A to Z about ECG

1. ECG
Asst. Prof. Bhaumika Sharma
Chitwan Medical College

2. Introduction
• The standard 12-lead electrocardiogram (ECG) is
one of the most commonly used medical studies
in the assessment of cardiovascular disease.
• It is the most important test for interpretation of
the cardiac rhythm, detection of myocardial
ischemia and infarction, conduction system
abnormalities, preexcitation, long QT syndromes,
atrial abnormalities, ventricular hypertrophy,
pericarditis, and other conditions.

3. Positioning
• The standard 12-lead ECG is generally
performed with the patient lying quietly in the
supine position.
• Care should be taken to ensure that the skin is
clean and trimmed of excess hair in the areas
in which the leads are to be placed.
• In some instances, a mild abrasive pad can be
used to prepare the skin in these areas to aid
in apposition of the leads.

4. Technique
After preparation of the patient, apply the
electrocardiographic (ECG) leads in the manner
outlined below.
• It is recommended that the standard limb
leads are placed one on each limb distal to the
shoulders and hips, but they do not
necessarily need to be as far distal as the
wrists and ankles.
• Next, apply the precordial leads, taking care to
be as precise as possible in their positioning.

5. Contd.
• Lead V1: place at the 4th ICS at right sternal
border (RSB).
• Lead V2: place at the LSB, directly across from
lead V1, also in the 4th ICS.
• Lead V4: place in the 5th ICS at the mid
clavicular line,
• And then lead V3: place midway between
leads V2 and V4.

6. Contd.
• Lead V6: place in the horizontal plane of V4 at
the mid-axillary line,
• And then lead V5: placed in the same
horizontal plane as that of lead V4 in the
anterior axillary line or midway between leads
V4 and V6 when the anterior axillary line is
not readily discernible.

7. Electrode label Electrode placement
RA (Red) On the right arm, avoiding thick muscle.
LA(Yellow) In the same location that RA was placed, but on the left arm this time.
LL (Green)
On the left leg, lateral calf muscle.
RL (Black) On the right leg, lateral calf muscle
V1
In the fourth intercostal space (between ribs 4 & 5) just to the right of the
sternum
V2
In the fourth intercostal space (between ribs 4 & 5) just to the left of the
sternum.
V3 Between leads V2 and V4.
V4 In the fifth intercostal space (between ribs 5 & 6) in the mid-clavicular line .
V5 Horizontally even with V4, but in the anterior axillary line
V6 Horizontally even with V4 and V5 in the midaxillary line.

9. Contd.
• Note that precordial electrode placement in
women with large breasts can be problematic
due to obfuscation (confusion) of bony
landmarks.
• Therefore, it is recommended that the
electrodes be placed beneath, rather than
overlying, the breast.

10. Placement of electrodes
➢Ten electrodes are used for a 12-lead ECG. The
electrodes usually consist of a conducting gel,
embedded in the middle of a self-adhesive pad
onto which cables clip. Sometimes the gel also
forms the adhesive.
➢Proper placement of the limb electrodes, color
coded as recommended.
➢Note that the limb electrodes can be far down on
the limbs or close to the hips/shoulders, but they
must be even (left vs. right).

11. Post-procedure
• Once the ECG is completed, it should be reviewed by
the operator.
• If significant issues with the quality of the tracing
exist, the cause of the issue should be addressed and
the tracing repeated.
• After having obtained an acceptable tracing, remove
the ECG leads and help the patient off the
examination table.
• In the event that the adhesive from the electrodes is
not easily removed from the skin, the patient may be
given an alcohol pad or moist paper towel to aid in
its removal.

12. Basics
• It is possible to change the output of most
galvanometer (ECG devices) but it is standard to
represent each mV on the y axis as 10 mm and each
second as 25mm on the x-axis (that is a paper speed of
25mm/s).
• At a paper speed of 25 mm/s, one small block of ECG
paper translates into 40 ms. Five small blocks make up
one large block, which translates into 200 ms. Hence,
there are 5 large blocks /s
• A standard signal of 1 mV must move the stylus
vertically 10 mm, that is two large squares on ECG
paper.

