Introduction to basic ECG interpretation

1. Basic ECG Interpretation in the ED

2. Learning Objectives.
• Interpret a basic 12 lead ECG.
• Recognize common cardiac arrhythmia's
• Recognize STEMI’s and STEMI equivalents.
• Recognize myocardial ischemia.
• Recognize common heart blocks.

4. 12 Lead ECG – Standard Position
4 Limb Leads
•Right Arm & Leg
•Left Arm and Leg
6 Chest Leads
•Placement from 4th
intercostal space to
the 5th intercostal
space laterally

6. 12 Lead ECG
Posterior
Leads
• Useful in the diagnosis of posterior infarcts
• 3 extra leads on the posterior chest
• V7– 9
• V7 (left posterior axillary line)
• V8 (tip of scapula)
• V9 (left paraspinal region)

8. ECG
Interpretation
• Standard paper speed is 25
mm/sec
• 1 small square equals 0.04
seconds
• Rough estimation of heart rate
from rhythm strip
• 300 bpm divided by the
number of large squares

9. Components of the ECG
Complex
• P wave
• QRS Complex
• T wave
• PR Interval
• ST Segment
• QT Interval

11. P Wave
Atrial Contraction
• 2 -3 mm high
• 2 -3 small squares (duration)
• 0.06 – 0.12 seconds (duration)

12. PR Interval
Transit time from sinus node to the ventricles
• 3 – 5 small squares (duration)
• 0.012 – 0.20 seconds (duration)

13. QRS Complex
Ventricular depolarization / contraction
• 5 -30 mm height
• 1.5 – 2.5 square (duration)
• 0.06 – 0.10 seconds (duration)

14. QT Interval
• Distance from beginning of Q wave to the end of the T
wave
• Represents ventricular systole (activation and recovery)
• 9 – 11 small squares (duration)
• 350 – 450 ms (duration)

15. T Wave
Represents
ventricular
repolarization
T waves are
normally upright
in most leads
Exceptions
are aVR and
V1

16. Common
Cardiac
Arrhythmia's

17. Heart Rates
Normal Heart Rate (60 – 100 bpm)
Tachycardia (More than 100 bpm)
Bradycardia (Less than 60 bpm)

18. Sinus Rhythm
• Narrow complex, regular rhythm
• QRS complex follows every P wave

19. Sinus
Rhythm

20. Sinus Arrhythmia
• Narrow complex, irregular rhythm
• QRS complex follows every P wave
• Beat to beat variability of the QRS complex
from respiration

21. Sinus Arrhythmia

22. Atrial
Fibrillation
• Arrhythmia characterized by irregular beating of the atrial
chambers of the heart
• Irregularly irregular rhythm
• No discernable P wave activity
• Can present with rapid ventricular response or a controlled
ventricular response

23. Atrial
Fibrillation
(Disorganized
Atrial Activity)

25. Atrial
Fibrillation
Rapid
Ventricular
Response

26. Atrial
Fibrillation
Controlled
Response

27. Atrial Flutter
• Re-entry circuit within the right atrium
• Regularly regular rhythm
• No discernable P wave activity
• Presence of flutter waves (saw tooth pattern waves)

28. Atrial Flutter

29. Atrial Flutter

30. AVNRT
• AV Nodal Re-entrant Tachycardia
(commonly known as SVT)
• SVT (Supraventricular Tachycardia)
• Functional re-entry circuit within AV node
• Regular narrow complex tachycardia (140 –
280 bpm)

31. AVNRT

32. Ventricular
Tachycardia
• Rapid tachycardia arising from the ventricles
• Regular broad complex tachycardia
• Rate is greater than 120 bpm
• More than 3 wide QRS complexes in a row
• 2 types
• Monomorphic (same amplitude)
• Polymorphic (variable amplitude – also known as
“torsade's de pointes”)

33. Monomorphic
VT
Common Causes
• Ischemic Heart Disease
• Dilated Cardiomyopathy
• Hypertrophic Cardiomyopathy

34. Monomorphic
VT

35. Polymorphic VT
Common Causes
• Ischemia
• Drugs
• Prolongation of the QT Interval
• Electrolyte Disturbance (Hypokalemia)

36. Polymorphic
VT

37. Ventricular
Fibrillation
• Chaotic irregular
deflections of variable
amplitude
• No identifiable P waves,
QRS complexes or T
waves
• Rate variable between
150 – 500 per minute
• Amplitude decreases
with time (coarse to fine)

38. Ventricular Fibrillation

39. STEMI’s and STEMI Equivalents

40. How to measure ST Elevation & Depression
ST elevation and depression is measured from the J point.
This is the junction of the QRS complex and the ST segment.
Elevation or depression is measured from this point to the baseline.

