Inferior STEMI • LITFL Medical Blog • ECG Library Diagnosis

HTTP Error 503.2 – Service Unavailable

The [email protected] setting is being exceeded.

Most likely causes:

  • Setting is too low.
  • The application is taking too long for the current load.

Things you can try:

  • Try increasing the value of the setting.
  • Check that external resources (for example, disk, database, etc..) are performing at expected levels.
  • Check that the application has not deadlocked.

Detailed Error Information:

Module   IIS Web Core
Notification   BeginRequest
Handler   ExtensionlessUrlHandler-Integrated-4.0
Error Code   0x00000000

Requested URL   https://www.healio.com:8085/cardiology/learn-the-heart/cardiology-review/topic-reviews/inferior-myocardial-infarction
Physical Path   C:\websites\_public\Wyanoke8\Website9\cardiology\learn-the-heart\cardiology-review\topic-reviews\inferior-myocardial-infarction
Logon Method   Not yet determined
Logon User   Not yet determined

More Information:

IIS will not allow more concurrent requests to an application than the [email protected] setting permits.

View more information »

  • Skip to primary navigation
  • Skip to content
  • Skip to primary sidebar
  • Skip to footer
Life in the Fast Lane

Life in the Fast Lane

Emergency Medicine and critical care education blog • LITFL

You are here: Home / ECG Library / Inferior STEMI

Inferior STEMI

by , last update

↪  ECG Library Homepage

Inferior ST Elevation Myocardial Infarction

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

  • Generally have a more favourable prognosis than anterior myocardial infarction (in-hospital mortality only 2-9%), however certain factors indicate a worse outcome.
  • Up to 40% of patients with an inferior STEMI will have a concomitant  right ventricular infarction . These patients may develop severe hypotension in response to nitrates and generally have a worse prognosis.
  • Up to 20% of patients with inferior STEMI will develop significant bradycardia due to  second-  or  third-degree  AV block. These patients have an increased in-hospital mortality (>20%).
  • Inferior STEMI may also be associated with  posterior infarction , which confers a worse prognosis due to increased area of myocardium at risk.

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)

Which Artery is the Culprit?

Inferior STEMI can result from occlusion of all three coronary arteries:

  • The vast majority (~80%) of inferior STEMIs are due to occlusion of the dominant right coronary artery (RCA).
  • Less commonly (around 18% of the time), the culprit vessel is a dominant left circumflex artery (LCx).
  • Occasionally, inferior STEMI may result from occlusion of a “type III” or “wraparound” left anterior descending artery (LAD). This produces the unusual pattern of concomitant inferior and anterior ST elevation.

While both RCA and circumflex occlusion may cause infarction of the inferior wall, the precise area of infarction in each case is slightly different:

  • The RCA territory covers the medial part of the inferior wall, including the inferior septum.
  • The LCx territory covers the lateral part of the inferior wall and the left posterobasal area.

This produces subtly different patterns on the ECG:

  • The injury current in RCA occlusion is directed inferiorly and rightward, producing ST elevation in lead III > lead II (as lead III is more rightward facing).
  • The injury current in LCx occlusion is directed inferiorly and leftward, producing ST elevation in the lateral leads I and V5-6.

These differences allow for electrocardiographic differentiation between RCA and LCx occlusion.

RCA occlusion is suggested by:
  • ST elevation in lead III > lead II
  • Presence of reciprocal ST depression in lead I
  • Signs of right ventricular infarction : STE in V1 and V4R

Circumflex occlusion is suggested by:
  • ST elevation in lead II = lead III
  • Absence of reciprocal ST depression in lead I
  • Signs of lateral infarction: ST elevation in the lateral leads I and aVL or V5-6

(NB. Relative Q-wave depth in leads II and III is not useful in determining the culprit artery. Both RCA and LCx occlusion produce a similar pattern of Q wave changes, often with deeper Q waves seen in lead III)

V4R ECG lead placement

ECG Examples

Example 1
ECG Inferior STEMI Hyperacute 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).

The concept of reciprocal change can be further highlighted by taking lead aVL and inverting it… see how the ST morphology now looks identical to lead III.

