STEMI Equivalents:
While ST-segment elevation has become the accepted clinical identifier of complete occlusive myocardial infarction; it is not the only ECG change that can represent a true MI. Paramedics are trained to recognize STEMI first, because this allows for the majority of community myocardial infarctions to be identified and treated appropriately in a cath lab. However, simply targeting the presentation that occurs “most often” is not in line with best practices in medicine, and does not serve the best interests of our patients. For this reason, we also learn to look for STEMI equivalents. That is, morphological ECG changes that, while they do not demonstrate ST-elevation, do represent occlusive MI. We cannot necessarily use these equivalents to bypass a closer hospital and go to a cath lab based only on our own interpretation however. We do need to contact the cardiologist and advocate for our patients in these cases. It is for the purpose of being a successful patient advocate, that we must become familiar enough with STEMI equivalents to accurately convey our concerns to the on-call cardiologist.
So what are we looking for?
There are several equivalents that we need to look for in the setting of suspected cardiac ischemia. I have already talked about Scarbossa criteria in the setting of LBBB, so I won’t cover that again here. We want to look for the following:
Posterior MI
Wellens’ Syndrome
De Winter’s T-Waves
Posterior MI:
A posterior MI affects the rear wall of the left ventricle. Because our ECG leads provide anterior, lateral, and inferior views of the heart, we will not be able to see ST-Elevation directly on a typical 12-lead. We do, however, get a “mirror image” of sorts, that gives a major red flag. The anterior and septal leads, V1-3 show us the electrical activity through the front of the heart muscle. In an anterioseptal STEMI we get elevation in these leads. Well, in a posterior MI, we can still see changes in these leads in the OPPOSITE direction. Instead of ST-Elevation we get significant ST-segment DEPRESSION. If you were to flip the 12-lead upside down, it will look exactly like an anterioseptal STEMI. We can then confirm this by moving leads V5 and V6 to the patient’s back in a modified 15 lead ECG. Doing this will show elevation in V8(V5) and V9(V6). This is a STEMI equivalent.
Wellens’ Syndrome:
Wellen’s syndrome usually is noted in patients who are not actively having chest pain, but do have a history of angina or other cardiac pathology. There are two variants. Type A Wellens’ presents with a biphasic T-wave that has a squared off upslope followed by a deep negative deflection. These changes are noted in the precordial leads V1-3. Type B Wellens’ presents in the same leads with deep inverted T-waves (Think hyperkalemic “Circus tents”, but upside down). This is an MI, make no mistake.
De Winter’s T-Waves:
This is a very interesting finding that is actually fairly unique. Seen in leads V1-3, it presents with J-Point depression, followed by tall peaked T-waves. There isn’t much else that will present this way, and it’s hard to miss.
There may be other equivalents that arise over time, as cardiology, and indeed all medicine, changes daily. Knowing these 3 morphologies could very well be the difference between life and death for some patients.
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