The document discusses the normal electrocardiogram (ECG). It explains that the ECG records and graphs the electrical activity of the heart over time. The conducting system of the heart initiates and coordinates the contractions of the cardiac chambers. The ECG is recorded using electrodes placed on the skin that detect voltage changes between electrode pairs, known as leads. There are 12 standard leads that provide different views of the heart's electrical activity. The ECG can be used to determine the heart rate and rhythm, detect abnormalities, diagnose conditions like myocardial infarction, and evaluate the cardiac axis.

1. TOPIC
NORMAL ELECTROCARDIOGRAM

2. 2
DIRECTION OF ELECTRICAL IMPULSE-
CONDUCTION & E.C.G. RECORDING
E.C.G.
RECORDING
FROM
SURFACE OF
CHEST
PACEMAKER
BODY FLUIDS
(VOLUME
CONDUCTOR)
HEART
(ELECTRIC GENERATOR)

3. 3
NORMAL SPREAD OF ELECTRICAL ACTIVITY IN THE HEART
SAN
AYN
ATRIAL ACTIVATION
SEPTAL ACTIVATION-
FROM LEFT TO RIGHT
ACTIVATION OF ANTEROSEPTAL
PROTION OF VENTRICLES
ACTIVATION OF POSTEROBASAL
PORTION OF VENTRICLES
ACTIVATION OF MAJOR PORTION OF
VENTRICLES- FROM ENDOCARDIAL
TO EPICARDIAL SURFACE
(1) (2)
(3)
(4)
(5)
R
L

4. • The conducting system of the heart consists of cardiac muscle cells and
conducting fibers (not nervous tissue) that are specialized for initiating
impulses and conducting them rapidly through the heart
• They initiate the normal cardiac cycle and coordinate the contractions of
cardiac chambers.
• Both atria contract together, as do the ventricles, but atrial contraction
occurs first.
• The conducting system provides the heart its automatic rhythmic beat.
• For the heart to pump efficiently and the systemic and pulmonary
circulations to operate in synchrony, the events in the cardiac cycle must be
coordinated

6. ELECTROCARDIOGRAM

7. WHAT IS ELECTROCARDIOGRAM ?
Recording (“gram”) of the electrical
activity (“electro”) generated by the cells
of the heart (“cardio”) that reaches the
body surface.

8. How is an ECG recorded ?
Recorded by a device called “Electrocardiograph” which is a
sophisticated “galvanometer” with a positive and negative pole
to which positive and negative body surface electrodes are
connected.
A pair of positive and negative surface electrodes constitute a
“lead” which detects and records changes in the electrical
potential both in ‘magnitude’ and ‘direction’ between its
electrodes

9. DEFINITIONS
Electrocardiogram
The record or graphical registration of
electrical activities of the heart, which
occur prior to the onset of mechanical
activities of heart.
Electrocardiograph
Instrument by which
electrical activities of heart
is recorded.
Electrocardiography
The technique by which electrical activities of
heart are studied.

10. 10
Basic Principle
When the net electromagnetic force is directed towards the positive pole, ‘an
upward deflection’ is recorded,
•While when it is directed towards the negative pole, ‘a net downward deflection’ is
recorded.
•When there is no electrical activity or the activity is perpendicular to the lead,  ‘no
deflection’ occurs and a flat baseline is recorded.
II
RE2
away from RE2 towards RE1
Negative-
Deflection
Positive-
Deflection
Direction of Excitation Wave
WAVE PATTERN DURING RECORDING : (RE = RECORDING ELECTRODE)
RE1
I

11. • These changes are recorded on a graph paper as a
plot of ‘Voltage’ on the Vertical axis and against
‘time’ on the Horizontal axis.
• Each lead provides a view of the electrical activity as
seen from its particular position on the surface.
• A combination of leads allows us to see the electrical
activity from various viewpoints.

12. The ECG Paper
Time
SPEED OF E.C.G. PAPER = 25 mm/sec.
(or, sometimes : 50 mm/sec, in severe tachycardia)
Voltage
(Amplitude)

13. Basic ECG deflections
(NORMAL ELECTROCARDIOGRAM)
Q-T interval
R-R
interval
P-P
interval
T-P
interval

14. NORMAL ELECTROCARDIOGRAM
1 Small Square (1 mm), horizontally, equals 0.04 sec.
1 Large Square equals 5 small squares, or 0.20 sec.
1 Small Square (1 mm), vertically, equals 0.1 mV
Speed of paper = 25 mm/sec.