15. Contd.
• For a routine analysis of the heart’s electrical
activity an ECG recorded from 12 separate
leads is used.
• A 12-lead ECG consists of three bipolar limb
leads (I, II, and III), the unipolar limb leads
(AVR, AVL, and AVF), and six unipolar chest
leads, also called precordial or V leads, (v1,
v2, v3, v4, v5 and v6).

16. • With these V leads, the second site is -0- so
there is no need to measure from two pointes,
only one point is needed.
• To obtain the measurements from these V
leads, you simply turn the dial on the EKG
machine to aVR, aVL, and aVF, respectively.

17. Normal Impulse Conduction
Sinoatrial node
AV node
Bundle of His
Bundle Branches
Purkinje fibers

19. Facts
• A typical ECG tracing of the cardiac cycle
(heartbeat) consists of a P wave, a QRS
complex, a T wave, and a U wave which is
normally visible in 50 to 75% of ECGs.
• The baseline voltage of the electrocardiogram
is known as the isoelectric line. Typically the
isoelectric line is measured as the portion of
the tracing following the T wave and
preceding the next P wave.

20. Analyzing ECG
• Standardized: 25 mm/s & 1mV= 10mm
• Rate, rhythm, axis
• 4 waves- P, Q, T & U
• 4 intervals- P-R, Q-T, QRS & R-R
• 2 segments- P-R & S-T,

22. Electrocardiogram

24. Waves & Interval
• P wave represents the sequential activation of
the right and left atria, and it is common to
see notched or biphasic P waves of right and
left atrial activation
– P duration < 0.12 sec/
– P amplitude < 2.5 mm
 QRS Complex
The QRS represents the simultaneous
activation of the right and left ventricles,
although most of the QRS waveform is derived
from the larger left ventricular musculature.

25. Waves
• The T wave represents the repolarization (or
recovery) of the ventricles.
• The normal T wave is usually in the same
direction as the QRS except in the right
precordial leads. In the normal ECG the T
wave is always upright in leads I, II, V3-6, and
always inverted in lead aVR.
• The U wave is not always seen. It is typically
low amplitude, and, by definition, follows the
T wave.

26. Waves & Interval
Normal PR interval
Measured from the beginning of the P wave to the
beginning of the QRS complex. The PR interval reflects
the time the electrical impulse takes to travel from the
sinus node through the AV node and entering the
ventricles. The PR interval is therefore a good estimate
of AV node function
0.12 to 0.20 s (3 - 5 small squares)
Normal QRS complex
< 0.12 s duration (3 small squares)

27. Waves & Interval
• Normal QT interval
–Measured from the beginning of the QRS
complex to the end of the T wave.
–A prolonged QT interval is a risk factor for
ventricular tachyarrhythmias and sudden
death. It varies with heart rate and for
clinical relevance requires a correction for
this, giving the QTc.
–Normal = 0.42 s. (2 big square)

28. ECG Grid

31. Normal Sinus Rhythm (NSR)
• Etiology: the electrical impulse is formed in
the SA node and conducted normally.
• This is the normal rhythm of the heart; other
rhythms that do not conduct via the typical
pathway are called arrhythmias.

32. Normal sinus Parameters
• Rate 60 - 100 bpm
• Regularity regular
• P waves normal
• PR interval 0.12 - 0.20 s
• QRS duration 0.04 - 0.12 s
Any deviation from above is sinus
tachycardia, sinus bradycardia or an
arrhythmia

33. P wave
• The P wave represents the electrical impulse
starting in the sinus node and spreading
through the atria.
• P wave represents atrial muscle
depolarization.
• It is normally <2.5 mm in height
• Duration: <0.12 second

34. QRS complex
• The QRS complex represents ventricular muscle
depolarization
• The first negative deflection after the P wave is
the Q wave, which is normally less than 0.04
second in duration and less than 25% of the R
wave amplitude;
• The first positive deflection after the P wave is
the R wave
• The S wave is the first negative deflection after
the R wave.
• The QRS complex is normally less than 0.12
seconds

35. T wave
• The T wave represents ventricular muscle
repolarization
(when the cells regain a negative charge; also
called the resting state).
• It follows the QRS complex and is usually the
same direction as the QRS complex.

