Dedicated to my students

1. PREPARED BY:
JOHNY
ECG

2. Electrocardiography:
Is trans-thoracic
interpretation of the
electrical activity of
the heart over time
captured and
externally recorded by
skin electrodes for
diagnostic or research
purposes on human
hearts.
What is
ECG?

3. THE HISTORY OF ECG MACHINE
1903
A Dutch doctor and physiologist. He
invented the first practical
electrocardiogram and received
Nobel Prize for Medicine in 1924.
Willem Einthoven

4. MODERN ECG INSTRUMENT
• The modern ECG machine has evolved into
compact electronic systems that often
include computerized interpretation of the
electrocardiogram.

5. ELECTRICITY OF HEART
• As action potential propagate through heart they
generate electrical current that can be detected at the
surface of the body.
• An electrocardiogram is abbreviated as ECG or EKG
(German: Elektokardiogram)
• Contraction of any muscle is associated with electrical
charges called depolarization
• These changes can be detected by electrodes attached
to the surface of the body
• Although the heart has 4 chambers, from the electrical
point it is having only 2 chambers.

6. ELECTRICITY OF HEART
• In the clinical practice, electrodes are positioned on the
arms and legs (limb leads) and six positions on the chest
(chest leads.)
• The ECG amplifies the electrical signals and produce 12
types of tracings from different combination of limb and
chest leads.
• The limb and chest leads record the electrical activity
differently and by comparing these records it is possible
to determine
1. Abnormality of the conducting pathways
2. Enlargement of heart
3. Regional damages of heart
4. Causes of Chest pain.

7. NORMAL ECG

8. NORMAL ECG
Typically three recognizable waves appear with each heart
beat.
P Wave: is the small upward deflection on the ECG. It
represents atria depolarization which spreads from the SA
node through contractile fibers in both atria.
QRS complex: begins as a downward deflection
continues as a large upright triangular wave and ends as a
downward wave. It represents rapid ventricular
depolarization as the action potential spreads through the
ventricular contractile fibers.
T wave: is a dome shaped upward deflection. It
represents ventricular re-polarization and occurs just as
the ventricles are starting to relax. It smaller and wider
than QRS complex as the re-polarization is slower.

9. INTREPRETATION OF ECG
• The term Systole refers to the phase of contraction and the
term diastole is the phase of relaxation.
• P wave:0.1 seconds: indicates atrial depolarization.
• QRS complex: 0.08 to 0.12 seconds: indicates ventricular
depolarization.
• T wave: 0.27 seconds: Ventricular re-polarization.
• P-R interval= 0.12 to 0.2 seconds: atrial and AV bundle
conduction.
• QT Interval 0.2 to 0.4 seconds: Ventricular depolarization
and re-polarization.
• 0.6 seconds gap between each cycle.
• In addition there is a U wave seen as a tiny hump after the T
wave. It represents late re-polarization of Purkinje fibers in
ventricles.

10. The graph paper recording produced by the machine is termed an
electrocardiogram,
It is usually called ECG or EKG
STANDARD
CALLIBRATION
Speed= 25mm/s
Amplitude = 0.1mV/mm
1mV 10mm high
1 large square 
0.2s(200ms)
1 small square 0.04s
(40ms) or 1 mV amplitude

11. The limb electrodes
RA - On the right arm,
LA – On the left arm this time.
RL - On the right leg, lateral calf muscle
LL- On the left leg this time.
The 6 chest electrodes
V1 - Fourth intercostal space, right sternal border.
V2 - Fourth intercostal space, left sternal border.
V3 - Midway between V2 and V4.
V4 - Fifth intercostal space, left midclavicular line.
V5 - Level with V4, left anterior axillary line.
V6 - Level with V4, left mid axillary line.
Placement of electrodes/Leads: 10 leads

12. Place all theelectrodes
correctly
These are all
electrodes

13. INTREPRETATION OF ECG
 The interpretation of ECG is based on the size and timing of
the waves. This indicates the structure and function of heart
including conduction system. The 12 reading indicates reading
from 12 different angles.
 Larger P wave indicates enlargement of atrium.
 Enlarged Q wave and Flat T wave indicates MI.
 Enlarges R wave indicates enlarged ventricles.
 P-Q interval: represents the conduction time from beginning
of atrial excitation to ventricular excitation. Time required for
the transmission of action potential. The longer duration
occurs in times of CAD & RHD
 The elevated ST segment and longer QT segment is also
observed in acute MI.
 ECG is also done during induced exercise/stress testing in
order to understand heart’s response to exercise.

