ECG basis (l ,ll)

2026

📘 Electrocardiography (ECG) - Complete Exam Notes

🖇 I. Introduction to ECG & Measurement Principles

📌 Measurement Challenge

• Direct, invasive measurement of heart's electricity (e.g., opening chest, attaching wires) = impractical and unrealistic

📌 ECG Principle

• Electrical impulse generated by heart travels through surrounding tissues
• Body Fluids act as electrical Conductor (موصل بالكهرب)
• Electricity measured on skin surface accurately reflects internal electrical activity of heart

📌 Important Concept

• Patient does NOT receive electricity from machine
• Patient's heart generates electricity
• Machine measures it

🖇 II. Clinical Utility of ECG

📌 General Diagnostic Purposes

• Required for many diagnostic purposes related to heart's properties:
• • Rhythm
  • Contractility
  • Conductivity

🟣 Primary Clinical Use

🚨 Main Purpose for Cardiologists:

• Diagnosing Angina Pectoris (ischemic heart disease)

📌 Main Clinical Goal

• Determine if patient has:
• • Ischemia (weakened blood supply)
  • Infarction (muscle death)
• Assess if immediate hospitalization required

🟠 Clinical Note: Infarction

• Means heart muscle tissues have died (عضلات نفسها ماتت)
• Usually due to blocked coronary arteries

🟣 Additional Uses

📌 ECG Also Helps:

• Assess heart's rhythm
• Diagnose severe issues like Heart Block

🖇 III. ECG Setup: Leads & Conductors

📌 ECG Measurement System

• Measured using 12 wires = called Leads (ليدز يعني سلك)
• 12 measured traces on final ECG paper
• Derived from various physical connections and internal mathematical calculations

📌 Physical Lead Placement

• Attached to extremities (arms and legs)
• Attached to chest
• Total physical leads often = 9 (3 on extremities + 6 on chest)
• Generate 12 distinct graphical representations (12 رسمة)

🟣 Lead Types

📌 Two Main Types:

1. Bipolar Leads:

• Measure Potential Difference (فرق الجهد) between two distinct points

2. Unipolar Leads:

• Measure electrical activity at Single Point compared to zero reference/baseline

🖇 IV. Anatomical Orientation & Electrical Axis (Vector)

🟣 Heart Position & Anatomy

📌 Heart Position

• Resembles a cone
• Base (broad part): superiorly
• Apex: inferiorly

🚨 Apex Characteristics (Exam Point)

• Strongest point of heart
• Oriented downward, forward, and to the left (للاسفل وللامام ولليفت)

🟣 Electrical Vector

📌 Electrical Impulse (Vector)

• Generally follows anatomical direction

🚨 Overall Electrical Activity (Exam Point)

• Moves predominantly toward Left Foot/Leg (الرجل الشمال)

🖇 V. Bipolar Leads & Einthoven's Triangle

📌 Observation Principle

• Observing heart from multiple directions
• Compared to observing elephant from all angles to get complete picture

📌 Einthoven's Triangle

• Basis for standard limb leads

🟣 Bipolar Lead Configuration Table

LeadTypeElectrode PlacementNotes

Lead I

Bipolar

Positive: Left Arm<br>Negative: Right Arm

Measures potential difference between two arms

Lead II

Bipolar

Positive: Left Leg<br>Negative: Right Arm

Measures potential difference between Right Arm and Left Leg

Lead III

Bipolar

Positive: Left Leg<br>Negative: Left Arm

Measures potential difference between Left Arm and Left Leg

🟣 Lead II Importance

🚨 Lead II = Most Important Lead (Exam Point)

• Direction closely aligns with heart's main electrical axis (Vector)

🟣 Einthoven's Law

🚨 Einthoven's Law (Exam Point)

• Electrical potential of Lead II = Sum of potentials of Lead I and Lead III
• Formula: Lead 2 = Lead 1 + Lead 3

🖇 VI. Unipolar Leads (Augmented & Precordial)

🟣 A. Unipolar Limb Leads (aVR, aVL, aVF)

📌 Initial Problem

• Electrical reading from single points on extremities (V R, V L, V F) = very weak (ضعيفة جدا)
• Device may not measure them accurately

