STEMIs in Disguise

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The 2013 ACC/AHA STEMI guidelines outline, with specific age and gender-related cutoffs for ST segment elevation in certain leads. While these are clinically important, there are several STEMI equivalents or EKG patterns that do not meet these criteria but should point the practitioner to consult with an interventional cardiologist.  These STEMI equivalents are found in 10-25% of cases of coronary occlusion, making it imperative that emergency personnel be familiar with these patterns.  The equivalents included on the 2013 ACC/AHA guidelines include: 

For the purposes of this post, we will focus on LMCA Occlusion, Posterior MI, Wellens, and De Winters Waves. For additional reading, follow some of the links throughout the post and take at look a previous TamingtheSRU post done by Robert Whitford, MD

LMCA occlusion taken from Life in the Fast Lane. Note that ST elevation in aVR>V1, with widespread ST depression. https://litfl.com/lmca-occlusion-st-elevation-in-avr/

ST elevation in aVR with diffuse ST depression

What Could this Represent?

  • Left main coronary artery critical stenosis

    • A recent study investigating the incidence of this ST elevation with diffuse ST depression found that complete occlusion occurred in only 10% of patients (Harshas 2019). This makes sense given that complete occlusion would cause quick cardiogenic shock. Instead, main culprit behind the ECG findings was sub-occlusive disease (multivessel in this particular study) along with other medical causes (PE, sepsis, dissection).

  • Left proximal LAD disease

  • Triple vessel disease

  • Subendocardial ischemia (taken in setting of something like severe tachycardia or sepsis)

    • aVR is reflective of the basal septum. This means that aVR is either a reciprocal change to the global perfusion, or it represents direct ischemia to the basal septum

Patterns to Look For

ST elevation in aVR: the degree of elevation varies with amount of myocardium involved and is an independent predictor of mortality.

  • >0.5mM: 81% sensitivity and 80% specificity for determining LMCA occlusions (Yamaji, 2001).

  • >1.0 mM: may be more specific to LMCA. For a more detailed discussion, see this Rebel EM Post for some more in-depth discussion

  • aVR > V1: can differentiate an LMCA from an LAD lesion (Rostoff, 2005)

Diffuse ST depression

  • Typically see in the lateral and precordial leads

  • No consensus on exact degree of deviation or which leads ST depression needs to be present. One study found that the mean number of leads with ST depression to be about 7 (Harhash, 2019).

Proximal LAD occlusion from Life in the Fast Lane. Note that the elevation in aVR and V1 are of similar magnitude. https://litfl.com/lmca-occlusion-st-elevation-in-avr/

Is this really a STEMI equivalent?

Yes. While a cutoff of about 0.5mm is thought to be a bit nonspecific, there is a fair amount of data suggesting that aVR elevation, particularly as it gets bigger, has some predictive role in determining significant coronary disease. In fact, mortality is directly correlated with the degree of elevation.

  • ST Elevation in aVR tends to occur more often and greater magnitude in LMCA lesions than in LAD occlusions.

  • In anterior STEMI patients, an elevation of aVR had a 43% sensitivity and 95% specificity for proximal LAD occlusion

What Should the Management Be?

Emergent vs urgent PCI? Probably neither, because you may be looking at a CABG. aVR elevation with ST depression is still located on the STEMI equivalent guidelines and while these may not necessarily indicate a full blown occlusion, there’s probably a good chance of significant sub-occlusive disease being present. Complete occlusion versus stenosis is not well defined in many of studies about this EKG pattern. That being said, there is still a fairly strong body of evidence that suggests a high sensitivity for elevations in aVR for significant occlusion (defined as at least 75% occlusion in the left main and at least 90%in proximal , with some studies showing sensitivities as high as 80% and specificity as high as 98% (Kosuge, 2011). Most of these patients, whether LMCA or triple vessel disease, will require CABG, so consider discussing dual anti-platelet therapy with your interventionalist prior to administration.

