This document provides an overview of basic ECG interpretation. It begins by describing the spatial orientation of the 12 lead ECG and how it relates to different areas of the heart. It then discusses normal cardiac conduction, including the roles of the sinoatrial node, atrioventricular node, bundle branches, and Purkinje fibers. Key intervals like the PR and QT intervals are also explained. Common rhythms are then summarized, focusing on identifying features like rate, regularity, and relationship between P waves and QRS complexes to determine if a rhythm is normal or abnormal.

1. BASIC ECG INTERPRETATION
Department of Cardiology
Yangon General Hospital

2. Spatial orientation of 12 lead ECG

3. Chest leads
 QRS complex in the V
leads
 Progression from lead
V1(predominantly d/w)
to lead V6 where
(predominantly u/w)
 The ‘ transition point ’,
where the R and S wave
are equal , indicates the
position of the
interventricular septum

4. The Cardiac Axis
 The cardiac axis is the
average direction of
spread of depolarization
as seen from the front and
is estimated from QRS
complex in leads I,II and
III

5. Normal axis
 QRS complex
predominantly upward
in leads I and II and III;
 Still normal if QRS
complex d/w in lead III
 Minor degrees of right
and left axis deviation
are within the normal
range

6. Right axis deviation
 QRS complex
predominantly d/w in
lead I
 If the right ventricle
become hypertrophied, it
will have more effect on
QRS complex than left
ventricle average
depolarization wave swing
towards right

7. Left axis deviation
 QRS complex
predominantly d/w in leads
II and III
 When the left ventricle
become hypertrophied ,it
exerts more influence on
QRS complex than Rt
ventricle, axis swing to the
left

8.  Inferior Changes in leads II, III and aVF
 Anteroseptal V1 V2 V3
 Anterolateral V4 V5 V6
 Extensive Anterior V1 to V6
 Lateral I, aVL
 Posterior Associated increase in height of
R and upright T wave in V1
(ST depression in V1-V2 )

10. Normal Cardiac Conduction
 Cardiac conduction results in
the mechanical beating of the
heart.
 Specific waves that appear on
an ECG correspond both to the
mechanical and the electrical
depolarization or repolarization
of a particular area of the
heart.

11. Cardiac Conduction: Cycle Initiation

12. Cardiac Conduction: P Wave

13. Cardiac Conduction: AV Node

14. Cardiac Conduction: Bundle Branches

15. Cardiac Conduction: Purkinje Fibers

16. Cardiac Conduction: QRS Complex

17. Cardiac Conduction: Plateau Phase

18. Cardiac Conduction: T-Wave

20. Label the ECG - Review
P – Wave: Atrial Depolarization.
• Can be positive, biphasic, negative.
QRS Complex: Ventricular Depolarization.
• Q – Wave: 1st negative deflection wave before R-Wave.
• R – Wave: The positive deflection wave.
• S – Wave: 1st negative deflection wave after R – wave.
T – Wave: Ventricular Repolarization.
• Can be positive, biphasic, negative.

21. One ECG period or one heartbeat
PR interval (containing P wave and PR segment)
QT interval (containing the QRS complex, ST segment and T wave)

22. Interval Measurement
 Time between waves is an important characteristic in
determining a normal heart rhythm (measured in
milliseconds).
 An interval outside of the normal duration can be an
indicator of heart problems.
 Two key intervals in particular aid
in the interpretation of ECGs.
1. PR interval: Normal is 120 –
200ms
2. QRS interval: Normal is 60 –
100ms

23. ECG tracing showing QT interval
From 12 – lead ECG printout , choose Lead II, V 5 or V 6
QT interval – from the beginning of the QRS complex to the end of
the T wave
Measure at least 3 successive beats, with the maximum interval
taken, in case these three beats differ

24. Reading ECG Squares
Intervals and Timing
Horizontal axis – time:
 Each small square = 40
ms
 Each block = 200 ms (5
ea. 40 ms squares)
Converting this to a rate in
bpm:
 1 min = 60,000 ms, so:
 60,000/ms = bpm
– 60,000/600ms = 100
bpm

25. Calculating Heart Rate
1) Measure Cycle Length (CL).
1) (# small boxes from R – R) (40ms) = CL .
2) Calculate HR
• 60,000/CL = “x” BPM
(20)(40ms) = 800ms
60,000/800 = 75 bpm
(25)(40ms) = 1000ms
60,000/1000 = 60 bpm
(12)(40ms) = 480ms
60,000/480 = 125 bpm

26. Rate – 6 second Rule
1) Count the # of complexes on a 6 second strip.
2) Multiply by 10 to get approx “bpm”
0 1 2 3 4 5 6 7
Approximately 70bpm

27. ECG Interpretations: Overview
 ECG interpretation can be simplified if approached
one step at a time.
 Understanding and practicing three basic steps will
aid in quickly and accurately identifying any given
rhythm.
 Step 1—Calculate the RATE of an ECG tracing
 Step 2—Determine the REGULARITY or irregularity of
a given ECG
 Step 3—Analyze the RHYTHM of a given ECG by
describing the relationship between the P waves and
QRS complexes

28. ECG Interpretation: RATE
 Rate generally refers to the ventricular rate or R-waves.
 Resting rate is typically 60 – 100 bpm.
 Focus is placed on the QRS complex.

