- The document discusses electrocardiography (ECG), including what an ECG is, how to perform one, and how to interpret the results. Key aspects include placing 10 electrodes on the patient and using them to form 12 leads that examine the heart from different angles. The ECG traces the heart's electrical activity through waves like the P, QRS, and T waves. Interpreting the ECG involves checking various parameters like rate, rhythm, intervals, and amplitudes to identify any abnormalities.

1. ElectroCardioGraphy
Dr. Anil gupta

2. • What is an ECG?
• Overview of performing electrocardiography
on a patient
• Simple physiology
• Interpreting the ECG

3. What is an ECG?
Electrocardiogram: Tracing of heart’s electrical
activity

4. Electrode placement
 10 electrodes in total are placed on the patient
 Firstly self-adhesive ‘dots ’ are attached to the
patient. These have single electrical contacts
on them.
 The 10 leads on the ECG machine are then
clipped onto the contacts of the ‘dots.

5. Electrode placement in 12 lead ECG
 6 are chest electrodes Called V1-6 or C1-6
 4 are limb electrodes
 Right arm
Left arm
Left leg
Right leg
• The right leg electrode is a neutral or “dummy”!

6. chest electrodes
 V1 - 4th intercostal space right sternal edge
 V2 - 4th intercostal space left sternal edge
 V4 - over the apex ( 5th ICS mid-clavicular
line)
 V 3 - halfway between V2 and V4
 V5 - at the same level as V4 but on the
anterior axillary line
 V6 at the same level as V4 and V5 but on the
mid-axillary line

7. Electrode placement

9. Electrophysiology
 Pacemaker = sinoatrial node
 Impulse travels across atria
 Reaches AV node
 Transmitted along interventricular septum in
Bundle of His
 Bundle splits in two (right and left branches)
 Purkinje fibres

11. How does the ECG work?
 Electrical impulse picked up by electrodes on
patient
 Voltage change is sensed by current change across
2 electrodes a positive electrode and a negative
electrode
 Towards the positive electrode : positive
deflection
 Away from the positive electrode: negative
deflection

12.  How are the 12 leads on the ECG 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

17. • Lead III is formed using the left arm
electrode as the negative electrode and
the left leg electrode as the positive

18. Types of Leads
• Coronal plane (Limb Leads)
 Bipolar leads — l , l l , l l l
Unipolar— aVL , aVR , aVF
• Transverse plane
 V1 — V6 (Chest Leads )

19. Leads and what they tell you
• 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

20. Leads look at the heart from different
directions

21. Chest leads
• V1 to V6 ‘look ’ at the heart on the transverse
plain
• V1 and V2 look at the anterior of the heart and Rt
ventricle
• V3 and V4 = anterior and septal
• V5 and V6 = lateral and left ventricle

22. Elements of the trace

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

24. Interpreting the ECG
• Check : Name ,DoB , Time and date &
Indication
• Calibration
• Rate
• Rhythm
• Axis
• Elements of the tracing in each lead

25. Calibration
• Height : 10mm = 1mV
large square = 0.5 mV
 small square = 0.1 mV
• Paper speed : 25mm/s
 25 mm (25 small squares / 5 large squares) equals
one second)
 large square = 0.2 sec
small square = .04 sec

26. 26
ECG Graph
Paper
X- Axis time in seconds
Y-AxisAmplitudeinmillvolts

27. Rate
• Count the number of large squares between R
waves
 Rate = 300/ no of large square between R wave
or
 Rate = 1500/ no of small square between R wave

29. Sinus Rhythm
• Definition:
 Cardiac impulse originates from the sinus
node
 Every QRS must be preceded by a P wave.
(This does not mean that every P wave must be
followed by a QRS )
 Normal P wave axis( 0-90 degrees)

30. Axis
• Axis : overall direction of the cardiac impulse or
wave of depolarisation of the heart
• An abnormal axis (axis deviation) can give a clue
to possible pathology

31. Mean and ranges of normal QRS axes
by age
• Normal ranges of QRS axis vary with age.
• Newborns normally have RAD compared with
the adult standard.
• By 3 years of age, the QRS axis approaches
the adult

32. Age Mean (Range)
1 wk–1 mo + 110° (+30 to +180)
1–3 mo + 70° (+10 to +125)
3 mo–3 yr + 60° (+10 to +110)
Older than 3 yr + 60° (+20 to +120)
Adult + 50° (–30 to +105

34. Axis determination
• Successive approximation
Locate quadrant with leads I and aVF
Narrow down by using leads within quadrant
Use most equiphasic lead
Axis is perpendicular to that lead, in the
quadrant previously identified
Equal amplitudes
If two leads with equal net QRS amplitudes
exist, the mean axis lies midway between the
axis of these two leads

35. Quadrant determination

36. Amplitude vector
• Add net R-S in lead I, R-S in aVF
• Plot in mm on grid (lead I horizontal, lead aVF
vertical)
• Draw vector from origin to net amplitude
• Angle of vector = axis

