So here’s the case: You’ve just run an 12-lead on a patient experiencing chest pain and recognized ST-depression in leads V2-V4. Being some manner of an astute provider, your next move is to set up posterior electrodes for leads V7-V9 to confirm the hidden STEMI. You’re about to press the print button, but suddenly your monitor dies. How can you confirm that this patient is experiencing an isolated posterior STEMI and would benefit from immediate PCI as opposed to medical management?
Hopefully you surmised from that title that I think you should look at V6. And not just look at it; really scrutinize it.
It’s a simple enough idea, but I don’t see it get a lot of discussion. Aside from doing the flipped-and-backwards trick when looking at V2-V4, V6 is the closest thing we have to a true posterior lead on the standard 12-lead. It makes sense that if you’re placing V6 correctly, it should be awfully close to where V7 would end up. It’s also uniquely positioned halfway between V2-V4 and V8-V9, the leads that exhibit the greatest magnitude of ST-depression and ST-elevation respectively during an isolated posterior STEMI.
Because of these two attributes, there’s actually two “V6 signs” that I’ve picked up on:
- The abnormal V6 sign – a result of changes in V7 affecting V6 next door
- The normal V6 sign – a result of the ST-deviations in V2-V4 and V8-V9 cancelling each-other out.
So let’s start with the less nuanced and controversial of the two.
The abnormal V6 sign
The “abnormal V6 sign” is any finding of ST-elevation, hyperacute T-waves, or loss of T-wave concavity in V6 when you suspect posterior wall MI because the ECG exhibits ST-depression in the right-precordial leads.
The 12-lead above is a subtle example. Yes, there are changes in the inferior leads as well, but let’s ignore those for now and zoom in on V6…
There is a very small amount of abnormal ST-elevation (0.5mm 60ms after the J-point). There is also worrying straightening of the upslope of the T-wave, where it has started to lose its upward concavity and “smile.” I actually find it easier to appreciate these changes zoomed-out and looking at the full 12-lead.
It’s tempting to dismiss these minor abnormalities, but let’s see what V7-V9 would show…
Here’s a similar tracing from the posterior MI section of an EMJ review article looking at the ECG in myocardial infarction:
More tracings? I’m always glad to oblige…
Here’s a tracing from my last post that partially inspired this one…
Here’s the tracing that first piqued my interest in V6. In this case the lead labelled V6 was actually located at V7 because of the presence of a defibrillator pad, but that slight position change resulting in drastic ST-elevation really got me thinking about how close V6 is to the posterior leads.
Here’s one with clear inferior STEMI. There is ST-depression from V1-V4, but elevation in V6 confirms this is secondary to posterior STEMI and not the common misdiagnosis of “anterior ischemia.”
Another clear inferior STEMI, but V6 clinches posterior extension…
An extremely subtle infero-posterior STEMI, but V6 is definitely abnormal in the presence of ST-depression from V1-V6.
Are you noticing a pattern yet?
As evidenced in the last tracing, there’s a very fine line between normal and abnormal when you’re looking at V6 during a posterior wall myocardial infarction. In fact, in part II of this discussion I’m going to look much more into the idea of a normal V6 being a significant finding when you suspect posterior STEMI, so look forward to that post soon.
With all the pretty pictures out of the way, let’s get something on the table. This trick isn’t really going to save lives or expose some previously unrecognized secret of electrocardiography, but let me know if it does. It’s just a shortcut I use on suspicious tracings when I don’t have the posterior leads. It’s rather unlikely that your ECG machine is going to kick the bucket on you between strips, but I’ve seen enough tracings where posterior leads were not run for some reason that I end up using it quite a bit.
I could honestly live without the V6 sign by just relying on the more concrete signs of posterior MI discussed elsewhere, especially at Dr. Smith’s ECG Blog and Life in the Fast Lane. Sometimes, however, we all just need a little extra convincing, and that’s where this comes into play. In fact, I could probably just as well call it the “lead III, aVL, or V6 sign” because those other two leads often show similar subtle changes, but in my experience V6 is slightly more useful during truly “isolated” posterior MI, so I’m going with that. Here’s a great “aVL sign” case posted last week by Dr. Brooks Walsh of Mill Hill Ave Command at EMS12Lead.com that proves V6 isn’t the only lead you should be looking at.
Lest I be accused of carelessly putting out information without context, let’s discuss some more of the shortcomings of the V6 sign:
- I just made this up based on the case series that is my experience and study. It has not been previously studied or validated as far as I’m aware. If someone wants to study this (or especially my next topic of the “normal V6 sign,” please contact me.
- It’s just a piece of the puzzle. You need to use this in combination with other ECG findings to make any diagnoses or decisions.
- It’s not even a unique sign, but just a common result of the other findings you see with a posterior wall MI. I’m not being overly creative here.
- As I’ll discuss in my next post, perhaps you should actually expect V6 to be NORMAL during a posterior MI, but this is for those cases when you get lucky.
- ST-elevation in the posterior leads is often focused towards V8 and V9, so it may not always extend out to V7 and V6. This is not even close to being a substitute for running posterior leads.
I’ve already gone on for way too long at this point. Make sure you check out Part II in a couple of days (or tomorrow or whenever I get around to it) for some more tracings and hopefully less reading! And don’t forget to let me know what you think in the comments!