36. U WAVE
• The U wave is thought to represent
repolarization of the Purkinje fibers, but it
sometimes is seen in patients with
hypokalemia (low potassium levels)

37. Waves & Interval
Normal PR interval
Measured from the beginning of the P wave to
the beginning of the QRS complex. The PR
interval reflects the time the electrical impulse
takes to travel from the sinus node through
the AV node and entering the ventricles.
0.12 to 0.20 s (3 - 5 small squares)
normal QRS complex
< 0.12 s duration (3 small squares)

38. RR interval
• The RR interval is measured from one QRS
complex to the next QRS complex.
• The RR interval is used to determine
ventricular rate and rhythm

39. Waves & Interval
• Normal QT interval
– measured from the beginning of the QRS complex
to the end of the T wave.
– A prolonged QT interval is a risk factor for
ventricular tachyarrhythmias and sudden death. It
varies with heart rate and for clinical relevance
requires a correction for this, giving the QTc.
– Normal = 0.42 s. (2 big square)

40. CALCULATION OF HEART RATE
0.2 sec for 1 heart beat
1sec=1/0.2 b
60sec=1/0.2*60=300
• count small or large square between two RR interval –
small = 1500 /small square, large = 300/large square
• Eg 1500/15=100, 300/3=100
• 1500/25 =60 300/5=60
if irregular count QRS complex in 30 large square = 6 sec.
multiply by 10
sinus rhthm :- normal 60 -100 bpm

41. Normal Sinus Rhythm
Implies normal sequence of conduction, originating in the sinus
node and proceeding to the ventricles via the AV node and His-
Purkinje system.
EKG Characteristics: Regular narrow-complex rhythm
Rate 60-100 bpm
Each QRS complex is proceeded by a P wave
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42. End
PART-1

43. PART-2
REPORTING ABNORMAL ECG

44. Cardiovascular circulatory

45. Sinus Bradycardia
30 bpm• Rate?
• Regularity? regular
normal
0.10 s
• P waves?
• PR interval? 0.12 s
• QRS duration?
Interpretation- Sinus Bradycardia

46. Sinus Tachycardia
• Etiology: SA node is depolarizing faster than normal,
impulse is conducted normally.
• Sinus tachycardia begins with regular rhythm
between 100-180 b/min
• The P wave and QRS complex are normal duration .
• Causes fever, heart failure, fluid loss hyperthyroidism,
hypercalcemia, medicine e.g. atropine.

47. Rhythm #3
70 bpm• Rate?
• Regularity? occasionally irreg.
2,7 different contour
0.08 s
• P waves?
• PR interval? 0.14 s (except 2,7)
• QRS duration?
Interpretation? NSR with Premature Atrial
Contractions

48. Premature Atrial Contractions
Deviation from NSR (normal sinus rhythm)
These ectopic beats originate in the atria (but
not in the SA node), therefore the contour of
the P wave, the PR interval, and the timing are
different than a normally generated pulse from
the SA node

49. Rhythm #4
60 bpm• Rate?
• Regularity? occasionally irreg.
none for 7th QRS
0.08 s (7th wide)
• P waves?
• PR interval? 0.14 s
• QRS duration?
Interpretation? Normal Sinus Rhythm with 1
Premature Ventricular Complex

50. Premature Ventricular Contractions
• Deviation from Normal Sinus Rhythm
– Ectopic beats originate in the ventricles resulting
in wide and bizarre QRS complexes.
– When there are more than 1 premature beats
and look alike, they are called “uniform”. When
they look different, they are called “multiform”.

