Electrocardiography Basics

Human Body
Screening
ELECTROCARDIOGRAPHY
DR RAMY ELGHWAS

Lecture Contents
 Introduction to Electrocardiograph
 Electrocardiogram
 ECG Leads
 Waveforms in ECG
 How to calculate heart rate from ECG?
 Heart Rhythm
 Common Heart problems

Introduction to Electrocardiograph
 Electrocardiograph (ECG): it is a recording of the electrical activity
of heart on a graph paper. In other words: it is a graphical
representation of the electrical activity of the heart.
 The machine used for recording ECG:
1. ECG machine
2. Power lab

Electrocardiogram
 The graph that represent the electrical
activity of the heart is called the
electrocardiogram.
 The significance of electrocardiogram include:
1. identify the cause of an arrhythmia
2. pursue high-risk arrhythmia syndrome.
3. investigate a history of syncope or palpitations
4. monitor a medication effect
5. determine a myocardial infarction, or “heart
attack”
6. Investigate coronary artery blockages
7. determine normal pacemaker or ICD functioning
8. Calculating the cardiac axis

ECG paper
 This paper is a part of long role
composed of small squares.
 The paper has the following properties:
1. The smallest square in this paper is 1
mm2
2. The small squares are drawn with thin
lines.
3. The larger squares are 5 mm2 and
drawn with thick lines.
4. The average speed of ECG machine
is 25 mm per second.
5. The vertical scale represent the
electric potential
6. The small square represent 0.1 mV
potential

ECG Leads
 The leads are simply group of
electrodes that record the electric
potential of heart from body sites.
 There are 12 ECG leads:
➢ 3 Bipolar limb leads (I,II,III)
➢ 3 unipolar augmented limb leads
(aVR, aVL, aVF) "Einthoven’s Triangle"
➢ 6 unipolar chest leads (precordial
leads)

ECG Leads
Regions of the Heart
1. AVL is on the left wrist or shoulder and looks at the upper left
side of the heart.
2. Lead l travels towards AVL creating a second high lateral lead.
3. AVf is on the left ankle or left lower abdomen and looks at the
bottom, or inferior wall, of the heart.
4. Lead ll travels from AVr towards AVf to become a 2nd inferior
lead
5. Lead lll travels from AVL towards AVf to become a 3rd inferior
lead.
6. V2 V3 and V4 look at the front of the heart and are the anterior
leads.
7. V5 and V6 look at the left side of the heart and are the lateral
leads.

Waveforms in ECG
 Basic ECG Terminologies:
1. Baseline: flat straight and isoelectric
line
2. Waveform: deviation or movement
away from baseline either upward or
downward.
3. Segment: a line between two
waveforms.
4. Interval: a waveform combined with
a segment to show a certain time
duration
5. Complex: combination of several
waveforms without segment

Waveforms in ECG
 Always remember:
1. The positive electrode is considered a reference electrode
2. The depolarization wave that moves toward the positive electrode
produces positive deflection.
3. The depolarization wave that moves away from the positive
electrode produces negative deflection.
4. P-wave: represents an arterial depolarization
5. QRS complex: represents a ventricular depolarization
6. T-wave: represents a ventricular repolarization

How to calculate heart rate from ECG?
The heart rate is basically the number of
heart beats per minute.
This rate can be determined by two ways:
1. Rule of 300
2. Rule of the 10 seconds

1. Rule of 300
Count the number of “big boxes”
between neighboring QRS
complexes, and divide this into 300.
this means:
Heart rate = 300/ ”#of big boxes”
Although fast, this method only
works for regular rhythms.
No. of big
boxes
Heart rate
1 300
2 150
3 100
4 75
5 60
6 50

1. Rule of 10 seconds
 As most ECG records 10 seconds of
rhythm per page, one can simply count
the number of beats present on the
ECG and multiply by 6 to get the
number of beats per 60 seconds:
Heart rate = No. of beats in ECG X 6
 This method works well for irregular
rhythms.
No. of beats
in ECG
Heart rate
10 60
15 90
20 120
25 150
30 180
35 210

Heart Rhythm
 It is important to know:
1. It is a way to check the regularity of ECG
2. This check simply depends on the measurement of the intervals
between two R waveforms or two S waveforms.
3. The regular rhythm of heart is characterized by equal number of
squares between to sequential R or S waveforms.
4. The irregular rhythm has no constant number of squares between the
R or S waveforms.
5. Irregular rhythm is called Arrythmias. Arrythmias does not imply you
are sick.
6. Take care: there is sinus rhythm, however, the R-R interval varies with
respiration, i.e., heart rate increases during inspiration and decreases
during expiration.

Heart Rhythm
• Sinus arrhythmia is a kind of
arrhythmia.
• For the common sinus
arrhythmia, the time
between heartbeats can be
slightly shorter or longer
based on your breath in or
out.
• Heart rate increases when
you breathe in and slows
down when you breathe out.
• It’s usually a sign that your
heart is healthy.

Common Heart problems
1- Atrial Flutter:
1. It is there when atrial rate is bet. 200 up to
300 beats/ min.
2. During atrial flutter, AV node becomes less
capable to transmit all the incoming
impulses to ventricles. Therefore, ventricular
rate is equal to 1/3 or ¼ the atrial rate.
3. The P-waveform becomes like sawtooth.
4. Ischemic Heart Disease (IHD) is regular cause
for atrial flutter.
5. IHD results when one or more of your
coronary arteries is narrowed or obstructed
or in rare situations.

2- Atrial Fibrillation:
1. It is a totally irregular and rapid atrial rate in
which there is a contraction of only small
partial musculature.
2. The P-waveform is replaced by irregular F-
waves, because the entire atrial is not
contracting.
3. QRS complex and T waves are normal in
their shapes but rhythm is irregular.

3- Ventricular Tachycardia:
1. The impulse originates at ventricular pacemaker, therefore an
odd/wide QRD complex is produced.
2. The irregular QRS complex is often due to myocardial infarction.
3. The heart rate, in this case, is about 120-200 beats/ min.

3- Ventricular Fibrillation:
1. Rapid, irregular and ineffective contractions of small segments of
ventricles is termed as ventricular fibrillation.
2. Peripheral pulse is absent because cardiac output is zero.
3. Haphazard ventricular depolarization and ineffective ventricular
pumping.
4. If continued, death is expected within minutes

Electrocardiography Basics

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