An ECG is a recording of waveforms that
reflects the electrical activity of the heart.
An Electrocardiogram is a graphic record
of the electrical impulses that are generated
by depolarization & repolarization
of the myocardium.
THE ELECTRICITY OF THE HEART
The contraction of any muscle is
associated with electrical changes called
“depolarization”& these changes can be
detected by electrodes attached to the
surface of the body.
Myocardial Infarction& other types of
CAD such as angina
Inflammatory diseases of the heart
Effects on the heart by drugs, such as
The baseline is the iso-electric line. It occurs
when there is no current flow.
If the current flows toward the lead, a
positive deflection, ie above the baseline.
If the current flows away from the lead , a
negative deflection, ie, below the baseline.
Left ventricle has more influence on the ECG,
because of its increased muscle mass.
As per speed of the paper, one minute is
equal to 1500 small squares or 300 big squares.
So Heart rate = 1500
No: of small squares in one RR interval
No: of big squares
P wave: the part of an electrocardiogram (ECG) that
reflects conduction of an electrical impulse through
• Atrial depolarization
.3mm in height & duration of 0.04 to 0.11 sec.
PP interval: the duration between the beginning of
one P wave and the beginning of the next P wave;
used to calculate atrial rate and rhythm
PR interval: the part of an ECG that reflects
conduction of an electrical impulse from the
sinoatrial (SA) node through the atrioventricular
0.12-0.2 SEC(impulse spread from atria to
represented by 3-5 SMALL SQUARES
QRS complex: the part of an ECG that
reflects conduction of an electrical impulse
through the ventricles; ventricular
It is about 0.08 to 0.12 sec,
represented by 3 small squares.
QT interval: the part of an ECG that reflects the
time from ventricular depolarization through
Normal 0.42 sec
RR interval: the duration between the beginning
of one QRS complex and the beginning of the next
used to calculate ventricular rate and rhythm
sinus rhythm: electrical activity of the heart
initiated by the sinoatrial (SA) node
ST segment: the part of an ECG that
reflects the end of the QRS complex to
the beginning of the T wave
Not elevated >1mm or depressed<0.5
T wave: the part of an ECG that reflects
repolarization of the ventricles
TP interval: the part of an ECG that
reflects the time between the end of the T
wave and the beginning of the next P wave;
used to identify the isoelectric line
U wave: the part of an ECG that may
reflect Purkinje fibre repolarization. Seen
A 12-lead ECG provides multiple electrical views
of the heart along a vertical & horizontal plane.
V1-Electrode positioned in the 4th
intercostal space in the right sternal border.
V2-4thICS in the left sternal border.
V3-Midway between V2&V4.
V4-5thICS in the left midclavicular line.
V5-Same level as V4, anterior axillary line.
V6-Same level as V4 & V5, midaxillary line.
3 Bipolar limb leads
( Standard limb leads )-I, II,& III.
3 Unipolar Augmented leads
(aVR, aVL&aVF). Obtained through 4
electrodes placed on the right arm,
right leg, left arm & left leg.
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.
• Limb electrodes
• There are four limb electrodes:
• Red (RA): on the ulnar styloid process of the
• Yellow (LA): on the ulnar styloid process of the
• Green (LL): on the medial or lateral malleolus
of the left leg
• Black (RL): on the medial or lateral malleolus of
the right leg
We can identify the side or wall of the
heart affected by identifying the changes
in particular leads.
Anterior wall-V2, V3, V4
Inferior wall - aVF, II, III
Lateral wall -I, aVL, V5, V6
The Holter monitor is a type of portable
electrocardiogram (ECG). It records the
electrical activity of the heart continuously
over 24 hours or longer while you are away
from the doctor's office. A standard or
"resting" ECG is one of the simplest and
fastest tests used to evaluate the heart
• To evaluate chest pain that can't be
reproduced with exercise testing
• To evaluate other signs and symptoms
that may be heart-related, such as
tiredness, shortness of breath, dizziness,
• To identify irregular heartbeats or
• To assess risk for future heart-related
events in certain conditions, such as
• To see how well a pacemaker is working
• To determine how well treatment for
complex arrhythmias is working