15. Wave/segment From -To Causes Duration (sec) Amplitude (mV)
P wave _ Atrial depolarization 0.1 0.1
QRS complex Onset of Q wave to the end of S-
wave
Ventricular depolarization 0.08 to 0.10 Q=0.1-0.2
R=1
S=0.4
T wave _ Ventricular repolarization 0.2 0.2
U wave _ Repolarization of purkinje fibres 0.16 to 0.2 0.1-0.2
P-R interval Onset of P wave to onset of Q
wave
Atrial depolarization and conduction
through AV node
0.18 _
Q-T interval Onset of Q wave and end of T
wave
Ventricular depolarization and
ventricular repolarization
0.4 to 0.42 _
S-T interval End of S wave and onset of T
wave
Isoelectric 0.8 _

16. 16
VARIOUS E.C.G. – LEADS
TO
RECORD ELECTROCARDIOGRAMS

17. ECG Leads
• ECG is recorded by placing series of electrodes on the surface
of the body. These electrodes are connected to the ECG
machine and form E.C.G. leads.
• Electrodes are fixed on the limbs.
• Usually right arm , left arm, and left leg are chosen.
ECG leads ECG machine

18. Electrodes
Usually consist of a conducting gel, embedded
in the middle of a self-adhesive pad onto
which cables clip. Ten electrodes are used for
a 12-lead ECG.
Placement of
electrodes
The limb electrodes
RA - On the right arm, avoiding thick muscle
LA – On the left arm this time.
RL - On the right leg, lateral calf muscle
LL- On the left leg this time.
The 6 chest electrodes
V1 - Fourth intercostal space, right sternal
border.
V2 - Fourth intercostal space, left sternal
border.
V3 - Midway between V2 and V4.
V4 - Fifth intercostal space, left
midclavicular line.
V5 - Level with V4, left anterior axillary line.
V6 - Level with V4, left mid axillary line.

20. 20
ECG Leads
• Frontal Plane Leads :
(A) I,II,III – Standard Bipolar Limb Leads
(B) aVR, aVL, aVF – Augmented Unipolar Limb Leads
• Transverse Plane Leads :
(Horizontal)
(C) V1 to V6 – Unipolar Chest Leads (Precordial Leads)
Bipolar Leads : Both electrodes are active (exploring)
Unipolar Leads : One electrode is active (exploring) & other electrode
is passive (indifferent), kept at zero-potential.

21. 21
[A] STANDARD BIPOLAR LIMB LEADS : (Both electrodes are active or exploring)
[ Records : (VL – VR) Potential]
[ Records : (VF – VL) potential
[ Records : (VF – VR) potential
I
II
III
Lead III
Einthoven’s
Triangle

22. EINTHOVEN’S LAW :
Sum of potentials, i.e. QRS – voltage, in Lead II
= QRS – voltage In Lead I + QRS voltage In Lead III
Wilhelm Einthoven : (Leyden Physiologist, 1860 – 1927)
1903 : Father of Electrocardiography.

23. 23
[B] AUGMENTED UNIPOLAR LIMB LEADS OF GOLDBERGER :
(= VR - (VL+VF) = VR) (= VL - (VR+VF) = VL)
(= VF - (VL+VF) = VF)
aVR aVL
aVF
(Einthoven’s - )
aVL
(LA)
(LF)
aVF
aVR
(RA)

24. 24
(A) aVR : reflects the electrical activity of cavity of ventricles,
- so, P-wave, QRS-Complex & T-wave, all are negative
deflection.
(B) aVL : reflects the electric activity of the left outer side of heart,
- therefore, QRS deflection will be predominantly ‘positive’-
(same as seen in Lead-V6)
(C) aVF : reflects the electric activity of inferior surface of heart of both
ventricles, - so, QRS deflection will be predominantly ‘biphasic’-
(same as in Leads- V3 or V4)

25. [C] UNIPOLAR CHEST (PRECORDIAL) – LEADS
(Chest electrode = active, or exploring electrode
& other electrode, (RA+LA+LF) = passive or indifferent, with zero potential)
(Records : V- (RA+LA+LF) = V)
( 5000 ohm- zero-potential)
+
-

26. UNIPOLAR E.C.G.- LEADS
Midclavicular Line
Anterior axillary line
Mid axillary line

27. • These Chest Leads represent electrical activity throughout the heart,
But specially of that part, which lies nearest to electrode.
• V1& V2 Leads reflect right ventricular activity
so small-R wave, & large S-wave,
Negative deflections.
• V3 & V4 Leads reflect activity of both ventricles & I.V. septum
so small-Q wave, & moderate R & S-waves,
Biphasic deflections.
• V5 & V6 Leads reflect activity of left ventricle mainly,
so small-Q, large-R, & small S-wave,
Positive deflections.

28. S-wave
gradually
decreasing
R-wave
gradually
decreasing
PATTERN OF VENTRICULAR COMPLEXES IN CHEST LEADS

29. The derivation of the standard leads from the recording limb electrodes
with defined directions as vectors in the frontal plane of the heart.

30. The derivation of the six V (chest) leads from the recording precordial
electrodes, with their representations as vectors in the cross-sectional plane
of the heart .

