1. How to read ECG

2. ECG
• Representation of Electrical activity of
heart

4. ECG Leads
• 12 lead ECG
• 6 limb leads: Lead I, II, III
aVL, aVR, aVF
• 6 Chest Leads: V1, V2,V3, V4, V5, V6

6. ECG paper
Speed 25mm/s
• 1 large square= 5 small square [5mm]
Voltage
• 10mm =1mV

9. Appearance of waves
• Positive deflection [upward]
• If electrical impulses flowing towards
that lead
• Negative deflection [downward]
• If electrical impulses flowing away from
that lead

15. Origin of waves

16. P wave Atrial depolarization
PR interval Atrial depolarization to start of
ventricular depolarization
QRS complex Ventricular depolarization
T wave Ventricular repolarization
QT interval Ventricular depolarization &
repolarization
U wave ? Interventricular septal
repolarization

17. Systematic approach
• The following 14 points
should be analyzed
carefully in every ECG:
• Standardization
• Heart rate
• Rhythm
• P waves
• PR interval
• QRS voltages
• QRS interval
• QT interval
• Mean QRS axis
• Precordial R-wave
progression
• Abnormal Q waves
• ST segments
• T waves
• U waves

18. Standardization

19. Heart Rate
• 1500/RR

21. •If HR is irregular
Count no. of QRS complexes in 30 large squares=
6 sec
Multiply it with 10
HR [per min]

22. Rate calculation
• Memorize the number sequence: 300,
150, 100, 75, 60, 50

23. • ECG machines: print out HR
• DO NOT RELY ON IT!!!!
• Always Calculate yourself.
• Bradycardia: <60/min
• Tachycardia: >100/min

24. Rhythm
• Rhythm strip: prolonged recording of
Lead II
• Sinus rhythm ?
• Each QRS complex preceded by P wave
• Regular/ irregular?

25. •Regular
Sinus rhythm

26. Irregular

27. QRS AXIS
• Indicator of overall direction that wave
of depolarization takes when passing
through ventricles
• Also called ANGLE
• Measured
• in degrees

28. • Photo

31. • Right axis deviation [RAD]
• Beyond +90°
• Left Axis Deviation [LAD]
• Beyond -30°

34. Method 1
• Most precise method
• Use of vectors
• Measure overall height of QRS in lead I
& aVF
• Plot in graph paper
• Measure the ANGLE of vector

38. Method 2
• Quick method
• Identify limb lead in which QRS complex
is isoelectric
• [with equal positive & negative
deflection]
• Implies: electric flow is at Right angle to
this lead

40. Method 3
• For quick assessment
• Look at QRS complexes in lead I & II

41. • Predominantly
positive QRS in
lead I
• Axis between
-90 to +90
• Excludes RAD

42. • Predominantly
positive QRS in
lead II 
• Axis between
-30 to +150
• Excludes LAD

43. Lead I Lead II Cardiac Axis
QRS Positive QRS Positive Normal Axis
QRS Positive QRS Negative Left Axis
Deviation
QRS Negative QRS Positive Right Axis
Deviation

44. • LAD
• WPW syndrome
• LBBB
• Inferior wall MI
• RAD
• RVH
• WPW syndrome
• Anterolateral MI
• Dextrocardia

45. P wave
• Present or not?
• Sinus rhythm
• If completely absent
•Atrial Fibrillation
•Hyperkalemia
• If intermittently absent
•Sinus arrest

48. • Inverted P waves?
• Incorrect positioned electrodes
• Dextrocardia
• Abnormal atrial depolarization

49. • Height of P waves
• > 2.5 mm: tall
• Indicative of Right Atrial enlargement
• P Pulmonale

51. P PULMONALE
P MITRALE

52. • Width of P waves
• >2mm width: abnormal
• Bifid P wave
• Indicates Left Atrial enlargement
• P Mitrale

55. PR Interval
• From start of P wave to start of R wave
• Normally
• Not <3 small squares
• Not > 5 small squares
• Consistent

56. Short PR Interval
• AV junctional rhythm
• WPW syndrome
• Lown –Ganong-Levine syndrome

57. Long PR Interval
• Denotes delay in conduction through AV
node
• First Degree Block
• PR prolonged, constant

59. Second degree Block
• Mobitz Type I
• PR progressively increase until one P
wave fails to produce QRS complex

61. • Mobitz Type II
• PR interval normal & fixed,
• But occasional P waves fail to produce
QRS

