The document provides an overview of performing and interpreting electrocardiograms (ECGs). It discusses what an ECG is, the procedure for performing one, how ECGs work by measuring electrical impulses in the heart, and lead placement. It also covers interpreting ECG tracings by examining elements like the P wave, QRS complex, T wave, and QT interval, as well as assessing the heart rate, rhythm, and axis. The document uses examples to illustrate abnormal P waves, QRS widths, ST segments, T waves, and other elements that may indicate underlying cardiac conditions.

1. BASIC ECG FOR MEM
DR MANAS PANDEY
MEM(GWU )
AMRI HOSPITAL.
CLASS- 1

2. Overview
• What is an ECG?
• Overview of performing
electrocardiography on a patient
• Lead and Lead placement.
• Interpreting the ECG

3. WHAT IS A ECG?
• Electrocardiogram
• Used for Tracing of heart’s electrical
activity.

4. Overview of procedure
GRIP
Greet, rapport, introduce,
identify, privacy, explain
procedure, permission
Lay patient down
Expose chest, wrists,
ankles
Clean electrode sites
May need to shave
Apply electrodes
Attach wires correctly
Turn on machine
Calibrate to 10mm/mV
Rate at 25mm/s
Record and print
Label the tracing
Name, DoB, hospital
number, date and
time, reason for
recording
Disconnect if
adequate and remove
electrodes

5. How does the ECG work?
Electrical impulse (wave of depolarisation) picked up by
placing electrodes on patient
The voltage change is sensed by measuring the current
change across 2 electrodes – a positive electrode and a
negative electrode
If the electrical impulse travels towards the positive
electrode this results in a positive deflection
If the impulse travels away from the positive electrode
this results in a negative deflection

6. Direction of impulse (axis)
Towards
the
electrode
= positive
deflection
Away from
the
electrode
= negative
deflection

7. Types of Leads
1.Coronal plane (Limb Leads)
1. Bipolar leads —l , l l , l l l
2. Unipolar leads —aVL , aVR , aVF
2.Transverse plane
1. V1 — V6 (Chest Leads)

8. Electrodes around the heart

9. Leads
How are the 12 leads on the
ECG (I, II, III, aVL, aVF,
aVR, V1 – 6) formed
using only 9 electrodes
(and a neutral)?
Lead I is formed using the
right arm electrode (red)
as the negative electrode
and the left arm (yellow)
electrode as the positive
- Lead I +
medics.cc

10. Leads
Lead II is formed
using the right arm
electrode (red) as the
negative electrode
and the left leg
electrode as the
positive
Lead II
medics.cc

11. Leads
Lead III is formed using the left arm
electrode as the negative electrode and
the left leg electrode as the positive
aVL, aVF, and aVR are composite leads,
computed using the information from the
other leads

12. Leads and what they tell you
Limb leads
Limb leads look at the heart in the coronal
plane
aVL, I and II = lateral
II, III and aVF = inferior
aVR = right side of the heart

13. Leads and what they tell you
Each lead can be thought of as ‘looking at’ an area
of myocardium
Chest leads
V1 to V6 ‘look’ at the heart on the transverse plain
V1 and V2 look at the anterior of the heart and R
ventricle
V3 and V4 = anterior and septal
V5 and V6 = lateral and left ventricle

14. Elements of the trace
medics.cc

15. What do the components
represent?
P wave =atrial depolarisation
QRS =ventricular depolarisation
T= repolarisation of the ventricles

16. medics.cc
medics.cc
Depolarisation begins at
the SA node
The wave of
depolarisation spreads
across the atria
It reaches the AV node
and the accessory bundle
Conduction is delayed as
usual by the in-built delay
in the AV node
However, the accessory
bundle has no such delay
and depolarisation begins
early in the part of the
ventricle served by the
bundle
As the depolarisation in this part of the ventricle
does not travel in the high speed conduction
pathway, the spread of depolarisation across the
ventricle is slow, causing a slow rising delta wave
Until rapid depolarisation
resumes via the normal
pathway and a more normal
complex follows

