Written by Pendell Meyers
A middle aged woman presented with chest pain and dyspnea. Her exam and vitals were within normal limits.
Here is her triage ECG:
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| What do you think? |
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| As marked, leads V1-V3 have been replaced by leads V7-V9. All other leads are standard. |
Comment by Smith: Never replace leads V1-V3 for posterior leads. Always replace V4-V6. Why? You want to be certain that the finding in V1-V3 are still present at the time you are recording V7-V8. Coronary thrombus is dynamic, propagating and lysing. Sometimes by the time the posterior leads are recorded, the ST depression in V1-V4 is gone and the absence of STE in V7-V9 is because the ischemia is no longer there!
Case continued
The posterior leads (in this case, in place of V1-V3) indeed show a very tiny amount of STE. But in my experience, "normal" providers" (not the ones who obsess over squiggly lines and read this blog avidly) look at this and simply report that there is no STE at all in leads V7-9. I have never met a cardiologist at my hospital who would agree/admit that there is in fact STE in those leads. It doesn't matter whether I zoom in to leads V7-9 and blow them up in an email later, nothing changes.
In my experience, this is the usual result of the posterior leads: yes, there is often STE in the posterior leads during posterior OMI. But it is almost always less STE by voltage, and less noticeable for novices, than the anterior STD maximal in V1-V4 on the normal 12 lead. The result for those who don't understand this: they feel that the posterior ECG dissuades them from posterior OMI, or that it looks "improved" from before, thus the patient is responding to medical therapy and does not represent "true persistent STEMI."
Both clinicians were skeptical about the ECGs. But, appropriately, they were both concerned about the patient with clear, ongoing ACS and "dynamic" ECG findings. The first troponin was "positive" (I was unable to get the result). So she was taken for cath fairly quickly.
They found a total LCX occlusion (I do not have exact location or TIMI flow details, but they state it was "totally occluded" which by definition should mead TIMI 0). A stent was placed.
Unfortunately I do not have details of the troponins or echo from this case.
The patient did well and was later discharged.
Learning Points:
This patient does not meet STEMI criteria but clearly benefits from emergent reperfusion.
I find this case to be a typical example of the role of posterior leads in the setting of a fairly subtle posterior OMI. This case is one of the many which have formed my opinion on posterior leads:
- Experts usually don't need them, since they can easily see posterior OMI by STD maximal in V1-V4. They are a waste of time for the clear posterior OMI cases. Their use in unnecessary scenarios perpetuates the idea that they have an important role, preventing the learning of STDmaxV1-4.
- Novices are sometimes falsely reassured by them, usually due to very low voltage of the posterior leads.
- Posterior leads are very rarely marked and saved appropriately in the EMR, making us completely unable to study them retrospectively in our posterior OMI study.
Although I do believe that posterior leads sometimes have an important role when being used by experienced electrocardiographers, I believe that providers should focus on STD maximal in V1-V4 as the most important indicator of posterior OMI.
If you record posterior leads, replace V4-V6, not V1-V3!
Same disclaimer as always about "posterior" vs. "lateral" walls, etc.; you all know where I'm talking about.
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