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‫بسم هللا الرحمن الرحيم‬
Cardiovascular System
ELECTROCARDIOGRAM (ECG)
ANALYSIS
Dr.Mohammed Sharique Ahmed Quadri
Asst. Professor Physiology
Almaarefa College
1
AT THE END OF THIS LECTURE WE WILL
LEARN

The simple steps to analyze the ECG

How to calculate the heart rate.

How to analyze the rhythm.

To calculate the QRS axis
2
THE 12-LEADS
The 12-leads include:
–3 Limb leads
(I, II, III)
–3 Augmented leads
(aVR, aVL, aVF)
–6 Precordial leads
(V1- V6)
3
VIEWS OF THE HEART
Some leads get a
good view of the:
Anterior portion
of the heart
(V1,V2,- setum
V3,V4-)- anterior
Inferior portion
of the heart
4
II, III, aVF
Left Lateral
portion of the
heart( I , Avl, v5,v6)
BASIC COMPONENTS
5
THE “PQRST”

P wave - Atrial
depolarization
• QRS - Ventricular
depolarization
• T wave - Ventricular
repolarization
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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)
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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

8
HOW TO READ THE ECG

Rhythm analysis

Analyzing individual wave & segments

Determine the mean electrical axis
9
RHYTHM ANALYSIS
•
•
•
•
•
Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Determine regularity.
Calculate rate.
Assess the P waves.
Determine PR interval.
Determine QRS duration.
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1-DETERMINE REGULARITY
R


R
Look at the R-R distances (using a caliper or markings
with a pen on paper).
Regular (are they equidistant apart)? Occasionally
irregular? Regularly irregular? Irregularly irregular?
Interpretation?
Regular
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2-CALCULATING HEART RATE
• Find the R wave that falls on, or nearly on, one of
the heavy lines.
• Count the number of large square or small square
until the next R wave
• Deter mine the heart rate by applying following
formula
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2-CALCULATING HEART RATE

H.R = 1500

OR

H.R = 300
NO OF SMALL SQURES
BETWEEN R-R WAVES
NO OF BIG SQURES
BETWEEN R-R WAVES
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That’s why I selected medical profession
CALCULATE RATE
R wave

Option 2
 Find
a R wave that lands on a bold line.
 Count the # of large boxes to the next R wave. If the
second R wave is 1 large box away the rate is 300,
2 boxes - 150, 3 boxes - 100, 4 boxes - 75, etc.
(cont)
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3-ASSESS THE P WAVES
Are there P waves?
 Do the P waves all look alike?
 Do the P waves occur at a regular rate?
 Is there one P wave before each QRS?
Interpretation?
Normal P waves with 1 P
wave for every QRS

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4-DETERMINE PR INTERVAL

Normal: 0.12 - 0.20 seconds.
(3 - 5 boxes)
Interpretation?
0.12 seconds
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5-QRS DURATION

Normal: 0.04 - 0.12 seconds.
(1 - 3 boxes)
Interpretation?
0.08 seconds
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RHYTHM SUMMARY
Regularity
 Rate
 P waves
 PR interval
 QRS duration
Interpretation?

regular
90-95 bpm
normal
0.12 s
0.08 s
Normal Sinus Rhythm
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Calculate Heart Rate.
Normal ECG
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VARIATIONS IN SINUS RHYTHM
•
•
•
•
•
Rate?
Regularity?
P waves?
PR interval?
QRS duration?
35 bpm
regular
normal
0.12 s
0.10 s
Interpretation? Sinus Bradycardia
VARIATIONS IN SINUS RHYTHM
•
•
•
•
•
Rate?
Regularity?
P waves?
PR interval?
QRS duration?
130 bpm
regular
normal
0.16 s
0.08 s
Interpretation? Sinus Tachycardia
INTERPRETE THE ECG ?
SINUS ARHYTHMIA
Observe Variation in Heart Rate during Inspiration and Expiration.
[Increased Heart Rate during Inspiration]
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ATRIAL FIBRILLATION
 Deviation
from NSR
 No
organized atrial depolarization, so no
normal P waves (impulses are not
originating from the sinus node).
 The atrial rate is usually above 350 beats
per minute
 Atrial activity is chaotic (resulting in an
irregularly irregular rate).

