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

5. 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

6. 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)

7. CHEST LEADS PLACEMENT

8.  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)

11. 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.

12. 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

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

14.  ST elevation in aVR indicates proximal LAD
Occlusion.

16. 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)

17. 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.

18. 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).

19.  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.

20. 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

21.  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

22. 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

23.  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.

25.  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.

26.  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.

27. 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.

28.  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.

29.  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

30. Posterior MI

31.  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.

32. 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

33. 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.

34.  Typical appearance of posterior infarction in V2