This document provides an overview of electrocardiograms (ECGs). It discusses how ECGs work to detect the heart's electrical activity and analyze rhythms. The key parts of an ECG waveform are explained. Normal sinus rhythm is defined as a heart rate of 60-100 bpm, regular rhythm, normal P waves, and PR and QRS durations between 0.12-0.20 and 0.04-0.12 seconds respectively. Common arrhythmias like sinus bradycardia, sinus tachycardia, atrial fibrillation, and ventricular tachycardia are summarized. Recognizing myocardial infarctions on a 12-lead ECG is also covered, focusing on identifying ST segment

1. ECG
By
Dr. Mostafa Sayed

2. Objectives
• To recognize the normal rhythm of the heart
- “Normal Sinus Rhythm.”
• To recognize the most common rhythm
disturbances.
• To recognize an acute myocardial infarction
on a 12-lead ECG.

3. • ECG Basics
• How to Analyze a Rhythm
• Normal Sinus Rhythm
• Heart Arrhythmias
• Diagnosing a Myocardial Infarction

4. • The body acts as a giant conductor of electrical
current.
• Electrical activity that originates in the heart can
be detected on the body’s surface through an
electrocardiogram
• (ECG). Electrodes are applied to the skin to
measure voltage changes in the cells between the
electrodes.
• These voltage changes are amplified and visually
displayed on an oscilloscope and graph paper.

5. The following summarizes a basic ECG
• An ECG is a series of waves and deflections
recording the heart’s electrical activity from a
certain “view.”
• Many views, each called a lead, monitor voltage
changes between electrodes placed in different
positions on the body.
• Leads I, II, and III are bipolar leads, which consist
of two electrodes of opposite polarity (positive and
negative). The third (ground) electrode minimizes
electrical activity from other sources.
• Leads aVR, aVL, and aVF are unipolar leads and
consist of a single positive electrode and a reference.

6. 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.

7. Rhythm Strip

8. The 12-Leads
The 12-leads include:
–3 Limb leads
(I, II, III)
–3 Augmented leads
(aVR, aVL, aVF)
–6 Precordial leads
(V1- V6)

9. Standard limb lead
Electrode placement

10. Augmented leads

11. Chest leads

12. Views of the Heart
Some leads get a
good view of the:
Anterior portion
of the heart
Lateral portion
of the heart
Inferior portion
of the heart

13. Normal Impulse Conduction
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
Left
bundle
branch
Purkinje
fibers
Right bundle
branch
Bundle of His
AV Node
Internodal
pathways
SA node

14. Impulse Conduction & the ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers

15. ECG Rhythm Interpretation
ECG Basics

16. The “PQRST”
• P wave - Atrial
depolarization
• T wave - Ventricular
repolarization
• QRS - Ventricular
depolarization

17. 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)

18. Pacemakers of the Heart
• SA Node - Dominant pacemaker with an
intrinsic rate of 60 - 100 beats/minute.
• AV Node - Back-up pacemaker with an
intrinsic rate of 40 - 60 beats/minute.
• Ventricular cells - Back-up pacemaker
with an intrinsic rate of 20 - 45 bpm.

19. The ECG Paper
• Horizontally
– One small box - 0.04 s
– One large box - 0.20 s
• Vertically
– One large box - 0.5 mV

20. The ECG Paper
• Every 3 seconds (15 large boxes) is
marked by a vertical line.
• This helps when calculating the heart
rate.
3 sec 3 sec

21. ECG Rhythm Interpretation
How to Analyze a Rhythm

22. Objectives
• To recognize the normal rhythm of the
heart - “Normal Sinus Rhythm.”
• To recognize the most common rhythm
disturbances.
• To recognize an acute myocardial
infarction on a 12-lead ECG.

23. • ECG Basics
• How to Analyze a Rhythm
• Normal Sinus Rhythm
• Heart Arrhythmias
• Diagnosing a Myocardial Infarction

24. Rhythm Analysis
• Step 1: Calculate rate.
• Step 2: Determine regularity.
• Step 3: Assess the P waves.
• Step 4: Determine PR interval.
• Step 5: Determine QRS duration.

