WHAT & WHY
What are STEMI equivalents? Why do I need to know them? Great questions! In order to answer these questions we first need to talk about how much the STEMI criteria sucks! Okay, maybe that was a little harsh, the STEMI criteria is something we all must know and utilize. But lets just say there are some new kids on the block.... who are not so new....they just don't get enough attention.
CURRENT STEMI CRITERIA
Current STEMI criteria is met when we have two contiguous leads with ST segment elevation per the figure from Dr. Smith ECG Blog. According to Smith's OMI manifesto, STEMI criteria misses routinely 25-30% of acute myocardial infarctions. OMI stands for occlusive myocardial infarction and this manifesto discusses how our current guidelines for management of acute myocardial infarction is wrong. Currently patients who are identified as having an MI are placed into one of two groups STEMI or NSTEMI. Patients who meet STEMI criteria go to the cath lab immediately for percutaneous coronary intervention (PCI), which results in the best possible outcome for the patient. The NSTEMI patients are the ones who wait hours to days to go to the cath lab. Because of this delay, the "NSTEMI" patients who ARE having an acute MI have poor outcomes in regards to: cardiac tissue death, ejection fraction, and risk of heart failure. This is why the OMI manifesto recommends shifting to OMI vs NOMI instead of STEMI vs NSTEMI.
EVIDENCE
Smith et al (2001) looked at patients who went to cath lab (based on clinical presentation and positive CK-MB); 418 of the 1,788 patients who underwent coronary angiography were found to have an acute coronary occlusion with 29% of them being STEMI negative. Wang et al (2009) looked at 1,957 NSTEMI patients and found 27% (528) to have an acute coronary occlusion. These studies are just two examples of how STEMI criteria routinely misses 25-30% of acute MIs. So how can we identify these patients that STEMI criteria misses? This is where STEMI Equivalents, cardiac biomarkers (including troponin), and ultrasound play an important role.
WHY STEMI EQUIVALENTS
Similar to STEMI criteria, STEMI equivalents are found by looking at a 12 lead EKG for specific indicators. But, where STEMI criteria lacks, STEMI equivalents shine.
STEMI equivalents have been identified and researched for years now with some impressive sensitivity (accuracy with identifying an MI) and specificity (accuracy with identifying no MI).
Applying these equivalents in practice will help us catch the 25-30% of people having an acute MI that the STEMI criteria misses.With practice we can accomplish this; it will take time and patience as we train our eye to recognize these patterns.
A study was conducted where two practitioners, trained in identifying STEMI equivalents, were shown 808 EKGs and asked if the patient was having an acute MI. They compared the sensitivity, specificity, and accuracy of these two providers to the STEMI criteria. The results: "Sensitivity, specificity, and accuracy of STEMI criteria vs Interpreter 1 using OMI ECG findings among 808 patients were 41% vs 86%, 94% vs 91%, and 77% vs 89%, and for Interpreter 2 among 250 patients were 36% vs 80%, 91% vs 92%, and 76% vs 89%. STEMI(-) OMI patients had similar infarct size and mortality as STEMI(+) OMI patients, but greater delays to angiography (Meyers et al., 2021)."
That, my friends, is impressive.
SENSITIVITY VS SPECIFICITY
Recall these two from stats class? Yeah, me neither. Here's the DL:
You have 100 pts. 10 are having an MI. You want a test that can definitively tell you which are having an MI and which are not with no overlap = high sensitivity and high specificity.
A test with HIGH SENSITIVITY will accurately identify our 10 MI pts.
A test with HIGH SPECIFICITY will accurately identify our 90 non-MI pts.
A HIGH SENSITIVITY and LOW SPECIFICITY test would accurately identify the 10 MIs but would inaccurately identify our non-MIs as having an MI. Ex: a test with results "100/100 pts are having an MI."
Conversely, a LOW SENSITIVITY and HIGH SPECIFICITY test would inaccurately identify our MI patients while accurately identify our non-MI pts. Ex: results showing "0/100 pts are having an MI."
