Download ECG Recording and Interpretation

12-Mar-17
ECG Recording and
Interpretation
Prof Dr Waqas Hameed
OBJECTIVES
Electrocardiogram (ECG):
• Define electrocardiogram and electrocardiograph
• Uses of ECG
• Explain ECG leads
It is the graphical record of electrical activities of the heart,
which occur prior to the onset of mechanical activities
• Describe how waves of normal ECG are formed
• What are the various intervals and segments of ECG
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Electrocardiograph:
ELECTROCARDIOGRAM
ELECTROCARDIOGRAPH
Uses of ECG:
ECG LEADS:
Electrocardiogram is useful in determining and diagnosing the:
• ECG is recorded by placing series of electrodes on the
1. Heart rate
2. Heart rhythm
3. Abnormal electrical conduction
4. Poor blood flow to heart muscle (Ischemia)
surface of the body
• These electrodes are called ECG leads and are connected to
the ECG machine
• A lead records potential difference between two electrodes
5. Heart Attack (Myocardial Infarction)
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Types of ECG leads:
Bipolar limb leads:
There are total 12 ECG leads:
• +ve electrode is placed on one limb and –ve electrode on
• Bipolar limb leads – 3
• Augmented unipolar limb leads – 3
• Chest leads – 6
LIMB LEAD I:
Lead I
the other limb
• These leads measure the electrical potential difference
between +ve and –ve electrodes
Limb lead II:
Lead II
• -ve electrode is on right arm
• -ve electrode is on right arm
• +ve electrode is on left arm
• +ve electrode is on left foot
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Limb lead III:
Augmented unipolar limb leads:
Lead III
• Unipolar limb leads are also called augmented limb leads.
• -ve electrode is on left arm
• +ve electrode is on left foot
• Here, one electrode is active electrode and the other one is
an indifferent electrode
• Active electrode is positive and the indifferent electrode is
serving as a composite negative electrode
Types of unipolar limb leads:
Unipolar limb leads are of three types:
1. aVR lead
aVR lead:
• Active electrode is
connected to right arm
• Indifferent electrode is
2. aVL lead
connected to left arm and
3. aVF lead
left leg
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aVL lead:
• Active electrode is
connected to left arm
• Indifferent electrode is
connected to right arm and
aVF lead:
• Active electrode is
connected left leg (foot)
• Indifferent electrode is
connected to the two
upper limbs
left leg
Chest leads:
• Chest leads are also called ‘V’ leads or precordial chest leads
• Indifferent electrode (negative electrode) is connected to three
limbs, viz. left arm, left leg and right arm
• Active electrode (positive electrode) is placed on six points over
the chest
Position of chest leads:
V1: Over 4th intercostal space near
right sternal margin
V2: Over 4th intercostal space near
left sternal margin
V3: In between V2 and V4
V4: Over left 5th intercostal space on
the mid clavicular line
V5: Over left 5th intercostal space on
the anterior axillary line
V6: Over left 5th intercostal space on
the mid axillary line
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Cardiac vector:
Degree of vector:
• Cardiac vector is an arrow that represents the direction of
• While recording the ECG in different limb leads, the degree
current flow (electrical potential) in the heart as well as its
amplitude
of vector is altered
• Forexample,if the potential travels from right side to left in
• Arrowhead of the vector represent direction of potential
horizontal plane, the degree of vector is zero
• Length of the arrow represent amplitude of potential
0°
Lead axis:
lead I
lead II
lead III
DIRECTION OF AXIS IS FROM
RIGHT SIDE TO LEFTSIDE
DIRECTION OF AXIS IS FROM
ABOVE TO DOWNWARD IN
LEFT DIRECTION
DIRECTION OF AXIS IS FROM
ABOVE DOWNWARD IN RIGHT
DIRECTION
• Imaginary straight line connecting the two electrodes of
ECG is called “Axis” of the lead
• By convention, axis of a lead directs toward +ve electrode
0°
60°
120°
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Einthoven’s Triangle:
Axes of Bipolar leads:
-
-
An equilateral Triangle formed by the Axes of three Bipolar
limb leads with heart in its center
+ I 0°
-
+
+
II
+60°
III
+120°
aVR
aVF
aVL
DIRECTION OF AXIS IS FROM
BELOW TO UPPER PART OF
HEART
DIRECTION OF AXIS IS ABOVE
DOWNWARD
DIRECTION OF AXIS IS FROM
BELOW UPWARD SLIGTHLY TO
THE LEFT
210°
90°
-330°
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SA NODE
Characteristics of ECG recording:
AV NODE
INTERVENTRICULER SEPTUM
(From base to apex ,this potential is strong)
INNER SURFACE OF VENTRICLE
(from apex to base, this potential is weal)
• Electrical activity is recorded when part of muscle fiber is
depolarized or repolarized
• No electrical activity is recorded when muscle fiber is fully
depolarized or repolarized
OUTER SURFACE OF VENTRICLE
(from base to apex, this potential is very
strong)
++++++++++++++
At rest
At rest
________________
0
----------+++++++
During depolarization
-
+
+++++++----------
-
+
++++++++++++++
________________
+++++++----------
During repolarization
----------+++++++
An isoelectric line
on ECG will be
recorded
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During depolarization
During depolarization
0
-
0
Wave of depolarization
moving away from
positive electrode
+
-
+
-
+
-
+
+++++++----------
Wave of depolarization
moving towards
positive electrode
+++++++----------
Upward deflection
on ECG will be
recorded.