41. ST Elevation
& Depression

42. Characteristics – Ischemic ST Elevation

43. Anterior
STEMI (V3-4
ST Elevation)

44. Inferior STEMI (II,III,aVF - ST Elevation)

45. Lateral STEMI (I,aVL,V5-6 - ST Elevation)

46. Posterior STEMI (ST Depression & Upright T Waves V1-3)

47. Posterior STEMI (Posterior V7-9 - ST Elevation)

48. De Winters Waves
• Anterior STEMI equivalent
• Associated with LAD occlusion
• Prominent symmetrical T waves in
precordial leads
• Upsloping ST depression in the
precordial leads

49. De Winters Waves

50. Wellen’s
Syndrome
• Biphasic or deeply inverted T waves in V2-3 with a history
of recent chest pain that has resolved.
• Highly specific for critical stenosis for the LAD (left anterior
descending artery).

51. Wellen’s Syndrome

52. Sgarbossa
Criteria
(Original)
• Allows diagnosis of infarction in presence of LBBB or paced
rhythm
• Concordant ST elevation > 1 mm in leads with positive QRS
complex (score of 5)
• Concordant ST depression > 1 mm in leads V1-3 (score of 3)
• Excessive discordant ST elevation in 1 lead as defined as
more than 5 mm in leads with negative QRS complex (score
of 2)
• Score > 3 (Sensitivity 36%, Specificity 90%)
• Use internet to check the criteria as difficult to remember

53. Sgarbossa
Criteria
(Original)

54. ST
Depression
(Ischemia)

55. ST Depression – Ischemia (V4-6)

56. ST Depression – Ischemia (II,III,aVF, V4-6)

57. Benign Early
Repolarization
• Normal variant, usually seen in younger patients
• ST segment elevation – elevated J point
• Notch at the end of the QRS complex
• ST segment is concave up
• Absence of reciprocal ST segment changes

58. Benign Early
Repolarization

59. Pericardial
Effusion
• Sinus tachycardia
• Low voltage
• Electrical alternans
• Alternating QRS complex height
• Heart swinging back and forward in fluid filled
pericardium
• Best seen in lateral leads (I, aVL, V4-6)

60. Low Voltage
(Electrical
impulses do not
travel through
fluid well)

61. Pericardial Effusion

62. Left
Ventricular
Hypertrophy
• Must have voltage and non-voltage criteria
• Voltage Criteria
• Sokolov – Lyon Criteria
• S wave depth in V1 and R wave height in V5 or 6
greater than 35 mm
• Non-voltage Criteria
• ST depression and T wave inversion in left sided leads
(II, III, aVF, V5-6)

63. Left Ventricular Hypertrophy

64. Common Heart Blocks

65. Left Bundle Branch
Block (LBBB)
• Prolonged QRS complex (more than 120
mS)
• Dominant S wave in V1
• Broad notched R wave

66. Left Bundle Branch Block (LBBB)

67. Right Bundle Branch
Block (RBBB)
• Prolonged QRS complex greater than 120
ms
• RSR pattern in V1-3 (M shaped pattern)

68. Right Bundle Block (RBBB)

69. First Degree
Heart Block
• Delay without interruption in conduction from atria to
ventricles
• Prolonged PR interval greater than 200 ms
• PR interval greater than 5 small squares

70. First Degree Heart Block

71. Second Degree
Heart Block
Mobitz 1
• Wenckebach Heart Block
• PR interval progressively increases
followed by a dropped QRS complex

72. Second Degree Block – Mobitz 1

73. Second Degree
Heart Block
Mobitz 2
Mobitz 2
• PR interval is fixed, but there are dropped beats
• Clarify by the number of dropped beats (2:1, 3:1)

74. Second Degree Heart Block – Mobitz 2

75. Third Degree
Heart Block
• Complete Heart Block
• AV dissociation
• P waves and QRS complexes and completely unrelated

76. Third Degree Heart Block

77. Revision Questions
• Describe the findings on the following
ECG’s
• The answer will be shown on the slide
following the ECG

79. ECG Number 1
• Irregularly Irregular Rhythm
• Narrow Complex Tachycardia (Rate – approximately 150 bpm)
• No P wave activity seen
• Diagnosis - Atrial Fibrillation

81. ECG Number 2
• P waves and QRS complexes with no relation between them
• AV dissociation
• Diagnosis - Complete (3rd Degree) Heart Block

83. ECG Number 3
• ST Elevation - Leads II, III, aVF
• Reciprocal ST Depression – Leads V1-2, 1, aVL
• Diagnosis - Inferior STEMI

85. ECG Number 4
• Chaotic irregular disorganized rhythm
• No P wave or QRS activity
• Diagnosis – Ventricular Fibrillation