The document provides a comprehensive overview of ECG interpretation, including key concepts such as rate, rhythm, axis, and chamber size assessment. It covers various conditions, waveforms, and physiological principles essential for accurate ECG analysis, as well as guidelines for recognizing abnormalities. Additionally, it highlights important ECG conventions, lead placements, and diagnostic criteria for common cardiovascular issues.

1. ECG interpretation
Dr Md Main Uddin
Assistant Professor
(Medicine)
Cox’s Bazar Medical
College

2. Why ECG is
so important?

3. The ECG is used
 Rate
 Rhythm
 Conduction
 Chamber size
 Myocardial ischaemia and infarction

4. Objectives
 The Basics
 Interpretation
 Clinical data
 Practice Recognition

5. Electrophysiology
•Generation and conduction of cardiac electrical activity
•Inscription of QRS complex
•Electrical axis

6. The Normal Conduction System

7. Lead Placement
aVF

8. All Limb Leads

9. Precordial Leads

10. EKG Distributions
 Anteroseptal: V1, V2, V3, V4
 Anterior: V1–V6
 Anterolateral: V4–V6, I, aVL
 Lateral: I and aVL
 Inferior: II, III, and aVF
 Inferolateral: II, III, aVF, and
V5 and V6

11. ECG conventions
 Depolarisation towards electrode: positive deflection
 Depolarisation away from electrode: negative
deflection
 Sensitivity: 10 mm = 1 mV
 Paper speed: 25 mm per second
 Each large (5 mm) square = 0.2 s
 Each small (1 mm) square = 0.04 s
 Heart rate = 1500/RR interval (mm) (i.e. 300 ÷
number of large squares between beats)

12. Waveforms

13. The normal ECG

14. Check quality of ECG
 Patient’s name, age, sex
 Date of ECG
 12 leads
 Rhythm strip (II or V1) at bottom
 Scale:
◦ 25mm/s horizontal
◦ 10mm/mV vertical
◦ Little square=0.04s; big square=0.2s

15. Interpretation
 Quality of ECG?
 Rate
 Rhythm
 Axis
 P wave
 PR interval
 QRS duration
morphology
abnormal Q waves
 ST segment
 T wave
 QT interval

16. Rate
 Rule of 300- Divide 300 by the number
of boxes between each QRS = rate
Number of
big boxes
Rate
1 300
2 150
3 100
4 75
5 60
6 50

17. Rate
 HR of 60-100 per minute is normal
 HR > 100 = tachycardia
 HR < 60 = bradycardia
 When rate is irregular, count the
number of R in 30 large square and
multiply by 10 to get HR.

18. What is the heart rate?
(300 / 6) = 50 bpm
www.uptodate.com

19. Rate

21. Rhythm
 Sinus
 Originating from
SA node
 P wave before
every QRS
 P wave in same
direction as QRS

22. What is this rhythm?
Normal sinus rhythm

23. What is this rhythm?

24. Differential Diagnosis of Tachycardia
Tachycardia Narrow Complex Wide Complex
Regular ST
SVT
Atrial flutter
Sinus arrythmia
ST with
aberrancy
SVT with
aberrancy
VT
Irregular AF
Atrial flutter with
variable conduction
AF with aberrancy
AF with VT

25. The QRS Axis
 Represents the overall direction of the heart’s activity
 Axis of –30 to +90 degrees is normal

26. The Quadrant Approach
 QRS up in I and up in aVF = Normal

27. Axis trick
Positive in I and II

28. Positive in I
Negative in II

29. Negative in I
Positive in II

30. What is the axis?
Normal- QRS up in I and aVF

31. Axis deviation
LAD
 Normal
 LVH
 LAHB
 LBBB
 Inferior MI
RAD
 Normal
 RVH
 High lateral MI
 LPHB
 Dextrocardia

32. P wave
 2.5 X 2.5 ssq
 Better seen in lead II
and V1
 Upright in all leads
except aVR
 Absent in AF, A Fl,
SA block, nodal
rythme, SVT, VT
 Tall in RAE
 Wide in LAE
 Inverted in
incorrectly placed
leads, dextrocardia