Augmentation Process

🚨 Augmentation (Exam Point)

• Signals from limb leads must be mathematically increased
• Factor: e.g., 50% increase
• Increased within device to make signals clear
• Process called Augmentation

📌 Resulting Leads

• Augmented Unipolar Leads: aVR, aVL, and aVF

🟣 B. Unipolar Chest Leads (Precordial Leads: V1–V6)

📌 Number of Chest Leads

• Six chest leads (V1 to V6)
• Primarily view anterior wall and adjacent structures

Placement Landmarks

📌 Starting Landmark

• Sternal Angle (Angle of Louis)
• Corresponds anatomically to Second Intercostal Space

📌 Specific Placements:

• V1 and V2: Fourth Intercostal Space (right and left of sternum)
• V4, V5, and V6: Fifth Intercostal Space
• V3: Halfway between V2 and V4

🖇 VII. ECG Waveforms, Segments & Intervals

📌 Final Output Components

• Waves: deflections above or below baseline
• Segments: isoelectric lines
• Intervals: time spans (may include waves and segments)

📌 Fundamental Components

• P, Q, R, S, T, and U waves

🟣 ECG Component Table

ComponentRepresentsNotes

P Wave

Atrial Depolarization (Contraction)

Typically positive<br>Normal Amplitude: 0.1 mV<br>Normal Duration: 0.11 seconds

Q Wave

Depolarization of Ventricular Septum

Negative Deflection (Mismatched/مخالف)

R Wave

Depolarization of Apex/Ventricles

Represents highest voltage/strongest electrical activity

S Wave

Depolarization of Base of Heart

Negative Deflection (Mismatched/مخالف)

QRS Complex

Ventricular Depolarization (Total)

Normal Amplitude: 1 mV (10 small squares)<br>Normal Duration: 0.08 seconds (2 small squares)

T Wave

Ventricular Repolarization (Relaxation)

Represents electrical return to stability

🖇 VIII. Core Principles of Deflection Direction

📌 Fundamental Principle

• Direction of recorded wave (positive or negative) depends entirely on direction of electrical current relative to recording electrode

🟣 Electrical Rule 1: Depolarization

📌 Depolarization Rules:

Positive Wave:

• Electrical current travels from Negative pole toward Positive pole (N → P)
• Results in Positive (upward deflection)

Negative Wave:

• Current travels in opposite direction (P → N)
• Results in Negative (downward deflection)

🟣 Electrical Rule 2: Repolarization

📌 Repolarization Rules:

• Repolarization = electrical opposite of Depolarization

Negative Wave:

• If Repolarization travels N → P
• Wave will be Negative

Positive Wave:

• If Repolarization travels P → N
• Wave will be Positive (upward deflection)

🟣 Application Example: Q Wave

📌 Why Q Wave is Negative

• Electrical flow within Septum runs from right to left
• Contrary to overall heart vector
• Therefore = negative deflection

🖇 IX. Time Measurements & Intervals

📌 ECG Paper Speed

• Typically 25 mm per second

📌 Time Scale

• Smallest squares on ECG paper = 0.04 seconds

📌 Cardiac Cycle Duration

• Entire PQRST sequence = one heartbeat
• Lasts approximately 0.8 seconds

🟣 P-R Interval

📌 Definition

• Extends from beginning of P wave to beginning of Q wave (P-Q)
• Commonly called P-R interval (because R is most famous part of complex)

📌 Function

• Represents time taken for impulse to travel:
• • From SA Node
  • Through Atrium
  • Through AV conduction system

🚨 Duration: Approximately 0.2 seconds (Exam Point)

🟠 Clinical Note

• If P-R interval prolonged → indicates conduction delay
• Example: First Degree Heart Block

🟣 Q-T Interval

📌 Definition

• Represents total electrical duration of Ventricle
• Includes: Depolarization + Repolarization

🚨 Duration: Approximately 0.4 seconds (Exam Point)

🖇 X. ST Segment (Clinical Significance)

📌 Segment Definition

• Portions of baseline (isoelectric line)
• Between end of one wave and start of next

🚨 ST Segment = Most Important Segment (Exam Point)

