The document provides an overview of ECG fundamentals, including the normal conduction system of the heart, principles of ECG recording and interpretation, and criteria for diagnosing common electrocardiographic conditions. It describes how transmembrane ionic currents generate the electrical signal detected as an ECG and outlines the process of depolarization and repolarization. The document also reviews the placement of ECG leads and introduces a 14-point method for clinical interpretation of ECG tracings to analyze rhythm, intervals, axes, waves and voltages. Key arrhythmias, conduction abnormalities, and conditions like myocardial infarction are exemplified.

1. ECG Fundamentals
Dr. Shashank K
FFICM (UK) MBA

2. Overview
• To have a basic understanding of ECG waves & intervals
• Interpretation of ECG
• Outline the criteria for the most common electrocardiographic
diagnoses in adults
• Describe critical aspects of the clinical application of the ECG

3. ECG
• The electrocardiogram (ECG) is a representation of the
electrical events of the cardiac cycle
• Each event has a distinctive waveform, the study of a
waveform can lead to greater insight into a patient’s cardiac
pathophysiology.

4. ECG
• Arrhythmias
• Myocardial ischemia and infarction Pericarditis
• Chamber hypertrophy
• Electrolyte disturbances (i.e. hyperkalemia, hypokalemia)
• Drug toxicity (i.e. digoxin and drugs which prolong the QT
interval)
Can identify

5. ECG fundamental principles
Transmembrane ionic currents are generated by ion fluxes
across cell membranes and between adjacent cells
These currents are synchronized by cardiac activation and
recovery sequences to generate a cardiac electrical field in and
around the heart that varies with time during the cardiac cycle
The currents reaching the skin are then detected by electrodes
placed in specific locations on the extremities and torso that
are configured to produce leads.

6. ECG fundamental principles
Transmembrane ionic currents are ultimately responsible for
the potentials recorded as an ECG
Electrophysiological currents are considered to be the
movement of positive charge
An electrode senses positive potentials when an activation
front moves toward it and negative potentials when it moves
away

7. ECG fundamental principles – depolarization
Contraction of any muscle is associated with electrical changes
called depolarization.
These changes can be detected by electrodes attached to the
surface of the body.

8. ECG fundamental principles – repolarization
A phase of recovery/relaxation
The dipole moment at any one instant during recovery is less
than during activation.
Recovery, is a slow process that lasts 100 msec or longer and
occurs simultaneously over extensive portions of the fiber.

9. Pacemakers of the heart
SA Node - Dominant pacemaker with an intrinsic rate of
60 - 100 beats/minute.
AV Node - Back-up pacemaker with an intrinsic rate of 40
- 60 beats/minute.
Ventricular cells - Back-up pacemaker with an intrinsic
rate of 20 - 45 bpm.

10. Normal conduction system

11. ECG leads
Measure the difference in electrical potential between
two points
Bipolar Leads: Two different points on the body
Unipolar Leads: One point on the body and a virtual
reference point with zero electrical potential, located in
the center of the heart

12. ECG leads
The standard ECG has 12 leads:
3 Standard Limb Leads
3 Augmented Limb Leads
6 Precordial Leads

13. ECG Recording
Limb leads are I, II, II.
Each of the leads are bipolar; i.e., it requires two
sensors on the skin to make a lead.
If one connects a line between two sensors, one has a
vector
There will be a positive end at one electrode and a
negative at the other.
The positioning for leads I, II, and III were first given by
Einthoven (Einthoven’s triangle).

14. ECG Recording – limb leads

15. ECG Recording – all limb leads

16. Axis-shortcuts

17. Electrode placements

18. Precordial leads

19. ECG paper
Horizontally
One small box - 0.04 s
One large box - 0.20 s
Vertically
One large box - 0.5 mV

20. Clinical interpretation
Accurate analysis of ECGs requires thoroughness and care.
The patient's age, gender, and clinical status should always be
taken into account.
Many mistakes in ECG interpretation are errors of omission.
Therefore, a systematic approach is essential.

21. Normal ECG

22. Normal ECG

23. 14 point analysis
• Standardization (calibration) and technical features (including lead
placement and artifacts)
• Rhythm
• Heart rate,
• PR interval/AV conduction
• QRS interval
• QT/QTc interval
• Mean QRS electrical axis
• P waves
• QRS voltages
• Precordial R-wave progression
• Abnormal Q waves
• ST segments
• T waves
• U waves

24. Atrial Arrhythmias - AF

25. Atrial Arrhythmias - AFlutter

26. Atrial Arrhythmias - AVNRT

27. Atrial Arrhythmias – Ectopic Atrial Rhythm

28. Conduction abnormalities – 2:1 AVB

29. Conduction abnormalities – Bifascicular block

30. Conduction abnormalities – First-degree ABV

31. Conduction abnormalities – LAFB

32. Conduction abnormalities – LBBB

33. Conduction abnormalities – LPFB

34. Conduction abnormalities – RBBB

35. Second-degree AVB - Wenkebach

36. Second-degree AVB – Type II

37. Third-degree AVB

38. Trifascicular block

39. IHD –AW STEMI

40. IHD –IW STEMI

41. IHD –PW STEMI

42. Ventricular Arrhythmias –Idioventricular

43. Ventricular Arrhythmias –Junctional

44. Ventricular Arrhythmias –PVCs

45. Ventricular Arrhythmias –VF

46. Ventricular Arrhythmias –VT

47. Ventricular Arrhythmias –VT Brugada