14. CARDIAC CYCLE
•Cardiac cycle includes all the activities of the heart
including systole and diastole of atrium and
ventricle.
•A cardiac cycle lasts up-to 0.8 seconds.
•Normal heart rate is 72 beats/ minutes.
•The cardiac cycle involves three stages such as Atrial
Systole, Ventricular Systole and Relaxation period.
Atrial systole includes depolarization of SA node (P
wave), contraction of atria (systole) and flow of
blood into ventricle. It lasts around 0.1 seconds.

15. CARDIAC CYCLE
Ventricular systole which lasts 0.3seconds are the
contraction of ventricles. The atrial relaxation also
takes place at this time. The concept of iso-
volumetric contraction takes place, which is the
contraction of ventricular valves for 0.05 seconds
before the semi lunar valves of pulmonary artery
and aorta are opened.
•This helps in the rise of pressure inside the
ventricles around 80-120 mmHg which forcibly open
the semi lunar valves to push the blood into aorta
and pulmonary trunk.
•Ventricular ejection lasts for 0.25 seconds and
around 70ml of blood is ejected by both ventricles.

16. CARDIAC CYCLE
•The volume of blood present in the ventricle at the
end of atrial systole or ventricular diastole is called
End –Diastolic Volume (EDV) (130ml).
•The volume of blood remaining in each ventricle at
the end of systole is called End Systolic volume
(ESV). (60ml)
•The volume ejected per beat from each ventricle is
called stroke volume. EDV – ESV = SV (130-60=70ml)
Relaxation Period: This last for about 0.4 seconds and
both atrium and ventricles are well relaxed. This is
known as ventricular diastole. This also helps in
atrial filling.

17. HEART SOUNDS
•Auscultation is the act of listening to sounds within
the body.
•It is done with stethoscope.
•Heart sounds are formed by the turbulent blood flow.
(a sound produced while blood flow through smaller
orifice.)
•There are four heart sounds such as S1, S2, S3 and S4.
But only S1 and S2 can be heard by stethoscope since
the other sounds are too mild.
•The first sound S1 can be described as a lubb sound
which is louder and bit longer than the second sound.
It is caused by blood turbulence associated with
closure of AV Valve before ventricular systole begins.

18. HEART SOUNDS
•The second sound S2 can be described as a dupp
sound which is shorter and less louder than the first
sound. It is caused by blood turbulence associated
with closure of SL Valve before ventricular diastole
begins.
•S4 is the sound of blood turbulence during atrial
systole. S3 is the sound of blood turbulence during
ventricular filling. Both are abnormal.

19. CARDIAC OUTPUT
•Cardiac Output: is the volume of the blood ejected
from the left ventricle or right ventricle to aorta or
pulmonary artery.
•This is equal to stroke volume.
CO = SV x HR
CO = 70ml x 75 beats
= 5250ml/min
=5.25L/mts. (315 L/ hour and 7560 L/day)
•Cardiac Reserve is the term used to show the
difference between a person’s cardiac output in rest
and activity(maximum).

20. REGULATION OF HEART BEAT
Autonomic Regulation:
•A regulation from cardiac center in medulla
oblongata. Innervations of the heart by sympathetic
and parasympathetic nervous system.
•The faster movement of muscle and limbs
(proprioceptor / limbic system) and chemoreceptor
(blood chemical changes) and baroreceptors
(monitoring stretch changes of blood vessels) send
impulse to cardiac center to increase/decrease
heartbeat.
•Important baroreceptors are present in the arch of
the aorta and carotid arteries. They detect changes
in blood pressure.

21. REGULATION OF HEART BEAT
•Sympathetic neurons (cardiac acceleratory nerves)
extend from thoracic region to SA node and AV
node. This release more nor-epinephrine which
activates the cardiac muscles. This increases the
heartbeat as demanded.
•The maximum heartbeat possible by this stimulation
is 200 beats/mts for adolescents.
•Parasympathetic nerve impulses reach heart via
right and left Vagus nerves. They release
acetylcholine which decreases heartbeat.
•The heart can slow up to 20beats/mts. Or stop
momentarily.

22. REGULATION OF HEART BEAT
•Chemical Regulation: certain chemicals such as
hormones (epinephrine, nor epinephrine) increase
cardiac activity. Eg: presence of tachycardia in
hyperthyroidism. The Cat-ions also have a special
role in heart beat. They are + charges ions such as
Na+, K+, Ca++ which if increased in body can create
an imbalance of ICF and ECF which decrease the
cardiac action potential conduction.
•Exercise: regular exercise keeps the heartbeat
normal. Sometimes brady-cardia also occurs in time
of decreased exercise.
•Age & Body temperature
•Post operative patients. (cardiac surgeries)

23. CARDIAC CONDUCTION AND CYCLE