This document provides an overview of how to read an electrocardiogram (ECG). It describes the basic anatomy and electrical conduction system of the heart and how the ECG machine records and displays the heart's electrical activity. It then outlines a systematic approach for interpreting an ECG, including evaluating the rhythm, rate, axes, voltages, waves, segments, intervals, and any signs of ischemia, injury, or arrhythmia. Localization of abnormalities is also addressed. Examples are provided throughout to illustrate various normal and pathological ECG patterns.

1. How to read ECG?
Ahmed Elborae, MSc, MD, PhD, MRCP UK (London)
Assistant Lecturer of Cardiology, Cairo University

2. A 45-year-old male patient, presenting to ER with chest pain

3. ECG
“Electrical activity”
Echocardiography
“Ultrasound imaging”
Angiography
“Coronary supply”
A single modality rarely gives the whole truth
 Simple
 Rapid
 Cheap
 Available

4. Our conduction system

5. SA node
Right atrium
SA node
Right Left

6. P Wave
Atrial depolarization
Right Left

7. AV node-His-Purkinje system
AV conduction

8. QRS Complex
ventricular depolarization
Atria
Ventricles
Downward

9. ST segment
ventricular repolarization

10. T-Wave
ventricular repolarization

11. How to record our heart electricity?

12. ECG machine
4 cables for upper and
lower limbs
6 cables for the chest

13. Right Left
4 Limb electrodes
x
Where to place ECG Leads ?
Fire > Not seen Desert > Green

14. Where to place ECG Leads ?
6 Chest electrodes
4th space
5th space

15. V1,V2
V3,V4
V5,V6
Capturing the same object from different angles…

16. Depolarization Vector of ventricles towards electrode
Depolarization Vector of septum away from electrode
Positive deflection (R wave)
1st negative deflection (Q wave)
3
Depolarization Vector of the base of heart away from electrode
Negative deflection after R (S wave)
How it looks from V6?

17. Depolarization Vector of ventricles away from electrode
Depolarization Vector of septum towards electrode
Negative deflection after R (S wave)
1st Positive deflection (R wave)
How it looks from V1?

18. 12 leads?
6 Limb leads
6chest leads
x
How these 3 limb electrodes gives 6 leads?
Einthoven’s triangle

19. 3 Augmented unipolar Limb Leads
aVR
aVL
aVF

20. How QRS looks from unipolar limb leads?

21. 3 Bipolar Limb Leads = record the difference
Lead
Lead
Lead
Downward & to the left
aVR
aVL
aVF

22. How QRS looks from Bipolar limb leads?

23. Lead I = LA - RA
Lead II = LL - RA Lead III = LL - LA
Where is the zero point?
(Lead III + Lead I) - Lead II = Zero
Lead III + lead I = LL – LA + LA – RA
Lead III + Lead I = LL – RA = Lead II

24. Localization of limb leads
aVR
Inferior wall
Lateral wall

25. 6 Precordial Leads (Camera)

26. Anatomical Groups

27. 12 leads ECG paper
6 Limb leads 6chest leads
We are commenting on Duration and Voltage of waves

28. Duration on the ECG paper
40 ms
200 ms One small square here = 40 millisecond on the earth

29. Voltage on the ECG paper
One small square
10
small
boxes
=Two
large
boxes
2 large 1 mv
Usual Half volt. Double volt.
1 large 1 mv 4 large 1 mv
2 large =1 mv

30. How to read ECG?
Systematic approach

31. Systematic approach
1- Rhythm
Sinus
AF
Regular R-R, each P followed by QRS, normal PR interval
Irregular R-R, absent P waves, fibrillation waves

32. 2- Rate
Rule of 300 (in regular rhythm only)
Each minute contains 300 large squares
So, HR = 300 / R-R interval in large boxes
So, heart rate here is 300/3 = 100 bpm

33. 6 second Rule
(Irregular rhythm)
No. of complexes in 6 second (30 large squares) x 10
0 1 2 3 4 5 6 7
So, heart rate here =7x10= 70 bpm

34. 3-Cardiac axis
Lead I = X axis
aVF = Y axis

35. Lead I aVF
Normal axis
Right axis
Left axis
Extreme axis
Cardiac axis

36. 4-ECG voltage
Normal voltage: QRS amplitude > 5 mm in limb leads
,> 10 mm precordial leads
Low voltage: QRS amplitude < 5 mm in all limb leads

38. 5-Comment on
-Waves( P,QRS,T) voltage& duration
-Segments (PR,ST) deviation
-Intervals (PR,QT) time

39. Normal P- wave
• Positive in lead II, biphasic in V1
• Duration less than 3 small squares
• Amplitude less than 2.5 small squares
Right atrium
Left atrium

40. ECG pattern of atrial enlargement
Left atrium Right atrium
Normal
V1
Lead II
Lead II

41. PR interval
(AV conduction)
PR segment
P wave
< 120 ms 120-200 ms > 200 ms
Wolff-Parkinson-White Normal (3-5 ss) 1st degree heart block