33. PR intervel
 Normal (0.12 to 0.20
sec)
 Short (<0.12 sec)
Nodal rythme, nodal
ectopics, WPW
syndrome
 Prolonged (>0.20
sec) (1o
HB)
IHD, myocarditis
 Variable
2o
or 3o
heart block

34. Blocks
 AV blocks
 First degree block

PR interval fixed and > 0.2 sec
 Second degree block, Mobitz type 1

PR gradually lengthened, then drop QRS
 Second degree block, Mobitz type 2

PR fixed, but drop QRS randomly
 Type 3 block

PR and QRS dissociated

35. What is this?
First degree AV block PR
is fixed and longer than 0.2 sec

36. What is this rhythm?
Type 1 second degree block
(Wenckebach)

37. What is this rhythm?
Type 2 second degree AV block
Dropped QRS

38. What is this rhythm?
3rd
degree heart block (complete)

39. QRS complex
 Q wave
<25% of R wave, depth <2
mm, wide 1 smm
 Pathological Q
Mentioned 3 plus
Loss of height of R wave
Present in >1 lead
Causes
MI, VH, Cardiomyopathy,
LBBB
 R wave
 Normal height
aVL <13mm, aVF <20mm,
V5 or V6 <25mm
 Causes of tall R wave
LVH
Tall R in V1 - Normal
RVH, RBBB, dextrocardia,
true posterior MI, WPW
syndrome type A

40. QRS complex
 Causes of small R
wave
Incorrect
standardization,
emphysema,
obesity, pericardial
effusion,
hypothyroidism
 Causes of poor R
wave progression
 MI (A/S), LBBB,
COPD, dextrocardia

41. QRS complex
 QRS may be high
voltage, low voltage,
wide, abnormal
shape
 Wide QRS
BBB, VES,VT,WPW,
pacemaker
 Abnormal shape
BBB, VT, VF

42. BBB
W I LL ia M = LBBB
M a RR o W = RBBB
Look at V1 and V6

43. T wave
 Upright in all leads
except aVR
 Usually >2mm height
(<5mm in limb leads
and <10 mm in chest
leads)
 Tip smooth or rounded
 Inverted
ischaemia, previous
infarct, VH, BBB,
pericarditis,
cardiomyopathy
 Peaked
hyperkalaemia
normal young man
hyperacute MI
 Small
Hypokalaemia
Hypothyroidism
Pericaddial effusion

45. Normal Intervals

46. QT interval
 Start of QRS to end of T wave
 Needs to be corrected for HR
 Various formulae
 Computer calculated often wrong
 Long QT can be genetic (long QT sy.) or
secondary eg. drugs (amiodarone, sotalol)
 Associated with risk of sudden death due to
Torsades de Pointes

47. Prolonged QT
 Normal
 Normal < 0.42 secs
 Causes prolonged QT
 Drugs (Na channel blockers)
 Hypocalcemia, hypomagnesemia, hypokalemia
 Hypothermia
 AMI
 Congenital
 Increased ICP

48. Prolongation of QT

49. Hypertrophy
 Add the larger S wave of V1 or V2 in
mm, to the larger R wave of V5 or V6.
 Sum is > 35mm = LVH

50. Ischemia
 Usually indicated by ST changes
 Elevation = Acute infarction
 Depression = Ischemia
 Can manifest as T wave changes
 Remote ischemia shown by q waves

51. ST segment
 ST depression
◦ Downsloping or horizontal = abnormal
◦ Ischaemia (coronary stenosis)
◦ If lateral (V4-V6), consider LVH with ‘strain’ or digoxin
(reverse tick sign)
 ST elevation
◦ Infarction (coronary occlusion)
◦ Pericarditis (widespread)
 These are usually in ‘territories’ eg. anterior/lateral/inferior
etc. and will be present in contiguous leads

