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.
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)
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)
9.
10.
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.
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.
24.
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
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.
