The document provides a comprehensive overview of ECG (electrocardiogram) history, its development as a clinical tool, and the mechanics of how it records the electrical activity of the heart. It details the nomenclature, standard leads, and methods for determining heart rhythm and rates, highlighting various normal and arrhythmic conditions. The document emphasizes the importance of clinical context in ECG analysis and includes tips for accurately interpreting ECG results.

1. UNDERSTANDI NG ECG
By
Dr. Sy e d Sa ifud d in.

2. History
Development as a clinically useful tool –
later half of nineteenth century.
12 lead standard ECG – early 20th century
– 1940
Alexander Muirhead – first to record
human ECG.
Augustus D Waller – first to publish in
1887, of Robert Goswell.

3. Nomenclature
Waller - ABCD for the 4 deflections
Later based on mathematical notation –
PQRST was started.
First used by Einthoven.

4. What does the ECG actually record
Electrical activity of the heart.
Also other muscles – skeletal muscles.
A ECG from relaxed patient is easy to
elicit.

5. ECG Paper: Dimensions
5 mm
1 mm
0.1 mV
0.04 sec
0.2 sec
Speed = rate
Voltage
~Mass

6. Measurements
ECG graphs:
1 mm squares
5 mm squares
Paper Speed:
25 mm/sec standard
Voltage Calibration:
10 mm/mV standard

8. How does ECG look at the heart?
Electrodes vs leads
Limb vs chest leads
Bipolar vs unipolar leads
Coranal vs transverse view

9. ECG Leads
The standard ECG has 12 leads:
3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads
The axis of a particular lead represents tthhee vviieewwppooiinntt ffrroomm
wwhhiicchh iitt llooookkss aatt tthhee hheeaarrtt..

10. The Concept of a “Lead”
RA
- - LA
- +
RA
+
LL +
LL
LA
LEAD II
LEAD I
LEAD III
Leads I, II, and III
• By changing the
arrangement of which
arms or legs are
positive or negative,
three unipolar leads
(I, II & III ) can be
derived giving three
"pictures" of the
heart's electrical
activity from 3 angles.
Remember, the RL
is always the ground
I
II III

11. Precordial Leads

12. Precordial Leads

13. Summary of Leads
Limb Leads Precordial Leads
Bipolar I, II, III
(standard limb leads)
-
Unipolar aVR, aVL, aVF
(augmented limb leads)
V1-V6

15. Direction of ECG deflection & direction of
current

16. Generation of waves

17. Wave forms

18. Duration of waves & segments

19. Normal
Summary
 Heart rate = 60 – 100 bpm
 PR interval = 0.12 – 0.20 sec
 QRS interval <0.12
 SA Node discharge = 60 – 100 / min
 AV Node discharge = 40 – 60 min
 Ventricular Tissue discharge = 20 – 40 min

20. Determining the Heart Rate
Rule of 300
10 Second Rule

21. Rule of 300
Take the number of “big boxes” between
neighboring QRS complexes, and divide this
into 300. The result will be approximately
equal to the rate
Although fast, this method only works for
regular rhythms.

22. 10 Second Rule
As most ECGs record 10 seconds of rhythm per
page, one can simply count the number of beats
present on the ECG and multiply by 6 to get the
number of beats per 60 seconds.
This method works well for irregular rhythms.

23. The QRS Axis
By near-consensus, the
normal QRS axis is defined
as ranging from -30° to +90°.
-30° to -90° is referred to as a
left axis deviation (LAD)
+90° to +180° is referred to as
a right axis deviation (RAD)

24. -90°
-60°
-30°
aVL
0°
I
30°
60°
aVR
II
90°
120°
III
-150°
180°
150°
-120°
aVF
Marked RAD
LAD
RAD
Normal Axis
-30° to +100°

26. Using leads I, II, III
LEAD 1 LEAD 2 LEAD 3
Normal UPRIGHT UPRIGHT UPRIGHT
Physiologica
l Left Axis UPRIGHT UPRIGHT /
BIPHASIC NEGATIVE
Pathological
Left Axis UPRIGHT NEGATIVE NEGATIVE
Right Axis NEGATIVE
UPRIGHT
BIPHASIC
NEGATIVE
UPRIGHT
Extreme
Right Axis NEGATIVE NEGATIVE NEGATIVE

