The document provides a comprehensive overview of the principles and recording of electrocardiograms (ECG), detailing the types of leads, waveforms, intervals, and their significance in diagnosing cardiac conditions. It discusses key aspects such as ECG calibration, heart rate calculation, axis deviation, ventricular hypertrophy, and the effects of electrolyte imbalances on ECG results. Additionally, it covers arrhythmias, their causes, classifications, and specific ECG patterns associated with various heart rhythm abnormalities.

1. UNDERSTANDING THE
ELECTROCARDIOGRAM (ECG):
PRINCIPLES AND RECORDING
Introduction to ECG

2. Introduction to ECG
● ECG: Record of electrical currents generated by
myocardial activity
● Detects depolarization and repolarization through body
fluids
● Crucial for diagnosing cardiac diseases
● Recorded using an electrocardiograph:
● Consists of a sensitive galvanometer
● Uses two electrodes applied to the skin

3. ECG Leads: Overview
● Lead: Specific arrangement of electrodes on the skin
● Typically 12 leads used (sometimes more)
● Two main types of ECG leads:
● Bipolar limb leads (Standard limb leads of Einthoven)
● Unipolar leads

4. Bipolar Limb Leads
● Record potential differences between two limbs
● Three standard leads:
● Lead I: Left Arm (LA) - Right Arm (RA)
● Lead II: Left Leg (LL) - Right Arm (RA)
● Lead III: Left Leg (LL) - Left Arm (LA)
● Einthoven's Triangle: Imaginary equilateral triangle
representing these leads

5. Einthoven's Law
● States: Sum of voltages in leads I and III equals voltage in
lead II
● Mathematically: VI + VIII = VII
● Useful for calculating unknown lead voltage if two are
known

6. Unipolar Leads: Principles
● Measure absolute potential at a specific point
● Use:
● One exploring (+ve) electrode at desired point
● One indifferent (-ve) electrode at zero potential
● Indifferent electrode creation:
● Connect electrodes from 3 limbs to a common terminal
● Forms closed circuit with zero potential (Wilson's
electrode)

7. Types of Unipolar Leads
● Unipolar Limb Leads:
● VR: Right Arm
● VL: Left Arm
● VF: Left Leg
● Unipolar Chest Leads (Wilson's precordial or V leads):
● V1 to V6: Six standard points on anterior chest wall

8. Chest Lead Positions
● V1: Right sternal margin, 4th right intercostal space
● V2: Left sternal margin, 4th left intercostal space
● V3: Midway between V2 and V4
● V4: Left midclavicular line, 5th intercostal space
● V5: Left anterior axillary line, level with V4
● V6: Left midaxillary line, level with V4 and V5

9. Augmented Unipolar Limb Leads
● Goldberger's leads: aVR, aVL, aVF
● Magnified by 50% without changing configuration
● Easier to interpret
● Routinely recorded by modern ECG machines
● Achieved by disconnecting electrode from central terminal

10. ECG Calibration
● Upward (+ve) deflection when:
● Depolarization wave moves toward exploring electrode
● Repolarization wave moves away from it
● Downward (-ve) deflection for opposite scenarios
● Voltage calibration: 1mV = 10mm deflection
● Time calibration: 25mm = 1 second (standard speed)

11. ECG Paper Measurements
● Vertical lines (voltage):
● Small square side = 0.1mV
● Horizontal lines (time):
● Small square side = 0.04 seconds
● Large square side = 0.2 seconds

12. Calculating Heart Rate from ECG
Method 1:
● Measure distance between two successive R waves (in
mm)
● Multiply by 0.04 to get duration of one cardiac cycle
● Calculate beats per minute: 60 / (cycle duration)
Method 2 (at 25mm/s speed):
● Count small squares between R waves
● Heart rate = 1500 / (number of small squares)

13. Spread of Cardiac Excitation
● Initiated in Sinoatrial (SA) node
● Spreads through atria from right to left
● Moves to interventricular septum (left to right)
● Progresses in ventricular wall from endocardial to
epicardial surface

