Thanks to those who commented for some very insightful comments!
Let's revisit one of the pre-conversion 12 Leads:
We can see an irregularly irregular WCT rhythm (note the conversion to narrow complex A-Fib at the end of the lead II rhythm strip). Our list of differentials should include:
- A-Fib with RVR and aberrant conduction
- A-Fib with WPW
- Slightly irregular VT
As it turns out, this patient was diagnosed with new onset A-Fib with WPW. Apparently, at least one other member of the family had it as well. However, i do not think this case was at all obvious. While the pre-conversion ECGs had an "appearance" of A-Fib with WPW, it was not as irregular and "bizarre" as we have typically seen. I think leads V2 and V3 showed morphologies that appeared most familiar to us when it comes to A-Fib/WPW:
If we determine that A-Fib is present (irregularly irregular rhythm), we must try to determine if it is A-Fib with aberrant conduction vs. WPW. How can we tell? If it is aberrant conduction, we would expect to see the same morphology of the QRS complex, and a ventricular rate that is not unreasonably fast. If we see changing QRS morphologies, and the shortest R-R intervals that are 250 ms or less, WPW is suspected. In this case, the rhythm appeared to be irregularly irregular, but not grossly, as in other cases. Also, the morphologies were not as bizarre as we have seen in past cases. The rate was very fast in spots, however, which supported an accessory pathway.
What was also quite confounding, however, was the post-conversion ECG, which as many of you correctly pointed out, did not show any obvious signs of WPW. On the flip side, there was the predominant R wave in V1, and the Q waves in leads III (most notable) and aVF, possibly showing a "pseudoinfarct" pattern:
This was a complex case. One of the great things about web 2.0 is the ability to "peer source." I forwarded this case to a few electrophysiologists who were kind enough to offer their insights on this case:
Dr. John M, of the Dr. John M blog, left some awesome comments in the comments section of this case. I strongly urge you to read his comments. To briefly summarize, he believes the rhythm is "AF with intermittent conduction over an infero-post accessory pathway." As to why there is no obvious pre-excitation present on the post conversion ECG, he says the pathway is "left sided and away from the septum; in other words, it is geographically distant from the AV node. Second, this patient has a really good AV node- as evidenced by a short PR interval despite an onslaught of AV nodal blocking drugs." He also adds, "it's not uncommon for accessory pathways to conduct intermittently when injured or aged, or suppressed with meds." This summary does not do justice to his comments. Make sure you read them in the comments section!
Dr. Wes, of the Dr. Wes blog, had this to say: "Sure looks like pre-excited AF (pre-conversion), and normal (no pre-excitation) post-conversion. Could he still have an accessory pathway? Of Course. If the accessory pathway is lateral enough, he may not reach the AP antegrade from the sinus node before the ventricle is activated via the AV node. Hence, no pre-excitation is seen." He adds that anything that would delay conduction in the AV node may reveal the pre-excitation.
Mark P, author of the Electrophysiology Fellow blog, offered this: "The WCT is very suggestive of a pre-excited AF, probably a left posterior AP. True, there is no obvious delta on the resting ECG, but there is a slurred Q wave in III and aVF (negative delta), and the dominant R wave in V1. So, putting it all together, a resting ECG suggesting a left post/lat AP and a tachycardia ECG (notice how the Q in III and aVF is exaggerated in this ECG- a negative delta) also suggests AF with a left post/lat."
So, we seem to have a consensus among the electrophysiologists, and i appreciate their contributions to this case greatly!
A few take home points:
- Social media and the ability to "peer source" is awesome.
- Seeking "expert opinions" leads to great knowledge and learning.
- There is much more to WPW on the ECG than what is "classically" taught.
- These cases are complex and can be missed in the ED.
- Learn as much as you can about these conditions–you just might save a life.
Hope you enjoyed this case! Comments and feedback are always appreciated.