25. Step 1: Calculate Rate
• Option 1
– Count the # of R waves in a 6 second
rhythm strip, then multiply by 10.
– Reminder: all rhythm strips in the Modules
are 6 seconds in length.
Interpretation? 9 x 10 = 90 bpm
3 sec 3 sec

26. Step 1: Calculate Rate
• Option 2
– Find a R wave that lands on a bold line.
– Count the # of large boxes to the next R
wave. If the second R wave is 1 large box
away the rate is 300, 2 boxes - 150, 3
boxes - 100, 4 boxes - 75, etc. (cont)
R wave

27. Step 1: Calculate Rate
• Option 2 (cont)
– Memorize the sequence:
300 - 150 - 100 - 75 - 60 - 50
3
0
0
1
5
0
1
0
0
7
5
6
0
5
0

28. Step 2: Determine regularity
• Look at the R-R distances (using a caliper or
markings on a pen or paper).
• Regular (are they equidistant apart)?
Occasionally irregular? Regularly irregular?
Irregularly irregular?
Interpretation? Regular
R R

29. Step 3: Assess the P waves
• Are there P waves?
• Do the P waves all look alike?
• Do the P waves occur at a regular rate?
• Is there one P wave before each QRS?
Interpretation? Normal P waves with 1 P
wave for every QRS

30. Step 4: Determine PR interval
• Normal: 0.12 - 0.20 seconds.
(3 - 5 small boxes)
Interpretation? 0.12 seconds

31. Step 5: QRS duration
• Normal: 0.04 - 0.12 seconds.
(1 – 3 small boxes)
Interpretation? 0.08 seconds

32. Rhythm Summary
• Rate 90-95 bpm
• Regularity regular
• P waves normal
• PR interval 0.12 s
• QRS duration 0.08 s
Interpretation? Normal Sinus Rhythm

33. ECG Rhythm Interpretation
Normal Sinus Rhythm

34. Objectives
• To recognize the normal rhythm of the
heart - “Normal Sinus Rhythm.”
• To recognize the most common rhythm
disturbances.
• To recognize an acute myocardial
infarction on a 12-lead ECG.

35. • ECG Basics
• How to Analyze a Rhythm
• Normal Sinus Rhythm
• Heart Arrhythmias
• Diagnosing a Myocardial Infarction

36. Normal Sinus Rhythm (NSR)
• Etiology: the electrical impulse is formed
in the SA node and conducted normally.
• This is the normal rhythm of the heart;
other rhythms that do not conduct via
the typical pathway are called
arrhythmias.

37. NSR Parameters
• Rate 60 - 100 bpm
• Regularity regular
• P waves normal
• PR interval 0.12 - 0.20 s
• QRS duration 0.04 - 0.12 s
Any deviation from above is sinus
tachycardia, sinus bradycardia or an
arrhythmia

38. SA Node Problems
The SA Node can:
• fire too slow
• fire too fast
Sinus Bradycardia
Sinus Tachycardia
Sinus Tachycardia may be an appropriate
response to stress.

39. ECG Rhythm Interpretation

40. Objectives
• To recognize the normal rhythm of the
heart - “Normal Sinus Rhythm.”
• To recognize the most common rhythm
disturbances.
• To recognize an acute myocardial
infarction on a 12-lead ECG.

41. • ECG Basics
• How to Analyze a Rhythm
• Normal Sinus Rhythm
• Heart Arrhythmias
• Diagnosing a Myocardial Infarction

42. Rhythm #1
30 bpm
• Rate?
• Regularity? regular
normal
0.10 s
• P waves?
• PR interval? 0.12 s
• QRS duration?
Interpretation? Sinus Bradycardia

43. Sinus Bradycardia
• Deviation from NSR
- Rate < 60 bpm

44. Rhythm #2
130 bpm
• Rate?
• Regularity? regular
normal
0.08 s
• P waves?
• PR interval? 0.16 s
• QRS duration?
Interpretation? Sinus Tachycardia

45. Sinus Tachycardia
• Deviation from NSR
- Rate > 100 bpm

46. Rhythm #3
100 bpm
• Rate?
• Regularity? irregularly irregular
none
0.06 s
• P waves?
• PR interval? none
• QRS duration?
Interpretation? Atrial Fibrillation

47. Rhythm #4
70 bpm
• Rate?
• Regularity? regular
flutter waves
0.06 s
• P waves?
• PR interval? none
• QRS duration?
Interpretation? Atrial Flutter

48. Atrial Flutter
• Deviation from NSR
–No P waves. Instead flutter waves (note
“sawtooth” pattern) are formed at a rate
of 250 - 350 bpm.
–Only some impulses conduct through
the AV node (usually every other
impulse).

