The document provides information about electrocardiograms (ECGs) including: 1) It describes the basic anatomy and electrical conduction system of the heart. 2) It explains what an ECG is and how it works by measuring the electrical signals produced by heart muscle depolarization and repolarization using electrodes placed on the body. 3) It details the 12-lead ECG system including the 10 wires attached to limbs and chest to measure electrical signals from different angles represented by 12 leads.

1. E.C.G
ELECTROCARDIOGRAM

2. THE HEART

6. Basics of Heart Anatomy
• The heart is the hardest working muscle in the
human body.
• Located at left side of the chest, the adult
human heart is about the size of one fist.
• The cardiovascular system, composed of the
heart and blood vessels
• Responsible for circulating blood throughout
your body to supply the tissues with oxygen
and nutrients

7. Intro to heart
• The human heart has a mass of between 250 and 350 grams and is about the size of a
fist. It is located anterior to the vertebral column and posterior to the sternum.
• It is enclosed in a double-walled sac called the pericardium. The superficial part of this sac
is called the fibrous pericardium. This sac protects the heart, anchors its surrounding
structures, and prevents overfilling of the heart with blood.
• The outer wall of the human heart is composed of three layers. The outer layer is called the
epicardium, or visceral pericardium since it is also the inner wall of the pericardium. The
middle layer is called the myocardium and is composed of muscle which contracts. The
inner layer is called the endocardium and is in contact with the blood that the heart
pumps. Also, it merges with the inner lining (endothelium) of blood vessels and covers
heart valves.
• The human heart has four chambers, two superior atria and two inferior ventricles. The
atria are the receiving chambers and the ventricles are the discharging chambers. The
pathway of blood through the human heart consists of a pulmonary circuit and a systemic
circuit. Deoxygenated blood flows through the heart in one direction, entering through
thesuperior vena cava into the right atrium and is pumped through the tricuspid valve into
the right ventricle before being pumped out through the pulmonary valve to
the pulmonary arteries into the lungs. It returns from the lungs through the pulmonary
veins to the left atrium where it is pumped through the mitral valve into the left
ventricle before leaving through the aortic valve to the aorta.

8. Consist of…
• Four chambers (two atria and two ventricles) that receive
blood from the body and pump out blood to it.
– The atria receive blood coming back to the heart.
– The ventricles pump the blood out of the heart.
• Blood vessels, which compose a network of arteries and
veins that carry blood throughout the body.
– Arteries transport blood from the heart to the body tissues.
– Veins carry blood back to the heart.
• Four valves to prevent backward flow of blood.
– Each valve is designed to allow the forward flow of blood and
prevent backward flow.
• An electrical system of the heart that stimulates
contraction of the heart muscle.

10. The heart's electrical system
• he heart's pumping action is regulated by an
electrical conduction system that coordinates
the contraction of the various chambers of the
heart.

11. • An electrical stimulus is generated by the sinus
node (also called the sinoatrial node, or SA node),
which is a small mass of specialized tissue located
in the right atrium (right upper chamber) of the
heart.
• The sinus node generates an electrical stimulus
regularly (60-100 times per minute under normal
conditions).
• This electrical stimulus travels down through the
conduction and causes the heart's lower
chambers to contract and pump out blood.

12. • The right and left atria (the two upper
chambers of the heart) are stimulated first
and contract a short period of time before the
right and left ventricles (the two lower
chambers of the heart).

13. • The electrical impulse travels from the sinus
node to the atrioventricular node (also called
AV node), where impulses are slowed down
for a very short period, then continue down
the conduction pathway via the bundle of His
into the ventricles.
• The bundle of His divides into right and left
pathways to provide electrical stimulation
to the right and left ventricles

14. • Normally at rest, as the electrical impulse moves
through the heart, the heart contracts about 60
to 140 times a minute, depending on a person's
age.
• Each contraction of the ventricles represents one
heartbeat.
• The atria contract a fraction of a second before
the ventricles so their blood empties into the
ventricles before the ventricles contract.