14. Last Areas of Depolarization
● Posterobasal portion of left ventricle
● Pulmonary conus
● Uppermost part of interventricular septum

15. Key Takeaways
● ECG is crucial for diagnosing cardiac diseases
● Uses various lead placements to capture electrical activity
● Understanding lead types and placements is essential
● ECG calibration and paper measurements are
standardized
● Heart rate can be calculated directly from ECG tracing
● Cardiac excitation follows a specific pattern of spread

16. Introduction to the ECG
● ECG: A graphical representation of the heart's electrical
activity
● Consists of 5 main waves: P, Q, R, S, and T
● Sometimes includes a U wave following the T wave
● Waves are separated by segments
● QRS complex: Combination of Q, R, and S waves
● J point: Termination of the QRS complex at the isoelectric
line

17. P Wave: Atrial Depolarization
● Represents atrial depolarization
● Normal characteristics:
● Amplitude: 0.1 mV
● Duration: ≤ 0.1 seconds
● Positive in all leads except aVR
● First part: Right atrial activation
● Terminal part: Left atrial activation

18. P Wave Abnormalities
● Left atrial hypertrophy (e.g., mitral stenosis):
● P mitrale: Enlarged and notched P waves
● Increased duration
● Right atrial hypertrophy (e.g., tricuspid stenosis):
● P pulmonale: Tall, peaked P waves
● Normal duration
● Other abnormalities:
● Inverted in AV nodal rhythm
● Absent in atrial fibrillation

19. QRS Complex: Ventricular Depolarization
● Represents ventricular depolarization
● Normal duration: 0.06-0.1 seconds
● Components:
● Q wave: Interventricular septum depolarization
● R wave: Apex and ventricular wall depolarization
● S wave: Posterobasal left ventricle and pulmonary conus
depolarization

20. QRS Complex Characteristics
● Q wave: Normally negative in leads facing left ventricle
● R wave:
● Large wave, amplitude ≈ 10 mm (1 mV)
● Positive in leads facing left ventricle
● S wave: Normally negative in leads facing left ventricle
● Larger amplitude than P wave due to greater ventricular
muscle mass

21. QRS Complex Abnormalities
● Ventricular hypertrophy
● Myocardial infarction
● Extrasystoles
● Bundle branch block
● Electrolyte disturbances

22. T Wave: Ventricular Repolarization
● Represents ventricular repolarization
● Normal characteristics:
● Amplitude: 0.2-0.4 mV
● Duration: 0.2-0.25 seconds
● Normally positive due to repolarization direction

23. T Wave Abnormalities
● Inverted or isoelectric in:
● Myocardial ischemia
● Ventricular hypertrophy
● Extrasystoles
● Bundle branch block
● Digitalis overdosage
● Increased amplitude in:
● Sympathetic overactivity
● Muscular exercise
● Hyperkalemia

24. U Wave
● Small positive wave following T wave
● Probable cause: Slow repolarization of Purkinje network
● Not consistently present
● Physiological significance remains uncertain

25. P-R Interval
● Interval from start of P wave to start of R wave
● Normal range: 0.12-0.21 seconds
● Represents AV nodal delay
● Prolonged in:
● First-degree heart block
● Increased vagal tone
● Shortened in:
● AV nodal rhythm
● Sympathetic overactivity
● Wolff-Parkinson-White syndrome

26. P-R Segment
● Segment between end of P wave and start of QRS
complex
● Represents conduction through AV node and bundle of
His
● Normally isoelectric (no visible waves)
● Silent due to small amount of depolarized tissue

27. Q-T Interval
● Interval from onset of Q wave to end of T wave
● Normal duration: 0.3-0.4 seconds
● Inversely related to heart rate
● Represents duration of ventricular action potential

28. S-T Segment
● Segment from end of S wave (J point) to start of T wave
● Normal duration: ≈ 0.12 seconds
● Normally isoelectric
● Deviation indicates myocardial injury or damage

