The document discusses electrocardiograms (ECGs) in the context of acute coronary syndrome. It begins by describing the normal conduction system and the 12 standard ECG leads. It then explains how ECGs are recorded and the positioning of limb and precordial leads. The document discusses ST segments, T waves, and how to evaluate for ST elevations. It defines acute coronary syndrome and describes the classifications of ST-elevation MI, non-ST-elevation MI, and unstable angina based on ECG and cardiac enzyme findings. Specific ECG patterns for lateral, inferior, septal, and posterior wall MIs are also shown.

1. ECG in Acute
Coronary
Syndrome
Dr Awadhesh Kumar sharma
Deptt of Cardiology

2. The Normal Conduction System

5. ECG Leads
• The standard EKG has 12 leads:
– 3 Standard Limb Leads
– 3 Augmented Limb Leads
– 6 Precordial Leads

6. ECG Limb Leads
• Leads are electrodes which measure the difference in
electrical potential between either:
1. Two different points on the body
(bipolar leads)
2. One point on the body and a virtual
reference point with zero electrical
potential, located in the center of the
heart (unipolar leads)

7. Recording of the ECG
• Limb leads are I, II, II.
• Each of the leads are bipolar; i.e., it requires two sensors on the
skin to make a lead.
• If one connects a line between two sensors, one has a vector.
• There will be a positive end at one electrode and
negative at the other.
• The positioning for leads I, II, and III were first
given by Einthoven (Einthoven’s triangle).

8. ECG Limb Leads

9. Precordial Leads

10. Standard Chest Lead Electrode Placement
The Right-Sided 12-Lead ECG
The 15-Lead ECG

11. Contiguous Leads
•
•
•
•
•
Lateral wall: I, aVL, V5, V6
Inferior wall: II, III, avF
Septum: V1 and V2
Anterior wall: V3 and V4
Posterior wall: V7-V9 (leads
placed on the patient’s back
5th intercostal space
creating a 15 lead EKG)

12. Ctn. Electrocardiogram (ECG)

14. Coronary Circulation
• Coronary arteries and veins
• Myocardium extracts the largest amount of oxygen as
blood moves into general circulation
• Oxygen uptake by the myocardium can only improve by
increasing blood flow through the coronary arteries
• If the coronary arteries are blocked, they must be
reopened if circulation is going to be restored to that
area of tissue supplied

16. ST segment
• Connects the QRS complex and T wave
• Duration of 0.08-0.12 sec (80-120 msec)

17. S – T Segment
I
V1
Normal
Elevated
V3
Depressed
7

18. T waves
• Represents repolarization or recovery of
ventricles
• Interval from beginning of QRS
to apex of T is referred to as the
absolute refractory period

19. T wave morphology
AVR
I
Upright T
8
Inverted T

20. Acute Coronary Syndrome
Definition: a constellation of symptoms related to obstruction
of coronary arteries with chest pain being the most common
symptom in addition to nausea, vomiting, diaphoresis etc.
Chest pain concerned for ACS is often radiating to the left
arm or angle of the jaw, pressure-like in character, and
associated with nausea and sweating. Chest pain is often
categorized into typical and atypical angina.

21. Acute coronary syndrome
• Based on ECG and cardiac enzymes, ACS is classified
into:
– STEMI: ST elevation, elevated cardiac enzymes
– NSTEMI: ST depression, T-wave inversion, elevated cardiac
enzymes
– Unstable Angina: Non specific EKG changes, normal cardiac
enzymes

22. Unstable Angina
• Occurs at rest and prolonged, usually lasting >20 minutes
• New onset angina that limits activity
• Increasing angina: Pain that occurs more frequently, lasts
longer periods or is increasingly limiting the patients
activity

23. ECG
• First point of entry into ACS algorithm
• Abnormal or normal
• Neither 100% sensitive or 100% specific for AMI
• Single ECG for AMI – sensitivity of 60%, specificity
90%
• Represents single point in time –needs to be read
in context
• Normal ECG does not exclude ACS – 1-6% proven
to have AMI, 4% unstable angina

24. • GUIDELINES:
• Initial 12 lead ECG – goal door to ECG time
10min, read by experienced doctor (Class 1 B)
• If ECG not diagnostic/high suspicion of ACS –
serial ECGs initially 15 -30 min intervals (Class 1
B)
• ECG adjuncts – leads V7 –V9, RV 4 (Class 2a B)
• Continuous 12 lead ECG monitoring reasonable
alternative to serial ECGs (Class 2a B)

25. Evaluating for ST Segment
Elevation
• Locate the J-point
• Identify/estimate where the isoelectric line is noted to be
• Compare the level of the ST segment to the isoelectric
line
• Elevation (or depression) is significant if more than 1 mm
(one small box) is seen in 2 or more leads facing the
same anatomical area of the heart

26. The J Point
• J point – where the QRS complex and ST
segment meet
• ST segment elevation - evaluated 0.04 seconds
(one small box) after J point

27. • Coved
shape
usually
indicates
acute injury
• Concave
shape is
usually
benign
especially if
patient is
asymptomatic

28. Significant ST Elevation
• ST segment elevation measurement
– starts 0.04 seconds after J point
• ST elevation
– > 1mm (1 small box) in 2 or more contiguous chest leads (V1-V6)
– >1mm (1 small box) in 2 or more anatomically contiguous leads (ie:
II, III, aVF; I, aVL, V5, V6)
• Contiguous lead
– limb leads that “look” at the same area of the heart or are
numerically consecutive chest leads (ie: V1 – V6)

29. EKG
 STEMI:
 Q waves , ST elevations, hyper acute T waves; followed by T wave
inversions.
 Clinically significant ST segment elevations:
> than 1 mm (0.1 mV) in at least two anatomical contiguous leads
 or 2 mm (0.2 mV) in two contiguous precordial leads (V2 and V3)
 Note: LBBB and pacemakers can interfere with diagnosis of MI on EKG

30. EKG
• NSTEMI:
– ST depressions (0.5 mm at least) or T wave inversions ( 1.0 mm at
least) without Q waves in 2 contiguous leads with prominent R
wave or R/S ratio >1.
– Isolated T wave inversions:
• can correlate with increased risk for MI
• may represent Wellen’s syndrome:
– critical LAD stenosis
– >2mm inversions in anterior precordial leads
• Unstable Angina:
– May present with nonspecific or transient ST segment depressions
or elevations

31. Evolution of AMI
A - pre-infarct (normal)
B - Tall T wave (first few minutes of infarct)
C - Tall T wave and ST elevation (injury)
D - Elevated ST (injury), inverted T wave
(ischemia), Q wave (tissue death)
E - Inverted T wave (ischemia), Q wave
(tissue death)
F - Q wave (permanent marking)

32. ST Segment
Elevation

33. Anatomic Groups

34. Anatomic Groups

35. Anatomic Groups

36. Anatomic Groups

37. Anatomic Groups

38. Lateral Wall MI: I, aVL, V5, V6
Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.

39. Inferior Wall MI II, III, aVF
Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.

40. Septal MI: Leads V1 and V2
Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.

41. Anterior Wall MI V3, V4
Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.

42. Posterior MI – Reciprocal Changes ST
Depression V1, V2, V3
Source: The 12-Lead ECG in Acute Coronary Syndromes, MosbyJems, 2006.

43. MI- Few ECGs

44. Evolution of acute anterior myocardial infarction at
3 hours

45. Lateral MI
Reciprocal changes

46. Inferior wall MI