ecg made easy for undergraduate students

1. Basics of Electrocardiography
Dr.Dheeraj kumar MD

2. Outline
1. Review of the conduction system
2. ECG leads and recording
3. ECG waveforms and intervals
4. Normal ECG and its variants
5. Interpretation and reporting of an ECG

4. What is an ECG?
The electrocardiogram (ECG) is a representation of
the electrical events of the cardiac cycle.
Each event has a distinctive waveform, the study of
which can lead to greater insight into a patient’s
cardiac pathophysiology.

5. Useful in diagnosis of…
• Cardiac Arrhythmias
• Myocardial ischemia and infarction
• Pericarditis
• Chamber hypertrophy
• Electrolyte disturbances
• Drug effects and toxicity

6. Waveforms and Intervals

7. Recording an ECG

8. BasicsBasics
ECG graphs:ECG graphs:
– 1 mm squares1 mm squares
– 5 mm squares5 mm squares
Paper Speed:Paper Speed:
– 25 mm/sec standard25 mm/sec standard
Voltage Calibration:Voltage Calibration:
– 10 mm/mV standard10 mm/mV standard

9. ECG Paper: DimensionsECG Paper: Dimensions
5 mm
1 mm
0.1 mV
0.04 sec
0.2 sec
Speed = rate
Voltage
~Mass

10. ECG LeadsLeads are electrodes which measure the difference
in electrical potential between either:
1. Two different points on the body (bipolar1. Two different points on the body (bipolar
leads)leads)
2. One point on the body and a virtual reference2. One point on the body and a virtual reference
point with zero electrical potential, located inpoint with zero electrical potential, located in
the center of the heart (unipolar leads)the center of the heart (unipolar leads)

11. +-
RA
RA
LL
+
+
--
LA
LL
LA
LEAD II
LEAD I
LEAD III
Remember, the RL
is always the ground
• By changing the
arrangement of which
arms or legs are
positive or negative,
three unipolar leads
(I, II & III ) can be
derived giving three
"pictures" of the
heart's electrical
activity from 3 angles.
The Concept of a “Lead”
Leads I, II, and III
I
II III

12. ECG Leads
The standard ECG has 12 leads: 3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents the viewpoint fromThe axis of a particular lead represents the viewpoint from
which it looks at the heart.which it looks at the heart.

13. Einthoven’s triangle

14. Standard Limb Leads

15. Standard Limb Leads

16. Augmented Limb Leads

17. All Limb Leads

18. Precordial Leads

19. Precordial Leads

20. Summary of Leads
Limb LeadsLimb Leads Precordial LeadsPrecordial Leads
BipolarBipolar I, II, IIII, II, III
(standard limb leads)(standard limb leads)
--
UnipolarUnipolar aVR, aVL, aVFaVR, aVL, aVF
(augmented limb leads)(augmented limb leads)
VV11-V-V66

22. Hexaxial Reference system in frontal
plane

23. Arrangement of Leads on the EKG

24. Anatomic Groups
(Septum)

25. Anatomic Groups
(Anterior Wall)

26. Anatomic Groups
(Lateral Wall)

27. Anatomic Groups
(Inferior Wall)

28. Anatomic Groups
(Summary)

29. Localising the arterial territoryLocalising the arterial territory
Inferior
II, III, aVF
Lateral
I, AVL,
V5-V6
Anterior /
Septal
V1-V4

30. Interpretation of an ECG

31. Steps involved
• Heart Rate
• Rhythm
• Axis
• Wave morphology
• Intervals and segments analysis
• Chamber enlargement
• Specific changes

32. Determining the Heart Rate
• Rule of 300
• 10 Second Rule

33. Rule of 300
Take the number of “big boxes” between
neighboring QRS complexes, and divide this into
300. The result will be approximately equal to the
rate
Although fast, this method only works for regular
rhythms.