STEMI EQUIVALENTS
Alright Let's dive in! Here is a great acronym to help us remember the most common ones (created by Jared Patterson):
Picture credit: Jared Patterson, FOAMfrat Blog
As mentioned in one of our previous blogs, the American College of Cardiology (ACC) released an update in 2021 suggesting that the following STEMI equivalents be treated as a STEMI (send em' to the cath lab):
- Hyperacute T Wave
- De Winters T Wave
- Smith's Modified Sgarbossa Criteria
- Isolated Posterior MI
In addition to the above equivalents we will discuss three more:
- Wellen's Syndrome
- South African Flag Sign
- Aslanger's Pattern
Hyperacute T Wave
Criteria: Unfortunately there is no defined criteria for this one. However, the T wave has a distinct appearance and is described as: symmetrical, broad (wide/fat), and/or tall. There is minimal to no ST segment elevation. Hyperacute T waves are tall when compared to their corresponding QRS complex. So if the QRS is short the T wave can still be considered tall even if it is only 3-4 mm in height. This pattern is seen early on in the setting of an MI and often progresses into a full blow STEMI OR if the patient's symptoms resolve has a Wellen's pattern (reperfusion pattern....we'll discuss this one later on).
Obtained from: Dr. Smith's ECG Blog: Subtle inferior Hyperacute T waves
This is a great example in lead III of a tall, fat T wave compared to the QRS complex. Some of these T waves can be even more impressive!
De Winter's T Wave
Criteria: Usually found in the precordial leads. In simple terms this is a hyperacute T wave with ST segment depression:
- Hyperacute (tall, fat, symmetric) T wave
- ST segment depression >= 1 mm, with a rapid take-off
- Reciprocal ST segment elevation in lead aVR
This pattern also occurs early on in the setting of an MI and can turn into a full blown STEMI or Wellen's pattern (reperfusion pattern).
Obtained from: Dr. Smith's ECG Blog: De winters pattern
Smith's Modified Sgarbossa Criteria
Criteria: This is used in the setting of a left bundle branch block (LBBB) or a paced ventricular rhythm to identify an acute MI. The STEMI criteria cannot be used in this setting because discordant ST segment elevation is normal for a LBBB and paced ventricular rhythms. Sgarbossa's cannot be applied to right bundle branch blocks (RBBB) as a RBBB does not normally have ST segment elevation. This criteria was developed by Dr. Stephen Smith:
- Criteria A: Any lead with concordant ST segment elevation >= 1 mm
- Criteria B: Any concordant ST segment depression >= 1 mm in leads V1, V2, or V3
- Criteria C: Any lead with excessively discordant ST segment elevation that is >= 25% the depth of the preceding S wave.
Image: ECGMedicalTraining.com
Image: ECGMedicalTraining.com Added info by: mylifeasaparamedicstudent.blogspot.com & paramedmovement.com
Obtained from: Dr. Smith's ECG Blog LBBB Scarbossa Positive
The above example i chose for a specific reason. When going thru these criteria be INTENTIONAL and look at every lead closely. Lead V4 meets the modified Sgarbossa criteria C, leads III and V5 are very close to meeting criteria as well. V5 shows concordance which is always abnormal in a LBBB. Lead III has a mildly elevated ST with an isoelectric QRS which is also abnormal. So we have two red flags (V5 and III) and one lead (V4) meeting criteria. Not good.
Isolated Posterior MI
Criteria: Most posterior MI will have some inferior and lateral signs of occlusion on the 12 lead EKG. Very rarely you will see an isolated posterior MI. Essentially what you will see is ST segment depression of at least 1 mm in leads V1-V4 with no reciprocal changes or ST elevation anywhere else on the 12 lead. Dr. Smith would argue that in the setting of a patient having chest pain or symptoms of acute coronary syndrome (ACS) that you do not need a posterior EKG to prove it is a posterior MI. "If you have ST segment depression of at least 1 mm that is MAXIMAL in leads V1-V4 it is a posterior MI until proven otherwise!" (Dr. Stephen Smith)
Obtained from: Dr. Smith's ECG Blog - Teaching Images
Now, most hospitals probably do not have interventional cardiologist that are on board with this yet so they may need a gentle reminder that the ACC now recommends treating this as a STEMI. Do it in a professional and polite way, even though you may be a little agitated with the discussion, or it will just fall on deaf ears. If you need further collateral to advocate for your posterior MI patient to go to cath, you can also do a posterior EKG (which may or may not show the elevation you're looking for but worth a shot).