49. Ventricular Arrhythmias
• Ventricular Tachycardia
• Ventricular Fibrillation

50. Rhythm #5
160 bpm
• Rate?
• Regularity? regular
none
wide (> 0.12 sec)
• P waves?
• PR interval? none
• QRS duration?
Interpretation? Ventricular Tachycardia

51. Ventricular Tachycardia
• Deviation from NSR
–Impulse is originating in the ventricles
(no P waves, wide QRS).

52. Rhythm #6
none
• Rate?
• Regularity? irregularly irreg.
none
wide, if recognizable
• P waves?
• PR interval? none
• QRS duration?
Interpretation? Ventricular Fibrillation

53. Ventricular Fibrillation
• Deviation from NSR
–Completely abnormal.

54. Ventricular Fibrillation
• Etiology: The ventricular cells are
excitable and depolarizing randomly.
• Rapid drop in cardiac output and death
occurs if not quickly reversed

55. Acute Myocardial Infarction

56. Objectives
• To recognize the normal rhythm of the
heart - “Normal Sinus Rhythm.”
• To recognize the most common heart
arrhythmias.
• To recognize an acute myocardial
infarction on a 12-lead ECG.

57. • ECG Basics
• How to Analyze a Rhythm
• Normal Sinus Rhythm
• Heart Arrhythmias
• Diagnosing a Myocardial Infarction

58. Diagnosing a 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

59. ST Elevation
One way to
diagnose an
acute MI is to
look for
elevation of
the ST
segment.

60. ST Elevation
Elevation of the
ST segment
(greater than 1
small box) in 2
leads is
consistent with a
myocardial
infarction.

61. Anterior View of the Heart
The anterior portion of the heart is best
viewed using leads V1- V4.

62. Anterior Myocardial Infarction
If you see changes in leads V1 - V4
that are consistent with a myocardial
infarction, you can conclude that it is
an anterior wall myocardial infarction.

63. example
Do you think this person is having a
myocardial infarction. If so, where?

64. Interpretation
Yes, this person is having an acute anterior
wall myocardial infarction.

65. Other MI Locations
Now that you know where to look for an
anterior wall myocardial infarction let’s
look at how you would determine if the MI
involves the lateral wall or the inferior wall
of the heart.

66. Other MI Locations
First, take a look
again at this
picture of the heart.
Anterior portion
of the heart
Lateral portion
of the heart
Inferior portion
of the heart

67. Other MI Locations
Second, remember that the 12-leads of the ECG look at different
portions of the heart. The limb and augmented leads “see” electrical
activity moving inferiorly (II, III and aVF), to the left (I, aVL)
and to the right (aVR). Whereas, the precordial leads “see”
electrical activity in the posterior to anterior direction.
Limb Leads Augmented Leads Precordial Leads

68. 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

69. Inferior MI
Now how about the
inferior portion of the
heart?
Limb Leads Augmented Leads Precordial Leads
Leads II, III and aVF

70. Putting it all Together
Now, where do you think this person is
having a myocardial infarction?

71. Inferior Wall MI
This is an inferior MI. Note the ST elevation
in leads II, III and aVF.

72. Putting it all Together
How about now?

73. Anterolateral MI
This person’s MI involves both the anterior wall
(V2-V4) and the lateral wall (V5-V6, I, and aVL)!

74. ECG Changes
Ways the ECG can change include:
Appearance
of pathologic
Q-waves
T-waves
peaked flattened inverted
ST elevation &
depression

75. ST Elevation Infarction
ST depression, peaked T-waves,
then T-wave inversion
The ECG changes seen with a ST elevation infarction are:
Before injury Normal ECG
ST elevation & appearance of
Q-waves
ST segments and T-waves return to
normal, but Q-waves persist
Ischemia
Infarction
Fibrosis