27. Sinus Rhythms
Normal Sinus Rhythm
Heart
Rate Rhythm P Wave
PR Interval
(sec.)
QRS
(Sec.)
60 -
100 Regular Before each
QRS, Identical .12 - .20 <.12

28. Sinus Rhythms
Sinus Bradycardia
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
<60 Regular Before each
QRS, Identical .12 - .20 <.12

29. Sinus Rhythms
Sinus Tachycardia

Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
>100 Regular Before each
QRS, Identical .12 - .20 <.12

30. Sinus Rhythms
Sinus Arrhythmia
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
Var. Irregular Before each
QRS, Identical .12 - .20 <.12

31. Sinus Arrest
Sinus Rhythms
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
NA Irregular Before each
QRS, Identical .12 - .20 <.12

32. Sinus Arrest
Sinus Rhythms
Stop of sinus rhythm
New rhythm starts
Sinus Pause
One dropped beat is a sinus pause
Beats walk through

33. Atrial Fibrillation
Atrial Rhythms
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
Var. Irregular Wavy irregular NA <.12

34. Atrial Fibrillation
Atrial Rhythms
 No discernable p-waves preceding the QRS complex
 The atria are not depolarizing effectively, but fibrillating
 Rhythm is grossly irregular
 HR <100 - controlled a-fib
 if >100 - rapid ventricular response
 AV node acts as a “filter”.
 Often a chronic condition, medical attention only
necessary if patient becomes symptomatic.

35. Atrial Flutter
Atrial Rhythms
Heart Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
Atrial=250
– 400
Ventricula
rVar.
Irregular Sawtooth
Not
Measur-able
<.12

36. Ventricular Rhythms
Ventricular Tachycardia
Heart
Rate Rhythm P Wave PR Interval
(sec.)
QRS
(Sec.)
100 –
250 Regular
No P waves
corresponding to
QRS, a few may be
seen
NA >.12

37. Ventricular Rhythms
Ventricular Tachycardia
No discernable p-waves with QRS
 Rhythm is regular
 Atrial rate cannot be determined, ventricular
rate is between 150-250 beats per minute
 Must see 4 beats in a row to classify as v-tach

38. Ventricular Rhythms
Ventricular Fibrillation
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
0 Chaotic None NA None

39. Ventricular Rhythms
Ventricular Fibrillation
No discernable p-waves
No regularity
Unable to determine rate
Multiple irritable foci within the ventricles all
firing simultaneously
May be coarse or fine
 This is a deadly rhythm
Patient will have no pulse
Call a code and begin CPR

40. Asystole
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
None None None None None

41. Heart Block
First Degree Heart Block
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
Norm
. Regular Before each
QRS, Identical > .20 <.12

42. Heart Block
Second Degree Heart Block
Mobitz Type I (Wenckebach)
Heart
Rate Rhythm P Wave PR Interval
(sec.)
QRS
(Sec
.)
Norm
. can
be
slow
Irregula
r
Present but
some not
followed by
QRS
Progressively
longer
<.1
2

43. Heart Block
Second Degree Heart Block
Mobitz Type II (Classical)
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
Usually
slow
Regular
or
irregular
2 3 or 4 before
each QRS,
Identical
.12 - .
20
<.12
depend
s

44. Heart Block
Third Degree Heart Block
(Complete)
Heart
Rate Rhythm P Wave
PR
Interval
(sec.)
QRS
(Sec.)
30 –
60 Regular
Present but no
correlation to QRS
may be hidden
Varies
<.12
depend
s

45. Identifying the cardiac rhythm
I hope that the advise given here will be
sufficient to keep you out of trouble when
trying to identify the cardiac rhythm in an
emergency.
However, the recognition of some
arrhythmias can be difficult, even for the
specialist.

46. REMEMBER
IF IN DOUBT ABOUT A PATIENT’S
CARDIAC RHYTHM, DONOT HESITATE
TO SEEK THE ADVISE OF A
CARDIOLOGIST.

47. Analysing the rhythm
 Two questions in your mind—
1. Where does the impulse come from?
2. How is the impulse conducted?