• For identifying Ischemia or Infarction

🟣 ST Segment Physiology

📌 Represents

• Plateau Phase (Phase 2) of ventricular action potential

📌 Normal ST Segment

• Should be Isoelectric (flat, aligned with baseline)

🟣 Pathological Changes (Clinical Note)

🟠 ST Elevation:

• ST segment raised high above baseline
• Indicates INFARCTION

🟠 ST Depression:

• ST segment lowered below baseline
• Indicates ISCHEMIA (weakened blood supply)

📌 Clinical Importance

• Diagnosis based on ST segment determines if patient requires immediate medical intervention

🖇 XI. Study Advice & Conclusion

📌 Lecturer's Recommendations

• Focus on memorizing for each wave/segment:
• • Cause
  • Direction
  • Specific amplitude/duration
• Memorize 2-3 facts per component
• Detailed mechanisms involve significant complexity and contradictions beyond lecture scope

📌 Diagnostic Approach

• Focus on specific chambers related to wave:
• • P wave pathology → relates to Atrium
  • QRS/T pathology → relates to Ventricle

ECG Abnormalities

📘 Electrocardiography (ECG) & Arrhythmia - Complete Exam Notes

🖇 I. Introduction, Administration & Relevance

📌 Lecture Context

• Current lecturer swapping slots with Dr. Hassan
• Class finished Normal ECG topic
• Now covering Abnormal ECG

🚨 Exam Importance (Exam Point)

• Material featured prominently in previous exams
• Two questions last year: one in midterm, one in final
• Physiologists known for covering pathology (pathophysiology) topics

📌 Lecture Notes

• Current lecture and upcoming Heart Rate lecture = both very long
• After completion: approximately half of Circulation textbook covered

📌 Study Advice

• Students who missed previous content should:
• • Focus on learning new material
  • Gradually catch up on old material
  • Rather than letting new material accumulate while only focusing on past

🖇 II. Normal ECG Components & Cardiac Cycle Relationship

📌 ECG Waveform Components

• Visually consists of: P wave, QRS wave (complex), and T wave

📌 Component Meanings:

ComponentElectrical RepresentationMechanical Correlation

P Wave

Atrial Depolarization

Atrial Systole (contraction)

QRS Complex

Ventricular Depolarization

Ventricular Systole

T Wave

Ventricular Repolarization

Ventricular Relaxation

🟣 Atrial Diastole

📌 Timing

• Not explicitly seen in ECG
• Occurs simultaneously with:
• • Most of Ventricular Depolarization (QRS complex)
  • Most of Ventricular Repolarization

🚨 Exam Point:

• Atrial Diastole is considered "masked" (لغيه من الحياة / literally "eaten up")
• Masked by large electrical events of Ventricular Systole

🖇 III. Crucial ECG Segments & Intervals

📌 Two Most Important Components for Abnormality Analysis:

1. P-R Interval (sometimes referred to as P-Q Interval)
2. S-T Segment

📌 Note

• Other intervals (like Q-T) considered less essential for primary focus of this lecture

🖇 IV. Electrical Axis & Vector Concept

🟣 Vector Definition

📌 Vector

• Refers to Direction of electrical activity (الكهربا) in heart

🟣 Axis Deviation

📌 Types of Axis Deviation:

• Normal Axis Deviation
• Right Axis Deviation: ECG shifted toward right
• Left Axis Deviation: ECG shifted toward left

🚨 Exam Point:

• Students instructed NOT to use term "Normal Axis Deviation"

🟣 Exam Note on Axis

📌 Main ECG Drawing for Exam

• Large ECG used for calculations (e.g., rate, rhythm) will show Normal Axis

🟠 Clinical Note:

• Abnormal axis deviations (Heart Block, Extrasystole) only tested in smaller identification (spot) questions

🖇 V. Directionality of Cardiac Impulse

📌 Normal Direction Rules

• Overall electrical impulse (Vector) must be Upward to Downward
• Electrical activity moves from Right Side to Left Side
• Deviations (horizontal or bottom-to-top movement) indicate problem

📌 Normal Path Confirmation

• Impulse must flow from Atrium to Ventricle

🟣 Base to Apex Movement

🚨 Exam Point:

