Clinical Notes : Cardiology

145. ECG STEMI - inferior

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ECG - Inferior STEMI

Inferior ST Elevation Myocardial Infarction

MI is myocardial cell death that occurs because of a prolonged mismatch between perfusion and demand.

This is usually caused by occlusion in the coronary arteries. ST-elevation myocardial infarction (STEMI) is suspected when a patient presents with persistent ST-segment elevation in 2 or more anatomically contiguous ECG leads in the context of a consistent clinical history.

 

Inferior MI accounts for 40-50% of all myocardial infarctions.

Generally have a more favourable prognosis than anterior myocardial infarction

However certain factors indicate a worse outcome:

  • concomitant right ventricular infarction

  • significant bradycardia due to second- or third-degree AV block

  • posterior infarction

 

How to recognise an inferior STEMI

  • ST elevation in leads II, III and aVF

  • Progressive development of Q waves in II, III and aVF

  • Reciprocal ST depression in aVL (± lead I)

 
 

Example 1 : Early inferior STEMI

 

  • Hyperacute (peaked) T waves in II, III and aVF with relative loss of R wave height.

  • Early ST elevation and Q-wave formation in lead III.

  • Reciprocal ST depression and T wave inversion in aVL.

  • ST elevation in lead III > lead II suggests an RCA occlusion; the subtle ST elevation in V4R would be consistent with this.

 

Note how the ST segment morphology in aVL is an exact mirror image of lead III.

This reciprocal change occurs because these two leads are approximately opposite to one another (150 degrees apart).

STEMI inf 1 - early.jpg

Early Inferior STEMI

 

Example 2 : Inferior STEMI

  • ST elevation in II, III and aVF.

  • Q-wave formation in III and aVF.

  • Reciprocal ST depression and T wave inversion in aVL

  • ST elevation in lead II = lead III and absent reciprocal change in lead I (isoelectric ST segment) suggest a circumflex artery occlusion

STEMI inf 1 - example 2.jpg

 Inferior STEMI

Example 3 : Inferior STEMI

  • Marked ST elevation in II, III and aVF with early Q-wave formation.

  • Reciprocal changes in aVL.

  • ST elevation in lead III > II with reciprocal change present in lead I and ST elevation in V1-2 suggests RCA occlusion with associated RV infarction: This patient should have right-sided leads to confirm this.

 
STEMI inf 1 - example 3.jpg

 Inferior STEMI

Example 4 : Hyperacute Inferior STEMI

  • Hyperacute T waves in II, III and aVF.

  • Early ST elevation and loss of R wave height in II, III and aVF.

  • Reciprocal change in aVL and lead I.

 
STEMI inf 1 - example 4.jpg

Hyperacute Inferior STEMI

Example 5 : Inferior STEMI vs Pericarditis

  • The concave ST elevation in II, III and aVF may be mistaken for pericarditis.

  • However, the fact that the ST elevation is localised to the inferior leads with reciprocal changes in aVL confirms that this is an inferior STEMI

 
STEMI inf 1 - example 5.jpg

 Inferior STEMI vs Pericarditis

Example 6 : Massive Inferorlateral STEMI 

  • Marked ST elevation in II, III and aVF with a “tombstone” morphology.

  • Reciprocal change in aVL.

  • ST elevation is also present in the lateral leads V5-6, indicating an extensive infarct of the inferior and lateral walls.

 

In patients with inferior STEMI, ST elevation of 2mm or more in leads V5 and V6 is predictive of extensive coronary artery disease and a large area of infarction.

 
STEMI inf 1 - example 5.jpg

Massive Inferorlateral STEMI 

 

Management

Refer A+E

In OOH settings where delay in transfer to A+E is inevitable : 

  • aspirin

    • 300 mg orally immediately, followed by 75 mg once daily

  • oxygen

    • Supplemental oxygen is indicated only if oxygen saturation is less than 90%

  • morphine

    • 2-4 mg intravenously every 5-15 minutes until adequate pain control is achieved

  • glyceryl trinitrate

    • if not hypotensive :

      • 0.3 to 1 mg sublingually every 5 minutes,

      • maximum 3 doses

    • if hypertensive or heart failure

      • 5 micrograms/minute intravenously initially,

      • increase by 5-20 microgram/minute increments every 3-5 minutes according to response,

      • maximum 200 micrograms/minute

 
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Life in the Fast Lane

Austalian Emergency Medicine website. 

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ST-elevation myocardial infarction

BMJ Best Practice

Last reviewed : March 2019

Last updated : September 2018

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