Electrocardiogram i.e. ECG, easy note for nursing students

1. Electrocardiogram

2. ECG/ Electrocardiography
• ECG is a three letter acronym for Electro-Cardio-Graphy.
• The word is derived from Greek word
‘electro(electricity),cardio(heart) and graph("to write“)
• It is a transthoracic interpretation of the electrical activity
of the heart over time captured and externally recorded by
skin electrodes.
• ECG is the gold standard for the noninvasive diagnosis of
cardiac diseases and may occasionally be the only marker
for the presence of heart disease.

3. INDICATIONS OF ECG
• Gold standard for diagnosis of cardiac arrhythmias
• Helps to detect electrolyte disturbances (hyper- &
hypokalemia)
• Allows for detection of conduction abnormalities
• Screening tool for ischemic heart disease during stress tests
• Helpful with non-cardiac diseases (e.g. pulmonary
embolism or hypothermia
• An ECG is a diagnostic tool, NOT a treatment No one is ever
cured by an ECG

4. ELECTROCARDIOGRAPHY TIMELINE
• 1872:Alexander Muirhead attached wires to a
feverish patient’s wrist to obtain a record of the
patients heart beat at St Bartholomews Hospital.

5. •
• 1887:British physiologist Augustus D. Waller of St Marys
Medical School, London publishes the first human
electrocardiogram. The trace from the heartbeat was
projected onto a photographic plate which was itself fixed
to a toy train.
• 1893: Dutch physiologist Willem Einthoven introduces the
term electrocardiogram at a meeting of the Dutch Medical
Association.
• 1895: Willem Einthoven distinguishes five deflections
which he names P, Q, R, S and T4

6. • 1895: Willem Einthoven distinguishes five deflections
which he names P, Q, R, S and T4
• 1902: Einthoven publishes the first electro -cardiogram
recorded on a string galvanometer.
• 1912: Einthoven addresses the Chelsea Clinical Society in
London and describes an equilateral triangle formed by his
standard leads I, II and III later called Einthovens triangle.
• 1924: Willem Einthoven wins the Nobel prize for inventing
the electrocardiograph.
• Einthoven recording his first ECG in
1902 by placing limbs in buckets of
conducting solution

7. Basic electrophysiology-physiological properties of
myocardial cell
• Automaticity: ability to initiate an impulse
• Excitability: ability to respond to a stimulus
• Conductivity: ability to transmit an impulse
• Contractility: ability to respond with pumping action
Depolarization and repolarization of a cardiac cell generates
action potential
• ECG is the composite representation of action potential of
all cardiac cell.

9. • CONDUCTION OF THE IMPULSE:
# Rapid Depolarization
- Due to rapid opening of Na Channels
- Duration: 2 miliseconds
- Amplitude: + 20mv
# Plateau
- phase when membrane potential becomes almost constant,
membranes slowly begins to repolarize
- Due to slow and prolonged opening of calcium channels
- Duration 200 and 300 m/s atrial and ventricle respectively
# Slow repolarization
- Due to closure of calcium channels and opening of potassium
channels
- Last for 50m/s
• Depolarization is followed by muscle contraction and
repolarisation is followed by muscle relaxation.

10. Velocity conduction of impulses (m/s)
• Arterial muscle fibers = 0.3 m/s
• Internodal fibers = 1m/s
• Av nodes = 0.05 m/s
• Bundle of His = 0.12 m/s
• Purkinje fibers = 4 m/s
• Ventricular muscle fibers = 0.5m/s

11. ECG waves

13. • P wave: first seen wave, small, upright (positive) wave
indicating atrial depolarization (0.1 s) (SA node towards the
AV node)
• Q wave: first negative wave
• R wave: first positive wave
• S wave: first negative after positive R wave
• T wave: rounded upright (positive) wave following QRS
complex indicating ventricular repolarization (0.2s)
• U wave: small rounded, upright (positive) wave following T
wave repolarization of purkinje muscle

14. • QRS complex: represents ventricular depolarization as well
as repolarization of atrium
• Q-T interval: measured from beginning of QRS complex to
end of T wave it represents the total ventricular activity and
the duration is 0.4-0.42s
• P-R interval: Distance beginning of P-wave and beginning
of QRS complex indicating the duration of depolarization
wave travelling from the atria to ventricles its duration is
0.12-0.2s
• S-T segment: Measured as a distance between S wave and
beginning of T wave and represents the time between the
ventricular depolarization and beginning of ventricular
repolarization its duration is 0.08 s.