29. ECG and Ventricular Action Potential Correlation
● QRS complex: Depolarization phase (Phase 0)
● S-T segment: Plateau phase (Phase 2)
● T wave: Repolarization phase (Phase 3)
● T-P segment: Resting phase (Phase 4)

30. ECG and Cardiac Cycle Events
● P wave precedes atrial systole by ≈ 0.02 seconds
● QRS complex precedes isometric ventricular contraction
by ≈ 0.02 seconds
● First heart sound coincides with R wave summit
● Second heart sound coincides with end of T wave

31. Lead aVR Characteristics
● P wave, QRS complex, and T wave are normally negative
(inverted)
● Due to depolarization and repolarization vectors moving
away from the right arm electrode

32. Precordial Leads
● Right precordial leads (V1, V2):
● Small R waves followed by deep S waves
● Left precordial leads (V5, V6):
● Small Q waves followed by large R waves
● Reflects direction of septal depolarization and
predominance of left ventricular mass

33. Mean Electric Axis of the Ventricles
● Represents overall direction of ventricular depolarization
● Determined from Einthoven's triangle
● Normal range: -30° to +110° (average +60°)
● Directed downwards and to the left
● Positive deflections in bipolar limb leads

34. Clinical Significance of ECG
● Diagnoses various cardiac abnormalities:
● Arrhythmias
● Conduction disorders
● Myocardial infarction
● Electrolyte imbalances
● Monitors cardiac function during procedures
● Screens for cardiovascular diseases
● Guides treatment decisions in cardiac patients

35. Introduction to Axis Deviation
● Axis deviation refers to shifts in the mean electrical axis of
the heart
● Can be right or left deviation
● Occurs normally in certain body types or pathologically in
various conditions
● Detectable through specific ECG patterns

36. Right Axis Deviation
● Normal in vertical hearts (e.g., tall subjects)
● Pathological in:
● Right ventricular hypertrophy
● Right bundle branch block
● ECG characteristics:
● Deep S waves in lead I
● High R waves in lead III

37. Left Axis Deviation
● Normal in horizontal hearts (e.g., short stout subjects,
pregnant women)
● Pathological in:
● Left ventricular hypertrophy
● Left bundle branch block
● ECG characteristics:
● High R waves in lead I
● Deep S waves in lead III

38. Ventricular Hypertrophy: Overview
● Refers to thickening of ventricular walls
● Can affect left or right ventricle
● Causes distinct ECG patterns
● Often associated with axis deviation

39. Left Ventricular Hypertrophy (LVH)
● ECG manifestations:
● High R waves in left precordial leads (V5, V6)
● Deep S waves in right precordial leads (V1, V2)
● T wave inversion in left precordial leads
● Left axis deviation

40. Right Ventricular Hypertrophy (RVH)
● ECG manifestations:
● High R waves in right precordial leads (V1, V2)
● Deep S waves in left precordial leads (V5, V6)
● T wave inversion in right precordial leads
● Right axis deviation

41. Coronary Insufficiency: Introduction
● Reduced blood supply to the heart muscle
● Can lead to ischemia, injury, or necrosis
● Each stage produces distinct ECG changes

42. Manifestations of Myocardial Ischemia
● Definition: Reduced oxygen supply to heart muscle
● ECG changes:
● Inverted T waves
● Mechanism:
● Hypoxia delays repolarization in epicardium
● Repolarization starts from endocardium to epicardium

43. Manifestations of Myocardial Injury
● Definition: Damage to heart muscle cells
● ECG changes:
● S-T segment shift (elevation or depression)
● Mechanism:
● Current of injury between damaged and healthy tissue
● Incomplete repolarization of cardiac muscle

44. Manifestations of Myocardial Necrosis (Infarction)
● Definition: Death of heart muscle cells
● Usually affects left ventricle or interventricular septum
● ECG changes:
● Deep Q waves (>0.2 mV) if full thickness affected
● Reduced R wave amplitude in partial necrosis