17. Interpreting the ECG

18. Interpreting the ECG
Check
Name
DoB
Time and date
Indication e.g. “chest pain” or “routine pre-op”
Calibration
Rate
Rhythm
Axis
Elements of the tracing in each lead

19. Calibration
Check that your ECG is calibrated correctly
Height
10mm = 1mV
Look for a reference pulse which should be the
rectangular looking wave somewhere near the
left of the paper. It should be 10mm (10 small
squares) tall
Paper speed
25mm/s
25 mm (25 small squares / 5 large squares)
equals one second

20. How to measure an ECG tracing

21. Rate
If the heart rate is regular
Count the number of large squares between
R waves
i.e. the RR interval in large squares
Rate = 300
RR
e.g. RR = 4 large squares
300/4 = 75 beats per minute

22. Rate
If the rhythm is irregular it may be better to
estimate the rate using the rhythm strip at the
bottom of the ECG (usually lead II)
The rhythm strip is usually 25cm long (250mm i.e.
10 seconds)
If you count the number of R waves on that strip
and multiple by 6 you will get the rate

23. Rate
Square Counting: 300-150-100-75-60-50-42A
Count QRS in 10 second rhythm strip x 6  use this method to determine
rate when rhythm is irregular (e.g., atrial fibrillation)

24. Rhythm
Is the rhythm regular?
The easiest way to tell is to take a sheet of paper and line up one
edge with the tips of the R waves on the rhythm strip.
Mark off on the paper the positions of 3 or 4 R wave tips
Move the paper along the rhythm strip so that your first mark lines
up with another R wave tip
See if the subsequent R wave tips line up with the subsequent
marks on your paper
If they do line up, the rhythm is regular. If not, the rhythm is irregular

25. Rhythm
Look at the rhythm strip below and answer the questions
• Are P waves present?
– yes
• Is there a P wave before every QRS complex and a QRS complex after
every P wave?
– yes
• Are the P waves and QRS complexes regular?
– yes
• Is the PR interval constant?
– yes
Yes to all these
questions, so this is
normal sinus rhythm!

26. Rhythm
Sinus arrhythmia
There is a change in heart rate depending on the phase of
respiration
Q. If a person with sinus arrhythmia inspires, what happens to their
heart rate?
A. The heart rate speeds up. This is because on inspiration there is
a decrease in intrathoracic pressure, this leads to an increased
venous return to the right atrium. Increased stretching of the right
atrium sets off a brainstem reflex (Bainbridge’s reflex) that leads to
sympathetic activation of the heart, hence it speeds up)
This physiological phenomenon is more apparent in children and
young adults

27. Axis
The axis can be thought of as the overall
direction of the cardiac impulse of
depolarisation of the heart
An abnormal axis (axis deviation) can give
a clue to possible pathology

28. Axis
Lead I and AVF – look at the QRS complex. Is it mostly upgoing or downgoing?
Lead I
Lead AVF
Deviation nml Left Right
(leaving) (reaching)

29. Practice!

30. Axis deviation - Causes
Wolff-Parkinson-White syndrome can cause both Left and Right
axis deviation
A useful mnemonic:
“RAD RALPH the LAD
from VILLA”
Right Axis Deviation
Right ventricular hypertrophy
Anterolateral MI
Left Posterior Hemiblock
Left Axis Deviation
Ventricular tachycardia
Inferior MI
Left ventricular hypertrophy
Left Anterior hemiblock

31. The P wave
The P wave represents atrial
depolarisation
It can be thought of as being
made up of two separate
waves due to right atrial
depolarisation and left atrial
depolarisation.
Which occurs first?
Right atrial depolarisation
right atrial depolarisation
Sum of
right and
left waves
left atrial depolarisation

32. The P wave
Dimensions
No hard and fast rules
Height
a P wave over 2.5mm should arouse suspicion
Length
a P wave longer than 0.08s (2 small squares) should
arouse suspicion

33. Common P wave abnormalities
include:
• P mitrale (bifid P waves)> left
atrial enlargement.(mitral
stenosis.)
• P pulmonale (peaked P waves), >
right atrial enlargement.
( pulmonary hypertension (e.g. cor
pulmonale from chronic respiratory disease).
• P wave inversion> ectopic atrial
and junctional rhythms.
• Variable P wave morphology >
multifocal atrial rhythms.

