The document discusses the basics of electrocardiography (ECG), including the 12-lead ECG system and cardiac rhythms. It explains that a standard ECG uses 6 limb leads (I, II, III, aVR, aVL, aVF) and 6 precordial/chest leads (V1-V6). It describes Einthoven's triangle and law. It discusses normal sinus rhythm, cardiac intervals, axis determination, hypertrophy, ischemia, blocks, arrhythmias, and bundle branch blocks. Key points are made about rate, regularity, P waves, PR interval, and QRS duration for interpreting rhythms.

1. E.C. G.- 2
DR. MANISHA GUPTA
PROF. & HOD
PHYSIOLOGY

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Let us Identify the
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3. • Standard ECG is recorded in 12 leads
• Six Limb leads – L1, L2, L3, aVR, aVL, aVF
• L1, L2 and L3 are called bipolar leads
• L1 between LA and RA
• L2 between LF and RA
• L3 between LF and LA
• aVR, aVL, aVF are called unipolar leads
• aVR – from Right Arm Positive
• aVL – from Left Arm Positive
• aVF – from Left Foot Positive
• Six Chest Leads – V1 V2 V3 V4 V5 and V6
ECG Bipolar Limb Leads

4. • Limb Leads
– I
– II
– III
– AVR
– AVL
– AVF
• Chest Leads or
precordial leads
– V1
– V2
– V3
– V4
– V5
– V6

5. +
+ +
- - -
ECG Bipolar Limb Leads
R L
F
R
F
L

6. Einthoven's triangle
• Einthoven's triangle is an imaginary formation
of three limb leads in a triangle used in
electrocardiography, formed by the two
shoulders and the pubis. The shape forms an
inverted equilateral triangle with the heart at
the center with current source that produces
zero potential at the end points of an
equilateral triangle when the voltages are
summed.

8. Einthoven's law
• The sum of potentials in lead I and lead
III equals to the potential in lead II
II = I + III.

9. ECG Augmented Limb Leads

10. 10
ECG Chest
Leads

11. Precardial (chest) Lead Position
• V1 Fourth ICS, right sternal border
• V2 Fourth ICS, left sternal border
• V3 Equidistant between V2 and V4
• V4 Fifth ICS, left Mid clavicular
Line
• V5 Fifth ICS Left anterior axillary
line
• V6 Fifth ICS Left mid axillary line
ECG Chest
Leads

12. Precordial Leads

13. Precordial Leads

14. ECG Precordial Leads

16. Cardiac vector or cardiac axis
• Since the standard limb leads I,II,III are
recorded of the potential difference between
two points, therefore, deflection in each lead
at any moment indicate the magnitude and
direction in the axis of the electromotive force
generated in the heart. This is called the
cardiac vector or cardiac axis

18. Cardiac vector or cardiac axis
• The electrical axis of the heart is plotted
using the average QRS deflection in any
two classical limb leads. This is called
mean QRS vector
• the average QRS deflection is the
distance equal to the height of ‘R’ wave
minus the height of the largest negative
deflection in the QRS complex

19. Determining the Axis
Predominantly
Positive
Predominantly
Negative
Equiphasic

20. Cardiac vector or cardiac axis
• The normal direction of QRS vector is -30 degree
to +110 degree
• -30 to +30 is normal left axis deviation(LAD). It
represent horizontal position of the heart
• +75 to +110 is normal right axis deviation(RAD).
It represent vertical position of the heart
• +30 to +75 represents oblique position of the
heart

21. Cardiac vector or cardiac axis
• If the calculated axis falls to the left of -30 or to
the right of +110, then it is considered to left or
right axis deviation.
• The following conditions in which cardiac axis
becomes abnormal are:
Abnormal RAD:
Right bundle branch block
Right ventricular hypertrophy
Posterior or inferior myocardial infarction (MI)

22. Cardiac vector or cardiac axis
Abnormal LAD:
Left bundle branch block
Left ventricular hypertrophy
Anterio- lateral MI

23. Mean QRS Axis Calculation
Lead II

24. Short PR Interval
• WPW (Wolff-
Parkinson-White)
Syndrome
• Accessory pathway
(Bundle of Kent)
allows early activation
of the ventricle (delta
wave and short PR
interval)

25. Long PR Interval
• First degree Heart Block

26. QRS in LVH & RVH

27. Conditions with Tall R in V1

28. Left Ventricular Hypertrophy
• Sokolow &Lyon Criteria
• Sin V1+ R in V5 or V6 > 35 mm
• An R wave of 11 to 13 mm (1.1 to 1.3 mV)
or more in lead aVL is another sign of
LVH

30. ST Segment
• ST Segment is flat (isoelectric)
• Elevation or depression of ST segment by 1
mm or more
• “J” (Junction) point is the point between
QRS and ST segment

31. Variable Shapes Of ST Segment
Elevations in AMI
Goldberger AL. Goldberger: Clinical Electrocardiography:ASimplifiedApproach. 7th
ed: Mosby Elsevier; 2006.

32. QT interval
1. Total duration of Depolarization and
Repolarization
2. QT interval decreases when heart rate increases
3. For HR = 70 bpm, QT<0.40 sec.
4. QT interval should be 0.35 0.45 s,
5. Should not be more than half of the interval
between adjacent R waves (RR interval).

