As ED doctors, we’re often handed EKGs every few minutes. Our minds initially will always go to ST elevations and possible myocardial infarctions. With this in mind however, what are the other, lesser seen variants that are equally as dangerous and also warrant immediate catheterization?
Hyper-acute T waves
Before starting to discuss STEMI equivalents, let’s start with a STEMI. You’re working, and a staff member hands you this EKG:
This is what’s considered hyper acute T waves. Broader than the waves seen with an elevated potassium, this is considered the first EKG stage for myocardial infarction and is seen prior to ST elevations. Important note to keep in mind, the t waves will be large in comparison to the QRS and may not look enlarged initially. Clinical considerations should take place, however it’s always important to keep the early stages of MI in mind when dealing with chest pain.
Posterior MI
The first concept to master in a posterior MI is identification from normal EKG. As these are not the standard ST elevations, they may go unnoticed however with a high index of suspicion, often the first signs will be noted in V1-V3:
- ST depression
- Broad R waves (>30 ms)
- Upright T waves
- Dominant R wave in V2
From here, the next step is appropriate lead placement for verification. This can be remembered by V7/8/9 staying on the same plane as previous V6, with V8 placement to the tip of the scapula. All that’s needed to diagnose a STEMI in V7V8/V9 is 0.5 mm elevation. This picture from LITFL
Source: LITFL
*Posterior EKG caption on wordpress*
As noted prior, remember an elevation of 0.5 mm is all that’s needed to diagnose STEMI on a posterior EKG on V7/V8/V9
Left Main Coronary Artery (LMCA) occlusion
Cite rosh review
Occlusion proximal to LAD is defined as left main coronary artery occlusion. Seen from Rosh review, this is an occlusion as pictured above which unlike an LAD occlusion, will have elevation in AVR of 1 mm with noted ST depressions diffusely. This can also be seen in proximal LAD lesions, triple vessel disease and left main occlusion. As seen from this EKG provided by LITFL;
As can be seen in AVR this is not only seen in board examinations but can be the only sign of occlusion on EKG. Quick glance at AVR can not only catch a STEMI but localize it prior to catheterization.
DeWinters Occlusion
This is seen in patients with an acute proximal LAD occlusion and can often be seen prior to Wellen Syndrome (subacute; next section) and can be identified by:
- Symmetrical T waves
- J point depression at ST segment
- Mild elevation of AVR
Wellens Syndrome
A classic EM vignette that will present is a 50 year old male, presenting to ED with fleeting chest pain that subsides at/prior to arrival. Troponin is found to be mildly elevated or normal, and the patient is now asymptomatic. EKG is as follows:
Send them home, right? WRONG. Wellens syndrome is defined by two types of waves that indicate an impending lesion. Type A is described as a biphasic wave in V2/V3 while Type B is a deeply inverted T wave (also V2/V3). Prior to its discovery in 1982, patients with Wellens were found to fail medical management, and as a result these patients should be taken urgently to the catheterization lab.
This is highly specific for a stenosis of the left anterior descending (LAD) coronary artery and may even present with a normal troponin.
**Crop just the EKG portion or use the provided EKGs**
Interestingly enough here is a direct example from Sala, 2015 noted in which a proximal impending occlusion provided the following results (picture A) provided with the concurrent EKG.
However following a re-perfusion, a repeat EKG noted the changes which interestingly moved to the previously discussed type 1 with upsloping ST elevation as seen:
Sgarbossa Criteria
Holy high yield Batman! As annoying as it is to memorize Sgarbossa criteria, it is here to stay and will be on our boards.
When a patient has a left bundle branch block (LBBB) or pacemaker, diagnosing a STEMI becomes a completely different ball game. This is where Sgarbossa criteria comes in:
- Concordant ST elevation > 1mm in leads with a positive QRS complex (score 5)
- Concordant ST depression > 1 mm in V1-V3 (score 3)
- Excessively discordant ST elevation > 5 mm in leads with a -ve QRS complex (score 2)
Keep clinical judgement and physical exam at the forefront for these patients as a score of >3 is 90% specific, it is only 36% sensitive. Accuracy has been improved by considering proportional discordance as noted by Smith, 2012. (https://pubmed.ncbi.nlm.nih.gov/22939607/), but for inservice/boards however, keep Sgarbossa criteria in mind.
New LBBB
An important note regarding left bundle branch blocks is the classic teaching that a new LBBB should be treated as a STEMI. Although a high degree of caution, discussion with cardiology and standard chest pain work-up should take place, a new LBBB is not always an acute myocardial infarction.
As noted by Jain 2011 (https://pubmed.ncbi.nlm.nih.gov/21296327/) in the American Journal of Cardiology that almost ⅔ of those with a new LBBB had a different diagnosis than acute myocardial infarction. This group should be treated as a high risk subgroup, however will not always necessarily require immediate catheterization.
Right ventricular MI
Although exceptionally rare, right ventricular myocardial infarctions affect almost 40% of inferior MIs.
Standard lead placement is noted to be:
With a right sided EKG, placement may follow several different configurations with the simplest including V4 being moved to the right sided mid clavicular line
From this perspective, both V4R and V1 are the leads facing the right ventricle, which can be noted on the EKG below. Important notes for management are to remember the pre load dependence of a right/inferior MI, and risk of hypotension.
Take home points
- When handed an EKG, STEMI equivalents should be kept in mind
- Sgarbossa criteria is high yield, review it one more time.
- Wellens Syndrome will be on inservice every year, be aware of both types
- Posterior/Right sided EKG can be useful tools when suspecting ACS without EKG verification.
Written by: Hakkam Zaghmout, MD
Peer Reviewed and Edited by: James Bohan, MD
References
- Dressler, W and Roesler, H. High T waves in the earliest stage of myocardial infarction. Am Heart J. 1947 Nov;34(5):627-45.
- https://www.revespcardiol.org/en-the-de-winter-pattern-can-articulo-S1885585715003163
- https://www.revespcardiol.org/en-proximal-left-anterior-descending-artery-articulo-S188558571500122X
- https://litfl.com/wp-content/uploads/2018/08/Posterior-leads-V7-V8-V9-ECG-placement.jpg
- https://litfl.com/ecg-library/
- Goldberger, Ary. “Electrocardiogram in the Diagnosis of Myocardial Ischemia and infarctin.” UptoDate, 14 Feb 2020
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