Common, affects 2-4%, up to 5-10% if > 80 years old
ATRIAL FLUTTER
•
•
•
•
•
Rate?
Regularity?
P waves?
PR interval?
QRS duration?
70 bpm
regular
flutter waves
none
0.06 s
Interpretation? Atrial Flutter
AV NODAL BLOCKS
 1st
Degree AV Block
 2nd
Degree AV Block, MobitzType I
 2nd
Degree AV Block,MobitzType II
 3rd
Degree AV Block
Take a look at this ECG. What do you notice
•
•
•
•
•
Rate?
Regularity?
P waves?
PR interval?
QRS duration?
60 bpm
regular
normal
0.36 s
0.08 s
Interpretation? 1st Degree AV Block
PR Interval
> 0.20 s
Etiology: Prolonged conduction delay in the AV
node or Bundle of His.
Take a look at this ECG. What do you notice
• Rate?
50 bpm
• Regularity?
regularly irregular
• P waves?
normal, but 4th no QRS
• PR interval?
lengthens
• QRS duration?
0.08 s
Interpretation? 2nd Degree AV Block, Type I
– PR interval progressively lengthens, then the impulse is completely
blocked (P wave not followed by QRS).
•
Etiology: Each successive atrial impulse encounters a longer and longer delay in
the AV node until one impulse (usually the 3rd or 4th) fails to make it through the
AV node.
Take a look at this ECG. What do you notice
• Rate?
40 bpm
• Regularity?
regular
• P waves?
normal, 2 & 3 no QRS
• PR interval?
0.14 s
• QRS duration?
0.08 s
Interpretation? 2nd Degree AV Block, Type II
Occasional P waves are completely
blocked (P wave not followed by QRS).
Etiology: Conduction is all or nothing (no prolongation of PR interval);
typically block occurs in the Bundle of His.
Take a look at this ECG. What do you notice
• Rate?
40 bpm
• Regularity?
regular
• P waves?
no relation to QRS
• PR interval?
none
• QRS duration?
wide (> 0.12 s)
Interpretation? 3rd Degree AV Block
Etiology: There is complete block of conduction in the AV junction, so the
atria and ventricles form impulses independently of each other. Without
impulses from the atria, the ventricles own intrinsic pacemaker kicks in at
around 30 - 45 beats/minute.
REMEMBER

When an impulse originates in a ventricle,
conduction through the ventricles will be
inefficient and the QRS will be wide and
bizarre.
Determination of Mean Electrical
Axis
Axis refers to the mean QRS axis (or vector) during ventricular
depolarization. As you recall when the ventricles depolarize (in a
normal heart) the direction of current flows leftward and downward
because most of the ventricular mass is in the left ventricle. We like
to know the QRS axis because an abnormal axis can suggest
disease such as pulmonary hypertension from a pulmonary
embolism.
32

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:
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FORMATION OF HEXA-AXIAL SYSTEM
I
II
III
I
III
II
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FORMATION OF HEXAAXIAL SYSTEM
aVR
aVL
aVF
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FORMATION OF HEXAAXIAL SYSTEM
-90
-120
-60
aVR
-150
aVL
-30
180
0I
+150
+30
III+120
+60 II
+90
aVF
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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
37
90o
60o
HOW TO CALCULATE THE QRS AXIS

Leads & there
isoelectric
partners
38
39
I TOLD YOU …..I HATE MATHEMATICS !
40
DETERMINING QRS AXIS
Indeterminant /extended RAD
RAD
LAD
NORMAL
AXIS
How to calculate the QRS axis
… if the QRS is negative in lead I and negative in lead II what is the QRS
axis? (normal, left, right or right superior axis deviation)
QRS Complexes
I
+
+
aVF
+
-
-
+
-
-
Axis
normal
left axis deviation
right axis deviation
right superior
axis deviation/
indeterminant
42
What is Axis ?
Normal ECG
43
References
• The ECG made Easy by John
R.Hampton 7th edition
• The only EKG book you will ever
need,Malcolm.S.Thaler, seventh edition
• Introduction to ECG interpretation BY
Frank G. Yanowitz