The document provides a comprehensive overview of ECG interpretation, detailing key components such as P-waves, QRS complexes, and intervals like PR and QT. It explains the normal ranges for these intervals and how deviations can indicate various cardiac conditions, including left and right axis deviations and arrhythmias such as atrial fibrillation and paroxysmal supraventricular tachycardia. Additionally, it outlines the anatomy of heart electrode placements and how to analyze ECG waveforms for diagnosing cardiac issues.

1. - Dr.Akif A.B

5. P-waves
P-waves represent atrial depolarisation.
In sinus rhythm, there should be a P-wave preceding each QRS complex.
PR interval
The PR-interval is from the start of the P-wave to the start of the Q
wave.
It represents the time taken for electrical activity to
move between the atria and ventricles.
QRS complex
The QRS-complex represents depolarisation of the ventricles.
It is seen as three closely related waves on the ECG (Q,R and S wave).

6. QT-interval
The QT-interval starts at the beginning of the QRS complex and finishes at the end
of the T-wave.
It represents the time taken for the ventricles to depolarise and then repolarise.
T-wave
The T-wave represents ventricular repolarisation.
It is seen as a small wave after the QRS complex.
ST segment
The ST-segment starts at the end of the S-wave and finishes at the start of the T-
wave.
The ST segment is an isoelectric line that represents the time between depolarization
and repolarization of the ventricles (i.e. contraction).

7. V1 – 4th intercostal space – right sternal edge
V2 – 4th intercostal space – left sternal edge
V3 – midway between V2 and V4
V4 – 5th intercostal space – midclavicular line
V5 – left anterior axillary line – same horizontal level as V4
V6 – left mid-axillary line – same horizontal level as V4 & V5
CHEST ELECTRODES POSITIONS

9. V1 Septal view of heart
V2 Septal view of heart
V3 Anterior view of heart
V4 Anterior view of heart
V5 Lateral view of heart
V6 Lateral view of heart

10. LIMB ELECTRODES
LA left arm
RA right arm
LL left leg
RL right leg – neutral – not used in
measurements

11. OTHER LEADS
Lead I Lateral view (RA-LA)
Lead II Inferior view (RA-LL)
Lead III Inferior view (LA-LL)
aVR Lateral view (LA+LL – RA)
aVL Lateral view (RA+LL – LA)
aVF Inferior view (RA+LA – LL )

13. -Each small square represents 0.04 seconds
-Each large square on the paper represents 0.2 seconds
-5 large squares therefore = 1 second
- 300 large squares = 1 minute
HOW TO READ ECG PAPER

14. The shape of the ECG waveform
-When the electrical activity of the heart travels towards a lead you get a positive
deflection.
- When the electrical activity travels away from a lead you get a negative deflection.
Electrical activity in the heart flows in many directions at once.
The wave seen represents the average direction.
The height of the deflection also represents the amount of electricity flowing in
that direction.
The lead with the most positive deflection is closest to the direction the
hearts electricity is flowing.
If the R-wave is greater than the S-wave it suggests depolarisation is moving towards that
lead.
If the S-wave is greater than the R-waves it suggests depolarisation is moving away from
that lead.
If the R and S-waves are of equal size it means depolarisation is travelling at exactly 90° to
that lead.

15. In healthy individuals you would
expect the axis to lie between
-30° and +90º.
The overall direction of electrical
activity is towards leads
I,II and III (the yellow arrow below).
As a result you see a positive
deflection in all these leads,
with lead II showing the most
positive deflection as it is the most
closely aligned to the
overall direction of electrical
spread.

16. You would expect to see the most negative deflection in aVR. This is due
to aVR looking at the heart in the opposite direction to the overall electrical activity.