19. ELECTROCARDIOGRAPH
• As the heart undergoes depolarization and
repolarization, electrical currents spread throughout
the body because the body acts as a volume conductor.
• The electrical currents generated by the heart are
commonly measured by an array of electrodes placed
on the body surface and the resulting tracing is called
an electrocardiogram (ECG, or EKG)
• The Electrocardiograph is an instrument, which records
the electrical activity of heart
• ECG provides valuable information about wide range of
cardiac disorders

20. • Electrodes are placed on each arm and leg,
and six electrodes are placed at defined
locations on the chest.
• These electrode leads are connected to a
device that measures potential differences
between selected electrodes to produce the
characteristic ECG tracings

21. ECG leads
• ECG leads are
– Bipolar leads (e.g., standard limb leads) that utilize a
single positive and a single negative electrode
between which electrical potentials are measured
– Unipolar leads
• Limb leads
• Precordial leads
• (augmented leads and chest leads) have a single positive
recording electrode and utilize a combination of the other
electrodes to serve as a composite negative electrode.

22. Bipolar limb leads
Lead I: RA (-) to LA (+)
Lead II: RA (-) to LF (+)
Lead III: LA (-) to LF (+)

23. UNIPOLAR LIMB LEADS
• LIMB LEADS: Two of the limb leads are tied
together and recorded with respect to the third
limb
• aVR-Right arm is recorded with respect to a
reference established by joining the Left arm and
Left leg electrodes
• aVL-Left arm is recorded with respect to common
junction of RA and LL
• aVF-Left leg is recorded with two arm electrodes
tied together

25. Augmented unipolar limb leads
Lead aVR: RA (+) to [LA & LF] (-)
Lead aVL: LA (+) to [RA & LF] (-)
Lead aVF: LF (+) to [RA & LA] (-)

26. PRECORDIAL LEADS
Leads V1, V2, V3, V4, V5, V6

27. Unipolar chest leads
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.

28. • Normally, when an ECG is recorded, all leads are
recorded simultaneously, giving rise to what is called
a 12-lead ECG
• Each of the 12 leads represents a particular
orientation in space, as indicated below (RA =
right arm; LA = left arm, LF = left foot)

29. Electrodes, leads & wires
• Between the patient and the ecg machine is a
patient cable, and this is divided into a
number of different coloured wires (10 wires
for a 12 lead ecg).
• A lead is a view of the electrical activity of the
heart from a particular angle across the body,
obtained by using different combinations of
these wires.

30. The 12-Lead System
• The most commonly used clinical ECG-system, the
12-lead ECg system, consists of the following 12
leads, which are:
I , II , III
aVR , aVL , aVF
V1 ,V2 ,V3 ,V4 ,V5 ,V6

31. • To measure any electrical activity you need at
least two electrodes (a positive and a
negative) in order to form an electrical circuit
• To obtain a 12 lead ecg you would have 4
wires attached to each of the limbs, and six
wires placed around the chest, 10 wires in
total but you get 12 "leads“

32. Precordial Leads
• For measuring the
potentials close to the
heart, Wilson introduced
the precordial leads (chest
leads) in 1944. These leads,
V1-V6 are located over the
left chest as described in
the figure.

34. Einthoven's Triangle

35. BLOCK DIAGRAM
BRIDGE
LEAD POWER
PRE AMP O/P
SELECTOR AMPLIFIER
CIRCUIT
FREQUENCY
SELECTIVE
AUXILLARY FEED BACK
CIRCUITS NETWORK
CHART
PEN MOTOR
TRANSPORT
MOTOR

36. DESCRIPTION
• The potentials picked up by the patient
electrodes are taken to the lead selector switch
• Here the electrodes are selected TWO by TWO
according to the lead program
• The signal is then given to the preamplifier
• A preamplifier (preamp), or control amplifier, is
an electronic amplifier which prepares an
electronic signal for further amplification or
processing

37. • It is usually a 3 or 4 stage differential amplifier
• The amplified O/P is then given to the power
amplifier
• The O/P of the power amplifier is fed to the
pen motor which deflects the writing arm of
the paper
• Frequency selective network is an R-C
network, which provides necessary damping
of the pen

38. • The auxiliary circuits provide a 1 mV
calibration signal and automatic blocking of
the amplifier during change in the position of
the lead switch
• It also include a speed control circuit for the
chart driver motor

39. Extras
• Typical wave forms
• Signal Characteristics
• Einthoven's Triangle
• CMRR
• valves present in heart?