Localisation of Myocardial Infarction

Localising MI with ECG is a clinical skill. The culprit artery involved can be identified with ECG even without coronary angiography.

1. Localisation of MI -Dr. Srikanth Reddy

2. Arterial supply of heart The heart receives its own supply of blood from the coronary arteries. Two major coronary arteries branch off from the aorta near the point where the aorta and the left ventricle meet.

3. LEFT MAIN CORONARY ARTERY The left main coronary artery branches into: Circumflex artery Left Anterior Descending artery (LAD) The left coronary arteries supply: Circumflex artery - supplies blood to the left atrium, side and back of the left ventricle Left Anterior Descending artery (LAD) - supplies the front and bottom of the left ventricle and the front of the septum

4. RIGHT CORONARY ARTERY The right coronary artery branches into: Right marginal artery Posterior descending artery The right coronary artery supplies: Right atrium Right ventricle Bottom portion of both ventricles and back of the septum

5. ECG LEADS REPRESENTATION ON HEART Septal (V1-2 ) Anterior (V3-4) Lateral (I + aVL, V5-6) Inferior (II, III, aVF) Right ventricular (V1, V4R) Posterior (V7-9)

6. Chest leads placement

7. V1 : 4th intercostal space (ICS), RIGHT margin of the sternum V2 :  4th ICS along the LEFT margin of the sternum V4 : 5th ICS, mid- clavicular line V3 : midway between V2 and V4 V5 :  5th ICS, anterior axillary line (same level as V4 ) V6 :  5th ICS, mid- axillary line (same level as V4)

8. Anterior STEMI

9. ANTERIOR STEMI Anterior STEMI results from occlusion of the  left anterior descending artery (LAD) . Anterior myocardial infarction carries the worst prognosis of all infarct locations, mostly due to larger infarct size.

10. HOW TO RECOGNISE ANTERIOR STEMI ST segment elevation with Q wave formation in the precordial leads (V1-6) ± the high lateral leads (I and aVL ). Reciprocal ST depression in the inferior leads (mainly III and aVF ). Left main coronary artery occlusion : widespread ST depression with ST elevation in aVR ≥ V1

11. Extensive Anterolateral STEMI (acute ) ST elevation in V2-6, I and aVL . Reciprocal ST depression in III and AVF.

12. ST elevation in aVR indicates proximal LAD Occlusion.

13. Inferior STEMI

14. 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)

15. INFERIOR STEMI Generally have a more favourable prognosis than anterior myocardial infarction 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.

16. Which artery is culprit ? 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 ).

17. 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.

18. 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

19. 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

20. 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

21. 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 suggest a circumflex artery occlusion.

22. Lateral STEMI

23. The lateral wall of the LV is supplied by branches of the left anterior descending (LAD) and left circumflex ( LCx ) arteries . Infarction of the lateral wall usually occurs as part of a larger territory infarction, e.g. anterolateral STEMI. Isolated lateral STEMI is less common Lateral extension of an anterior, inferior or posterior MI indicates a larger territory of myocardium at risk with consequent worse prognosis.

24. ST elevation in the lateral leads (I, aVL , V5-6). Reciprocal ST depression in the inferior leads (III and aVF ). ST elevation primarily localised to leads I and aVL is referred to as a  high lateral STEMI.

25. CATEGORIES OF LATERAL STEMI Anterolateral   STEMI due to LAD occlusion . Inferior-posterior-lateral  STEMI due to LCx occlusion. Isolated lateral  infarction due to occlusion of smaller branch arteries such as the D1, OM or ramus intermedius .

26. High Lateral STEMI ST elevation is present in the high lateral leads (I and aVL ). There is also subtle ST elevation with hyperacute T waves in V5-6. There is reciprocal ST depression in the inferior leads (III and Avf ) The culprit vessel in this case was an occluded first diagonal branch of the LAD.

27. Anterolateral STEMI : ST elevation is present in the anterior (V2-4) and lateral leads (I, aVL , V5-6 ). Q waves are present in both the anterior and lateral leads, most prominently in V2-4. There is reciprocal ST depression in the inferior leads (III and aVF ). This pattern indicates an extensive infarction involving the anterior and lateral walls of the left ventricle

28. Posterior MI

29. Isolated posterior MI is less common (3-11% of infarcts ). Posterior extension of an inferior or lateral infarct implies a much larger area of myocardial damage, with an increased risk of left ventricular dysfunction and death . Isolated posterior infarction is an indication for emergent coronary reperfusion.

30. Explanation of the ECG changes in V1-3 The anteroseptal leads are directed from the anterior precordium towards the  internal  surface of the posterior myocardium. Because posterior electrical activity is recorded from the anterior side of the heart, the typical injury pattern of ST elevation and Q waves becomes  inverted: ST elevation becomes ST depression Q waves become R waves Terminal T-wave inversion becomes an upright T wave

31. Posterior MI is suggested by the following changes in V1-3 : Horizontal ST depression Tall, broad R waves (>30ms ) Upright T waves Dominant R wave (R/S ratio > 1) in V2 Posterior infarction is confirmed by the presence of ST elevation and Q waves in the posterior leads (V7-9). In patients presenting with ischaemic symptoms, horizontal ST depression in the anteroseptal leads (V1-3) should raise the suspicion of posterior MI.

32. Typical appearance of posterior infarction in V2