29. ECG Interpretation: REGULARITY
 The consistency of the interval
between each QRS complex.
 PR intervals should remain
consistent.
 PR interval should be 120-200ms.
 The PR interval is the time from
beginning of the P-wave to the
beginning of the QRS complex.

30. ECG Interpretation: RHYTHM
 PR ratio is the number of P-waves compared to
QRS complexes.
 Every P-wave should have an associated QRS
complex.

31. Knowledge Checkpoint
Is the rate normal or abnormal?

32. Normal Sinus Rhythm
Rate 60-100bpm
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Normal

33. Sinus Bradycardia
Rate Less than 60bpm
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval
Normal, gradually lengthens with HR
decrease
QRS Width Normal

34. Sinus Tachycardia
Rate Greater than 100bpm, Gradual onset
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval Normal, gradually shortens with HR increase
QRS Width Normal

35. Sinus Arrhythmia
Rate 60-100bpm
P-P Regularity Irregular
R-R Regularity Irregular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Normal

36. Sinus Pause/Arrest
Rate Varies
P-P Regularity Irregular
R-R Regularity Irregular
P wave Present, except during pause
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Normal

37. Sinus Node Exit Block
Rate Varies
P-P Regularity Irregular
R-R Regularity Irregular
P wave Present, except during dropped beats
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Normal

38. Sinus Rhythm w/ PAC
(Premature Atrial Contraction)
Rate Depends on underlying sinus rate
P-P Regularity Irregular
R-R Regularity Irregular
P wave Present, may be different morphology during PAC
P:QRS Ratio 1:1, associated
PR Interval Normal, varies during PAC
QRS Width Normal

39. Atrial Tachycardia
Rate 100-180bpm, Sudden onset
P-P Regularity Regular
R-R Regularity Regular
P wave Morphology will differ from sinus p-wave
P:QRS Ratio 1:1, associated
PR Interval Interval of ectopic focus will differ from sinus PR
QRS Width
Normal, but can develop aberrant (wide)
complexes

40. Multifocal Atrial Tachycardia
Rate Greater than 100bpm
P-P Regularity Irregularly irregular
R-R Regularity Irregularly irregular
P wave At least 3 different p-wave morphologies
P:QRS Ratio 1:1, associated
PR Interval Varies
QRS Width Normal

41. Atrial Flutter
Atrial Rate
Ventricular Rate
Atrial Rate commonly 250-350bpm
Ventricular Rate will vary with conduction
P-P Regularity Regular
R-R Regularity Usually regular, but may be variable
P wave “Saw-tooth” p-wave morphology
P:QRS Ratio Varies, can be 1:1, 2:1, 3:1, 4:1, etc.
PR Interval Varies
QRS Width Normal

42. Atrial Fibrillation
Rate Varies, ventricular response can be fast or slow
P-P Regularity Chaotic atrial activity
R-R Regularity Irregularly irregular
P wave No discernable p-waves
P:QRS Ratio None
PR Interval None
QRS Width
Normal, but can develop aberrant (wide)
complexes

43. Junctional Rhythm
Rate 40-60bpm
P-P Regularity None, or Regular if antegrade or retrograde
R-R Regularity Regular
P wave Variable (none, antegrade, or retrograde)
P:QRS Ratio None, or 1:1 if antegrade or retrograde
PR Interval None, short, or retrograde
QRS Width Normal

44. Accelerated Junctional Rhythm
Supraventricular Tachycardia (SVT)
Rate
60-100bpm (Accelerated Junctional Rhythm)
Greater than 100bpm (Supraventricular
Tachycardia)
P-P Regularity None, or Regular if antegrade or retrograde
R-R Regularity Regular
P wave Variable (none, antegrade, or retrograde)
P:QRS Ratio None, or 1:1 if antegrade or retrograde
PR Interval None, short, or retrograde
QRS Width Normal

45. Sinus Rhythm w/ PVC
(Premature Ventricular Contraction)
Rate Depends on underlying sinus rate
P-P Regularity Irregular
R-R Regularity Irregular
P wave No P-waves with the PVC
P:QRS Ratio No P-waves with the PVC
PR Interval None
QRS Width Wide complex (>/= 0.12sec).

