Fundamentals of ECG -Introduction

Fundamentals of ECG
Introduction of Electrocardiogram (ECG/EKG)
Dr. Md.Toufiqur Rahman
MBBS, FCPS, MD, FACC, FESC, FRCP, FSCAI,
FCCP,FAPSC, FAPSIC, FAHA,FACP
Professor & head of Cardiology
CMMC, Manikganj
Ex professor of cardiology,
NICVD, Dhaka

History of electrocardiogram
Indications of electrocardiogram
Electrocardiogram machine
Different types of electrocardiography
Procedure of electrocardiogram
Electrodes and leads
ECG paper
ECG reporting
 Recent advancement of electrocardiogram
Fundamentals of ECG
Introduction of Electrocardiogram(ECG/EKG)

History of electrocardiogram
Willem Einthoven 1860-1927, Inventor of the first practical ECG in 1903
In 1924, Einthoven was awarded the Nobel Prize in Medicine for his pioneering work
in developing the ECG.

The first ECG machines were very large and bulky, weighing around 275 Kgs (600 lbs).

Figure: ECG from 1957
In 1937, Taro Takemi invented a new portable electrocardiograph machine

Indications of an ECG
to obtain information about the electrical function of the heart.
• Medical uses for this information are varied
• often need to be combined with knowledge of the structure of
the heart and
• physical examination signs to be interpreted.
Some indications for performing an ECG include the following:
• Chest pain or suspected myocardial infarction (heart attack),
such as ST elevated myocardial infarction (STEMI) or non-ST
elevated myocardial infarction (NSTEMI)
• Symptoms such as shortness of breath, murmurs,
fainting, seizures, funny turns, or arrhythmias including new
onset palpitations or monitoring of known cardiac arrhythmias
• Medication monitoring (e.g., drug-induced QT
prolongation, Digoxin toxicity) and management of overdose
(e.g., tricyclic overdose)

• Electrolyte abnormalities, such as hyperkalemia
• Perioperative monitoring in which any form of anesthesia is
involved (e.g., monitored anesthesia care, general
anesthesia). This includes preoperative asessment and
intraoperative and postoperative monitoring.
• Cardiac stress testing
• Computed tomography angiography (CTA) and magnetic
resonance angiography (MRA) of the heart (ECG is used to
"gate" the scanning so that the anatomical position of the
heart is steady.
• Clinical cardiac electrophysiology, in which a catheter is
inserted through the femoral vein and can have several
electrodes along its length to record the direction of
electrical activity from within the heart.

• ECGs can be recorded as short intermittent tracings
or continuous ECG monitoring.
• Continuous monitoring is used for critically ill
patients, patients undergoing general anesthesia, and
patients who have an infrequently occurring cardiac
arrhythmia that would unlikely be seen on a
conventional ten-second ECG. Continuous monitoring
can be conducted by using Holter monitors, internal
and external defibrillators and pacemakers,
and/or biotelemetry.
• Screening

Screening
• Evidence does not support the use of ECGs among those
without symptoms or at low risk of cardiovascular
disease as an effort for prevention. This is because an ECG
may falsely indicate the existence of a problem, leading
to misdiagnosis, the recommendation of invasive
procedures, and overtreatment.
• However, persons employed in certain critical occupations,
such as aircraft pilots, may be required to have an ECG as
part of their routine health evaluations.
• Hypertrophic cardiomyopathy screening may also be
considered in adolescents as part of a sports physical out of
concern for sudden cardiac death.

Electrocardiogram machine

• Electrocardiographs are recorded by machines that
consist of a set of electrodes connected to a central
unit.
• Early ECG machines were constructed with analog
electronics where the signal drove a motor to print
out the signal onto paper.
• Today, electrocardiographs use analog-to-digital
converters to convert the electrical activity of the
heart to a digital signal.
• Many ECG machines are now portable and commonly
include a screen, keyboard, and printer on a small
wheeled cart.

• Recent advancements in electrocardiography include
developing even smaller devices for inclusion in fitness
trackers and smart watches.
• These smaller devices often rely on only two electrodes to
deliver a single lead.
• Recording an ECG is a safe and painless procedure.
• The machines are powered by mains power but they are
designed with several safety features including an earthed
(ground) lead.
• Other features include:
Defibrillation protection: any ECG used in healthcare
may be attached to a person who requires defibrillation and
the ECG needs to protect itself from this source of energy.

