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Transcript
‫بسم هللا الرحمن الرحيم‬
Cardiovascular System (CVS 227)
ELECTROCARDIOGRAM (ECG)
BASIC PRINICPLES
Dr.Mohammed Sharique Ahmed Quadri
Asst. professor in physiology
Al Maarefa College
1
OBJECTIVES
Identify the concept of ECG leads.
 Describe basic components of ECG.
 Relate each components of ECG with the
electrical event in the heart.
 Understand the concept of QRS axis.

2
3
CONDUCTION SYSTEM OF THE HEART
4
ELECTROCARDIOGRAM

Electrocardiogram:
Measure of the electrical activity of the heart per unit
time.
 Potential
differences generated by heart’sectrical activity
are conducted to body surface where they can be
recorded by electrodes placed on the skin.

Does NOT measure the flow of blood through the
heart.

Electrocardiograph : device that records the electrical
activity of the heart
5
PRINCIPLE OF RECORDING ECG
The body is a good conductor of electricity
Battery
6
ELECTROCARDIOGRAPH
7
ECG
What is Lead?
 ECG tracing recorded on the paper
by a single electrode.

What is Electrode?
 It is a metallic plate placed on skin which
conducts electricity.

8
LEADS ARE LIKE PICTURES OF THE HEART
9
LEADS ARE LIKE PICTURES OF THE HEART
10
BE CAREFUL !! DON’T PUT WRONG LEADS
DON’T PUT WRONG LEADS
11
STANDARD 12-LEAD ELECTROCARDIOGRAM

Six Limb Leads :
Frontal plane currents (right, left, inferior, superior)
 Three Bipolar Limb Leads( standard limb leads)
 named
 Three


as , I, II , III
Unipolar Limb Leads ( augmented limb leads)
named as aVR, aVL, aVF
Six precordial (chest) leads
Horizontal plane (anterior, posterior, right and left
forces)
12
BIPOLAR / STANDARD LIMB LEADS
Record the electrical potential difference in the
frontal plane
 In bipolar lead, we record potential difference
between two active electrodes.

13
UNIPOLAR (AUGMENTED) LEADS
Record electrical potential in the frontal
plane
 In Unipolar lead, we record potential
difference between active electrode and
other electrode at zero potential.

14
EINTHOVEN’S TRIANGLE
The axis of the limb
leads form an
equilateral triangle
around the heart’s
electrical field
15
PRECORDIAL (CHEST) LEADS
16
HEART IN THREE DIMENSION
17
ELECTRODES & WAVES
If current is flowing towards the recording electrode,
we get upward deflection.
If current is flowing away from the recording
electrode, we get downward deflection.
18
Standard 12 Lead ECG
19
THE ECG PAPER

Horizontally
 One
small box - 0.04 s
 One large box - 0.20 s

Speed of paper is 25mm/sec
1mm
Vertically
 One
large box - 0.5 mV
20
BASIC COMPONENTS

Waves

Segments & intervals
21
BASIC COMPONENTS
NORMAL IMPULSE CONDUCTION
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
23
IMPULSE CONDUCTION & THE ECG
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers
24
THE “PQRST”
• P wave - Atrial
Depolarization
• QRS - Ventricular
Depolarization
• T wave - Ventricular
Repolarization
25
THE PR INTERVAL
Atrial depolarization
+
delay in AV junction
(AV node/Bundle of His)
(delay allows time for
the atria to contract
before the ventricles
contract)
26
SEGMENTS & INTERVALS

PR interval: 0.12 – 0.20 sec

QRS interval : 0.08 – 0.10sec

QT interval : 0.40-0.43sec

ST interval :0.32 - sec
27
THE ELCTRICAL AXIS OF THE HEART

Vector is diagrammatic way to show strength &
direction of impulse
28
MEAN ELECTRICAL AXIS

Is some total of all
vectors generated by
the action potential of
individual ventricular
myocytes.

we measure the way
the vectors looks as it
travels under each of
various electrode
29
Axis
Determination of Mean Electrical
The QRS axis is determined by overlying a circle, in the frontal
plane. By convention, the degrees of the circle are as shown.
The normal QRS axis lies between -30o and +110o.
A QRS axis that falls between -30o
and -90o is abnormal and called left
axis deviation.
-90o
-60o
-120o
-150o
A QRS axis that falls between
+110o and +180o is abnormal and
called right axis deviation.
-30o
180o
o
A QRS axis that falls between +180
and -90o is abnormal and called
Indeterminant (extende rt axis ) .
0o
30o
150o
120o
90o
60o
FORMATION OF HEXAAXIAL SYSTEM
I
III
II
31
FORMATION OF HEXAAXIAL SYSTEM
aVR
aVL
aVF
32
FORMATION OF HEXAAXIAL SYSTEM
-90
-120
-60
aVR
-150
aVL
-30
180
0I
+150
+30
III+120
+60 II
+90
aVF
33
THE HEXA-AXIAL SYSTEM FOR DETERMINING QRS AXIS

When a vector is exactly
horizontal and directed
toward the person’s left
side,the vector is said to
extend in the direction of
0 degrees

From this zero reference
point, the scale of
vectors rotates
clockwise:
34
HOW TO CALCULATE THE QRS AXIS

Leads & there
isoelectric
partners
35
REFERENCES

Text book of medical physiology by GUYTON &
HALL 11th edition

Text book physiology by GANONG

The ECG made Easy by John R.Hampton sixth
edition
36