46. Ventricular Rhythm
Rate 20-40bpm
P-P Regularity None
R-R Regularity Regular
P wave None
P:QRS Ratio None
PR Interval None
QRS Width Wide complex (>/= 0.12sec).

47. Accelerated Ventricular Rhythm
Rate 40-100bpm
P-P Regularity None
R-R Regularity Regular
P wave None
P:QRS Ratio None
PR Interval None
QRS Width Wide complex (>/= 0.12sec).

48. Ventricular Tachycardia
Rate 100-200bpm
P-P Regularity Variable
R-R Regularity Regular
P wave Dissociated atrial rate
P:QRS Ratio Variable
PR Interval None
QRS Width Wide complex (>/= 0.12sec).

49. Fast VT (Ventricular Flutter)
Rate 200-300bpm
P-P Regularity None
R-R Regularity Regular
P wave None
P:QRS Ratio None
PR Interval None
QRS Width Wide complex (>/= 0.12sec).

50. Polymorphic VT (Torsades)
Rate 200-250bpm
P-P Regularity None
R-R Regularity Irregular
P wave None
P:QRS Ratio None
PR Interval None
QRS Width Variable with wide complexes

51. Ventricular Fibrillation
Rate Indeterminate
P-P Regularity None
R-R Regularity Chaotic Rhythm
P wave None
P:QRS Ratio None
PR Interval None
QRS Width None

52. Sinus Rhythm
w/ 1st Degree AV Block
Rate Depends on underlying rhythm
P-P Regularity Regular
R-R Regularity Regular
P wave Present, Normal
P:QRS Ratio 1:1, associated
PR Interval Prolonged, > 0.20sec
QRS Width Normal

53. Sinus Rhythm
w/ 2nd Degree AV Block Type I (Wenckebach)
Rate Depends on underlying rhythm
P-P Regularity Regular
R-R Regularity Regularly irregular
P wave Present
P:QRS Ratio Variable; 2:1, 3:2, 4:3, etc
PR Interval Variable, gradually lengthens until dropped
QRS Width Normal

54. Sinus Rhythm
w/ 2nd Degree AV Block Type II
Rate Depends on underlying rhythm
P-P Regularity Regular
R-R Regularity Regularly irregular
P wave Present
P:QRS Ratio Variable; 2:1, 3:2, 4:3, etc
PR Interval Normal for conducted beats
QRS Width Normal

55. Sinus Rhythm
w/ 3rd Degree AV Block (Complete Heart Block)
Atrial Rate
Ventricular Rate
Atrial rate is the underlying rhythm (i.e, Sinus, Atrial Fib,
etc.)Ventricular rate is from the dissociated escape rhythm
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio Variable, dissociated
PR Interval Variable, No pattern
QRS Width Normal (Junctional escape rhythm)
Wide (Ventricular escape rhythm)

56. Sinus Rhythm w/ BBB
(Bundle Branch Block)
Rate Depends on the underlying sinus rhythm
P-P Regularity Regular
R-R Regularity Regular
P wave Present
P:QRS Ratio 1:1, associated
PR Interval Normal
QRS Width Wide (>0.12ms)

57. Atrial Fibrillation with BBB
(Bundle Branch Block)
Rate Depends on the underlying Atrial Fibrillation,
Ventricular rate can be fast or slow.
P-P Regularity Chaotic atrial activity
R-R Regularity Irregularly irregular
P wave Present
P:QRS Ratio None
PR Interval None
QRS Width Wide (>0.12ms)

58. Knowledge Checkpoint
Identify the Rhythm:
A.Ventricular Tachycardia
B.Sinus Bradycardia
C.Complete Heart Block
D.Atrial Fibrillation
E.Ventricular Fibrillation

59. Knowledge Checkpoint
Identify the Rhythm:
A.Ventricular Tachycardia
B.Sinus Bradycardia
C.Complete Heart Block
D.Atrial Fibrillation
E.Ventricular Fibrillation

60. Knowledge Checkpoint
Identify the Rhythm:
A.Ventricular Tachycardia
B.Sinus Bradycardia
C.Complete Heart Block
D.Atrial Fibrillation
E.Ventricular Fibrillation

61. Knowledge Checkpoint
Identify the Rhythm:
A.Ventricular Tachycardia
B.Sinus Bradycardia
C.Complete Heart Block
D.Atrial Fibrillation
E.Ventricular Fibrillation

62. The End