waves running continuously "behind" and "through" the QRS complexes.

There is one beat that is obviously different from the others.  This beat is about the same width as the other QRS complexes, but is opposite in direction.  This probably represents aberrant conduction, possibly a hemiblock that occurs only in this beat.  Careful measurement will show that this QRS is very slightly early, while the others are all very regular. The slight width of all the QRS complexes suggests that there is a conduction delay, which cannot be diagnosed on one strip with no patient history available.

There are other differential diagnoses, such as ventricular tachycardia with a captured sinus beat.  We welcome discussion of this interesting strip. 

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Comments

Dave Richley's picture

This is quite a trivial point, but I think that the ‘different’ QRS is a ventricular premature, or more likely, fusion beat. It could be, as Dawn says, an example of intermittent aberrant conduction, but this usually happens for a reason, eg a change in atrial rate. The QRS following the different one appears very slightly delayed, consistent with retrograde concealed conduction of a ventricular impulse into the AV node. The reason the different QRS is not abnormally broad is probably because it is actually a fusion beat. This is a bit conjectural, though, because it’s probably not possible to be sure of the origin of one beat in a single-lead rhythm strip. The important thing here is to recognise that the rhythm, as Dawn points out, is atrial flutter.

Dave R

ekgpress@mac.com's picture
 
As per Dawn — this interesting rhythm strip provides an excellent example for discussion with your group. The monitoring lead is unfortunately not labeled — but we might presume it was taken from a lead II. The rhythm is a regular SVT (SupraVentricular Tachycardia) at ~150/minute without normal sinus P wave activity. As per Dawn — We can march out 2 atrial deflections for each QRS — which given the rate of ~ 150/minute, virtually secures the diagnosis of AFlutter.
 
  • For those interested — I walk through a similar case in detail in Part 3 of my ECG Video Series on the Basics of Cardiac Arrhythmias — CLICK HERE to go directly to 1:20 where the case begins (and continues for the next 11 minutes).
As to the different-looking beat toward the end — my bet is not on aberrant conduction — but rather that this is a PVC, perhaps with fusion. Since we only have a single monitoring lead — we have no idea if this different beat really is “narrow” — or whether it might be wide with part of its QRS occurring on the baseline OR due to fusion with the supraventricular large R wave complex. The fact that this beat occurs early supports my suspicion that it is a PVC. There is just no reason for aberrant conduction at this point in this AFlutter rhythm strip (not to mention that this beat manifests a QS and not the rS that would be expected with LAHB aberration). And statistically, when you have an early beat that looks dramatically different — the odds strongly favor ventricular ectopy.
 
  • All that said — the primary problem here is AFlutter with fast ventricular response — and any abnormal beats will probably “go away” once the primary rhythm disturbance is controlled.

Ken Grauer, MD  www.kg-ekgpress.com   [email protected] 

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