4. What is an ECG?
The Electrocardiogram (ECG) is a Graphic
Representation of the Electrical Events of the
Each Event has a DistinctiveWaveform
Electrocardiography is the Method of
Recording of ECG
Electrocardiograph is the Machine that
Records ECG, which Amplifies theVoltages
and gives a Plot ofVoltage as a Function of
6. Concept behind ECG
Body is aVolume Conductor, i.e. Body Fluids
are a Good Conductor Of Electricity
Therefore, Electrical Changes occurring in the
Heart with Each Beat are Conducted all over
the Body and can be Picked Up from the Body
The Record of these Electrical Fluctuations
during the Cardiac Cycle is called
7. ECG is Useful for Assessing:
1. Anatomical Orientation of the Heart.
2. Relative Size of the Chambers.
3. Disturbances of Rhythm and Conduction.
4. Ischemia of the Myocardium, if Present.
5. Location, Extent and Progress of Myocardial
6. Effects of Altered Electrolyte Concentration.
7. Influence of Certain Drugs like Digitalis.
8. Efficiency of Electronic Pacemaker Function.
8. With ECGs we can Identify
Myocardial Ischemia and Infarction
Electrolyte Disturbances (i.e. Hyperkalemia,
DrugToxicity (i.e. Digoxin and Drugs which
Prolong the QT Interval)
9. The Advancement
In Modern Electrocardiography,TwoTypes of
ECG machines are used:
(1) the String Galvanometer
(2) the Radioamplifier
10. ECG paper
ECG paper is a Strip of Graph Paper that containsVertical
and Horizontal Lines 1 mm apart.
The Horizontal Axis representsTime whereas theVertical
Axis denotes Amplitude.
There are Small Squares of 1 mm x 1 mm, and Big Squares
of 5 mm x 5 mm.
After every 5 Big Squares, the HeavyVertical Line
overshoots the margin.
The ECG paper is a Heat-Sensitive Plastic-Coated Paper.
The ECG is inscribed on this paper by a Hot Stylus.
Conventional ECG is taken at a Speed of 25 mm/s.
One Small Square (1 mm) corresponds to 0.04 second,
while the Big Square (5 mm) is Equivalent to 0.20 second.
12. Einthoven 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 that
produces Zero Potential when theVoltages
13. ECG Leads
An ECG Lead is a pair of Electrodes used to
detect the Potential Differences of the Heart.
Two Categories -The Direct, and the Indirect
1.When a Lead is Directly Applied to the Surface
of the Heart, it is called Direct Lead - Used to
Record Cardiac Activities during Cardiac Surgery.
2.When the Leads are Applied Away from the
Heart (Usually on the Body Surface) to Record
the Cardiac Activities, they are called Indirect
14. Conventionally, ECG is recorded using
Indirect Leads are Limb Leads, Chest Leads,
and Esophageal Leads.
Usually, aTwelve-Lead Recording is
performed for Complete Analysis of the ECG -
Six Limb Leads and Six Chest Leads.
15. Limb Leads
Limb Leads lie in the Frontal Plane.
TwoTypes: Bipolar and Unipolar Limb Leads.
1. A Bipolar Lead Records the Potential
Difference BetweenTwo Electrodes placed at
2. A Unipolar Lead is a pair of Electrode giving
the Potential Difference Between An Exploring
And An Indifferent Electrode
3.The Reference Input comes from a
Combination Of Electrodes at different sites that
roughly gives a Zero Potential.
16. Bipolar Limb Leads
Three Bipolar Standard Limb Leads (Leads I,
II, and III) are the Original Leads Selected By
Einthoven to Record Electrical Potential on
the Frontal Plane.
The Electrodes are attached to the Right
Arm, Left Arm, and Left Foot.
Another Electrode is applied to the Right Leg,
which Acts As A GroundWire to Prevent
External Disturbances during Recording.