45. Progression of Myocardial Infarction on ECG
● S-T segment elevation (within minutes)
● Deep Q waves (after a few hours)
● T wave inversion (follows Q waves)
● S-T segments return to baseline (1-2 weeks)
● T waves become upright (after a few months)
● Deep Q waves persist (permanent sign of old MI)

46. Effects of Serum Sodium (Na+) on ECG
● Hyponatremia:
● Low-voltage QRS complexes
● Hypernatremia:
● Minimal effects on ECG

47. Effects of Serum Potassium (K+) on ECG: Hyperkalemia
● Progressive changes:
● Tall, peaked T waves
● Absence of P waves (atrial arrest)
● S-T segment depression
● QRS complex prolongation
● A-V block
● Ventricular arrhythmia
● Ventricular standstill

48. Effects of Serum Potassium (K+) on ECG: Hypokalemia
● ECG changes:
● Prolongation of P-R and Q-T intervals
● Prominent U waves
● T wave inversion

49. Clinical Significance of Axis Deviation
● Helps in diagnosing ventricular hypertrophy
● Indicates bundle branch blocks
● Assists in identifying cardiac chamber enlargement
● Guides further diagnostic tests and treatment plans

50. Importance of ECG in Coronary Insufficiency
● Non-invasive tool for detecting myocardial ischemia,
injury, and infarction
● Helps in determining the extent and location of damage
● Guides treatment decisions in acute coronary syndromes
● Useful for monitoring progression and recovery

51. Electrolyte Imbalances and ECG
● ECG changes can indicate potentially life-threatening
electrolyte disturbances
● Particularly important for monitoring potassium levels
● Guides urgent treatment in severe cases
● Helps in managing patients with renal dysfunction or on
certain medications

52. Limitations and Considerations
● ECG changes may not always correlate perfectly with
clinical condition
● Other diagnostic tools (e.g., cardiac enzymes, imaging)
often necessary
● Serial ECGs may be needed to detect evolving changes
● Interpretation should always be done in context of clinical
presentation

53. Summary and Key Points
● Axis deviation reflects changes in heart's electrical
orientation
● Ventricular hypertrophy produces characteristic ECG
patterns
● Coronary insufficiency manifests as progressive ECG
changes
● Electrolyte imbalances, especially K+, can significantly
affect ECG
● ECG is a valuable tool but should be interpreted alongside
clinical findings

54. Introduction to Arrhythmias
● Arrhythmias (or dysrhythmias) are abnormalities in heart
rate or rhythm
● Can affect heart's ability to pump blood effectively
● Understanding arrhythmias is crucial for diagnosing and
treating heart conditions
● This presentation will cover types, causes, and ECG
manifestations of arrhythmias

55. Classification of Arrhythmias
● Disturbances in impulse formation:
● Alterations of SA node rhythmicity
● Presence of ectopic foci
● Disturbances in impulse conduction:
● SA block
● AV block
● Wolff-Parkinson-White syndrome

56. Sinus Rhythms
● Sinus Tachycardia:
● Heart rate increases to 100-120/minute
● Caused by increased sympathetic activity (e.g., exercise)
● Sinus Bradycardia:
● Heart rate decreases below 60/minute
● Often seen in athletes due to increased vagal tone
ECG shows normal complexes with altered rate

57. Respiratory Sinus Arrhythmia
● Normal finding, common in children and young adults
● Heart rate increases during inspiration and decreases
during expiration
● Caused by fluctuations in vagal tone affecting SA node
rhythmicity
ECG shows normal complexes with rate variations
corresponding to respiratory phases

58. AV Nodal Rhythm
● Occurs when AV node becomes the pacemaker (SA node
damaged)
ECG characteristics:
● Bradycardia (AV node rhythmicity slower than SA node)
● Short PR intervals
● Inverted P waves (often buried in QRS complexes)
● P waves may follow QRS complexes (negative PR
intervals)