• Electrostatic discharge is similar to defibrillation
discharge and requires voltage protection up to
18,000 volts.
• Additionally circuitry called the right leg driver can be
used to reduce common-mode interference (typically
the 50 or 60 Hz mains power).
• ECG voltages measured across the body are very
small. This low voltage necessitates a low noise circuit
and instrumentation amplifiers.
• Simultaneous lead recordings: Earlier designs
recorded each lead sequentially, but current models
record multiple leads simultaneously.

• Most modern ECG machines include automated
interpretation algorithms.
• This analysis calculates features such as the PR
interval, QT interval, corrected QT (QTc) interval,
PR axis, QRS axis, rhythm and more.
• The results from these automated algorithms are
considered "preliminary" until verified and/or
modified by expert interpretation.
• Despite recent advances, computer
misinterpretation remains a significant problem
and can result in clinical mismanagement.

Telelectrocardiogram
Wireless ECG
12 lead ECG test - standard ECG machine
3 lead ECG monitoring
5 lead ECG monitoring
Cardiac Event Recorder
Cardiac Loop Recorder
Implantable Loop Recorder (ILR)
Stress ECG
Different types of electrocardiography

Right: 5 lead wireless ECG sensor with seprate transmitter and receiver. © LifeSync
Left: Low cost compact wireless ECG sensor. © Isansys Lifecare.
This is a modern day innovation of the traditional clinical ECG machine with similar
functional capabilities.
Electrodes do not have wirers directly attached to the recording or monitoring machine.
These electrodes can transmit the signal wirelessly over to the receiver in the ECG machine.
• Wireless ECG machine
can offer more
flexibility for the
patients.
• useful when combined
with a treadmill test
where the lack of
cables can offer more
freedom of movement
during the test.
Wireless ECG

• modern adaptation of the original Willem Einthoven ECG machine
based on the Einthoven’s Triangle principles.
• the standard ECG machine used in clinical settings today.
• In 1942 Emanuel Goldberger added 3 more leads know as
augmented limb leads (aVR, aVL and aVF) to Willem Einthoven's
limb leads (I, II & III) and six chest leads (V1, V2, V3, V4, V5 & V6)
forming the basis of the 12 lead ECG.
12 lead ECG test - standard ECG machine

• used for continuous monitoring of heartbeat, heart rate, and heart
rhythm in critical situations like when the patient is under
anesthesia, in surgery or being transported in an ambulance to a
health center.
• requires the use of 4 electrodes that are placed on each of the
limbs.
• used in combination with other medical devices like an
echocardiogram.
3 lead ECG monitoring

Occasionally a 5 lead ECG is also used for monitoring purposes.
It uses 4 electrodes like a 3 lead ECG with an additional 5th electrode
placed on the chest.
Usually these devices do not produce a print out of the
electrocardiogram and may not store the information for further
review.
5 lead ECG monitoring

• a portable ECG monitor that can be worn by a patient for duration
of 24 to 48 hours while the device continuously monitors the heart
rhythm.
• fewer leads than a normal clinical ECG machine.
• The patient is free to move around and go around their usual daily
routines.
• useful for detecting abnormalities in heart rhythm that could be
easily missed during a clinical ECG test, which last less than a
minute.
• The device is returned to the
doctor at the end of the
monitoring period and the data
from the device is retrieved and
analyzed.
Holter Monitor Test

the symptoms may not appear during the ECG and a Holter Monitor test.
In such cases, a Cardiac Event Recorder can be worn continuously for
an extended period of time (2-4 weeks).
the size of a deck of cards and cables to the recording device connect
the electrodes.
Unlike the Holter Monitor, it continuously record the heart rhythm.
When the patient is experiencing the symptoms, he or she can activate
the recorder and the device will record the incident.
Depending on the model of the device,
multiple events can be recorded in the
internal memory.
The data can be transferred to the
consulting doctor for detailed analysis and
the doctor can make a more an accurate
diagnosis based on data obtained during the
abnormal incident.
Cardiac event recorder

• a compact USB pen drive sized medical device to monitor the heart function.
• attached to the surface of the skin around the area of the patient's heart.
• continuously records the heart rhythm for a certain duration, depending on the memory
capacity of the device and when the device memory is full, it starts overwriting from the
beginning of the recording, Hence the name, loop recorder.
• An event recorder can miss the starting of an abnormal heart activity due to the delay in
initiating the record function, A loop recorder has a record button when pressed can save
the immediate few minutes prior to the start of the abnormal heart activity and continue
recording for few additional minutes and then stop recording. This way the entire episode is
captured and not overwritten.
• When the patient experiences an abnormality the
recorder can be set to automatically record the
incident or can manually instruct the device to
record the incident.
• A loop recorder can be worn for many days or
weeks (up to 30 days), while the patient goes
around their routine day-to-day activities. It can be
removed during showering or swimming.
Cardiac loop recorder