31. Leads I, II, & III : Einthoven’s Law :
QRS-Complex in Lead II = QRS – Complex in Lead – I +
QRS – Complex in Lead – III
Leads aVR, aVL, aVF :
aVR = Negative E.C.G., P-inverted, Q-deep, T-inverted
Leads V1 to V6 :
Lead V1 : R-smallest & S-largest
From Lead V1 to V6 : R-increasing & S-decreasing
Lead V6 : R-largest & S-smallest

32. 32
The Recording Of The Clinical Electrocardiogram
Normal 12-lead electrocardiogram (ECG).

33. MEAN CARDIAC VECTOR
OR
CARDIAC AXIS

34. 34
CARDIAC VECTOR
OR
CARDIAC AXIS
- Since the standard (classical) bipolar limb-leads- I,II & III  are records
of the potential difference between two points.
- Therefore, deflection in each lead at any moment indicates 
‘magnitude’ and ‘direction’ in the axes of ‘electromotive force (e.M.F)’-
generated in the heart.
-This is called  ‘cardiac vector’ or ‘cardiac axis’.
the potential difference between two points,

35. INSTANTANEOUS MEAN VECTOR
Instantaneous Mean-Vector
(Through partially depolarized ventricles - when current flows
through I.V septum of the heart  from depolarized portion,
towards non-depolarized (polarized) part of I.V septum.)
Note - Instantaneous Mean Vector  can’t be determined by E.C.G record,
but can be determined by ‘Vector Cardiogram’.
Depolarised
portion of Heart
Non-depolarised portion
of Heart

36. 36
Einthoven’s- Triangle
-
- -
+ +
+

37. Modified Einthoven’s Triangle
(Showing degree of instantaneous-vectors at different Leads)
aVL
aVR
aVF
+210
III II
I
(-150 )

38. - +
-
+
+
+
-
RA LA
CALCULATION OF
CARDIAC VECTOR, OR MEAN QRS-VECTOR, OR CARDIAC AXIS
[ It can be calculated  by measuring amplitude of QRS-Complex,
in Leads I, II & III. It is useful in diagnosis of heart diseases.]
[ Einthoven’s Law :
QRS-Voltage in Lead-II =
QRS-Voltage in Lead-I +
QRS-Voltage in Lead-III ]
[ Arrow in the centre indicates the direction and magnitude of Cardiac vector,
which is parallel to QRS in Lead-II ]

39. (B) NORMAL LEFT AXIS
DEVIATION: (LAD)
(+30o to -30o)
(HORIZONTAL HEART) [
MAXIMUM-QRS IN LEAD-I ]
(A) NORMAL CARDIAC AXIS
(+30o to +75o)
(OBLIQUE HEART)
[MAXIMUM-QRS IN LEAD-II]
(C) NORMAL RIGHT- AXIS
DEVIATION : (RAD)
(+75o to +110O)
(VERTICAL HEART)
[MAXIMUM-QRS IN LEAD-III]
Beyond - 300 : Abnormal Left Axis Deviation.
Beyond + 100 : Abnormal Right Axis Deviation.
REFERENCE AXES FOR DETERMINING-
THE DIRECTION OF THE VECTOR.
III II
I
180
-120
+30
+90 +60
0
-30
-60
+120
+110 +75

40. CONDITIONS IN WHICH CARDIAC AXIS BECOMES – ABNORMAL:
(A) Abnormal – L.A.D. : (Maximum QRS in Lead-I)
(1) Shift of heart to the left
(2) Left ventricular hypertrophy
(3) Left bundle branch block.
(4) Damage of myocardial muscle of right side
(Posterior or Inferior M.I.)
(B) Abnormal – R.A.D. : (Maximum QRS in Lead- III)
(1) Shift of heart to the right.
(2) Right Ventricular hypertrophy
(3) Right bundle branch block
(4) Damage of myocardial muscle of left side
(Antero-lateral M.I.)

41. 41
Normal Cardiac Axis
Abnormal – L.A.D
Abnormal – R.A.D

42. IMPORTANCE OF E.C.G. RECORDING :
TO FINDOUT / TO DIAGNOSE :
(1) Heart-Rate: ( Normal, Tachycardia, or Bradycardia )
1500
No. of small squares in one R-R interval
( when speed of paper= 25 mm/sec)
(2) Rhythm of heart: (Regular or Irregular, i.e. Arrhythmias)
(3) Heart Blocks: (S.A.N- Block, A.V.N.-Block, B.B.B.)
(4) Ventricular Hypertrophy: (R.V.H or L.V.H.)
(5) Ischemic Heart Disease: ( Angina-Pectoris &
Myocardial infarction - ant. wall / post. wall / inf .wall )
(6) Ionic / Electrolyte disbalance:
( e.g. Hyperkalemia, Hypokalemia, Hypocalcemia etc. )
(7) Cardiac-Axis or Mean Cardiac Vector :
( Normal Cardiac Axis , L.A.D or R.A.D )
Heart-Rate =
(1)