42. QRS (Morphology, duration, voltage)
Poor R wave progression (R in V3 < 3 small squares) might denotes anterior ischemia

43. Pathological Q wave of MI
Pathological = More than 1x1 small squares
Pathological Q = Black hole

44. QRS duration
< 100 ms 100-120 ms > 120 ms
Normal
Incomplete
bundle branch
block
BBB
Ventricular beat

45. BBB
LBBB:M shaped V6
RBBB: M shaped V1

46. QRS voltage

47. ST segment
Ventricular repolarization

48. ST Segment Elevation
Earliest reliable sign of STEMI

49. MI localization

50. Other causes of ST elevation e.g. Brugada syndrome
Syncope
Sudden death in young

51. ST Segment Depression
Myocardial ischemia or NSTEMI (ST≥ 0.5 mm)
Depression are not localizing

52. How to diagnose MI in LBBB?

53. T wave
Ventricular repolarization

54. T wave inversion
• Ischemia (deep, symmetrical)
• Strain with hypertrophy
• 2ry to BBB
• Hypokalemia
• Intracranial hge (Very deep)

55. Hyper acute T wave
• Ischemia (Early STEMI)
• Hyperkalemia
• Hypertrophy

56. QT interval

57. QTc interval
< 440 ms > 440 ms
Normal Long QT Long QT
Bazzet formula

58. How to read ECG?
Rapid focused approach

59. Focused approach
1- Ischemia (Q wave, ST segment , T wave),localization
2- Arrhythmia: 4 items to reach diagnosis
(Rate, rhythm, P-QRS relation, QRS duration)

60. 46 male presenting to ED with chest pain
Ischemia (Q wave, ST, segment, T wave), localization

61. Antero-septal STEMI

62. 65 male, presenting to ED with chest pain
Ischemia (Q wave, ST, segment, T wave), localization

63. Inferior STEMI

64. MI equivalent ECG

65. De winter ECG (MI equivalent) -- Proximal LAD
Depressed J point + hyper acute T wave

66. Wellen ECG (MI equivalent) -- Proximal LAD
Type 2 > Biphasic T wave
Type 1 > deep symmetrical T wave inversion

67. (Left main or multi-vessel occlusion equivalent)
Diffuse ST depression+ aVR ST elevation

68. Posterior wall MI
Tall R in v2,V3+ ST depression
Mirror image
Posterior leads

69. 40-year-old , acute dyspnea 1 week post-partum C/S
Pulmonary embolism
Tachycardia, S1Q3T3, tall R in aVR, RV strain (Inverted T in precordial leads)

70. Heart rate
Slow
Tachycardia
Normal
P-QRS relation
Progressive
PR
Prolongation
Mobitz I
Multiple P
Followed by QRS
Fixed PR
Mobitz II
No relation
between
P /QRS
Complete AV block
Multiple P
Followed by QRS
Atrial flutter
1-QRS duration
Narrow Wide
2-Rhythm 2-Rhythm
Regular Regular
Irregular Irregular
3-P-QRS relation VT
SVT+BBB
AF+WPW
AF+BBB
Multiple P
Followed by QRS
Atrial flutter
QRS followed by P
Or no P
SVT
Multiple P
Followed by QRS
Atrial flutter+ variable block
Absent P
Atrial fibrillation
P-QRS relation
Absent P
Irregular
Atrial fibrillation

71. 33-year-old athlete, routine ECG
Slightly bradycardic, group beating, progressive PR prolongation then dropped beat, narrow QRS
x x

73. 73-year-old lady, presenting to ER with syncope
Bradycardia, multiple P followed by QRS with fixed PR interval, narrow QRS
x x x x x x

75. 75-year-old gentleman, presenting to ER with delirium
Bradycardia, multiple P followed by QRS with variable PR interval (Complete AV dissociation)

77. 77 female presenting to ED with palpitations
(Rate, rhythm, P-QRS relation, QRS duration)
Normal rate, irregular, absent P wave, narrow QRS

79. 60 female, presenting to ED with palpitations
(Rate, rhythm, P-QRS relation, QRS duration)
Normal rate, regular, Multiple P waves followed by QRS, narrow QRS

81. 20 female, presenting to ED with palpitations
(Rate, rhythm, P-QRS relation, QRS duration)
Tachycardia, regular, P wave after QRS, narrow QRS

83. 55 male IHD, presenting to ED with palpitations
(Rate, rhythm, P-QRS relation, QRS duration)
Tachycardia, regular, P wave after QRS, wide QRS

85. VT vs. SVT+BBB

86. 25 male, presenting to ED with dizziness
Very fast tachycardia, irregular, no clear P waves, wide QRS
(Rate, rhythm, P-QRS relation, QRS duration)

87. AF+BBB

88. Hyperkalemia (Sine wave)
65-year-old ESKD, missed dialysis session, confused
Hyperkalemia stretch ECG (PR, QRS, T wave)

89. https://litfl.com/ecg-library/
For more practice…

90. THANK YOU !
Einthoven