• miniature loop recorder that can be implanted between the chest skin and the rib
cage, above the heart.
• Like the loop recorder it can be programmed to automatically start recording
when an abnormality is detected in the heart rhythm.
• activated by an external trigger device that the patient can carry around in the
form of a wrist band or a remote control.
• more suitable for patients who
experience symptoms that cannot be
monitored easily within the 30 days’
period of a normal external loop
recorder.
• have a battery life of up to 3 years
and suitable for long term continuous
monitoring in high-risk patients.
Implantable Loop recorder(ILR)

• also known as Cardiac stress test or treadmill test.
• In patients that can walk, the test is conducted on a treadmill.
• The patient is connected to an ECG monitoring machine and is asked to start
walking on the treadmill.
• As the test progresses, the intensity of the physical activity is increased.
• Patients with walking disability can use hand pedaling stationary bike.
• In some cases, a pharmaceutical drug is used to simulate the same effect in
disabled patients.
• designed the study how the patient's heart can cope up with added external
stress.
• abnormalities on ECG during the test
can be an indication of underlying
heart disease.
• The test is useful for overall
assessment of a person's health and is
often used by professionals like
Aviators and Astronauts during their
routine health checkups.
Stress ECG

• safe, noninvasive, painless tests and have no major risks.
• The electrodes (sticky patches) that connect the sensors to the chest do not send
out electric shocks.
• There may develop a mild rash or skin irritation where the electrodes were
attached.
• If any paste or gel was used to attach the electrodes, there may be an allergic
reaction to it.
• This irritation usually goes away once the patches are removed, without requiring
treatment.
• Ensure that electronic devices (e.g. smartphone)
are removed from the patient.
• These devices can produce artifact
(interference) and cause problems with the
readings.
• Place patient in supine or Semi-Fowler's
position. If both positions are impossible,
perform ECG with the patient in a more
elevated position.
Procedure of Electrocardiogram

 With arms lying flat on the side, ask the patient to relax the shoulders
and keep the legs uncrossed.
 For patients that do not fit comfortably on the bed or exam table due to
size, ask them to cross their arms on their stomach to reduce muscle
tension and movement.
 Unless performing a stress ECG test, ask the patient to lie still and
quietly until the test is done.
 A slight ECG artifact is not uncommon. However, further interference can
be reduced through the following steps:
 Switch off non-essential electrical devices and equipment within
the vicinity if possible.
 Check for cable loops and avoid running cables adjacent to
metallic objects as they can affect the signal.
 Inspect wires and cables for cracks or breaks. Replace as needed.
 If possible, use surge suppressors with the power supply.
 Ensure that filters and preamplifiers are appropriately adjusted.
 Ensure securely connection between patient cable and the ECG
device. Double check for gaps between connectors.
Procedure of Electrocardiogram

• An electrode is a conductive pad which is attached to the skin and
enables recording of electric currents.
• An ECG lead is a graphical description of the electrical activity of the
heart and it is created by analyzing the electrical currents detected
by several electrodes.
• each ECG lead (equivalent to a different video camera angle)
records a different view of cardiac electrical activity.
• The use of multiple ECG leads is necessitated by the requirement to
generate as full a picture of the three-dimensional electrical activity
of the heart as possible.
• The 12 ECG leads are divided into two
sets: the 6 extremity leads (3 unipolar
and 3 bipolar), which record voltages
on the frontal plane of the body; and
the 6 chest (precordial) leads, which
record voltages on the horizontal plane.
Electrodes and leads

• Together these 12 leads provide a three-dimensional picture of
atrial and ventricular depolarization and repolarization .
• The reason for exactly 12 leads is partly historical, a matter of the
way the ECG has evolved over the years since Einthoven's original 3
limb leads
• The heart, after all, is a three-dimensional structure, and its
electrical currents spread out in all directions across the body
• heart voltages directed upward and downward and to the right and
left are recorded by the frontal plane leads.
• The six chest leads (V1 through V6) record
heart voltages transmitted onto
the horizontal plane of the body
• the chest leads record heart voltages
directed anteriorly (front) and posteriorly
(back), and to the right and left.

• The standard ECG has 12 leads. Six of the leads are considered “limb leads” because they
are placed on the arms and/or legs of the individual.
• The other six leads are considered “precordial leads” because they are placed on the torso
(precordium).
• The six limb leads are called lead I, II, III, aVL, aVR and aVF. The letter “a” stands for
“augmented,” as these leads are calculated as a combination of leads I, II and III.
• The six precordial leads are called leads V1, V2, V3, V4, V5 and V6.