ECG aVL flip Inferior STEMI

(For more about lead aVL and its utility in diagnosing subtle inferior STEMI, check out this post from Dr Smith’s ECG Blog )


Example 2
ECG Inferior AMI STEMI

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

Example 3
ECG Inferior AMI STEMI 2

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.

Example 4
ECG Inferior AMI STEMI Hyperacute

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.

Example 5
ECG Inferior AMI STEMI 3

Inferior STEMI:

  • 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.

Example 6
ECG Inferior AMI STEMI Massive tombstones

Massive inferolateral 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.


Example 7

ECG Recent inferolateral STEMI

Recent inferolateral STEMI:

  • Well-formed Q waves in III and aVF suggest that this STEMI is not acute.
  • The T waves in III and aVF are beginning to invert.
  • There is still some residual ST elevation in the inferior (II, III, avF) and lateral (V5-6) leads. ST elevation may take 2 weeks to resolve after an acute inferior MI (even longer for an anterior STEMI).

NB. If this patient had ongoing chest pain you would still treat them as an acute STEMI!


Bradycardia and AV Block in Inferior STEMI

Up to 20% of patients with inferior STEMI will develop either second- or third degree heart block. There are two presumed mechanisms for this:

  • Ischaemia of the AV node due to impaired blood flow via the AV nodal artery. This artery arises from the RCA 80% of the time, hence its involvement in inferior STEMI due to RCA occlusion.
  • Bezold-Jarisch reflex = increased vagal tone secondary to ischaemia.

The conduction block may develop either as a step-wise progression from 1st degree heart block via Wenckebach to complete heart block (in 50% of cases) or as abrupt onset of second or third-degree heart block (in the remaining 50%).

Patients may also manifest signs of sinus node dysfunction, such as sinus bradycardia, sinus pauses, sinoatrial exit block and sinus arrest. Similarly to AV node dysfunction, this may result from increased vagal tone or ischaemia of the SA node (the SA nodal artery is supplied by the RCA in 60% of people).

Bradyarrhythmias and AV block in the context of inferior STEMI are usually transient (lasting hours to days), respond well to atropine and do not require permanent pacing.


Example 8
ECG Inferior AMI STEMI CHB Complete heart block
  • Inferior STEMI with third degree heart block and slow junctional escape rhythm.

Example 9
ECG Inferior STEMI with sinus node dysfunction
  • Inferior STEMI with sinus node dysfunction (either sinus arrest or extreme sinus bradycardia) and a slow junctional escape rhythm.

Related Topics

  • Anterior STEMI
  • Lateral STEMI
  • Right ventricular infarction
  • Posterior infarction

References

  • Edhouse J, Brady WJ, Morris F. ABC of clinical electrocardiography: Acute myocardial infarction-Part II. BMJ. 2002; 324: 963-6.
  • Morris F, Brady WJ. ABC of clinical electrocardiography: Acute myocardial infarction-Part I . BMJ. 2002; 324: 831-4.
  • Berger PB, Ryan TJ. I nferior myocardial infarction: High-risk subgroups. Circulation. 1990; 81(2): 401-11.

LITFL Further Reading
  • ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
  • ECG A to Z by diagnosis – ECG interpretation in clinical context
  • ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
  • 100 ECG Quiz – Self-assessment tool for examination practice
  • ECG Reference SITES and BOOKS – the best of the rest

Advanced Reading
  • Brady WJ, Truwit JD. Critical Decisions in Emergency and Acute Care Electrocardiography
  • Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric
  • Wagner GS. Marriott’s Practical Electrocardiography 12e
  • Chan TC. ECG in Emergency Medicine and Acute Care
  • Rawshani A. Clinical ECG Interpretation
  • Mattu A. ECG’s for the Emergency Physician
  • Hampton JR. The ECG In Practice, 6e

ECG LIBRARY 700

ECG LIBRARY

Electrocardiogram

EKG Library

Share this:

  • Click to share on Twitter (Opens in new window)
  • Click to share on Facebook (Opens in new window)
  • Click to share on LinkedIn (Opens in new window)
  • Click to share on Pocket (Opens in new window)
  • Click to share on WhatsApp (Opens in new window)

Reader Interactions

Leave a Reply Cancel reply

This site uses Akismet to reduce spam. Learn how your comment data is processed .