CONTENTS
- (Introduction)
- ECG findings in posterior MI
- Differential diagnosis of posterior OMI
- Echocardiography in posterior OMI
- Posterior MI occurs in up to 20% of acute MI, usually in association with IMI and/or lateral MI. (26828074)
- Isolated posterior OMI is much less common, accounting for ~5% of all OMIs.
- Isolated posterior OMI usually reflects ischemia involving the left circumflex artery (LCX). (26828074) The LCX is the dominant vessel in 15% of patients, supplying the left posterior descending artery. (36030271)
Findings #1-2 are largely required for a confident diagnosis of posterior OMI. Findings #3-5 may be supportive if they are encountered, but they are often absent and are not required for the diagnosis.
[1/5] maximal STD in V1-V4
- Normally, there is a small degree of STE in V2-V3. Therefore, any degree of STD may be significant.
- Ischemic STD maximal in V1-V4 indicates posterior OMI (as opposed to subendocardial ischemia, which causes maximal STD in V5-V6). (34775811)
[2/5] T-waves in the right precordial leads reveal some sort of ischemic morphology
- TWI can occur as a mirror image of hyperacute posterior T-waves.
- Prominent upright T-waves can occur as a mirror image of posterior TWI (due to reperfusion).
mirror test to evaluate ischemic morphology
- 🔑 Before diagnosing a posterior MI, always perform the Mirror test to see if morphology is consistent with ischemia!
- Mirror test
- With paper: flip the ECG and look through it (this will mimic the appearance of the posterior leads).
- With a smartphone: take a picture of the precordial leads, then flip horizontally (once) and rotate 90 degrees (twice). This has the same effect as the traditional mirror test (if you don't have the ECG on a piece of paper).
- The mirror test can help make sense of T-wave morphological abnormalities (which otherwise are not intuitive).
[3/5] tall R-waves in the right precordial leads
- This represents a Q-wave equivalent.
- It's not invariably present (just as Q-waves are not invariably present in other types of OMI).
[4/5] inferior and/or lateral ischemia
- There is often simultaneous STE in the interior leads or lateral lead(s), such as V6.
- This isn't required for the diagnosis, but if seen, it supports the presence of ischemia.
[5/5] posterior ECG
- STE in the posterior leads (V7-V9) might help confirm the diagnosis and potentially meet “STEMI criteria.” >0.5 mm STE in one posterior lead is sufficient to meet STEMI criteria (unless the patient is a man <40 years old, in which case the cutoff is 1 mm).
- The value of posterior ECG is not precisely clear:
- In rare cases of posterior MI, posterior ECG may show STE despite a lack of STD in the precordial leads. (36030271)
- Posterior ECG may be falsely negative, especially among patients with obesity or lung hyperinflation (the posterior leads are increasingly far away from the heart).
- Bottom line: Posterior ECG may be helpful in some patients, but don't assume that the posterior ECG is superior to a thoughtful interpretation of the standard 12-lead ECG.
[1/4] posterior OMI vs. diffuse subendocardial ischemia 📖
common features
- Both may cause STD in many leads.
- Both may cause STE in aVR.
differentiation
- [1] Location of maximal STD:
- Posterior MI: maximal STD occurs in V2-V4 and it tends to be more focal (although simultaneous LVH may add STD in the lateral precordium leading to a confusing picture).
- Diffuse subendocardial ischemia: maximal STD in ~V4-V6 & inferior leads.
- [2] Morphology in V2-V3 (mirror test ⚡️).
- Posterior OMI is supported if the mirror test shows morphology suggestive of an acute OMI.
- [3] Other features that may favor posterior OMI, if present:
- Tall R-waves in the right precordium.
- Evidence of inferior and/or lateral OMI.
[2/4] anterior De Winter T-wave pattern 📖
- Clues to De Winter T-waves:
- Lack of tall R-wave.
- T-wave is broad and hyperacute.
[3/4] PE or RVH
- Right precordial STD may be caused by right ventricular strain.
- Further discussion here: 📖
[4/4] digoxin or hypokalemia
- These can cause scooped STD in the right precordial leads, mimicking a posterior MI.
- Clues to suggest digoxin or hypokalemia:
- [1] ST depression is diffuse throughout the entire ECG (including inferior leads).
- [2] Other features of digoxin or hypokalemia:
- Echo may show posterior basal and/or inferolateral wall motion abnormality (apical 2-chamber view shows posterior wall).
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References
- 26828074 Levis JT. ECG Diagnosis: Isolated Posterior Wall Myocardial Infarction. Perm J. 2015 Fall;19(4):e143-4. doi: 10.7812/TPP/14-244 [PubMed]
- 36030271 Alsagaff MY, Amalia R, Dharmadjati BB, Appelman Y. Isolated posterior ST-elevation myocardial infarction: the necessity of routine 15-lead electrocardiography: a case series. J Med Case Rep. 2022 Aug 28;16(1):321. doi: 10.1186/s13256-022-03570-w [PubMed]