17. Right axis deviation
Right axis deviation (RAD) is usually caused by right ventricular hypertrophy.
In right axis deviation the overall direction of electrical activity is distorted to
the right (between +90º and +180º).
Extra heart muscle causes a stronger
positive signal to be be picked up by leads
looking at the right side of the heart.
This causes the deflection in lead I to become
more negative and the deflection in III
to be more positive.
RAD is associated with pulmonary
conditions as they put strain on the right
side of the heart.
It can also be a normal finding in very
tall individuals

18. deflection in lead I to become more negative and the
deflection in III to be more positive.
RIGHT AXIS DEVIATION
Normally : Lead II is more positive than Lead I & III

19. In left axis deviation (LAD) the direction of overall electrical
activity becomes distorted to the left (between -30° and -90°).
This causes the deflection in lead I to become more positive and
the deflection in III to be more negative.
LAD is usually caused by conduction defects and not by increased mass of the left
ventricle.
LEFT AXIS DEVIATION

20. Normal Cardiac axis Right axis deviation Left axis deviation
Lead II is more positive
than Lead I & III
Lead III is more positive
than Lead I & II
Lead I is more positive and
Lead II & III are negative
Normal Cardiac axis
Right axis deviation
Left axis deviation

21. The mnemonic RRAW can help you remember what you
should be looking for and in what order:
Rate
Rhythm
Axis
Waveform (the various parts of the ECG mentioned above)
Reading ECGs

22. Heart rate can be calculated simply with the following method:
Work out the number of large squares in one R-R interval
Then divide 300 by this number and you have your answer
e.g. if there are 4 squares in an R-R interval 300/4 = 75 beats per minute
RATE

23. Look at the R-R intervals again – if they are equally spaced from each other the
rhythm is regular. If not the rhythm is irregular.
You can use the ‘card method’ to mark out the distance between each R wave to
check the spacing.
An irregular rhythm with no distinct P-waves suggests atrial fibrillation.
RHYTHM

24. Cardiac axis describes the overall direction of electrical spread within the heart.
In a healthy individual the axis should spread from 11 o’clock to 5 o’clock.
To figure out the cardiac axis you need to look at leads I,II and III.
AXIS

25. Normal cardiac axis
In normal cardiac axis Lead II has the most pos
itive deflection compared to Leads I and III
Right axis deviation
In right axis deviation Lead III has the most
positive deflection and Lead I should be
negative.
This is commonly seen in individuals with right
ventricular hypertrophy.
Left axis deviation
In left axis deviation Lead I has the most
positive deflection and Leads II and III are
negative.
Left axis deviation can suggest underlying heart
conduction system defects.

26. Normal duration = 120 msec Represents Atrial Depolarisation

27. P-waves represent atrial depolarisation.
In sinus rhythm, there should be a P-wave preceding each QRS complex.
Look at the p waves and comment on a number of things:
•Are P-waves present?
•Do they occur regularly?
•Is there sinus rhythm (does a P-wave precede each QRS complex?)
•Do the P-waves look normal? (smooth, rounded and upright)
•If P-waves are absent and there is an irregular rhythm it may suggest atrial
fibrillation.
P-waves

28. Seen in MITRAL STENOSIS
P-PULMONALE
Seen in Right Atrial
Hypertrophy
P-MITRALE

29. The P-R interval should be between 0.12-0.2 seconds (3-5 small squares).
P-R INTERVAL
Normal duration = 120-
200 msec
PR interval
The PR-interval is from the start of the P-wave to the start of the Q
wave.
It represents the time taken for electrical activity to
move between the atria and ventricles.
Short PR Interval (<120msec) Prolonged PR Interval
(>200msec)
Tachycardia Heart Blocks
Wolf Parkinson White Sx

31. SA Node
AV Node
ECG :
PR interval is
Prolonged but remains
constant
Treatment :
Oral Atropine ( Pacemakers is of no use since defect is in conduction but not at nodes)

32. Dropped
Beat
-Poor conduction of AV node
-PR interval lengthens i.e is not constant
-Sudden missed beats present

34. -Poor conduction of Bundle of His
-PR interval= Normal and is constant
-Heart rate is low
-Treatment : Pacemakers

35. -Complete destruction of AV node
-P-P Interval : Not constant
-R-R Interval : Mot constant
-Rx: Pacemaker

36. Used In Not used in
Sick sinus Sx 1st
Degree Heart Block
Mobitz type II Mobitz Type I
3rd
Degree Heart Block

37. Duration =80-120msec (2 small
squares)
QRS complex
The QRS-complex represents depolarisation of the
ventricles.
It is seen as 3 closely related waves on the
ECG (Q / R / S wave):
•The first downward deflection is the Q-wave
•Any upward deflection is an R-wave
•A downward deflections after an R-wave is called
the S-wave
Check the width of the QRS complexes:
•The QRS complexes should be approximately 0.12
seconds (3 small squares)
If longer than 0.12 seconds it suggests the complex
originated in the ventricles.
If shorter than 0.12 seconds it suggests the
complex is supraventricular in origin.

