The depolarising wave is immediately followed by repolarising (-ve) current Atria begin to repolarise when ventricles are depolarising Ventricles repolarise before the next wave of depolarisation begins

Graphical representation of electrical activity of the heart The electrodes placed in the body captures movement of ions and records it

positive deflection = +ve current moving towards +ve electrode will give a +ve deflection - neglative deflection +ve current moving away from +ve electrode will give a -ve deflection isoelectrric point/ straight line +ve current moving perpendicular to the electrodes will give isoelectric line

Positive deflection = -ve current moving towards -ve electrode will give a +ve deflection Negative electrode = -ve current moving away from -ve electrode will give a -ve deflection Isoelectric point/ straight line = -ve current moving perpendicular to the electrodes will give isoelectric line

ventricular (apex) depolarisation Left bundle depolarises interventricular septum and right bundle After right bundle is depolarised charges move down and depolarise ventricular apex More depolarisation happens in left ventricle than right due to its thicker wall So movement of positive charges are more towards left ventricle = movement more towards positive electrode • Atria begin to repolarise as ventricles are depolarising: but this repolarising wave is ‘hidden’ within the big R wave

Positive charges move up to lateral walls o'f ventricles Positive charges move away from potisitve electrode = negative deflection • Purkinje fibers depolarises the walls of the ventricles

Short delay before ventricular repolarisation Isoelectric line Entire ventricular myocardium is depolarised and is not repolarised yet. No net movement of ions

---> ventricular repolaraisation • Repolarization = all positive charges become negative ○ Negative ions move away from positive electrode and up towards negative electrode = negative reflection Negative charge moving towards the negative electrode giving a positive deflection QT interval: time taken for ventricular depolarisation and repolarisation

Clinical ECG recording typically uses 4 limb electrodes and 6 chest electrodes Leads are also called views

6. ECG basics And Leads Flashcards by Gursimran Kang

SA node

—> generate action potentials (depolarising currents) that are transmitted by channels to certain areas causing muscles to contracts

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Impulse conducting system of the heart -steps

The depolarising (+ve) current is generated in SA node
1. Spreads to Atrium and then to the AV node
2. From the AV node the +ve current moves to bundle branches depolarising the interventricular septum
3. The +ve current then moves to the purkinje fibers depolarising the ventricles (causing ventricles to contract)

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Repolaraisation

The depolarising wave is immediately followed by repolarising (-ve) current
Atria begin to repolarise when ventricles are depolarising
Ventricles repolarise before the next wave of depolarisation begins

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ECG - what is it

Graphical representation of electrical activity of the heart
The electrodes placed in the body captures movement of ions and records it

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3 charges

Positive deflection
Negative defection
Isoelectric point

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Positive charges

positive deflection = +ve current moving towards +ve electrode will give a +ve deflection -
- neglative deflection +ve current moving away from +ve electrode will give a -ve deflection
- isoelectrric point/ straight line +ve current moving perpendicular to the electrodes will give isoelectric line

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Negative charges

Positive deflection = -ve current moving towards -ve electrode will give a +ve deflection
- Negative electrode = -ve current moving away from -ve electrode will give a -ve deflection
- Isoelectric point/ straight line = -ve current moving perpendicular to the electrodes will give isoelectric line

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Lead II

—-> used as a rhythm strip = as it has a more prolonged time period of 10seconds
• Used to determine rate and rhythm of heart beat

Most commonly used to produce the normal sinus rhythm (NSR) tracing
• -ve electrode placed in right arm and +ve electrode in left leg

Waves
• Pqrst
• Rarely may get a u wave

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P wave

• Formed by atrial depolarisation

SA node generate positive charge and sends it down depolarising the atria
• Red arrow is the net movement of the charges towards the av node
• Positive charges move towards positive electrode = positive deflection

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P-R interval

In the AV node the positive charges remain ‘ there for 0.1 seconds
• 0.1 s delay in conduction in AV node leading to P-R segment
• +ve charge is not moving!
Isoelectric line

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Q wave

—> septal depolarisation

• Positive charges move down into bundle branches 
• Left bundle branch receives positive charges first  = Left bundle branch depolarises the interventricular septum and right bundle branch

• Positive charges move away from positive electrode = negative deflection

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R wave

ventricular (apex) depolarisation

Left bundle depolarises interventricular septum and right bundle
- After right bundle is depolarised charges move down and depolarise ventricular apex
- More depolarisation happens in left ventricle than right due to its thicker wall
- So movement of positive charges are more towards left ventricle = movement more towards positive electrode