15. Basic Electrocardiography
• The ECG is the graphical record of the electrical activity of
the heart
• The spread of the electrical impulse through the heart
produces weak electrical currents through the entire body
• which can be detected and amplified by the ECG machine
and recorded on calibrated graph paper
• The electrocardiograph uses thermal paper, which is a
graph paper & runs normally at a speed of 25mm/sec
• The grid on the paper consists of a series of small and large
boxes.

16. • Horizontal boxes measures time and vertical measures
voltages. OR Time is plotted on the X axis & voltage is
plotted on the Y axis.
• In X axis, 1 second is divided into 5 large squares each of
which represents 0.2 sec. Each large square is further
divided into 5 small squares which represents 0.04 sec.
• The ECG machine is calibrated in such a way that an
increase of voltage by 1 mVolt should move the stylus
vertically by 1cms.
• Each small box horizontal is equal to 0.04 sec and each
large box horizontal is equal to 0.20sec.
• On vertical axis, small box measures 1mm is equal to 0.1
mV and large box measures 5mm i.e. 0.5mV.

18. The 12-lead Electrocardiogram
• The standard 12-lead ECG consists of 4-standard limb leads
that record electrical activity in the frontal plane-traveling
up/down and right/left in the heart.
• 6-precordial leads that record electrical activity in the
horizontal plane-traveling anterior/posterior and right/left.
• Limb leads are recorded by electrodes placed on the arms
and legs, whereas precordial leads are recorded by
electrodes placed on the chest.
• Bipolar leads: has a positive pole and negative pole, with
each contributing equally to the recording lead I,II,III are
bipolar limb leads.

19. • Unipolar leads: A unipolar lead has one positive pole and a
reference pole in the centre of the chest that is
algebraically determined by the ECG machine.
• The reference pole represents the centre of the electrical
field of the heart and has a zero potential, so only the
positive pole of a unipolar lead contributes to the tracing.
• Unipolar leads are aVR, aVL, aVF these are also called as
augmented limb leads. These augmented leads are
produced when the current flows from right arm (aVR), left
arm (aVL), and left leg (aVF) respectively to the centre of
heart.

20. • The chest leads V1 to V6 are also
called unipolar leads.
• Right Chest and Posterior Leads:
additional leads can be recorded
on the chest or posterior thorax
to gain additional information
about right ventricular or
posterior infraction or right
ventricular hypertrophy

21. 12 conventional leads, physiologically
divided into two groups
1. Bipolar leads- 3 Standard limb leads
2. Unipolar leads-3 Augmented limb leads and 6
precordialc hest leads.
• Bipolar leads : These record the actual difference in
potential across the two electrodes. There are three
standard limb lead:
- Lead I Left arm Right arm
- Lead II Left foot Right arm
- Lead III Left foot Left arm
• These lead axes form the sides of an equilateral
triangle with the heart at the center ( Einthovens
triangle)

22. • The sum total of the potential in the three leads
equals zero and mathematically it could be
demonstrated that the potential in L II equals sum
of the potentials in L I and L III i.e. Einthovens law.
• Unipolar limb leads: Constituted by the indifferent
electrode which forms the negative electrode and
the exploring electrode which forms the positive
electrode.

23. • The indifferent electrode is constituted by
connecting all limb lead electrodes together
through an electrical resistance there by
maintaining the zero potential.
• The positive electrode records the true potential at
a given point.
• Here the cord is of low voltage.
• Goldberger augmented these leads for proper
recording, came to be known as augmented
unipolar limb leads, represented by aVR, aVF, aVL
leads.

