7. Impulse Conduction & the ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
8. The PR Interval
Atrial depolarization
+
Delay in AV junction
(AV node/Bundle of His)
(Delay allows time for the
atria to contract before
the ventricles contract)
9. The “PQRST”
• P wave - Atrial
depolarization
• T wave - Ventricular
repolarization
• QRS - Ventricular
depolarization
12. Lead I
extends from
the right to the
left arm
Lead II
extends from the
right arm to the
left foot
Lead III
extends from the left
arm to the left foot
Einthoven’s Triangle
+-
+
-
13. Diagnosing MI
To diagnose a myocardial infarction you need
to go beyond looking at a rhythm strip and
obtain a 12-Lead ECG.
Rhythm
Strip
12-Lead
ECG
14. The 12-Lead ECG
• The 12-Lead ECG sees the heart from 12
different views.
• Therefore, the 12-Lead ECG helps you
see what is happening in different
portions of the heart.
• The rhythm strip is only 1 of these 12
views.
15. The 12-Leads
The 12-leads include:
–3 Limb leads
(I, II, III)
–3 Augmented leads
(aVR, aVL, aVF)
–6 Precordial leads
(V1- V6)
20. ST Elevation (cont)
Elevation of the ST
segment (greater
than 1 small box) in
2 leads is
consistent with a
myocardial
infarction.
21. Left Main Coronary Artery
Branches quickly into the LAD & LCX.
Involves almost 2/3 of the heart muscle
primarily anterior
Right Coronary Artery (RCA)
The RCA supplies blood to the bottom
(inferior) portion and part of the back
(posterior) portion of the left ventricle.
The posterior portion of the septum is also
supplied with blood from the RCA.
•SA Node 55%
•AV Node 90%
•AV Blocks
Left Anterior Descending Branch (LAD)
The LAD supplies blood to the front
(anterior) portion of the left ventricle, apical
including most of the anterior portion of the
septum separating the ventricles.
•Bundle Branch Block, AMI, CHF
Left Circumflux Branch (LCX)
The LCX supplies blood to the left
side (lateral) portion and the back
(posterior) portion of the left ventricle.
•SA Node 45%
•AV Node 10%
•Lateral & posterior MI
22. MI Locations
Look again at this
picture of the heart.
Anterior portion
of the heart
Lateral portion
of the heart
Inferior portion
of the heart
23. MI Locations
Look again at this
picture of the heart.
Anterior portion
of the heart
Lateral portion
of the heart
Inferior portion
of the heart
24. Anterior View of the Heart
The anterior portion of the heart is best
viewed using leads V1- V4.
25. Anterior MI
Remember the anterior portion of the heart is best
viewed using leads V1- V4.
Limb Leads Augmented Leads Precordial Leads
26. • Leads V3, V4
– Looks at anterior heart wall
– Looks from the left anterior chest
Anterior Wall MI
View of Anterior Heart Wall
27. Lateral MI
So what leads do you think the
lateral portion of the heart is
best viewed?
Limb Leads Augmented Leads Precordial Leads
Leads I, aVL, and V5- V6
28. • Leads I and aVL
– Looks at lateral heart wall
– Looks from the left arm toward
heart
Lateral Wall MI
View of Lateral Heart Wall
*Sometimes known as High Lateral*
29. Inferior MI
Now how about the inferior
portion of the heart?
Limb Leads Augmented Leads Precordial Leads
Leads II, III and aVF
30. • Leads II, III, aVF
- Looks at inferior heart wall
Inferior Wall MI
View of Inferior Heart Wall
-Looks from the left leg up
31. Putting it all Together
Now, where do you think this person is having
a myocardial infarction?
32. Inferior Wall MI
This is an inferior MI. Note the ST elevation in
leads II, III and aVF.
33. Inferior Wall MI
This is an inferior MI. Note the ST elevation in leads II, III and aVF.
