Written by: Sasha Becker (NUEM ‘27) Edited by: Mike Tandlich (NUEM ‘24)
Expert Commentary by: David Zull, MD
Expert Commentary
The emergency physician should be an expert regarding STEMI equivalents. This is the advanced course.
Hyperacute T waves
Hyperacute T waves refer to tall broad based symmetric T waves (not pointy T’s as seen in hyperkalemia). The hyperacute T wave may sometimes encroach upon the QRS leading to an upsloping ST segment. Hyperacute T’s are are at least one-third the height of the associated R wave and occur in contiguous leads. Hyperacute T waves can be a harbinger of impending STEMI but also can be seen with reperfusion of a STEMI, a dynamic equilibrium similar to Wellens T waves (the latter being marked by deeply inverted or biphasic T waves).
Hyperacute T waves V4-V6
De Winter T waves
De Winter T waves are hyperacute T waves in the precordial leads with ST depressions that upslope into the T wave unlike the isoelectric ST segment with terminal upsloping into the T wave as seen in isolated hyperacute T’s. There is often reciprocal ST elevation in AVR when there is a De Winter pattern in the precordium. STEMI in the precordial leads may precede or follow the De Winter pattern and are related to a complete or near complete LAD occlusion.
De Winter pattern
New RBBB and LBBB
New RBBB, especially in conjunction with a new LAFB may be associated with a proximal LAD occlusion. New RBBB with LAFB is not a STEMI equivalent but it is a signal to look carefully for ST changes in V1 or AVL or the presence of hyperacute T waves. RBBB is increasingly prevalent with aging, affecting over 10% of patients by 80 years of age, such that the significance of a new RBBB depends upon the acuity of the change.
RBBB with LAFB
New LBBB is no longer considered a STEMI equivalent yet it does indicate elevated risk for underlying coronary artery disease or cardiomyopathy. Sgarbossa criteria should be relied upon in interpreting the presence of ischemia in this setting, not that the LBBB is new.
Posterior MI
Posterior MI’s are usually associated with Inferior ischemia such that ST elevations in II, III, and AVF are the obvious clue. Inf-post MI’s involve a large portion of the myocardium fed by the RCA and circumflex and have a worse prognosis. If there is isolated Circumflex occlusion w/o RCA involvement, an isolated Posterior MI will occur, which will not have ST elevation in the inferior leads. We look for ST depression in leads V2-V4 with a prominent R wave in V2. In order to activate the cath lab in this setting, we look for ST elevation in the posterior leads V7-V9 which are in a mirror image location to V2-V4 below the scapular tip. Since these posterior leads are so far from the heart due to intervening lung tissue, the voltage is very low and the ST elevation is minimal, usually only 0.5 mm. If there is high clinical suspicion of posterior wall OMI with ST segment depression in V2-V4, ST elevation in the posterior leads may not be required to activate.
Posterior MI without inferior changes
STEMI evident on posterior leads
Wellens T waves
Wellens T waves are deeply inverted or biphasic T waves in V2-V4 which often result from a high grade LAD occlusion that has reperfused. Since Wellen’s T waves reflect a reperfused LAD, the patient is by definition asymptomatic at this time. This is a dynamic situation that often leads to anterior STEMI within hours or days. Both Wellens and De Winter patterns are harbingers of impending LAD occlusion, although these patterns may sometimes be seen in the inferior or lateral leads reflecting OMI in other vascular territories.
Wellens sign with ST segments rising of falling in V2-V3
AVL and AVR
A special mention should be made regarding ST segment abnormalities in AVL and AVR. Any ST depression in AVL is concerning for inferior OMI and special attention should to be made to the ST segments in II, III, and AVF even if the ST segment in those leads are only 0.5mm elevated.
ST depression in AVL associated with inferior ischemia
ST elevation in AVL is associated with high lateral ischemia and close attention should be made for ST elevation in I, V5, V6, and ST as well as ST depression in II, III, AVF.
ST elevation of AVR in conjunction with ST depression in the Inferior and lateral leads result from diffuse subendocardial ischemia, often attributed to Left main or proximal LAD occlusion. This pattern, however, is more often seen in global ischemia resulting from triple vessel disease, post ROSC, or hypotension/hypoxemia, hence cardiology may elect to cath once the patient is fully stabilized.
RV infarct
RV infarction is almost always associated with inferior wall STEMI with ST elevations in 2,3, and AVF, and ST depression in AVL. Right sided leads will identify RV involvement in this setting which can be helpful if there is hemodynamic instability. There are rare cases of isolated RV infarction in which ST elevation is only seen on right sided leads VR3-VR5.
Summary
There are some points I would like to emphasize. In terms of STEMI equivalent patterns in which there are no ST segment elevations or depressions, hyperacute T waves and Wellen’s T waves will get the cath team’s attention since these patterns often progress to STEMI. Don’t forget to look carefully at AVL, with ST depression signally inferior OMI and ST elevation may be the only clue to the presence of a high lateral OMI. Posterior leads are invaluable in confirming posterior wall STEMI, distinguishing ST depression in V1-V3 from Right heart strain. Right-sided leads can demonstrate RV involvement in inferior STEMI but is rarely abnormal in isolation. Don’t be surprised if cardiology is skeptical of STEMI with isolated ST elevation in AVR even in conjunction with reciprocal ST depressions diffusely as this pattern suggests global subendocardial ischemia from demand or shock states. However, if the patient’s history sounds like an acute MI, emphasize your concern for proximal LAD or Left main OMI to the cath team. Lastly, the newness of a LBBB or RBBB are not very useful in identifying OMI, so focus upon the Sgarbossa criteria.
David Zull, MD
Emergency Medicine, Internal Medicine, Addiction Medicine
Northwestern Memorial Hospital
How To Cite This Post:
[Peer-Reviewed, Web Publication] Becker, S. Tandlich, M. (2025, 3/19/2025). STEMI to OMI: Rethinking who will benefit from PCI. [NUEM Blog. Expert Commentary by Zull, D]. Retrieved from http://www.nuemblog.com/blog/STEMI-to-OMI
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