Anatomical relations of leads in a standard 12 lead electrocardiogram
 II, III, and aVF: inferior surface of the heart
 V1 to V4: anterior surface
 I, aVL, V5, and V6: lateral surface
 V1 and aVR: right atrium and cavity of left ventricle

Right sided lead

Posterior lead

Lewis lead (S5-lead) placement
• The Lewis lead configuration can help to detect atrial activity and its relationship
to ventricular activity.
• Named after Welsh cardiologist Sir Thomas Lewis (1881-1945) who first
described in 1913.
• Useful in:
 Observing flutter waves in atrial flutter
 Detecting P waves in wide complex tachyarrhythmia
to identify atrioventricular dissociation
Lewis lead placement
Right Arm (RA) electrode on manubrium
Left Arm (LA) electrode over 5th ICS, right sternal border.
Left Leg (LL) electrode over right lower costal margin.
Monitor Lead I

Color coding of 12 lead ECG
IEC (International Electrotechnical Commission) system and AHA (American Heart Association) system
If using AHA's system, use this mnemonic to easily recall limb electrode placement:
smoke over fire (black lead above the red lead) & snow over grass (white lead above the
green lead)

Electrode Reversal

FILTERING
• An electrocardiogram (ECG) is obtained analog and, in current
machines, is converted into a digital signal, where it is filtered to
block out some of the “noise” while keeping relevant parts of the
“signal.”
• Low frequency signals such as respiration are eliminated using a
high pass filter.
• High frequency signals such as noncardiac muscle potentials are
attenuated using a low pass filter.
• Specific “notch” filters that eliminate electromagnetic
interference at 50 to 60 Hz may also be used.
• Digital ECG data may also be compressed when sent to a
database to be retrieved for later use.
• Therefore, there may be a small difference in appearance of an
ECG printed at the bedside versus one downloaded from an
electronic medical record .

ECG paper

ECG paper
The electrocardiogram (ECG) is a plot of voltage on the
vertical axis against time on the horizontal axis.
The electrodes are connected to a galvanometer that
records a potential difference.
The needle (or pen) of the ECG is deflected a given
distance depending upon the voltage measured.
The ECG waves are recorded on special graph paper
that is divided into 1 mm2 grid-like boxes .
The ECG paper speed is ordinarily 25 mm/sec. As a
result, each 1 mm (small) horizontal box corresponds
to 0.04 second (40 ms), with heavier lines forming
larger boxes that include five small boxes and hence
represent 0.20 sec (200 ms) intervals.

ECG paper
 On occasion, the paper speed is increased to 50 mm/sec to
better define waveforms. In this situation, there are only six
leads per sheet of paper. Each large box is therefore only
0.10 sec and each small box is only 0.02 sec. In addition, the
heart rate appears to be one-half of what is recorded at 25
mm/sec paper speed, and all of the ECG intervals are twice
as long as normal. Other paper speeds are occasionally
used.
 Vertically, the ECG graph measures the height (amplitude) of
a given wave or deflection.
 The standard calibration is 10 mm (10 small boxes), equal to
1 mV. On occasion, particularly when the waveforms are
small, double standard is used (20 mm equals 1 mv).
 When the wave forms are very large, half standard may be
used (5 mm equals 1 mv). Paper speed and voltage are
usually printed on the bottom of the ECG for reference.

ECG reporting
The ECG ‘Rule of Fours’
Four Initial Features
Four Waves
Four Intervals
The key is to read each ECG methodically, following
the basic structure, looking at all leads.

The FOUR INITIAL FEATURES to look for on an ECG
(1) History/ Clinical Picture
• This is THE MOST IMPORTANT thing to look at on
ANY ECG.
• ECG is just like any other test, and should always
be interpreted in the clinical context, perhaps
even more so.
• Simple things need to be recorded, like the name,
age, time, patient symptoms (e.g. chest pain) and
other clinical features.
ECG reporting

A quick check for lead placement errors:
Limb leads: (a) check aVR for upside down P, QRS and T waves,
(b) aVL and aVR should generally be mirror images.
Chest leads: look for RS pattern in V1 – changing progressively
to QR pattern in V6.
(2) Rate
• The normal value is between 60-100/min. Lower than this is
bradycardia, higher is tachycardia.
(3) Rhythm
• Is the rhythm sinus or is it another rhythm? If so, what?
(4) Axis
ECG reporting

ECG reporting

Fundamentals of ECG -Introduction

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