37. RVH
• Large R wave in V1 and large S wave in V6
• Upright T wave in V1-V3
• RAD
• Persistent pattern of RV dominance
• Diagnosis depends on age adjusted values for R
wave and S wave amplitudes
• A qR complex or rSR’ pattern in V1 can also be
seen

38. LVH
• R wave > 98th percentile in V6 and S wave > 98th
percentile in V1
• LV “strain” pattern in V5 and V6 or deep Q waves
in left precordial leads
• “Adult” precordial R wave progression in the
neonate

39. T Axis
• Determined by the same methods used to
determine the QRS axis.
• In normal children, including newborns, the mean
T axis is +45 degrees, with a range of 0 to +90
degrees, the same as in normal adults.
• Upright in leads I and aVF.
• Can be flat but must not be inverted in these leads.
• The T axis outside of the normal quadrant suggests
conditions with myocardial dysfunction

40. QRS-T Angle
• The QRS-T angle is formed by the QRS axis and
the T axis.
• A QRS-T angle of >60* is unusual & > 90* is
certainly abnormal.
• Abnormally wide QRS-T angle with the T axis
outside the normal quadrant is seen in
Severe ventricular hypertrophy with “strain,”
 Ventricular conduction disturbances, and
 Myocardial dysfunction of a metabolic or
ischemic nature.

41. P wave
• Atrial depolarisation
• Best seen in leads II and V1
• Duration and amplitude are important in the
diagnosis of atrial hypertrophy.
• Normally, the P amplitude is less than 3 mm.
• The duration of P waves is shorter than 0.09 second
in children and shorter than 0.07 second in infants

42. Criteria for atrial hypertrophy

43. The PR interval
• Start of the P wave to the start of the QRS
complex
• if there is a Q wave before the R wave
 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 normal PR interval varies with age and heart
rate

44. Prolongation of the PR interval
• Myocarditis (rheumatic, viral, or diphtheric),
• Digitalis or quinidine toxicity, certain
• Congenital heart defects (endocardial cushion
defect, atrial septal defect, Ebstein’s anomaly),
• Hyperkalemia, and
• Normal heart with vagal stimulation.

45. Short PR interval
• Wolff-Parkinson-White (WPW) preexcitation
• Lown- Ganong-Levine syndrome
• Myocardiopathies of glycogenosis
• Duchene’s muscular dystrophy
• Friedrich’s ataxia,
• pheochromocytoma

46. Q wave
• The average duration is 0.02 second
• Pathological :Deeper than (0.5mV) and/or Wider
than 0.03sec
• In a lead other than III, avF
V5& V6 where small Qs (i.e. not meeting the criteria
above) can be normal
• Deep Q waves may be present in ventricular
hypertrophy of the “volume overload” type and in
septal hypertrophy.
• Deep and wide Q waves are seen in MI.
• Q waves in the right precordial leads (e.g., severe
RVH )

47. QRS
• The QRS duration varies with age
• Prolonged
 RBBB, LBBB, preexcitation (e.g., WPW
preexcitation)
 Intraventricular block (as seen in
hyperkalemia, toxicity from quinidine or
procainamide, myocardial fibrosis, and
myocardial ).
 Ventricular arrhythmias

48. ST segment
• The ST segment should sit on the isoelectric line
• It is abnormal if there is planar (i.E. Flat) elevation or
depression of the ST segment
• Elevation or depression of 1mm in limb leads and 2
mm in chest leads is normal
• An elevation or a depression of the ST segment is
judged in relation to the PR segment asthe baseline
• Planar ST depression can represent ischaemia

49. Non pathologic ST-Segment Shift
• J-depression is a shift of the junction between the
QRS complex and the ST segment (J
point)without sustained ST segment depression
• The J-depression is seen more often in the
precordial leads than in the limb leads

50. J DEPRESSION

51. Pathologic ST segment shift
• Abnormal shifts of the ST segment often are
accompanied by T-wave inversion.
• Downward slant followed by a diphasic or
inverted T wave
• Horizontal elevation or depression sustained for
longer than 0.08 second

53. The T wave
• Are the T waves too
tall?
• No definite rule for
height
• T wave generally
should not be taller
than half the size of
the preceding QRS
• Causes:
Hyperkalaemia/ LVH

54. • Flat T wave may indicate normal newborn,
hypokalaemia, hypothroidism, myocarditis, ischemia
• If the T wave is inverted it may indicate ischaemia
• T waves are frequently upright throughout the
precordium in the first week of life
• Thereafter, T waves in V1-V3 invert and remain
inverted from the newborn period until 8 years of age
• This is called the “juvenile T wave pattern”, and can
sometimes persist into adolescence
• Upright T waves in the right precordial leads in
children can indicate right ventricular hypertrophy

55. 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
• Correct the QT interval with respect to rate :
QTc = QT/√RR ( QTc = corrected QT)

56. • The upper limit of normal for QTc is
0.44 in > 6months
 0.45 in < 6 months
 0.47 in < 1week
• A short QTc may indicate hypercalcaemia,
digitalis effect and short QT syndrome
• A long QTc has many causes
• Long QTc increases the risk of developing an
arrhythmia