How interesting that this should come up...it is actually the title of my lecture at EM Today 2014!
"It can't be VT with that axis!
...and other deadly ECG myths."
(
I have a blog post which may be helpful as well)
I was reviewing axis deviation today and wondered why Vtach is commonly ruled out if axis isn't extreme right. I would think that this would have to depend on where the focus is originating and the direction it depolarizes. Does vtach always depolarize towards the SA node or right side of the heart? If the focus depolarizes toward the left ventricle wouldn't lead 1 be mostly positive? What's your thoughts?
If you think about it, the axis could go in any direction really: even a normal axis. Nobody should rule out VT because the axis isn't ERAD. That would actually be a really, really, really bad choice for a "rule out."
ERAD is not even close to the most common axis for VT. Left axis deviation is the most common (~70% of all VT).
If you use ERAD alone you'll account for only
~20% of VT! That is, it is poorly sensitive for VT. Talk about a miserable choice in axis.
That being said, ERAD is very
specific for VT. If you've got a wide, fast arrhythmia with ERAD you're probably looking at VT. Very probably.
Check out this slide from my presentation:
Consider you had VT arising from Location #1. Notice how it would travel with a nearly normal axis! Look at Location #2, notice how it too would travel in a nearly normal axis!
These are your outflow tract VT's, both of which feature inferior axes, as they travel from the Base towards the Apex.
VT's traveling from the Apex towards the Base have ERAD. But like we said early, that's only about 20% of all VT.
You are correct. It's an okay rule-in but a bad rule-out.
@Christopher is a big fan of this topic...
You forgot to say my name 3 times...
Thoughts on ERAD, positive aVR, and reverse R wave progression?
Yes, Yes, and Yes. All are suggestive of VT.
