Basics and interpretation with easy explanation

1. ECG
ANIKA DAHAL

2. INTRODUCTION
 ECG stands for electrocardiogram: electro =
electrical; cardio = heart; gram = recording.
 Therefore, the ECG records electrical activity
of the heart. When the heart beats, the cells
of the heart depolarize. When depolarization
occurs, positively and negatively charged ions
(Na+, Ca2+, K+, and Cl-) move in and out of the
heart cells. This movement of ions creates
electrical changes on the surface of each cell.

3.  At any given time, one could imagine that the
myocytes that are depolarizing are causing
microscopic electrical charges at each individual
cell.
 Adding up all those microscopic charges, you get a
total electrical charge. It is this total charge that
can be measured from the skin as an ECG. The
“size” of this charge will be determined by how
many microscopic charges are being added up at a
given time.
 The position in space of the total charge moves as
the wave of depolarization moves through the
heart. The ECG measures movement of the
electrical charge.

4.  12 lead Ecg: examines the electrical
activity of the heart from 12 points of
view. Only uses 10 electrodes.
 Two types of leads – unipolar and bipolar

5. CONTD
• ECG paper divided in to horizontal lines and
vertical lines, large square and small square
• Voltage is represented in the vertical axis of the
ECG paper .
• Each small square is 1 mm in height 1largee square
is 5mm which is equivalent to 0.5mv.
• Time is measure on the horizontal axis .each small
square signifies the passage of 0.04 sec
• Each large square indicate the passage of 0.20
sec.

6. THE ECG PAPER
 Horizontally
 One small box - 0.04 s
 One large box - 0.20 s
 Vertically
 One large box - 0.5 mV

7. BASIC PRINCIPLES OF ECG
 It is the record of electrical impulse generated
in the heart by depolarization and repolarization
of the myocardium.
 These impulses are transmitted to the surface
of the body where they are detected and picked
up by the electrodes and measured by
galvanometer (electrocardiograph).
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8. CLINICAL USES
The ECG is a useful tool in the diagnosis of conditions :
♪ MI and other types of CAD such as
angina.
♪ Cardiac dysrhythmias.
♪ Cardiac enlargement.
♪ Electrolyte disturbances (calcium,
potassium, magnesium, and phosphorous).
♪ Inflammatory diseases of the heart.
♪ Effects on the heart by drugs, such as
antiarrhythmics and tricyclic
antidepressants. 6/4/2018 Cardio Diagnostics 8

9. LEAD PLACEMENT
Bipolar limb leads (frontal plane):
 Lead I
 Lead II
 Lead III
Augmented unipolar limb leads (frontal plane):
 Lead aVR
 Lead aVL
 Lead aVF
Unipolar chest leads (horizontal plane):
 Leads V1, V2, V3: (Posterior Anterior)
 Leads V4, V5, V6:(Right Left, or lateral)
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10. Bipolar limb leads (frontal)
 Measure electric potentials of 2 of 3
electrodes
 Lead I: from Right arm to left arm (left view
of heart)
 Lead II: from Right arm to Left leg (inferior
left view)
 Lead III: from Left arm to Left leg (inferior
right view)

12.  Einthoven’s triangle : triangle formed by
limb leads

13. Augmented Limb Leads (Unipolar)
 Use one limb electrode as positive pole
and take average of inputs of the other
2 limb leads
AVR: Upper right side of heart
AVL: Upper left side of heart
AVF: Inferior wall of heart

14. LEAD PLACEMENT
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15. LEAD PLACEMENT
 V1: 4th intercostal space to the right of
sternum
 V2: 4th intercostal space to the left of
sternum
 V3: half way between v2 and V4
 V4: 5th intercostal space in the mid-clavicular
line
 V5: 5th intercostal space in the anterior axillary
line
 V6: 5th intercostal space in the mid axillary line
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17. NORMAL ECG
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18. P WAVE
 It is the first positive deflection, smoothly
rounded.
 Presence of P wave indicates that the
stimulus began in the S.A. node and
subsequently spreads through both atria
causing atrial contraction.
 It has a duration of less than 0.12 seconds
 And a height of 2.5mm.
 (3 small squares in width and height)6/4/2018 Cardio Diagnostics 18

19. Characteristics of a normal p wave:
 The maximal height of the P wave is 2.5
mm in leads II and / or III
 The p wave is positive in II and AVF, and
biphasic in V1
 The p wave duration is shorter than 0.12
seconds

20. QRS COMPLEX
 Q-wave; initial downward deflection
 R-wave; a large upward deflection
 S-wave; a second downward deflection
 It represents the depolarization of
ventricles, time required for the impulse
to spread through ventricles and complete
ventricular contraction.
 Normal QRS complex measures 0.08-0.11
sec or less than 3 small squares in width.
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21. P-R INTERVAL
 It measures from the beginning of P
wave to the beginning of QRS complex.
 It represents the time duration the
wave of contraction passes through the
entire conduction system from AV node
to the purkinje fibres in the
myocardium.
 Normally, it measures less than 0.20
seconds
 (5 small squares in width)6/4/2018 Cardio Diagnostics 21