17. Bipolar Limb Leads
Lead I : Between the Right Arm (Negative
Electrode) and the Left Arm (Positive
Lead II : Between the Right Arm (Negative
Electrode) and the Left Leg (Positive
Lead III: Between the Left Arm (Negative
Electrode) and the Left Leg (Positive
19. Unipolar Limb Leads
In the method of recording by Unipolar Leads, one
Electrode is the Active or Recording Electrode and
the other one is the Indifferent Electrode
Three Unipolar Limb Leads: aVR, aVL, and aVF
‘a’ stands for Augmentation of the Leads
‘V’ stands for Unipolar
R, L, and F indicate that the Exploring or Active
Electrode is on the Right Arm, LeftArm, and Left
The Indifferent Electrode is connected to the
remainingTwo Leads through a Resistance Coil
20. Positioning of Unipolar Limb
aVR: Between the Right Arm (Positive
Electrode) and Left Arm + Left Leg (Negative
aVL: Between the Left Arm (Positive
Electrode) and Right Arm + Left Leg
aVF: Between the Left foot (Positive
Electrode) and Right Arm + Left Arm
22. Chest Leads
Chest Leads or Precordial Leads lie in the
TwoTypes: Unipolar and Bipolar Chest Leads.
23. Unipolar Chest Leads
There are Six Precordial Leads that are used
These areV1 toV6
‘V’ stands for Unipolar
These Leads employ an Exploring Electrode on the
The reference or the Indifferent Electrode is
connected to the Right Arm, LeftArm and Left Leg
through the High Resistance, which is calledWilson’s
Terminal that is Maintained at Zero Potential.
The Right Leg is connected with a Grounding
Electrode to Avoid Electrical Interference
24. Unipolar Chest Leads
V1 : In the Right Fourth Intercostal Space at the
Right Border of the Sternum.
V2 : In the Left Fourth Intercostal Space at the
Left Border of the Sternum.
V3 : At the Midpoint BetweenV2 andV4.
V4 : In the Left Fifth Intercostal Space on the
V5 : In the Left Fifth Intercostal Space on the
Anterior Axillary Line.
V6 : In the Left Fifth Intercostal Space on the
26. Bipolar Chest Leads
Used Before the Discovery of Unipolar Chest
Lewis Lead is a Special Bipolar Chest Lead
used for Recording ECG in Atrial Arrhythmias.
This Lead Amplifies theWaves of Atrial
27. Esophageal Leads
In these Leads, an Electrode is fixed on the tip
of the Esophageal Catheter, which is
Positioned in the Esophagus close to the
Here E stands for ‘Esophageal’ and the
Number indicates the Distance of the
Electrode from the IncisorTeeth expressed in
28. Esophageal Leads
E15–25 : Used for Recording the Activity of
the Right Atrium.
E25–35 : Used for Recording the Activity
from the AV Groove Region.
E40–50 : Used for Recording the Activity
from the Posterior Surface of the Left
32. P Wave
PWave is the First Positive Deflection in the
ECG, produced by Atrial Depolarization.
33. P Wave - Waveform
TheVoltage Change due to Atrial
Depolarization appears on the ECG as the P
Wave, which is Positive with Less Height and
The Height of P wave is Less Because of Less
Atrial Muscle Mass and Dome Shape is due to
the Slow Nature of Depolarization of Atrial
When Atria are Completely Depolarized, the
ECG tracing Returns to Zero.
34. P Wave - Abnormalities
PWave may be Abnormal due to Atrial
Enlargement and Intra-Atrial Conduction
Atrial Enlargement results inTall and Peaked
36. QRS Complex
This consists of Q, R, and SWaves.
The QRS complex consists of Deflections
produced byVentricular Depolarization
37. QRS Complex - Waveform
The Q, R, and SWavesTogether form the
QRS Complex, which RepresentsVentricular
The Duration, Magnitude and Sharpness of
the QRS Complex Indicate the Greater Muscle
Mass of theVentricles Depolarized and the
Rapidness ofVentricular Excitation.
39. Q Wave - Waveform
TheWave of Depolarization Passes Along the
Bundle Branches, and Purkinje Fibers to First
Excite the Interventricular Septum, which
Depolarizes from Left to Right.