48. Narrowing down on the possible
diagnosis!!!
1. How is the patient?
2. Is ventricular activity present?
3. What is the ventricular rate?
4. Is the ventricular rhythm regular or irregular?
5. Is the QRS complex width normal or broad?
6. Is atrial activity present?
7. How is the atrial activity and ventricular activity
related?

49. How is the patient?
 Never analyse ECG without the clinical
context in which it was recorded.
 NSR vs PEA
 Arrhythmia vs Artifact
 ALWAYS ---
1. Insist on knowing the clinical context
2. Make a note of the clinical context at the
top of the ECG

50. Is ventricular activity present?
Check for the electrical activity
Asystole – check for the electrodes and of
course the patient
P waves only – responds to emergency
pacing manoeuvres
If QRS present – proceed next

51. What is the ventricular rate?
Bradycardia - <60 beats/min
Normal - 60-100 beats/min
Tachycardia - 100 beats/min

52. Is the ventricular rhythm regular or
irregular?
 Spacing of the QRS complexes
1. Regular – equal
2. Irregular – variable
 Using a strip of paper
 Irregular cardiac rhythms –
1. Atrial fibrillation
2. Sinus arrhythmia
3. Any supraventricular rhythm with intermittent
AV block
4. Ectopic beats

53. Is the QRS complex width normal or
broad?
Clue about the origin of the rhythm.
Narrowed to one half of the heart.
Supraventricular vs ventricular
Ventricular repolarisation via AV node –
0.12s – narrow QRS complex.
Any block/impulse directly from ventricular
muscle – myocyte to myocyte conduction
– prolonged depolarisation - broad QRS
complex.

55.  Broad QRS complex –
1. Ventricular rhythm
2. Supraventricular rhythm with aberrant
conduction.
A GOOD GENERAL RULE IS THAT
BROAD COMPLEX TACHYCARDIA IS
ALWAYS ASSUMED TO BE VT
UNLESS PROVEN OTHERWISE.

56. VT vs SVT
Elderly
H/o Cardiac disease
Atypical broad
complexes
Diagnostic of VT –
Independent P wave
activity, fusion beats,
capture beats.
Young
No H/o Cardiac
disease
Typical LBBB/RBBB
morphology.

57. Is atrial activity present?
 4 categories –
1. P waves (atrial depolarization) – check
for orientation
2. Flutter waves – 300/min
3. Fibrillation waves – 400-600/min
4. Unclear activity –
 Hidden in QRS complex – AVNRT
 Absent – SA block / sinus arrest

58. How is the atrial activity and ventricular
activity related?
Association between QRS complex and P
wave –
Every QRS followed by P wave –
activated by common source – SA / AV
node
More P waves than QRS – Block
(partly/completely)
More QRS complexes than P waves – AV
dissociation

59. ST segment changes

60. Anatomic Groups
(Summary)

61. Ventricular hypertrophy

62. LVH

63. Bundle branch blocks

65. Artefacts
 If you encounter abnormalities that appear
atypical or do not fit with the patients clinical
condition, always consider the possibility that
they are artefacts caused by –
1. Electrode misplacement
2. External electrical interference
3. Incorrect calibration
4. Incorrect paper speed
5. Patient movement

66. Deflections occurring at a rate of 400-to-500
times/minute especially in view of the
morphology, irregularity, and clinical history
(of tremor) in this case.
ventricular fibrillation in a awake and alert
patient.

67. ECG-1

68. ECG-2

69. ECG-3

70. ECG-4

71. ECG-5

72. ECG-6

73. ALWAYS KEEP THINGS SIMPLE AND TRY
TO AVOID GETTING SIDE TRACKED BY
UNNESSARY DETAIL – THE DIAGNOSIS
WILL OFTEN OFTEN BE OBVIOUS ONCE
YOU HAVE IDENTIFIED THE KEY
FEATURES OF ECG.
--- THANK YOU !!!

74. Study resources
 www.ecglibrary.com
 www.skillstat.com/6sECG_rdm.html
 http://www.randylarson.
rhythmst.htmlcom/acls/master/
 Rapid Interpretation of EKG’s, Dale Dubin M.D.