Dr. C. Kannan, PG, MGMCRI, Puducherry

1. ECG INTERPRETATION
Dr. C. Kannan
Post graduate
Pediatrics
MGMCRI

2. DISCUSSION
• Anatomy of conduction system of heart
• ECG leads and attachment
• Anatomy of ECG
• Basic concepts
• Cardiac Axis/Angle
• Conduction abnormalities
• Rhythm abnormalities
• Abnormalities P, QRS and T waves
• Exercises

3. ANATOMY OF CONDUCTION SYSTEM

4. LEADS & ATTACHMENT
Six standard leads
• Attached to all four limbs (1,2,3,VR,VL& VF)
• Right leg attachment has no value – act as earth
• Looks the heart in vertical plane
Six chest leads
• Attached to chest (V1-6)
• Looks the heart horizontal plane
Attachment
• Chest should be dry
• Patient should be calm with zero muscular activity

5. CHEST LEADS ATTACHMENT

6. LEADS LOOKING @
LEADS LOOKING @
1, 2 & VL Left lateral surface
3 & VF Inferior surface
V1, V2 & VR Right ventricle
V3 & V4 Septum & anterior wall of left ventricle
V5 & V6 Anterior & lateral wall of left ventricle

7. ANATOMY OF ECG
ECG machine
• Consists of stylus
• Runs at standard rate of 25 mm/s
• Over the ECG paper
• Calibration
• For signal of 1 millivolt
• Stylus should move 1cm vertically up

8. ANATOMY OF ECG
ECG paper
• Made up of squares
• Small square
• Each small square is 1 mm
• Represents 0.04 seconds/40 milliseconds
• large square
• Made up of 5 small squares = 5 mm
• Represents 0.2 seconds/200 milliseconds

9. HR FROM ECG
• HR
• 1500/No of small squares (or)
• 300/No of large squares
R-R INTERVAL (Large square) HEART RATE (Beats/Minute)
1 300
2 150
3 100
4 75
5 60
6 50

10. ANATOMY OF ECG
• P wave – Atrial depolarisation
• QRS wave – Ventricular depolarisation
• T wave – Ventricular repolarisation
• Note: Atrial repolarisation masked by vent. Depolarisation
• Segments are straight lines / but not the intervals

11. ANATOMY OF ECG
PR interval
• From beginning of P wave to the beginning of QRS wave
• Time taken for the excitation to spread
• From the SA node
• Upto ventricular muscle
• Should be called as PQ interval
• Commonly used as PR interval
• Duration: 3-5 small squares/120-220 ms

12. ANATOMY OF ECG
QRS complex
• Duration is 120 ms/3 small squares
• Low voltage QRS (<5 mm in limb leads/<10 mm in chest leads)
• High voltage QRS (>20 mm in LL/>30 mm in CL)
• Time taken for the excitation to
• Spread through the ventricles
• Represents
• Only vent. depolarisation
• No vent. Contraction
• Contraction is proceeding during ST segment

13. ANATOMY OF ECG
QT interval
• Represents both ventricular de/repolarisation
• Should be less than 450 ms
• Prolonged in electrolyte abnormalities/some drugs
T wave
• Repolarisation/relaxation of ventricles

14. BASIC CONCEPT
• If electrical signal passes towards the lead
• Positive deflection
• If electrical signal passes away from the lead
• Negative deflection
• If the electrical signal passes at right angle to lead
• Equally positive and negative deflection

15. CARDIAC AXIS
Normal cardiac axis
• If we see from front, depolarisation
• Spreads through ventricles
• From 11 o’ clock to 5 o’ clock
• Electric signal passes towards the lead 2/away from VR
• Hence lead 2 has more +ve deflection/ VR has –ve deflection

16. RIGHT AXIS DEVIATION
• Any change in the heart or surrounding
• Which shifts towards right side
• Physiological: Short stature/obese individuals
• Pathological: Any pathology leads to RVH

17. LEFT AXIS DEVIATION
• Any change in the heart or surrounding
• Which shifts the heart towards left side
• Physiological: Thin/tall individuals
• Pathological: Any pathology leads to LVH