34. The Rule of 300It may be easiest to memorize the following table:
# of big# of big
boxesboxes
RateRate
11 300300
22 150150
33 100100
44 7575
55 6060
66 5050

35. 10 Second Rule
As most ECGs record 10 seconds of rhythm per
page, one can simply count the number of beats
present on the ECG and multiply by 6 to get the
number of beats per 60 seconds.
This method works well for irregular rhythms.

36. The QRS Axis
The QRS axis represents the net overall direction
of the heart’s electrical activity.
Abnormalities of axis can hint at:
Ventricular enlargement
Conduction blocks (i.e. hemiblocks)

37. The QRS AxisBy near-consensus, the
normal QRS axis is defined
as ranging from -30° to +90°.
-30° to -90° is referred to as a
left axis deviation (LAD)
+90° to +180° is referred to as
a right axis deviation (RAD)

38. Determining the Axis
• The Quadrant Approach
• The Equiphasic Approach

39. Determining the Axis
Predominantly
Positive
Predominantly
Negative
Equiphasic

40. The Quadrant Approach1. Examine the QRS complex in leads I and aVF to determine
if they are predominantly positive or predominantly
negative. The combination should place the axis into one
of the 4 quadrants below.

41. The Quadrant Approach2. In the event that LAD is present, examine lead II to
determine if this deviation is pathologic. If the QRS in II is
predominantly positive, the LAD is non-pathologic (in other
words, the axis is normal). If it is predominantly negative, it
is pathologic.

43. Example 1
Negative in I, positive in aVF  RAD

44. Example 2
Positive in I, negative in aVF  Predominantly positive in II 
Normal Axis (non-pathologic LAD)

45. The Equiphasic Approach1. Determine which lead contains the most equiphasic
QRS complex.
2. The overall QRS axis is perpendicular to the axis of this
particular lead
3. Examine the QRS complex in whichever lead lies 90°
away from the lead identified in step 1
4. If the QRS complex in this second lead is
predominantly positive, than the axis of this lead is
approximately the same as the net QRS axis
5. If the QRS complex is predominantly negative, than
the net QRS axis lies 180° from the axis of this lead.

46. -90°
-60°
-30°
0°
aVL
I
30°
60°
aVR
II
90°
120°
III
150°
180°
-150°
-120°
aVF
Marked RAD
LAD
RAD
Normal Axis
-30° to +100°

47. Example 1
Equiphasic in aVF  Predominantly positive in I  QRS axis ≈ 0°

48. Example 2
Equiphasic in II  Predominantly negative in aVL  QRS axis ≈
+150°

49. Using leads I, II, III
LEAD 1LEAD 1 LEAD 2LEAD 2 LEAD 3LEAD 3
NormalNormal UPRIGHTUPRIGHT UPRIGHTUPRIGHT UPRIGHTUPRIGHT
PhysiologicaPhysiologica
l Left Axisl Left Axis
UPRIGHTUPRIGHT
UPRIGHT /UPRIGHT /
BIPHASICBIPHASIC
NEGATIVENEGATIVE
PathologicalPathological
Left AxisLeft Axis
UPRIGHTUPRIGHT NEGATIVENEGATIVE NEGATIVENEGATIVE
Right AxisRight Axis NEGATIVENEGATIVE
UPRIGHTUPRIGHT
BIPHASICBIPHASIC
NEGATIVENEGATIVE
UPRIGHTUPRIGHT
ExtremeExtreme
Right AxisRight Axis
NEGATIVENEGATIVE NEGATIVENEGATIVE NEGATIVENEGATIVE

50. Common causes of LAD• May be normal in the elderly and very obese
• Due to high diaphragm during pregnancy,
ascites, or ABD tumors
• Inferior wall MI
• Left Anterior Hemiblock
• Left Bundle Branch Block
• WPW Syndrome
• Congenital Lesions
• RV Pacer or RV ectopic rhythms
• Emphysema

51. Common causes of RAD
• Normal variant
• Right Ventricular Hypertrophy
• Anterior MI
• Right Bundle Branch Block
• Left Posterior Hemiblock
• Left Ventricular ectopic rhythms or pacing
• WPW Syndrome