51. Atrial fibrillation
Ventricular and atrial rate: Atrial rate is 300 to 600.
Ventricular rate is usually 120 to 200 in untreated atrial fibrillation
Ventricular and atrial rhythm: Highly irregular
QRS shape and duration: Usually normal, but may be abnormal
P wave: No discernible P waves; irregular undulating waves are seen
and are referred to as fibrillatory or f waves
PR interval: Cannot be measured
P: QRS ratio: many1

52. Atrial fibrillation
• Atrial fibrillation may occur for a very short
time (paroxysmal), or it may be chronic.
• Atrialfibrillation is usually associated with
advanced age, valvular heart disease,
coronary artery disease, hypertension,
cardiomyopathy,

53. Atrial Flutter
Ventricular and atrial rate: Atrial rate ranges between 250 and 400;
ventricular rate usually ranges between 75 and 150.
Ventricular and atrial rhythm: The atrial rhythm is regular; the ventricular
rhythm is usually regular but may be irregular because of a change in the AV
conduction.
QRS shape and duration: Usually normal, but may be abnormal or may be
absent
P wave: Saw-toothed shape. These waves are referred to as F waves.
PR interval: Multiple F waves may make it difficult to determine the PR
interval.
Causes are similar to that of atrial fibrillation.

54. Supra-ventricular Tachycardia
Narrow complex tachycardia.
Rate :150-250

55. Ventricular Tachycardia (VT)
VT is usually associated with coronary artery
disease and may precede ventricular fibrillation.
Ventricular and atrial rate: Ventricular rate is 100 to 200 beats
per minute; atrial rate depends on the underlying rhythm(eg,
sinus rhythm)
Ventricular and atrial rhythm: Usually regular; atrial rhythm
may also be regular.
QRS shape and duration: Duration is 0.12 seconds or more
abnormal shape (Wide complex tachycardia)

56. Supraventricular Tachycardia
Ventricular Tachycardia

57. Ventricular Fibrillation
Causes of ventricular fibrillation are the same as for VT; it may
also result from untreated or unsuccessfully treated VT.
Ventricular rate: Greater than 300 per minute
Ventricular rhythm: Extremely irregular, without specific
pattern
QRS shape and duration: Irregular, without recognizable
QRS complexes

58. Right bundle branch block

59. RBBB

60. Left bundle branch block

61. LBBB

62. Views of the Heart
Some leads get a
good view of the:
Anterior portion of
the heart- (V1-4)
Lateral portion of the
heart- (I, aVL, V5-6)
Inferior portion of the
heart-(II, III, aVF)

64. Blood Supply of Heart
Rt coronary artery: Inferior
wall: II, III, AVF
Lt coronary artery:
LAD: anterior wall: V1, V2,
V3, V4
Cx: Lateral wall: V5,V6, I,
AVL

67. ST Elevation Infarction
ST depression, peaked T-waves, then T-
wave inversion
The ECG changes seen with a ST elevation infarction are:
Before injury Normal ECG
ST elevation & appearance of Q-
waves
ST segments and T-waves return to
normal, but Q-waves persist
Ischemia
Infarction
Fibrosis

68. Non ST elevation

69. ST elevation MI

70. ST elevation MI

71. Non-ST Elevation Infarction
Here’s an ECG of an evolving non-ST elevation MI:
Note the ST
depression and
T-wave
inversion in
leads V2-V6.
Question:
What area of
the heart is
infarcting?
Anterolateral

72. ST Elevation (cont)
Elevation of the ST
segment (greater
than 1 small box) in
2 leads is
consistent with a
myocardial
infarction.

73. Anterolateral MI
This person’s MI involves both the anterior wall (V2-
V4) and the lateral wall (V5-V6, I, and aVL)!

74. DIGOXIN TOXICITY
Reverse ticks sign

75. DIGOXIN TOXICITY
Effect Toxicity

76. DIGOXIN TOXICITY

77. HYPERKALEMIA

78. HYPOKALEMIA
U wave present

79. Thank You

80. Axis

81. 12 lead ECG

82. 12 lead ECG

83. Q wave

84. T wave

85. Rt. Atrial Enlargement

86. Left atrial Enlargement