22. S-T SEGMENT
 It begins at the end of S wave and terminates at the
beginning of T-wave.
 It correlates with the period between the
ventricular depolarization and repolarization.
 Normally, S-T segment remains on the isoelectric
line.
 If the S-T segment is more than 1 mm above or
below the base line, it indicates possible myocardial
ischemia or infarction.
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23. T-WAVE
 It represents the electrical recovery of
ventricles (repolarization).
 Normally, it appears upright and measures less
than 0.20 seconds in width and not more than
5mm in height.
 Flat T waves indicate myocardial ischemia
 Inverted T waves indicate myocardial infarction
 Unusually tall T waves indicate elevated serum
potassium levels.
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24. U WAVE
 It is the small upright wave of low voltage,
sometimes seen following T-wave.
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25. REPORTING OF THE ECG:-
1. heart rate
2. Rhythm
3. PR interval
4. QRS interval
5. QT interval
6. P wave
7. QRS complex
8. STsegment
9. T wave
10. U wave

26. RATE

30. CALCULATING RATE
Interpretation bpm Causes
 Normal 60-99
 Bradycardia <60 hypothermia, increased
vagal tone (due to vagal stimulation or e.g.
drugs), atheletes (fit people)
hypothyroidism, beta blockade, marked
intracranial hypertension, obstructive
jaundice, and even in uraemia, structural
SA node disease, or ischaemia.

31.  Tachycardia >100 Any cause of adrenergic
stimulation (including pain);
thyrotoxicosis; hypovolaemia; vagolytic
drugs (e.g. atropine) anaemia, pregnancy;
vasodilator drugs, including many
hypotensive agents; FEVER, myocarditis

32. RHYTHM
 Look at p waves and their relationship to QRS
complexes.
 Lead II is commonly used
 Regular or irregular?
 If in doubt, use a paper strip to map out
consecutive beats and see whether the rate is
the same further along the ECG.
 Measure ventricular rhythm by measuring the R-R
interval and atrial rhythm by measuring P-P
interval.

42. CARDIAC AXIS
Electrical impulse that travels towards
the electrode produces an upright
(positive) deflection (of the QRS
complex) relative to the isoelectric
baseline. One that travels away produces
negative deflection. And one that travels
at a right angle to the lead, produces a
biphasic wave.

44. Axis Lead I Lead II Lead III
Normal Positive Positive Positive/Negative
Right axis Negative Positive Positive
Left axis Positive Negative Negative

45. Remember, positive(upgoing) QRS
complex means the impulse travels
towards the lead. Negative means
moving away

48.  +90 to -30 – Normal
 -30 to -90 – left axis deviation
 +90 to +180 - Right axis deviation

52. Cardiac Axis Causes
 Left axis deviation Normal variation in
pregnancy, obesity; Ascites, abdominal
distention, tumour; left anterior
hemiblock, left ventricular hypertrophy,
Inferior MI
 Right axis deviation normal finding in
children and tall thin adults, chronic lung
disease(COPD), left posterior hemiblock,,
anterolateral MI.

53. P WAVE

54. Normal P- wave
3 small square wide, and 2.5 small
square high.
Always positive in lead I and II in
NSR
Always negative in lead aVR in NSR
Commonly biphasic in lead V1

55. P PULMONALE
TALL PEAKED P WAVE. GENERALLY DUE TO ENLARGED
RIGHT ATRIUM- COMMONLY ASSOCIATED WITH
CONGENITAL HEART DISEASE, TRICUSPID VALVE
DISEASE, PULMONARYHYPERTENSION AND DIFFUSE
LUNG DISEASE

56. BIPHASIC P WAVE
ITS TERMINAL NEGATIVE DEFLECTION MORE
THAN 1 MM DEEP IS AN ECG SIGN OF LEFT
ATRIAL ENLARGEMENT.

57. P MITRALE
WIDE P WAVE, OFTEN BIFID, MAY BE DUE TO
MITRAL STENOSIS OR LEFT ATRIAL
ENLARGEMENT.

66. Left Bundle Branch Block (LBBB)
 indirect activation causes left ventricle
contracts later than the right ventricle.
 QS or rS complex in V1 - W-shaped
 RsR' wave in V6- M-shaped
 Mnemonics: WILLIAM

69. Right bundle branch block (RBBB)
 indirect activation causes right ventricle
contracts later than the left ventricle
 Terminal R wave (rSR’) in V1 - M-
shaped
 Slurred S wave in V6 - W-shaped
 Mnemonics: MARROW

76. LVH
 Hypertension (most common cause)
 Aortic stenosis
 Aortic regurgitation
 Mitral regurgitation
 Coarctation of the aorta
 Hypertrophic cardiomyopathy

77. RVH
 Pulmonary hypertension
 Tetralogy of Fallot
 Pulmonary valve stenosis
 Ventricular septal defect (VSD)
 High altitude
 Cardiac fibrosis
 COPD
 Athletic heart syndrome