18. CARDIAC ANGLE
• No much clinical significance
• Normal cardiac angle is -30 to +90 degree
• Left axis deviation is -30 to -90 degree
• Right axis deviation is +90 to -90 degree
• At birth +90 to +150 degree (N)
• 1-8 years <90 degree (N)

19. HOW TO REPORT AN ECG ?
• Rhythm
• Rate
• Conduction intervals (PR/QT interval)
• Cardiac axis
• Description of the QRS complexes
• Description of ST segment and T wave

20. CONDUCTION ABNORMALITIES
First degree heart block
• Delay in conduction b/w SA node to ventricle
• So prolonged PR interval (>220 ms)

21. SECOND DEGREE BLOCK
Wenckebach/mobitz type 1
• Progressive lengthening of PR interval and then
• Failure of conduction of atrial beat followed by
• Conducted beat with shorter PR interval
• Again cycle continues

22. SECOND DEGREE BLOCK
Mobitz type 2
• Constant PR interval
• Occasionally P wave without subsequent QRS complex

23. THIRD DEGREE BLOCK
• Complete heart block
• Atrial beats are normal which is not conducted to the ventricle
• Atrium and ventricle contracts irrespective to each other

24. RBBB
• Right ventricle depolarises after the left
• Impulse will be received from left ventricle
• So 2 R waves in the form of RSR pattern in V1 lead
• Deep S wave in V6 lead

25. LBBB
• Left ventricle depolarises after the right
• Impulse will be received from right ventricle
• So 2 R waves in the form of W pattern in V1 lead
• M pattern in V6 lead

26. RHYTHM ABNORMALITIES
Sinus arrhythmia
• Changes in the heart associated with respiration
• Common in young people
• One P wave per QRS complex
• Constant PR interval
• Progressive beat to beat change in RR interval

27. VENTRICULAR EXTRASYSTOLE
• Any part of heart depolarises earlier than it should and the
• Accompanying beat is called extra systole
• Occasionally vent. contracts on its own without atrial beat

28. ATRIAL FLUTTER
• Atrium contracts more than 300/min
• Giving saw tooth appearance
• 4 P waves per QRS complex
• Ventricular contraction is perfect at 75/min

29. ATRIAL FIBRILLATION
• No P waves and irregular baseline
• Normal shaped & Irregular QRS complexes
• Normal T waves

30. VENTRICULAR TACHYCARDIA
• Excitation spreads through abnormal path
• Through ventricular muscle mass
• Ventricle contract as a mass
• Irrespective of atrium
• In a very fast manner
• Hence no P wave/T wave
• Wide QRS complex (>200/min)

31. VENTRICULAR FIBRILLATION
• Each muscle fibre contracts independently
• No QRS complex
• Totally disorganised

32. SUPRAVENTRICULAR TACHYCARDIA
• P wave present but superimposed on T wave
• QRS complex have same shape throughout
• Atrium beats more than 180/min

33. WOLF PARKINSON WHITE SYNDROME
• His bundle
• Electrically connects atrium and ventricle
• In WPW syndrome
• An extra or accessory conducting bundle present
• No AV node, hence no AV nodal delay
• Impulse reaches ventricle very fast
• Leads to premature excitation of ventricle
• Short PR interval
• QRS complex with slurred upstroke called delta wave

34. RAH
• Peaked P wave
• Tricuspid stenosis
• Pulmonary hypertension

35. LAH
• Bifid P wave
• Mitral stenosis

36. RVH
• Right axis deviation
• Tall R wave in V1 & V2
• Deep S in lead 1
• Inverted T waves in lead 2,3,VF and V1-3

37. LVH
• Left axis deviation
• Tall R wave in V5 & V6
• Deep S in lead 3
• Inverted T waves in lead 1,VL and V5-6

38. ELECTROLYTE ABNORMALITIES
• Hyperkalaemia
• Peaked T waves
• Disappearance of ST segment
• Hypokalaemia
• Flat T waves F/B U waves with
• Prolonged QT interval
• Hypocalcaemia
• Prolonged QT interval
• Hypercalcaemia
• Short QT interval

39. REFERENCES
• ECG made easy written by John R. Hampton

40. ECG 1

41. ECG-2

42. ECG-3

43. 4. AXIS ?

44. 5. HOW TO REPORT THIS ECG ?

45. ECG-6

46. ECG-7

47. ECG-8

48. THANK YOU