39. J Wave or Osborne wave

41. 2) Atrial Fibrillation
3) PSVT

42. -Paroxysmal Supraventricular Tachycardia
-Only Arrhythmia which can occur in Normal Heart
-Spontaneous termination with vomiting since it stimulates vagus
-R-R Interval is shortened but is constant
-Hidden P waves
Sudden onset of PSVT

43. -Ectopic focus = At Cavo Tricuspid Isthmus
-Rate = 240-350
-AV Nodal block = 2:1
-Max. Heart rate : 175bpm
-R-R Interval : Shortened but constant
-Narrow complex QRS
-Flutter/ Saw tooth waves

44. ATRIAL FLUTTER ATRIAL FIBRILLATION
Ectopic focus : Cavo Tricuspid Isthmus Left atrium
Atrial Rate : 240-350 300-600bpm
AV nodal block : 2:1 4:1
Max. Heart rate : 350/2 = 175bpm (AV
nodal block=2)
600/4 = 150bpm
R-R Interval : Decreased and constant Decreased and variable
Narrow complex QRS Narrow complex QRS
PSVT is differentiated from Atrial flutter by
presence of only one P wave

45. -Ectopic site of firing is present on ventricle
-Ventricular rate = 200bpm
-Atria is under SA node control. Hence Atrial Rate =100bpm
-So Atrio Ventricular Dissociation

46. CAUSES
Hypokalemia ( Cholera)
Hypomagnesemia ( Gitelman Sx)
Class IA/IC/III Anti-arrhytmic drugs
Erythromycin +
Astemizole/Terfinadine/Ketoconaz
ole
Erythromycin + Cisapride
Treatment : Magnesium Sulphate

47. -Na+ channel defect
-ST segment elevation + T wave inversion
+ve h/o sudden death of sibling

49. -MC Arrhythmia of Digoxin Toxicity
-Most characteristic arrhythmia of Digoxin Toxicity = Non Paroxysmal Atrial
Tachycardia with AV block

50. The ST-segment starts at the end of the S-wave and finishes at the start of the T-
wave.
It represents the interval between ventricular depolarisation and repolarisation.
It should be level with the PR-segment and the T-P segment in healthy individuals.
ST SEGMENT

51. ST ELEVATION
ST elevation is significant when it is
greater than 1mm (1 small square) in 2 or more contiguous limb leads or
>2mm in 2 or more chest leads.
It is most commonly caused by acute full thickness M.I

52. Normal ECG

53. Artery compromised Leads
Lateral wall M.I Left Circumflex vessels V5, V6 , I, aVL
Septal wall M.I Septal Br. Of Left Anterior
descending A.
V1, V2, I,aVL
Anterior wall M.I LAD V1- V4 , I, aVL
Extensive AWMI LMCA V1- V6 , I, aVL
Post. Wall M.I Post. Descending Artery >
Lt. Circumflex A.
V7, V8,V9 : ST elevation
V1-V4 : ST depression

58. ST DEPRESSION
ST depression ≥ 0.5 mm in ≥ 2 contiguous leads indicates myocardial ischaemia.
ST depression

59. ST SEGMENT Elevation
Other Features
1)Pericardial Friction Rub
2)MC Cause : TB

61. Causes
1)Pericardial effusion
2)Restrictive cardiomyopathy
3)Myxoedema
4)Obesity

62. ECG Changes in Atrial Fibrillation
1) Variable R-R Interval
2) Narrow QRS (normal QRS=80-100msec : 2 small
squares)
3) Absent P waves