Sunday, September 6, 2015

A large R-wave in lead V1. And why is the PR interval not short?

This 20-something male presented with alcohol withdrawal, alcoholic hepatitis, and alcoholic steatosis.  There was no chest pain or syncope, but an ECG was recorded as part of his workup.
What is it?

I received this message about it:


I was just looking back at this patient and noticed that he was diagnosed with WPW based on his ED EKG, and I certainly did not pick up on it. I was thinking it looked like an incomplete right bundle pattern.  I'm curious about the EKG - the admitting IM resident notes "wide QRS and delta wave with short PR" but his PR is 152 and 145 on both EKGs. Looking at it, I see the delta wave, but thought a short PR was a requirement for WPW diagnosis. Any thoughts on how I can spot this next time? Any other thoughts on his somewhat odd-looking EKG?

Dr. _______

My answer:

Dear _____

I saw this ECG and knew instantly it was WPW.  I actually put the formal interpretation into the system.  

How did I know?  By pattern recognition.

How can I make the diagnosis if I don't recognize the pattern?

There are only a few causes of large R-wave in V1:

1. Right Ventricular Hypertrophy (RVH) [on first glance, that could be etiology here, since there is also a deep S-wave in lead I (a requirement -- right axis deviation)].
2. WPW
3. Posterior MI (at first glance, this could be posterolateral MI: there is STE in aVL and ST depression in V1-V4).
4. Lead placement
5. RBBB (this requires an rSR' in lead V1, and deep S-wave in V6, which are not present here). By the way "incomplete" RBBB just means RBBB with a QRS duration less than 120 ms.  The QRS here was 166 ms.  So if it were RBBB, it would be complete.
6. Septal hypertrophy (HOCM).  That should have a narrow R-wave in V1, not wide

The R-wave is far too wide to be just RVH or posterior MI or Septal hypertrophy, so it can't be these things.

That leaves WPW.  And there is definitely a delta wave.

Not all WPW has a short PR interval!  Sometimes the accessory pathway is far from the sinus node and it takes a long time for the signal to reach it.  If this is combined with delayed AV conduction, you will see a normal PR interval and a delta wave.  You can see here that if there were no delta wave, there would be a prolonged PR interval.

Preexcitation and delta waves may not be apparent in sinus rhythm in patients with WPW who have a left-lateral bypass tract.   In this setting, the time for the atrial impulse to reach the atrial insertion of the accessory pathway is longer than the time to reach, and transmit through, the AV node.  This patient does in fact have a left lateral bypass tract and that is why it has right axis deviation and some of the characteristics of RBBB, with the majority of forces going from left to right, causing large R-wave in V1.

If there were a normal conduction through the AV node (here it is slowed - 1st degree AV block), then the impulse would have gotten through the AV node before pre-excitation and there would be no delta wave.   Some call this "concealed conduction," because on the baseline ECG you cannot see a delta wave, yet the patient can have WPW related tachycardias.

You can read more about concealed conduction here.

Here AV nodal conduction delay revealed the delta wave

So WPW just shortens whatever PR interval would have been present without the WPW and the degree to which is shortens it is dependent on time of conduction from sinus node to bypass tract.

Good question!



  1. It could be an 'old' Mahaim-ECG ?


    1. Yes, Mahaim fibers, or fasciculo-ventricular fibers, can cause delta waves, though they usually do not. But they should not have this pattern of activation from the far left lateral wall.


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