The Net Dipole of Initial Depolarization is a
Small Downward SharpWave.
The Small Wave is due to Less Quantity of
Septal Muscle and Less time of
Depolarization and Sharpness is Due to the
Rapidity of Depolarization.
40. Q Waves - Abnormalities
When the Depth of QWave is more than 25%
of the Height or more than 0.04 s in Duration
is considered Pathological.
1. Acute or Old Myocardial Infarction
2. Unstable Angina
3. Dilated Cardiomyopathy
4. Hypertrophic Cardiomyopathy
41. R Wave - Waveform
TheWave of Depolarization then Spreads
from the Subendocardial Muscle Layer to the
Subepicardial Muscle Layer.
The Deflection in the ECG appears as RWave,
which is an Upward, Bigger and SharpWave.
R is LargestWave in ECG because of the
Greater Muscle Mass ofVentricles.
The Sharpness of theWave Represents the
Rapidity of Depolarization.
42. S Wave - Waveform
The Last Parts to be Depolarized are the
Posterobasal Portion of the LeftVentricle and
the Pulmonary Conus.
Appears in ECG as a Small Downward Wave.
The SWave is a Small, Negative and Sharp
49. PR Segment
This Lies Between the End of the PWave and
the Beginning of the QRS Complex.
50. ST Segment
This Lies Between the End of the QRS
Complex and the Beginning of theTWave.
The Point where the QRS Complex Ends and
the ST Segment Begins is the J Point.
Elevation of J Point Suggests Myocardial
Ischemia or Infarction.
51. ST Segment - Abnormalities
ST Elevation: Commonly seen in Acute
Myocardial Infarction and Sometimes in
ST Depression: Commonly seen in Myocardial
53. PR Interval
This is the Interval Between the Beginning of
the PWave and the Beginning of the QRS
The Range of PR Interval is from 0.12 to 0.20
second (Average 0.18 s).
Represents Atrial Depolarization and
Conduction through AV Node.
54. PR Interval - Waveform
Represents Atrial Depolarization (P wave) and
The PR segment is an Isoelectric Line.
During PR Segment, theWave of
Depolarization passes Slowly through the AV
Node, and then through the His Bundle.
The Net Dipole isToo Small in Magnitude to
Produce any Deflection on the ECG
56. QRS Interval
This is the Interval of the QRS Complex. It is
Measured from the Beginning of the QWave
(or RWave if QWave is Absent) to the J Point.
The Normal Range is from 0.08 to 0.10
Atrial Repolarization also Occurs inThis
57. QT Interval
This is the Interval for QRS Complex, ST
Segment andTWave. It is Measured from the
Beginning of the QRS Complex to the End of
The Normal Range is Between 0.40 and 0.43
RepresentsVentricular Depolarization and
Ventricular Repolarization. It Corresponds to
the Duration of Electrical Systole.
58. QT Interval - Abnormalities
Prolonged QT interval:
2. Antiarrhythmic Drugs, e.g. Quinidine
4. Acute Myocardial Infarction
Shortened QT interval:This is of Less Clinical
Significance and May be Seen in
59. ST Interval
This is the Interval Between the J Point and
the End ofTWave. It is Calculated by
Deducting QRS Interval from QT interval.
The Average Duration is 0.32 second.
60. PP Interval
This is the Interval Measured Between Either
the Peak or the Beginning ofTwo Successive
PP Interval is Measured for Calculation of the
61. RR Interval
This is the Interval BetweenTwo Successive R
It is Measured Between the Peaks ofTwo
RR Interval is Measured for Calculating the
Heart Rate (Ventricular Rate).
63. Heart Rate
The Comment should be Made on Both Atrial
The Heart Rate means theVentricular Rate.
At a Paper Speed of 25 mm/s,
Atrial Rate per minute is Calculated by dividing 1500
with PP interval (in mm).
Ventricular Rate per minute is Calculated by dividing
1500 with RR interval (in mm).
Normally, the RR Interval is equal to the PP
The Normal Heart Rate is 60 to 100 per minute