52. What is the diagnosis?
Acute inferior MI

53. What do you see in this EKG?
ST depression II, III, aVF, V3-V6 = ischemia

54. How to read a 12-lead ECG:
examination sequence
 Rhythm strip (lead II) - To determine heart rate and rhythm
 Cardiac axis - Normal if QRS complexes +ve in leads I and II
 P-wave shape - Tall P waves denote right atrial enlargement
(P pulmonale) and notched P waves denote left atrial
enlargement (P mitrale)
 PR interval - Normal = 0.12-0.20 secs. Prolongation denotes
impaired AV nodal conduction. A short PR interval occurs in
Wolff-Parkinson-White syndrome
 QRS duration - If > 0.12 secs then ventricular conduction is
abnormal (left or right bundle branch block)

55.  QRS amplitude - Large QRS complexes occur in slim
young patients and in patients with left ventricular
hypertrophy
 Q waves - May signify previous myocardial infarction (MI)
 ST segment - ST elevation may signify MI, pericarditis or
left ventricular aneurysm; ST depression may signify
myocardial ischaemia or infarction)
 T waves - T-wave inversion has many causes, including
myocardial ischaemia or infarction, and electrolyte
disturbances
 QT interval - Normal < 0.42 secs. QT prolongation may
occur with congenital long QT syndrome, low K+
, Mg2+
or
Ca2+
, and some drugs

56. Normal Sinus Rhythm
Mattu, 2003

57. First Degree Heart Block
PR interval >200ms

58. Junctional Rhythm
Rate 40-60, no p waves, narrow complex QRS

59. Hyperkalemia
Tall, narrow and symmetric T waves

60. Premature Atrial Contractions
Trigeminy pattern

61. Atrial Flutter with Variable Block
Sawtooth waves
Typically at HR of 150

62. Torsades de Pointes
Notice twisting pattern
Treatment: Magnesium 2 grams IV

63. Digitalis
Dubin, 4th ed. 1989

64. Lateral MI
Reciprocal changes

65. Inferolateral MI
ST elevation II, III, aVF
ST depression in aVL, V1-V3 are reciprocal changes

66. Anterolateral / Inferior Ischemia
LVH, AV junctional rhythm, bradycardia

67. Left Bundle Branch Block
Monophasic R wave in I and V6, QRS > 0.12 sec
Loss of R wave in precordial leads
QRS T wave discordance I, V1, V6
Consider cardiac ischemia if a new finding

68. Right Bundle Branch Block
V1: RSR prime pattern with inverted T wave
V6: Wide deep slurred S wave

69. First Degree Heart Block, Mobitz Type I (Wenckebach)
PR progressively lengthens until QRS drops

70. Supraventricular Tachycardia
Narrow complex, regular; retrograde P waves, rate <220
Retrograde P waves

71. Right Ventricular Myocardial Infarction
Found in 1/3 of patients with inferior MI
Increased morbidity and mortality
ST elevation in V4-V6 of Right-sided EKG

72. Ventricular Tachycardia

73. Prolonged QT
QT > 450 ms
Inferior and anterolateral ischemia

74. Second Degree Heart Block, Mobitz Type II
PR interval fixed, QRS dropped intermittently

75. Acute Pulmonary Embolism
SIQIIITIII in 10-15%
T-wave inversions, especially occurring in
inferior and anteroseptal simultaneously
RAD

76. Wolff-Parkinson-White Syndrome
Short PR interval <0.12 sec
Prolonged QRS >0.10 sec
Delta wave
Can simulate ventricular hypertrophy, BBB and previous MI

77. Hypokalemia
U waves
Can also see PVCs, ST depression, small T waves

82. Question 1
 What is the rate, rhythm and axis?
 Any other abnormalities?

83. Question 2
What is the rate, rhythm and axis?
Any other abnormalities?

84. Question 3
What is the rate, rhythm and axis?
Any other abnormalities?

85. Question 4
What is the rate, rhythm and axis?
Any other abnormalities?
How would you manage this patient?

86. Question 5
What is the rate, rhythm and axis?
What is the main problem with the patient?

88. Take home messages
 Remember your system
 See lots
 Comment least

89. Thank You
Any Questions?