• Electrical activity normally moves from Base (top) to Apex (bottom)

📌 Electrical Strength:

• Base to Apex: electricity is STRONG
• Apex to Base: electricity is WEAK (encounters resistance, indicates disease state)

🟣 Vector Components & Wave Drawing

📌 Two Vector Properties:

1. Head (Direction) of Vector Arrow:

• Determines if ECG wave is:
• • Positive (upward deflection)
  • Negative (downward deflection)
• Shows direction of action potential

2. Length of Vector:

• Indicates Amplitude (height) of wave

🟣 Arrhythmia Connection

📌 Vector Confusion

• If vector direction not singular (moves in various directions)
• Leads to cardiac confusion
• Results in Arrhythmia

🖇 VI. Vector Degrees & Leads

📌 Horizontal Movement

• If electrical activity moves Horizontally (horizontal plane)
• Vector Degree = Zero
• Occurs because opposing electrical forces cancel each other out

📌 Leads for Axis Deviation Determination

• Leads 1, 2, 3, aVL, aVF, and aVR

🚨 Lead 1 (Exam Point)

• Measures horizontal plane
• Therefore its Vector = Zero

📌 Typical Lead Directions

• Leads 2 and 3 typically show positive directions

📌 Note

• Exact numerical degrees associated with specific leads NOT required for memorization

🖇 VII. Calculation of QRS Complex Vector/Amplitude

📌 QRS Complex Use

• Used for vector calculations

🟣 Amplitude Calculation

📌 Formula

• Amplitude (height) = Positive deflection (R wave) - Negative deflection (Q wave and/or S wave)

🚨 Q Wave Definition (Exam Point)

• Q wave = first negative wave in ECG complex

🟣 Einthoven's Triangle Method for Vector

📌 Complex Steps (Likely Beyond Standard Requirements):

Step 1:

• Find midpoint of voltage/amplitude for Lead 1, Lead 2, and Lead 3

Step 2:

• Draw imaginary line from each midpoint
• Line must be perpendicular (عمودي) to corresponding lead axis

Step 3:

• Three perpendicular lines will intersect at single point

Step 4:

• Determine midpoint of positive wave only (R wave) for each lead

Step 5:

• Final vector calculation involves measuring distance between intersection points
• Represents amplitude/duration of QRS complex

🖇 VIII. Abnormal Rhythms (Arrhythmia)

🟣 Definition

📌 Arrhythmia

• Irregular heartbeat
• Heart normally beats rhythmically (تك تك تك)

🟣 Pulse Measurement

📌 Proper Detection Method

• To detect irregularity: count pulse for full 60 seconds
• Do NOT extrapolate from short 10-second count

🟣 Causes of Rate Changes

📌 Physiological Causes

• Pregnancy (due to hyperdynamic state)
• Fever

📌 Pathological Causes

• Thyrotoxicosis (thyroid disease)
• Atherosclerosis

🟣 Classification of Arrhythmia (Exam Point)

🚨 Two Main Types:

1. Normotopic Arrhythmia: Originates from normal pacemaker (SA Node)
2. Ectopic Arrhythmia: Originates from secondary pacemaker (NOT SA Node)

🖇 A. NORMOTOPIC ARRHYTHMIA (Sinus Rhythms)

📌 Group Includes

• Sinus Tachycardia
• Sinus Bradycardia
• Sinus Arrhythmia

🟣 1. Sinus Arrhythmia (Respiratory Sinus Rhythm)

📌 Definition

• Heart rate changes with respiration

📌 Pattern:

• During Inspiration: Heart Rate INCREASES (acceleration)
• Increased rate results in shortening of P-R Interval (waves move closer together)

📌 Mechanism

• Lung inflation during inspiration stretches lungs
• Decreases negative intrathoracic pressure
• Accelerates heart rate via reflexes (related to Vagal stimulation)

🟣 2. Sinus Tachycardia

📌 Definition

• Increased discharge rate from SA Node
• Example: 110-120 beats/min instead of 90 beats/min

📌 ECG Change

• Causes shortening of P-R Interval

🟣 3. Sinus Bradycardia

📌 Definition

• Decreased impulse discharge from SA Node

📌 ECG Change

• Causes prolongation (lengthening) of P-R Interval

🟣 Sick Sinus Syndrome (SSS)