De Winter T waves

This is from an anterior STEMI with classic de Winter T waves from Life in the Fast Lane https://litfl.com/de-winter-t-wave-ecg-library/

De Winter T waves are found in only about 2% of proximal LAD lesions  (Verouden, 2009). But when present, they have a PPV of 95.2-100% of signficant stenosis of LAD, 70% stenosis or greater (Morris, 2017).   Patient’s with these EKG findings typically present with substantial, acute chest pain and tend to be younger with a history of dyslipidemia (Verouden, 2009)

Patterns to Look For

  • Upsloping T waves in precordial leads, V1-V6 (1-3mm)

    • Static, whereas Hyperacute T waves evolve → get serial EKG’s 

  • ST depression at the J point, >1mm

  • Mild ST elevation in aVR (0.5-1mm)

    • ST elevation in aVL sometimes also seen 

  • The most prominent ST depression and highest T waves noted in V3

Management - PCI within 2 hours of presentation 

Wellens Syndrome

Here is an example of Wellens with Type A waves from LIFTL (https://litfl.com/wellens-syndrome-ecg-library/)

These EKG changes typically represent critical LAD stenosis (either plaque or spasm). Patients may present with chronic chest pain or history of recent chest pain that is usually typical, anginal pain. Notably, the classic T wave patterns are seen only during chest pain-free episodes, not during active chest pain. Troponin levels are usually either normal or minimally elevated (only 12% reported to have abnormal troponin vales in 1 study) 

What Patterns to Look For?

T wave morphology, typically in precordial leads, particularly V2 and V3 

  • Type A: initial positive deflection (~25%) 

  • Type B: deep, symmetric T wave inversions

  • Note: Type A can evolve into Type B if stenosis persists 

Type A: biphasic with initial positive deflection https://litfl.com/wellens-syndrome-ecg-library/

Type B: negative inverted T waves, symmetric https://litfl.com/wellens-syndrome-ecg-library/

Wellens Mimics

There are both cardiac and non-cardiac causes of T wave inversions.  PE is one of the most common ECG patterns that can look like anterior ischemia.  Also found a variety of case studies outlining cases of “pseudo-Wellens” related to toxicologic sources including marijuana, PCP, or cocaine use. There are also cases of intermittent LBBB and acute cholecystitis being associated with a pseudo-Wellens phenomenon.  Takotsubo cardiomyopathy is another Wellens mimic thought to be related to myocardial edema (Miner, 2019).  LVH and HTN are also noted to be causes of pseudo-Wellens, so just be aware and take into account the likelihood that the patient is presenting with ACS. 

Wellens in the setting of LBBB? It is possible for the Wellens morphology to be seen in the setting of LBBB. A published case report from 2017 (Meyers, 2017) describes the presentation of a 65 yo male with PMH of SCC of head and neck, with 1 hour history of chest pain and dyspnea.  The initial EKG, done while the patient was having active chest pain demonstrated a LBBB that did not meet Sgarbossa criteria. On a repeat EKG done after chest pain resolved, the Wellens morphology of the t-waves are clearly visible.

Management Considerations

PCI definitive, but this is pre-infarct state rather than a complete occlusion.  You would likely either see pseudonormalization or progressive to ST elevation if the vessel completely occludes as discussed in pseudonormalization section.  

Why is urgent PCI important? 

  •  75% found to go on to have anterior wall STEMI per original study from 1982, at a mean of 8.5 days from admission (de Zwaan, 1982) 

  •  In a follow up study, found that all patients with Wellens T wave morphology had at least 50% occlusion of the LAD (de Zwaan, 1989)

Do not stress test these patients for theoretic risk of inciting AMI (although this risk is based primarily on case studies)

Posterior STEMI

This typically represents a left circumflex or RCA occlusion. It is often seen in the setting of inferior STEMI (15-20%) and isolated posterior STEMI is less likely (~8% of infarcts)

What Patterns to Look For

  • ST depression in V1-V3 (at least 1mm)