downward
deflection on ECG
will be recorded.
During repolarization
During repolarization
0
-
-
0
Wave of repolarization
moving away from
positive electrode
+
+
-
-
+
+
----------+++++++
Wave of
repolarization
moving towards
positive electrode
----------+++++++
Downward
deflection on ECG
will be recorded
upward deflection
on ECG will be
recorded
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Depolarization of atria-P wave
Negative electrode
Depolarization of atria begins in SA node and
then spread in all direction in atria
Area near SA node depolarized a long time
before the distal part of the ventricle
Wave of depolarization moving towards
positive electrode
Direction of vector is in positive direction
So recording on ECG is also positive and it
represent atrial depolarization
It is known as P wave
Positive electrode
Repolarization of atria-Atrial T wave
Negative electrode
Depolarization of ventricle-QRS complex
• Area around SA node repolarize first
• Wave of repolarization moving toward the
positive electrode
• This lead to formation of atrial t wave
• But we can not appreciate it in ECG because
it form at the same time when QRS complex
of ventricle is formed.
Negative electrode
• Cardiac impulse enters into the ventricles
through AV node
• First enter into the left endocardial surface of
the septum
• Then spread to the both endocardial surfaces of
the septum
• Then to the endocardial surface of the
ventricles
• Then spread through the ventricle to outside of
the heart
T
Positive electrode
Positive electrode
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Repolarization of ventricle-T wave
Graphical representation of ECG waves:
Negative electrode
• Entire outer surface of ventricle especially
near the apex of heart repolarize first
• The endocardial surface repolarize last
• Sequence of this repolarization is due to
high blood pressure inside the ventricle
during contraction---reduce the blood flow
to the endocardium-----slow down the
repolarization in endocardial area
• Wave of repolarization moving away from
positive electrode
• As a result T wave is formed also in the
positive direction
Positive electrode
ELECTROCARDIOGRAPHIC GRID:
• It refers to the markings(lines) on ECG paper.
Voltage(mv)
Time(sec)
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2 large squares are equal to
1mv(0.5+0.5)
voltage
voltage
1 large squares are equal to
0.5mv
1 small square is equal to
0.1mv
Time
Time
P wave-atrial depolarization:
5 large box=1sec
1 large box=0.2 sec
1 small box =0.04sec
Voltage(mv)
voltage
Amplitude
0.1+0.1=0.2mv
Duration
0.04+0.04+0.02=0.1sec
Time(sec)
Time(sec)
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QRS complex-ventricular depolarization:
Duration
0.08 to 0.10sec
Voltage(mv)
Voltage(mv)
Amplitude
Q = 0.1 to 0.2
R=l
S = 0.4
T wave-ventricular repolarization:
Amplitude
0.3mv
Time(sec)
Interval
A flat line on ECG tracing having at least one ECG wave
Duration
0.2sec
Time(sec)
P-R interval:
• ‘P-R’ interval is the interval between
the onset of ‘P’ wave and onset of ‘Q’
wave
• It shows the duration of conduction of
the impulses from the SA node to
ventricles through atrial muscle and AV
node
• Duration of PR interval 0.12 – 0.20 sec
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Q-T interval:
• Q-T interval is the interval
R-R interval:
• ‘R-R’ interval is the time interval between two consecutive waves
between the onset of ‘Q’ wave
• Normal duration of ‘R-R’ interval is 0.8 second
and the end of ‘T’ wave
• Measurement of ‘R-R’ interval helps to calculate:
• It signifies the electrical activity
in ventricles
• Duration of Q-T interval
1. Heart rate
2. Heart rate variability
Duration of RR interval = 0.6 – 1.0 sec
0.4 – 0.43 sec
Isoelectric line or segment:
A flat line on ECG tracing with out any wave
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