33. QT Interval

34. U wave
• U wave related to afterdepolarizations which
follow repolarization
• U waves are small, round, symmetrical and
positive in lead II, with amplitude < 2 mm
• U wave direction is the same as T wave
• More prominent at slow heart rates

35. Classification
• Sinus Bradycardia
• Junctional Rhythm
• SinoAtrial Block
• Atrioventricular block

36. Sinus Bradycardia

37. Junctional Rhythm

38. SinoAtrial Block
• Initially whole heart beat is lost after an
interval of approx. two cardiac cycle, the heart
resumes its normal action as some new pace
maker other than SAN takes over

39. A-V NODAL BLOCK
• This produces disturbance of conduction
between atria and ventricle.
• It is of two types
1)incomplete heart block : it is of two types
a) First degree heart block
b) Second degree heart block
2) Complete or lllrd degree heart block

40. Complete or lllrd degree heart block
• It is due to complete interruption of
conduction between atria and ventricles.
Therefore ventricles beat with a slower rate
(45beats) and independent of rhythm of SAN
called as idio-ventricular rhythm.

41. Stokes adam syndrome

42. First Degree AV Block
• Delay in the conduction through the conducting
system
• Prolong P-R interval
• All P waves are followed by QRS
• Associated with :AC Rheumati Carditis, Digitalis,
Beta Blocker, excessive vagal tone, ischemia,
intrinsic disease in the AVjunction or bundle
branch system.

43. Second Degree AV Block
• Intermittent failure of AV conduction
• Impulse blocked byAV node
• Types:
• Mobitz type 1 (Wenckebach Phenomenon)
• Mobitz type 2

44. The 3 rules of "classic AV Wenckebach"
2. Decreasing RR intervals until pause;
2. Pause is less than preceding 2 RR intervals
3. RR interval after the pause is greater than RR prior to
pause.
Mobitz type 1 (Wenckebach Phenomenon)

45. Mobitz type 1 (Wenckebach
Phenomenon)

46. •Mobitz type 2
•Usually a sign of bilateral bundle branch disease.
•One of the branches should be completely blocked;
•most likely blocked in the right bundle
•P waves may blocked somewhere in the AV junction, the
His bundle.

47. Third Degree Heart Block
•CHB evidenced by the AV dissociation
•A junctional escape rhythm at 45 bpm.
•The PP intervals vary because of ventriculophasic sinus arrhythmia;

48. Third Degree Heart Block
3rd degree AV block with a left ventricular escape
rhythm, 'B' the right ventricular pacemaker rhythm is
shown.

49. Rhythm #6
70 bpm
regular
flutter waves
none
0.06 s
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation? Atrial Flutter

50. PSVT
• Deviation from NSR
– The heart rate suddenly speeds up, often
triggered by a PAC premature atrial
contractions (not seen here) and the P waves
are lost.

51. Ventricular Arrhythmias
• Ventricular Tachycardia
• Ventricular Fibrillation

52. Rhythm #8
160 bpm
regular
none
none
wide (> 0.12 sec)
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation? Ventricular Tachycardia

53. Ventricular Tachycardia
• Deviation from NSR
– Impulse is originating in the ventricles (no P
waves, wide QRS).

54. Rhythm #9
• none
• irregularly
irreg. none
• none
• wide, if
recognizable
• Rate?
• Regularity?
• P waves?
• PR interval?
• QRS duration?
Interpretation? Ventricular Fibrillation

55. Ventricular Fibrillation
• Deviation from NSR
– Completely abnormal.

56. Diagnosing a MI
To diagnose a myocardial infarction you need
to go beyond looking at a rhythm strip and
obtain a 12-Lead ECG.
Rhythm
Strip
12-Lead
ECG

57. ST Elevation
One wayto
diagnose an
acute MI is to
look for
elevation of the
ST segment.

58. STElevation (cont)
Elevation of the ST
segment (greater
than 1 small box) in
2 leads is consistent
with a myocardial
infarction.

59. Bundle Branch Blocks

60. Normal Impulse Conduction
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers

61. Bundle Branch Blocks
So, conduction in the
Bundle Branches and
Purkinje fibers are seen
as the QRS complex on
the ECG.
Therefore, a conduction
block of the Bundle
Branches would be
reflected as a change in
the QRS complex.
Right
BBB

62. Bundle Branch Blocks
With Bundle Branch Blocks you will see two changes
on the ECG.
– QRS complex widens (> 0.12sec).
– QRS morphology changes (varies depending on ECG lead,
and if it is a right vs. left bundle branch block).

63. Right Bundle Branch Blocks
What QRS morphology is characteristic?
For RBBB the wide QRS complex assumes a
unique, virtually diagnostic shape in those
leads overlying the right ventricle (V1 and V2).
V1
“Rabbit Ears”

64. RBBB

65. Left Bundle Branch Blocks
What QRS morphology is characteristic?
For LBBB the wide QRS complex assumes a
characteristic change in shape in those leads
opposite the left ventricle (right ventricular
leads - V1 and V2).
Broad,
deep S
waves
Normal

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