59. Extrasystoles (Premature Beats)
● Impulses from ectopic foci during normal SA rhythm
● Two main types:
● Supraventricular premature beats
● Ventricular premature beats
ECG shows complexes early in the T-P interval

60. Supraventricular Premature Beats
● Origin: Ectopic foci in atria or AV node
ECG characteristics:
● Abnormal P wave (often inverted)
● Normal QRST waves
● Almost normal T-Q interval (no or short compensatory
pause)
● Shortened PR interval if focus near AV node

61. Ventricular Premature Beats
● Origin: Ventricular ectopic foci
ECG characteristics:
● Wide, high, abnormally-shaped QRS complex (bizarre
QRS)
● No P wave
● Prolonged following T-Q interval (complete compensatory
pause)
● Inverted T wave
● Axis deviation

62. Paroxysmal Tachycardia
● Characterized by sudden attacks of tachycardia
● Ectopic foci discharge at 150-220/minute (avg.
200/minute)
● Suppresses SA node during attacks
● Two main types:
● Paroxysmal supraventricular tachycardia
● Paroxysmal ventricular tachycardia

63. Paroxysmal Supraventricular Tachycardia
ECG shows abnormal P waves in all complexes
● May occur in Wolff-Parkinson-White syndrome
● Often associated with some degree of AV block
● Ventricular rate typically 170-180/minute

64. Paroxysmal Ventricular Tachycardia
ECG characteristics:
● Wide, high, bizarre-shaped QRS complexes
● Inverted T waves without preceding P waves
● Ventricular rate 150-220/minute
● More dangerous than atrial type:
● Marked reduction in cardiac output
● Predisposes to ventricular fibrillation
● Atrioventricular dissociation present

65. Atrial Flutter
● Atria beat regularly at 250-350/minute
● Caused by hyperexcitable ectopic focus
● Physiological incomplete heart block develops
ECG characteristics:
● 2 or 3 P waves followed by one QRST
● Abnormal P waves, normal QRS and T waves
● Regular but rapid ventricular rate

66. Atrial Fibrillation
● Atria beat irregularly at 350-500/minute
● Caused by multiple ectopic foci or circus movement
● Irregular physiological heart block
ECG characteristics:
● No P waves (replaced by F waves)
● Normal QRS and T waves, irregular rate
● Complications: Inefficient atrial contraction, blood
stagnation, thrombosis risk

67. Ventricular Fibrillation
● Caused by multiple ectopic foci or re-entry/circus
movements
● Fatal due to loss of ventricular pumping power
ECG characteristics:
● Irregular QRS complexes in shape, rhythm, and amplitude
● Indistinguishable waves
● Often follows paroxysmal ventricular tachycardia or occurs
during vulnerable period

68. The Vulnerable Period
● Short period at end of cardiac repolarization
● Coincides with downslope of T wave
● Dangerous due to varying states of repolarization in
cardiac fibers
● Favors re-entry and circus movements
● May lead to ventricular fibrillation

69. Mechanisms of Cardiac Rhythm Alterations
● Abnormal automaticity of SA node
● Changes in slope of prepotential
● Re-entry phenomenon (Circus movement)
● Impulse spreads in circular pathway
● More likely during vulnerable period
● Can be triggered by weak electric shock

70. Atrioventricular (AV) Block
● Often due to ischemia of AV nodal or infranodal regions
● Three degrees of severity:
● First-degree heart block
● Second-degree heart block
● Third-degree (complete) heart block

71. Bundle Branch Block (BBB)
● Injury to right or left bundle branches
● Commonly due to ischemia
● Causes activation of one ventricle before the other
ECG characteristics:
● Prolonged, slurred QRS complexes (>0.12 sec)
● T wave inversion in leads facing affected side
● Right or left axis deviation

72. Conclusion
● Arrhythmias are complex disturbances in heart rhythm
● Understanding ECG patterns is crucial for diagnosis
● Various mechanisms contribute to different types of
arrhythmias
● Proper identification and treatment are essential for
patient care
● Continued research and education in this field are vital for
improving cardiac health outcomes