25. lead Positive input Negative input View of the heart
Standard limb leads
Lead I Left arm Right arm lateral
Lead II Left leg Right arm inferior
Lead III Left leg Left arm inferior
Augmented limb leads
aVR Right arm Centre of the heart none
aVL Left arm Centre of the heart Lateral
aVF Left leg Centre of the heart Inferior

26. Lead positive input Negative input View of heart
Chest leads
V1 4th intercostal space to
right of sternum
Center of heart Septum
V2 4th intercostal space to
left of sternum
Center of heart Septum
V3 Midway between V2
and V4
Center of heart Anterior
V4 Left midclavicular line,
5th intercostal space
Center of heart Anterior
V5 Left anterior axillary
line 5th intercostal
space
Center of heart Lateral
V6 Left midaxillary line
5th intercostal space
Center of heart Lateral

28. Axis determination
• The electrical axis of the heart is the mean direction of the
action potentials traveling through the ventricles during
ventricular depolarization.
• The QRS complex, which represents ventricular
depolarization, is used for the determination of the
electrical heart axis.
• Generally perpendicular leads are taken account
a. Lead I and aVF are perpendicular leads
b. Lead II and aVL are perpendicular leads
c. Lead III and aVR are perpendicular leads

29. Methods of Axis determination
1. Simple method
2. Classic method
3. Equiphasic method

30. • The normal electrical axis of the heart is situated between -
300 and +900 with respect to the horizontal line
• Left axis deviation: the electrical heart axis is between -300
and -900 with respect to the horizontal line. Causes: Q
waves of inferior MI, emphysema, tricuspid atresia

31. • Right axis deviation: between +900 and 1800 with respect
to horizontal line. Causes are: normal in children, right
ventricular hypertrophy, chronic lung disease, anterolateral
MI, atrial septal defect.
• Extreme axis deviation /northwest axis : between +1800
and -900 with respect to horizontal line. Causes:
emphysema, hyperkalaemia, artificial cardiac pacing,
ventricular tachycardia

32. Classic method for axis determination

34. ECG interpretation
• Heart Rate
• Rhythm
• Various conduction intervals (Pr interval, QT interval)
• Description of QRS complex, ST segments and Twaves
• Cardiac axis
• Any abnormal waves i.e. j or u wave
• Regularity : measures R-R interval, P-P intervals
regularity, regular irregular or irregularly irregular
• P waves: same in size, shape, position, absence of p
wave, upright positive wave (normal), M-shaped or
negative wave
• Constant PR interval, o.12-0.20 sec
• Qrs interval: 0.06-0.10
• QT interval: normally less than half of r-r interval

35. Heart rate calculation
• Method: if rhythm is regular rate
1. Large boxes: counting the number of R-R interval and
should divided by 300 to get heart rate. Each large box is
0.2 sec so when we multiply it with 300 we get 60sec,
that’s why large boxes are divided by 300.
2. Small boxes: count small box between R-R interval and
divide 1500 to get heart rate. As a small box is 0.04 sec so
when we multiply to 1500 we get 60 sec.
3. If the rhythm is irregular: count p waves for 6-sec (30 large
box) and multiply with 10, the result will be heart rate.

37. Nursing Consideration
• Inform the patient regarding procedure
• No specific preparation is needed
• Instruct the patient to remove jewelries, any metal
substances, tight clothes/may need to wear gown
for comfortness
• Maintain supine position, no one should touch the
metal portion of bed.
• Open the chest area

39. • Connect the limb electrodes as per colour code
[red- right hand, yellow-left hand, green –left leg
and black (neutral)- right leg)
• Attach the chest leads
• To attach leads we must need gel to reduce air
conduction.
• Instruct patient not to move while procedure
• Calibrate the record with 1MV signal.
• Label the record with patient identification, time
and date
• Make comfort the patient after procedure.

40. Pooja Prakash
Cardio-vascular and Thoracic
Nursing