34. The PR interval
• The PR interval is measured between the start of the P
wave to the start of the QRS complex
• (therefore if there is a Q wave before the R wave the PR
interval is measured from the start of the P wave to the
start of the Q wave, not the start of the R wave)
• The PR interval corresponds to the time period between
depolarisation of the atria and ventricular depolarisation.
• A normal PR interval is between 0.12 and
0.2 seconds ( 3-5 small squares)

35. The Q wave
Are there any pathological Q
waves?
A Q wave can be
pathological if it is:
Deeper than 2 small
squares (0.2mV)
and/or
Wider than 1 small
square (0.04s)
and/or
In a lead other than III or
one of the leads that look
at the heart from the left (I,
II, aVL, V5 and V6) where
small Qs (i.e. not meeting
the criteria above) can be
normal
Normal if in
I,II,III,aVL,V5-
6
Pathologic
al
anywhere

36. medics.cc
Differential Diagnosis
1. Myocardial infarction
2. Cardiomyopathies — Hypertrophic (HCM), infiltrative
myocardial disease
3. Rotation of the heart — Extreme clockwise or counter-
clockwise rotation
4. Lead placement errors — e.g. upper limb leads placed on
lower limbs
Loss of normal Q waves
The absence of small septal Q waves in leads V5-6 should be
considered abnormal.
Absent Q waves in V5-6 is most commonly due to LBBB.

37. QRS width
The width of the QRS complex should be less
than 0.12 seconds (3 small squares)

38. The ST segment
The ST segment should sit on the isoelectric line
If the ST segment is elevated but slanted, it may
not be significant

40. The T wave
Are the T waves too tall?
No definite rule for height
T wave generally shouldn’t
be taller than half the size
of the preceding QRS
Causes:
Hyperkalaemia
Acute myocardial
infarction

41. The QT interval
The QT interval is measured from the start of the
QRS complex to the end of the T wave.
The QT interval varies with heart rate
As the heart rate gets faster, the QT interval gets
shorter
It is possible to correct the QT interval with
respect to rate by using the following formula:
QTc = QT/√RR (QTc = corrected QT)

42. The QT interval
The normal range for QTc is 0.38-0.42
A short QTc may indicate hypercalcaemia
A long QTc has many causes
Long QTc increases the risk of developing
an arrhythmia

43. The U wave
U waves occur after the T wave and are
often difficult to see
They are thought to be due to
repolarisation of the atrial septum
Prominent U waves can be a sign of
hypokalaemia, hyperthyroidism

44. Osborn Wave (J Wave)
• The Osborn wave (J wave) is a positive
deflection at the J point (negative in
aVR and V1). It is usually most
prominent in the precordial leads
• seen in hypothermia (typically T<30C
• Acute myocardial ischaemia
• Hypercalcaemia
• Takotsubo cardiomyopathy
• Left ventricular hypertrophy due to
hypertension
• Neurological insults such as intracranial
hypertension, severe head injury and
subarachnoid haemorrhage
• Severe myocarditis
• Brugada syndrome [Bjerregaard et al]

45. Elements of the tracing
P wave
Magnitude and shape,
e.g. P pulmonale, P mitrale
PR interval (start of P to start of QRS)
Normal 3-5 small squares,
0.12-0.2s
Pathological Q waves?
QRS complex
Magnitude, duration and
shape
  3 small squares or 0.12s
duration
ST segment
Should be isoelectric
T wave
Magnitude and direction
QT interval (Start QRS to end of T)
Normally < 2 big squares or
0.4s at 60bpm
Corrected to 60bpm
(QTc) = QT/RRinterval

46. Lets Practice Few

47. ECG 1

48. ECG 2

49. ECG 3

50. ECG 4

51. ECG 5

52. ECG 6

53. Further work
Check out the various quizzes / games
available on the Imperial Intranet
Get doctors on the wards to run through a
patient’s ECG with you