🟠 Clinical Note (Exam Point)

📌 Diagnostic Example

• 30-year-old male patient presenting with Bradycardia

📌 Features:

• Prolonged P-R Interval
• Sinus Bradycardia
• Dizziness
• Disturbed level of consciousness

🖇 B. ECTOPIC ARRHYTHMIA

📌 Definition

• Occurs when center other than SA Node acts as pacemaker
• Examples: AV Node, muscle tissue

📌 Key Topics Covered

• Heart Block
• Extrasystole

📌 Topics Explicitly Excluded

• Paroxysmal Tachycardia
• Atrial Flutter
• Atrial Fibrillation
• Ventricular Fibrillation

🖇 IX. DETAILED ANALYSIS OF HEART BLOCK

📌 Definition

• Heart Block occurs when conduction blocked at:
• • SA Node (SA Nodal Block)
  • AV Node (AV Nodal Block)
  • Lower system (requiring Idioventricular Rhythm)

🟣 1. SA Nodal Block / AV Nodal Block (Junctional Rhythms)

📌 General Principle

• If SA Node blocked → AV Node takes over

A. Defect in Upper Part of AV Node

🚨 ECG Finding (Exam Point)

• Inverted P Wave (negative deflection)

📌 Mechanism

• Electrical impulse travels backward (from AV Node up to Atrium)
• Causes vector to be reversed
• Draws negative P wave

B. Defect in Middle Part of AV Node

📌 ECG Finding

• P Wave is ABSENT

📌 Mechanism

• AV Node cannot send electricity up to Atrium
• Atrium and Ventricle work independently
• Atrial Depolarization (P wave) not recorded

C. Defect in Lower Part of AV Node

📌 ECG Finding

• QRS Complex merges with T wave
• QRS Complex appears BEFORE P wave

🟣 2. INCOMPLETE HEART BLOCK

A. First Degree Heart Block

📌 Problem

• AV Nodal conduction is slow

📌 ECG Result

• Prolonged P-R Interval (delay significantly increased)

🟠 Clinical Note

• Can occur in:
• • Individuals taking long-acting Penicillin (e.g., for rheumatic fever)
  • Physiologically in athletes (due to cardiac adaptation)

B. Second Degree Heart Block

📌 Problem

• Not every impulse reaches Ventricle

📌 ECG Result

• One Ventricular Contraction (QRS complex) follows 2, 3, or 4 Atrial Contractions (P waves)
• Ratios: 1:2, 1:3, 1:4

📌 Characteristic

• Missed QRS complexes
• Example: two P waves but only one QRS complex

C. Wenckebach Phenomenon (Wenckebach Syndrome)

📌 Problem

• Progressive increase in delay within AV Node

📌 ECG Result

• P-R interval progressively increases
• Until one entire beat is MISSED

📌 Differentiation

• Wenckebach: progressive, increasing delay followed by missed beat
• Unlike fixed delay of First Degree Heart Block

D. Bundle Branch Block (BBB)

📌 Problem

• Dysfunction of Right or Left Bundle Branches

📌 Mechanism

• Electrical impulse first travels to healthy/unaffected part of Ventricle
• Causes contraction
• Impulse then returns to stimulate affected/diseased part of Ventricle
• Block due to diseased ventricular tissue

🟣 3. COMPLETE HEART BLOCK (Third Degree Heart Block)

📌 Problem

• Impulse from SA Node reaches AV Node
• FAILS to transmit to Ventricle

📌 Result

• Atrium works independently
• Ventricle works independently

📌 Ventricular Maintenance

• Maintained by lower, automatic pacemaker:
• • Either AV Node
  • Or Idioventricular Rhythm

Rates in Complete Heart Block

📌 Rate Comparison:

• SA Node (Atrium) rate: ≈ 90 beats/min
• AV Node rate: ≈ 60 beats/min
• Idioventricular Rhythm rate: ≈ 25 beats/min

🟠 Clinical Note

• Heart muscle remains functional after death due to Idioventricular Rhythm
• Though at very low rate

📌 Cause

• Defects in AV Node or lower conduction system