This article is the fourth in our latest series, The 12 Leads of Christmas, where each day we examine a new finding particular to an individual electrocardiographic lead.
Today’sÂ review is going to be light on textÂ (but heavy on EKG’s) to make time for Wednesday’s big post on aVR. It also helps that a lot of the principles that we discussed in yesterday’s post on lead III apply here as well. In summary: aVL is great for identifying STEMI’s too!
In addition to lead III and V3, aVL is the third lead I usually choose to continuously monitor for patients who present with signs and symptoms concerning for ACS but no diagnostic changes on their initial 12-lead.
The main reason I like aVL for this purpose is that it is the lead most reciprocal to lead III. As we just discussed, III is the lead that best shows ST-elevation or T-wave changes during most inferior STEMI’s, so being able to observe reciprocal ST/T-changes in aVL can help seal the diagnosis. Since inferior STEMI’s are much more common than isolated lateral STEMI’s, I use aVL to observe reciprocal changes a lot more often than I use it to directly spot ST-elevation.
In another reference back to yesterday’s post, recall that the “injury vector” during inferior STEMI usually points in the 110â€“120 degree range in the frontal place. Rearranged in our 360 Degree Heart format, the above tracing looks like this:
The “injury vector” in inferior STEMI tends to point almost directly at lead III. While that means that lead III will show the most ST-elevation, it also means that (-)III shows the most reciprocal ST-depression. We don’t monitor lead (-)III because the standard lead III already shows us all the information that would convey, but we do use the lead immediately adjacent to it: aVL. That is why aVL is so good at showing reciprocal changes during inferior STEMI.
Even better, sometimes it’s actually easier to spot these reciprocal changes in aVL than it is to see the direct signs of injury in lead III. The cases below are roughly arranged from easiest to most difficult. As they become more subtle, the role of aVL as an aide to confirm the diagnosis grows significantly.
…and now they get really subtle…
Even in the most subtle of the above inferior STEMI’s, there was always at least a tiny bit of ST-depression in aVL to help confirm the diagnosis.
What about using aVL to diagnose “high-lateral” STEMI? That turns out to be another case where III and aVL work together to seal a diagnosis that would be quite difficult to confirm otherwise.
“High-lateral” STEMI’s are typically quite subtle on the EKG, especially if there isn’t mid-precordial ST-depression from concomitant posterior MI. The only signs you will usually have to go on are subtle ST-elevation and straightening of the initial portion of the T-wave in aVL with minor ST-depression in lead III. Using only one lead you wouldn’t be able to make the diagnosis, but with III and aVL in conjunction the diagnosis becomes much more clear.
I hope youâ€™re enjoying our 12 Leads of Christmas series. You can check out the rest of the posts below (updated as new posts come out):
12 Leads of Christmas: Lead I
12 Leads of Christmas: Lead II
12 Leads of Christmas: Lead III
12 Leads of Christmas: aVR
12 Leads of Christmas: aVF
12 Leads of Christmas: V1
12 Leads of Christmas: V2
12 Leads of Christmas: V3
12 Leads of Christmas: V4
12 Leads of Christmas: V5
12 Leads of Christmas: V6