63. • Third Degree Block [Complete AV Block]
• No relationship between P waves & QRS
complex

64. • 2:1 Block
• Alternate P waves are not followed by
QRS complex

65. Q WAVE
• First negative deflection in QRS complex
• ? Pathological Q waves
• If
• >2 small squares deep
• >1 small square wide
• >25% of height of the following R wave
in depth

66. QRS complex
• Appearance of QRS Complex vary from
lead to lead

67. • Width: Narrow/ wide
• Wide QRS:
• > 3 small squares
• Bundle branch block
• Ventricular arrhythmia

68. • Size of QRS complex
• Small:
• Pericardial effusion
• ?incorrect calibration

69. • Big QRS complex
• Ventricular hypertrophy: R/L
• WPW syndrome

70. Progression of R wave
• V1: small R wave , large S wave,
• Gradually R wave increases, S wave
decreases
• V6: small Q wave, large R wave
• V3 and V4 : located midway between V1
and V6, QRS complex nearly isoelectric
in one of these leads

71. Progression of R wave

72. Left ventricular Hypertrophy
• R Wave in V5 or V6 >25mm
• S Wave in V1 or V2 > 25mm
• Sum of R wave in V5 Or V6 & S wave in
V1 or V2 >35mm

74. LVH

75. Right Ventricular Hypertrophy
• Right axis deviation
• Deep S Waves in leads V5 & V6
• R>S in V1
• RBBB

78. RBBB
• Right Bundle Branch Block
• Broad QRS complex
• Small r wave in V1, small Q wave in V6
• S wave in V1, R wave in V6
• R‟ wave in V1, S wave in V6

81. LBBB
• Left Bundle Branch Block
• Broad QRS
• Small Q wave in V1, Small r wave in V6
• R wave in V1, S wave in V6
• S wave in V1, R‟ wave in V6

84. • “WILLIAM MORROW”
• William: „W‟ in V1 & „M‟ in V6: LBBB
• Morrow: „M‟ in V1 & „W‟ in V6: RBBB

86. • LBBB
• Ischemic Heart
Disease
• Cardiomyopathy
• LVH
• Fibrosis
• RBBB
• Ischemic heart
disease
• Cardiomyopathy
• ASD
• Massive pulmonary
embolism

87. ST Segment
• From end of S wave to start of T Wave
• Normally: Isoelectric
• ? Depressed/ elevated

90. • Elevated ST segment
• Acute MI
• Prinzmetal’s angina
• Pericarditis
• LV aneurysm
• High take off

96. • Depressed ST segment
• Myocardial ischemia
• Posterior MI
• Ventricular hypertrophy with ‘Strain’
• Drugs: Digoxin

98. Ventricular Hypertrophy with
“strain” pattern
• Tall R waves
• Deep S waves
• ST segment depression
• T wave inversion

100. T Wave

101. T wave
• Inverted?
• Normal in aVR
• V1,V2, III
• Size
• Normal: not > ½ size of preceeding
QRS complex
• Too small?
• Too large?

102. Tall T waves
• Hyperkalemia
• Acute MI

105. Too small T Waves
• Hypokalemia
• Pericardial effusion
• hypothyroidism

106. Inverted T waves
• Normal in few leads: aVR, V1, V2, III
• MI
• Myocardial ischemia
• Ventricular hypertrophy with “strain”
• Digoxin toxicity

108. QT Interval
• From start of QRS complex to end of T
wave
• Varies with HR

109. Corrected QT interval
• QTC
• QTC =QT/√RR
• Normal: 0.35-0.43 sec

110. Prolonged QTc
• If ≥0.44 sec
• Hypocalcemia
• Acute myocarditis
• Torsades de pointes

111. U waves
• Mostly in anterior chest leads
• Difficult to identify clearly

113. • Prominent U Waves
• Hypoklemia
• Hypercalcemia
• Hyperthyroidism

114. Common ECG Problems

117. ACUTE MI

119. Ischemia

120. HYPERKALEMIA

121. LVH WITH STRAIN

122. PERICARDITIS