52. Normal Axis
Normal Axis = -30 to +120
RAD =+120 to +180
LAD = -30 to -90
• LAD
• Anterior Hemiblock
• Inferior MI
• WPW – right pathway
• Emphysema
• RAD
• Children, thin adults
• RVH
• Chronic Lung Disease
• WPW – left pathway
• Pulmonary emboli
• Posterior Hemiblock
• No Man’s Land
• Emphysema
• Hyperkalemia
• Lead Transposition
• V-Tach
No Man’s Land Axis
= -90 to +- 180

53. The Normal ECG

54. Normal Sinus Rhythm
• Originates in the sinus node
• Rate between 60 and 100 beats per min
• P wave axis of +45 to +65 degrees, ie. Tallest p
waves in Lead II
• Monomorphic P waves
• Normal PR interval of 120 to 200 msec
• Normal relationship between P and QRS
• Some sinus arrhythmia is normal

55. Sinus ArrhythmiaSinus Arrhythmia
ECG Characteristics: Presence of sinus P waves
Variation of the PP interval which cannot be
attributed to either SA nodal block or PACs
When the variations in PP interval occur in phase with respiration, this is
considered to be a normal variant. When they are unrelated to respiration,
they may be caused by the same etiologies leading to sinus bradycardia.

56. Normal P wave
• Atrial depolarisation
• Duration 80 to 100 msec
• Maximum amplitude 2.5 mm
• Axis +45 to +65
• Biphasic in lead V1
• Terminal deflection should not exceed 1 mm in
depth and 0.03 sec in duration

57. Normal QRS complex
• Completely negative in lead aVR , maximum
positivity in lead II
• rS in right oriented leads and qR in left oriented
leads (septal vector)
• Transition zone commonly in V3-V4
• RV5 > RV6 normally
• Normal duration 50-110 msec, not more than
120 msec
• Physiological q wave not > 0.03 sec

58. Normal T wave
• Same direction as the preceding QRS complex
• Blunt apex with asymmetric limbs
• Height < 5mm in limb leads and <10 mm in
precordial leads
• Smooth contours
• May be tall in athletes

59. ST segment
• Merges smoothly with the proximal limb of the T
wave
• Does not ‘hug’ the baseline
• No true horizontality

60. Normal u wave
• Best seen in midprecordial leads
• Height < 10% of preceding T wave
• Isoelectric in lead aVL (useful to measure QTc)
• Rarely exceeds 1 mm in amplitude
• May be tall in athletes (2mm)

61. QT interval
• Normally corrected for heart rate
• Bazett’s formula
• Normal 350 to 430 msec
• With a normal heart rate (60 to 100), the QT
interval should not exceed half of the R-R
interval roughly

62. Normal Variants in the ECG

63. • Sinus arrhythmia
• Persistent juvenile pattern
• Early repolarisation syndrome
• Non specific T wave changes

64. Features of ERPS• Vagotonia / athletes’ heart
• Prominent J point
• Concave upwards, minimally elevated ST segments
• Tall symmetrical T waves
• Prominent q waves in left leads
• Tall R waves in left oriented leads
• Prominent u waves
• Rapid precordial transition
• Sinus bradycardia
Early Recognition Prevents Streptokinase infusion !

65. Normal T wave changes
• Inverted in V1-V3: Persistent juvenile pattern
• Inverted normally in
 Anxiety
 Hyperventilation
 Orthostatic
 Postprandial

66. Reporting an ECG

67. 1. Patient Details
“ Whose ECG is it ?!”

68. 2. Standardisation and lead
placement
“Is it properly taken ?”
Look for technical Dextrocardia
LV or RV leads?

69. 3. Analysis of Rate, Rhythm and
Axis

70. 4. Segment and wave form
analysis

71. 5. Chamber enlargements

72. 6. Other specific points of
interest based on case history

73. Final Impression
“ Does the ECG correlate with the
clinical scenario ?”

74. Treat the patient and not the
ECG !

75. Thank you !