  • Tall broad R waves 

  • Upright T waves 

  • Dominant R/S ratio >1 in V2 (think of this as the Q wave equivalent, so can be absent in early infarctions)

  • Note: The inferior and lateral with posterior extension (seen in the first 2 EKGs in the slideshow below) are more worrisome given the larger infarct area. Duration of the STD in the right precordial leads is also suggestive of worse outcome 

Management - Immediate reperfusion 

Posterior EKG Lead Placement - Courtesy https://litfl.com/posterior-myocardial-infarction-ecg-library/

Can perform a posterior EKG (replace leads V4-V6 with V7-V9) to differentiate true posterior involvement from reciprocal changes related to inferior STEMI. Leads should show a typical STEMI pattern (with V9 having the best PPV)

Look for ST morphology 

  • Tends to be more horizontal, although noted that it can be both upsloping and downsloping 

  • Note that STE in posterior leads does not have to be as elevated as typical STEMI criteria, given distance between chest wall and posterior leads 

T wave morphology - More likely to be upright, but can be inverted in very early infarcts 

(EM Resident, 2019) https://www.emra.org/emresident/article/stemi-equivalents/

T wave inversions in aVL

These can represent mid-segment LAD lesions but can also be seen in LVH or LBBB

  • High specificity for isolated T waves (86.9%, although this was small number and in a Japanese single center, retrospective study) but very low sensitivity (Nakanishi, 2016).  

  • Other studies showed a sensitivity of 76.7% in isolated T wave inversions in aVL, specificity of 71.4%.  Again, single center with low numbers (Hassen, 2014).  

  • Note: specificity of T wave inversions in aVL were increased when included with other T wave changes, specifically in lead I 

RV infarction

Along with posterior MI, you may want to look at RV infarction when you see an inferior MI.  Right ventricular infarctions are noted to occur with as many as 40% of inferior AMI.   They typically do not occur in isolation, due to improved collateral blood supply of the right ventricle and overall smaller mass of this chamber.  The importance of recognizing this pathology is that it is a preload dependent state, meaning that these patients are prone to becoming hypotensive.  Initial management of this state revolves around avoiding nitrates, and giving fluids should they become hypotensive.

What Patterns to Look For? 

Schematic of right-sided EKG from LIFTL https://litfl.com/right-ventricular-infarction-ecg-library/

You will typically see ST elevation in the right facing leads, namely V1 and III.  You may also consider obtaining a right-sided EKG.  V4R is thought to be the most sensitive lead for showing a right ventricular infarct, with high sensitivity (88%), specificity (78%).  The following EKG findings are listed below, as well as how to perform a right-sided EKG: 

  • ST elevation in V1 with ST depression in V2 

  • ST elevation in III>II 

  • ST elevation in V4R  

Right-sided conduction blocks including RBBB and complete conduction blocks are also associated with RV infarction.  In a review article from NEJM, found that these high grade conduction blocks can occur upwards of 48% of RV infarctions.  One additional factor to note is the transient nature of this ST elevation, with many resolving 10 hours prior to presentation.

Example EKGs

Inferior STEMI with right-sided leads, showing RV infarction (LIFTL). Note the inferior STEMI, particularly the ST elevation in III>II along with the diagnostic ST elevation in V4R.

Below is a slightly trickier one from Dr.Stephen Smith’s ECG blog

http://hqmeded-ecg.blogspot.com/2018/07/is-there-right-ventricular-mi-in.html

Any RV MI? While ST elevation in V1 can cue you into considering a right ventricular MI, keep in mind that this can have low sensitivity, and you may want to go ahead and get a right sided EKG if you see evidence of an inferior MI.

Here’s the right-sided leads for the above patient, clearly showing ST elevation in V4R

http://hqmeded-ecg.blogspot.com/2018/07/is-there-right-ventricular-mi-in.html

References 

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Written by Laura Frankenfeld, MD PGY-1 University of Cincinnati Department of Emergency Medicine

Peer Review and Editing by Jeffery Hill, MD MEd