• Atria begin to repolarise as ventricles are depolarising: but this repolarising wave is ‘hidden’ within the big R wave

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S wave

Positive charges move up to lateral walls o’f ventricles
- Positive charges move away from potisitve electrode = negative deflection

• Purkinje fibers depolarises the walls of the ventricles

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S- T segment

Short delay before ventricular repolarisation
- Isoelectric line
Entire ventricular myocardium is depolarised and is not repolarised yet.
No net movement of ions

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T wave

—> ventricular repolaraisation

• Repolarization = all positive charges become negative 
	○ Negative ions move away from positive electrode and up towards negative electrode = negative reflection

Negative charge moving towards the negative electrode giving a positive deflection
QT interval: time taken for ventricular depolarisation and repolarisation

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Rare u wave

• Due to repolarisation of papillary muscles

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ECG electrodes

Clinical ECG recording typically uses 4 limb electrodes and 6 chest electrodes
Leads are also called views

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The three bipolar limb leads

–> 3 limb leads in the legs or arms, organised in a triangle
• Leads I, II, and III can be represented schematically in terms of a triangle, called Einthoven’s triangle

Lead 1

-ve electrode in right arm
- +ve electrode in left arm
- Looking at the heart from slightly above = High lateral wall of left ventricle

Lead 2

-ve electrode in right arm
- +ve electrode in left leg
- Looking at the heart from the base – inferior rv and lv

Lead 3

-ve electrode in left arm
- +ve electrode in left leg
- Looking at the heart from the base – inferior rv and lv

What is the view from a lead

Look at the +ve lead to determine where info is connecting

Lead I waves

• Same waves as lead 2 but lower amplitude

Lead Il waves

• Same waves as lead 3

Lead Ill waves

• Same waves as lead 2 but lower amplitude

Lead equation

• The bipolar leads are related by the ' equation: Lead I + Lead III = Lead II Good way to check if electrodes are in the right place Lead 2 waves should look like lead 1 and 3 waves together

How leads view heart

• The area of heart covered by the leads: ----> ecg focuses on the ventricles – Lead I: High lateral wall of left ventricle – Lead II and III: Inferior portion of right and left ventricle As lead 2 and lead 3 have the same view, they will have same wave view but just at different amplitudes

3 Augmentated unipolar limb leads

aVR - right arm - aVL - left arm aVF - foot

aVR

* Augmented vector right * -ve electrode on left arm * -ve electrode on foot * +ve electrod in right arm * Look from the +ve electrode – augmented view from the right side * Gives a triangle * Waves are an opposite pattern

aVL

* +ve elctrodre on the left arm * It is looking from the left side like lead 1 - it has the same wave pattern as lead 1 (2 and 3) * Location is looking at high lateral wall of left ventrical like lead 1

aVF

• +ve foot * Same wave patternas lead 2 (1 and 3) * As it is looking from same direction as lead 2 – inferior wall of ventricles)

aVR waves

The area of heart covered by the aVR: – Right ventricle and basal septum • ECG tracing waves will be the opposite of lead I, II and III Almost reflected All waves are interved Pqrst

aVL waves

• The area of heart covered by the aVL: – High lateral wall of left ventricle • ECG tracing similar to lead I, II and III

aVf waves

• The area of heart covered by the aVF: – Inferior wall of the heart • ECG tracing similar to lead I, II and III

Six precordial chest leads - what are they

---> these leads are unipolar- have only one positive electrode

– V1: Right 4th intercostal space

– V2: Left 4th intercostal space

– V4: Left 5th intercostal space, midclavicular line

– V5: Left 5th intercostal space, anterior axillary line (where the clavicle is ending)

– V6: Left 5th intercostal space, mid axillary line (middle of armpit)

– V3: Between V2 and V4

Six precordial chest leads - which parts of the heart are covered

– V1-V2: Right ventricle – V2-V3: Basal septum – V2-V4: Anterior wall of the heart – V5-V6: Lateral wall of the heart

Six precordial chest leads - the waves

Same waves pqrst – R-wave increase in size from V1- V6 • V1 has small r wave • V2 has large r wave – S-wave decrease in size from V1-V6 • V1 has large s wave • V6 has small s wave