CONTENTS

• Core ECG findings in IMI
  • Involvement of additional walls:
    • IMI + posterior MI
    • IMI + lateral MI
    • IMI + RVMI
• Differential diagnosis of inferior OMI
  • LVH
  • PE
  • Early repolarization
  • Anterior Wellens B pattern
  • Inferior LV aneurysm
  • Myocarditis

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core ECG findings in IMI

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[1] basic features of IMI

• 🔑 Inferior STE (may be subtle).
• 🔑 STD in aVL (+/- Lead I):
  • aVL may also show down-up T-waves (mirroring inferior hyperacute T-waves).
  • If STD in aVL is absent, you should question the diagnosis of IMI. However, STD in aVL can rarely be hidden by simultaneous lateral ischemia (in which case you would expect to see STE in V5/V6).

[2] consider adjacent ischemia in three territories

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[2a] posterior ischemia (either RCA/LCX occlusion)

• ~V2-V4 shows ST depression/flattening (a more subtle form of ST depression).
• Hyperacute posterior ischemia may cause loss/inversion of T-waves in V2-V4.
• Reperfusion may cause down-up T-waves or tall T-waves in V2-V4.
• Occurs with ~70% of RCA lesions and ~30% of LCX lesions.

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[2b] lateral MI (in LCX occlusion)

• STE in V5, V6.

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[2c] RVMI (in RCA occlusion) 

key features of combined IMI-RVMI

• 🔑 Features implicating the RCA:
  • Bradycardia/blocks (suggests proximal RCA occlusion).
  • STE in III > STE in II.
  • STD in Lead I.
• 🔑 Features of RV ischemia:
  • STE of ≧0.5 mm in V1 (although STE can occasionally extend to V3).
  • ST depression in V2 with markedly less STD or isoelectric ST segment in V1. (38551563)

RVMI in conjunction with inferior MI from RCA occlusion

• RVMI occurs in the context of proximal RCA occlusions (not LCX occlusions). Features in the table above may be used to identify the occluded artery.
• STE of ≧0.5 mm in V1 is specific for RVMI (but not sensitive) in the context of inferior MI.
  • STE can extend a bit into the precordial leads, but should be maximal in V1-V2.
  • ⚠️ The differential diagnosis may include inferior MI plus diffuse subendocardial ischemia (which can cause diffuse STD with STE in aVR and V1).
• Substantial STD in V2, without STD in V1:
  • If there is STD in V2, this reduces the sensitivity of lead V1 (posterior MI may cause ST depression across the right precordial leads, obscuring RVMI).
  • In the presence of significant STD in V2 due to posterior MI, an absence of STD in V1 implies the presence of an RVMI as a superimposed second process that is causing relative STE in V1. 🌊 (30497759) Some authors have stated that any STE in V1 relative to the degree of ST deviation in V2 may suggest RVMI. 🌊

right-sided ECG (consider if no STE in V1)

• >0.5 mm STE in V4r supports a diagnosis of RVMI (or >1 mm for men <30 years old).  Unfortunately, other things can cause this besides RVMI, including:
  • Anteroseptal MI.
  • Anterior myocardial aneurysm.
  • Acute PE.
  • Pericarditis.
• Unfortunately, this test also may be falsely negative in the presence of a posterior MI.

echocardiography

• Echo should show RV systolic failure (e.g., reduced tricuspid annulus excursion).
• Severe RV dilation may be absent, which may help sort this out from pulmonary embolism (wherein the cardinal finding is often RV dilation).

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differential diagnosis of inferior OMI

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[1/6] LVH mimic of IMI

• ECG findings:
  • (1) LVH causes primary STD and TWI in aVL.
  • (2) This leads to reciprocal STE in III (often with a saddle-back morphology).
• Further discussion of diagnosing MI in the context of LVH: 📖

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[2/6] PE mimicking IMI 📖

PE can mimic inferior MI, with features including:

• STE in inferior leads and V1, with reciprocal changes in aVL (figure below).
• SI-QIII-TIII pattern.

features that may favor PE 

• Terminal right-axis deviation (e.g., deep S-wave in Lead I).
  • ⚠️ However, IMI due to right coronary artery occlusion may cause RBBB or partial RBBB, producing a deep S-wave in Lead I.
• Diffuse TWI (involving inferior and right precordial leads).

features that may favor IMI

• Q-wave in II favors MI (PE may cause a Q-wave in III, but it is usually not in lead II). (O'Keefe 2021)
• Evidence of posterior MI, e.g.:
  • Tall R-waves in the right precordium.
  • Mirror test shows ischemic-appearing morphologies in V1-V3.
• Evidence of lateral MI (e.g., STE and/or TWI in V5-V6).

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[3/6] ER (early repolarization) – especially with vertical axis – mimicking IMI

key features of ER

• 🔑 Usually men (75%), <50-70 years old.
• 🔑 Widespread STE (greatest in V3-V4; often limb leads esp. II).
• 🔑 Notching/slurring at the J-point is followed by concave STE.
• 🔑 T-waves are usually tall and asymmetric, with STE in V6 <25% of the T-wave height (but benign TWI is possible).
• 🔑 R-waves and generally tall.
• 🔑 Often associated with STD in aVR.

clues to support the diagnosis of early repolarization (vs. IMI)

• [1] Benign early repolarization is usually also seen in the precordial leads.
• [2] ER has a benign-appearing morphology (e.g., concave upwards).
• [3] STD in aVL can occur if the QRS complex in aVL is also negative (in patients with a vertical axis; see example below).

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[4/6] anterior Wellens B 📖

• A dramatic anterior Wellens-B pattern may cause reciprocal STE and hyperacute T-waves in the inferior leads.
• Clues to this diagnosis:
  • (1) Very dramatic Wellens-B pattern in the anterior leads (with deep precordial TWI).
  • (2) The patient is pain-free when the ECG is obtained. 🌊

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[5/6] inferior aneurysm

⚠️ Be cautious about diagnosing inferior aneurysm

• It's often impossible to differentiate a chronic inferior aneurysm from an active inferior MI based on a single ECG. Some helpful hints are listed below, but these are highly fallible. In reality, clinical management depends on the integration of the history, serial ECGs, cardiac enzymes, echocardiography, etc. 🌊
• When in doubt, it's generally better to call the ECG a “possible OMI.”

ECG findings in inferior aneurysm

• Inferior Q-waves:
  • Q-waves don't need to be very deep.
  • Inferior MI develops Q waves more slowly than anterior MIs, indicating a subacute or chronic inferior MI.
• Unlike anterior aneurysm, the R-waves are often preserved.
• Inferior STE.
• Reciprocal STD in aVL can occur.

trying to differentiate aneurysm vs. active MI

• [1] Do the ST-T wave complexes look ischemic? For example:
  • Unequivocally hyperacute T-waves support active ischemia.
  • If ST-T wave complexes look benign (e.g., concave upwards or saddleback configuration), this is less worrisome for active ischemia.
• [2] Larger amounts of STE may favor acute OMI.

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[6/6] myocarditis 📖

• Myocarditis may be considered for patients with STE that don't fit well with other diagnoses.

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echocardiography of IMI

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(1) easiest view = parasternal short-axis 

• The inferior segment comes close to the posterior papillary muscle

(2) two-chamber view

• Obtain by starting at the apex and then rotate counterclockwise until the RV disappears.
• This image shows the anterior wall and the inferior wall (figure below).

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questions & discussion

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