Here is an example of an isolated Posterior MI:
Obtained from: Dr. Smith's ECG Blog Isolated Posterior MI
Wellen's Syndrome
Criteria: This syndrome is also referred to as a "reperfusion pattern." In order for Wellen's Syndrome to be present the patient must have 1) had a recent episode of ACS/chest pain and 2) Is now symptom free with no complaints of chest pain. Since this is a reperfusion pattern it makes sense that the patient now has no complaints as the occlusion has spontaneously opened and flow is restored in the coronary artery. It is a good reminder that even if the patient is now symptom free DO A 12 LEAD EKG! So what will we see on the EKG? Contrast to popular belief, this pattern can be present in any lead!
- Pattern A will present with ST segment elevation with a biphasic T wave
- Pattern B will present with a deeply inverted T wave.
Obtained from: Life in the fast lane: Wellen's Syndrome
If they reperfused why is it important to recognize? Due to the fact that they just had a acute coronary occlusion they are at high risk of a future reocclusion. I would describe this pattern as "the TIA of myocardial infarction." It is not a matter of IF but WHEN will they have an MI. Some progressive hospitals will take these patients to the cath lab, even without symptoms, to just go ahead and stent it now while the patient is stable.
Obtained from: Dr. Smith's ECG Blog - Wellen's Pattern B
South African Flag Sign
Criteria: Think of this one as the subtle high lateral equivalent. If we were to place the South African Flag over the 12 lead EKG, this pattern would make up part of the flag. The flag helps us to remember which leads are involved.
- Subtle ST segment elevation in leads: I, aVL, and V2
- Subtle ST segment depression in lead III
Obtained from: Dr. Smith's ECG Blog - South African Flag Sign
Aslanger's Pattern
Criteria: This is the newest mentioned STEMI equivalent. According to the clinicians who first described this pattern, it is suggestive of a inferior MI with possible right ventricular involvement (Aslanger et al., 2020).
- ST segment elevation in lead III (but not any other inferior lead)
- ST segment depression in any of leads V4-V6 (but not in V2) with an upright T wave
- ST segment elevation in lead V1 > ST segment elevation in lead V2
Obtained from: Dr. Smith's ECG Blog - Aslanger's Pattern
Lastly, I want to leave you with this chart showing the specificity and sensitivity for the various STEMI equivalents we discussed.
* Remember this is a reperfusion pattern and these patients WILL have an MI in the NEAR future. According to one study, 75% of patients that were treated medically (no PCI) reported back to the hospital with acute MI within a few weeks after first presenting with Wellen's Syndrome (De Zwaan et al., 1982).
* This equivalent can be present in several conditions including: post-cardiac arrest, LMCA occlusion, LAD occlusion, or severe triple vessel disease. According to one study, "The finding of lead aVR ST segment elevation greater than or equal to lead V1ST segment elevation distinguished the LMCA group from the LAD group, with 81% sensitivity, 80% specificity and 81% accuracy." (Yamaji et al., 2001)
* No data could be found in regards to specificity and sensitivity. This most likely is due to the fact that these two patterns are present early on in the setting of a MI; they progress into one of two patterns: Wellen's Syndrome OR STEMI. Which means they are very good indicators of an active MI.
I thoroughly enjoyed writing this blog and hope you found it helpful in understanding what STEMI equivalents are and why they are important to know. If you find any additional studies/research on specificity and sensitivity please send them our way and we'll update the chart!
Take care and be safe!
Tyler
References:
Aslanger, E., Yıldırımtürk, Ö., Şimşek, B., Sungur, A., Cabbar, A. T., Bozbeyoğlu, E., Karabay, C. Y., Smith, S. M., & Degertekin, M. (2020). A new electrocardiographic pattern indicating inferior myocardial infarction. Journal of Electrocardiology, 61, 41–46. https://doi.org/10.1016/j.jelectrocard.2020.04.008
Bischof, J., Worrall, C. I., Thompson, P. L., Martí, D., & Smith, S. M. (2016). ST depression in lead aVL differentiates inferior ST-elevation myocardial infarction from pericarditis. American Journal of Emergency Medicine, 34(2), 149–154. https://doi.org/10.1016/j.ajem.2015.09.035
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