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📘 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:

P-R Interval (sometimes referred to as P-Q Interval)
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:

Normotopic Arrhythmia: Originates from normal pacemaker (SA Node)
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