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Electrocardiography

Cells in humans act like little batteries These cells have different ion concentrations inside and outside of their membranes which create small electric potentials called biopotentials When there is a disturbance in a biopotential this gives rise to an action potential which is the depolarization and repolarization of the cell

Essentially the action

potentials from different

nodes in the heart are

what make up

electrocardiograph (ECG)

signals

ECG signals are

comprised of the

superposition of the

different action potentials

from the heart beating as

shown in Figure

ECG machines use

electrodes to convert the

ionic signals from the

body into electrical

signals to be displayed

and used for data analysis

However due to the size of the signals and outside noise ECG requires amplification and

filtering to produce high quality signals

Leads and what

they tell you

Each lead can be thought of as

lsquolooking atrsquo an area

of myocardium

Chest leads

V1 to V6 lsquolook rsquo at the heart on

the transverse plain

1048707

V1 and V2 look at the anterior

of the heart and R ventricle

1048707

V3 and V4 = anterior and septal

1048707

V5 and V6 = lateral and left

ventricle

Electrode label (in the USA) Electrode placement

RA On the right arm avoiding thick muscle

LA In the same location where RA was placed but on the left arm

RL On the right leg lateral calf muscle

LL In the same location where RL was placed but on the left leg

V1 In the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum

V2 In the fourth intercostal space (between ribs 4 and 5) just to the left of the sternum

V3 Between leads V2 and V4

V4 In the fifth intercostal space (between ribs 5 and 6) in the mid-clavicular line

V5 Horizontally even with V4 in the left anterior axillary line

V6 Horizontally even with V4 and V5 in the mid axillary line

The ECG measures

differences in the

electric potential V

VE

The Electric Potential is the Potential ability to do

work

Alternatively Work = Q V

Where V = 21 VV

For uniform electric fields dEVd

VE ||||

Electric Potential

bull Interior of Heart muscle cells are negatively

charged at rest

bull Called ldquopolarisationrdquo

bull K+ ions leak out leaving interior ndashve

bull Depolarisation occurs just proir to

contraction

Na+ ions enter cells

Occurs in waves across the heart

Re-polarisation restores ndashve charge in

interior

+ + + + - - - - -+ +

+ +

- -

- -

Polarisation Depolarisation

ECG

Works by

measuring changes

in electric field as

heart pumps

Heart can be

modeled as a

rotating dipole

Depolarisation begins at the SA node

The wave of depolarisation spreads across the atria

It reaches the AV node and the accessory bundle

Conduction is delayed as usual by the in-built delay in the AV node

However the accessory bundle has no such delay and depolarisation begins

early in the part of the ventricle served by the bundle

As the depolarisation in this part of the ventricle does not travel in the high

speed conduction pathway the spread of depolarisation across the ventricle is

slow causing a slow rising delta wave

Until rapid depolarisation resumes via the normal pathway and a more

normal complex follows

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection

Cells in humans act like little batteries These cells have different ion concentrations inside and outside of their membranes which create small electric potentials called biopotentials When there is a disturbance in a biopotential this gives rise to an action potential which is the depolarization and repolarization of the cell

Essentially the action

potentials from different

nodes in the heart are

what make up

electrocardiograph (ECG)

signals

ECG signals are

comprised of the

superposition of the

different action potentials

from the heart beating as

shown in Figure

ECG machines use

electrodes to convert the

ionic signals from the

body into electrical

signals to be displayed

and used for data analysis

However due to the size of the signals and outside noise ECG requires amplification and

filtering to produce high quality signals

Leads and what

they tell you

Each lead can be thought of as

lsquolooking atrsquo an area

of myocardium

Chest leads

V1 to V6 lsquolook rsquo at the heart on

the transverse plain

1048707

V1 and V2 look at the anterior

of the heart and R ventricle

1048707

V3 and V4 = anterior and septal

1048707

V5 and V6 = lateral and left

ventricle

Electrode label (in the USA) Electrode placement

RA On the right arm avoiding thick muscle

LA In the same location where RA was placed but on the left arm

RL On the right leg lateral calf muscle

LL In the same location where RL was placed but on the left leg

V1 In the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum

V2 In the fourth intercostal space (between ribs 4 and 5) just to the left of the sternum

V3 Between leads V2 and V4

V4 In the fifth intercostal space (between ribs 5 and 6) in the mid-clavicular line

V5 Horizontally even with V4 in the left anterior axillary line

V6 Horizontally even with V4 and V5 in the mid axillary line

The ECG measures

differences in the

electric potential V

VE

The Electric Potential is the Potential ability to do

work

Alternatively Work = Q V

Where V = 21 VV

For uniform electric fields dEVd

VE ||||

Electric Potential

bull Interior of Heart muscle cells are negatively

charged at rest

bull Called ldquopolarisationrdquo

bull K+ ions leak out leaving interior ndashve

bull Depolarisation occurs just proir to

contraction

Na+ ions enter cells

Occurs in waves across the heart

Re-polarisation restores ndashve charge in

interior

+ + + + - - - - -+ +

+ +

- -

- -

Polarisation Depolarisation

ECG

Works by

measuring changes

in electric field as

heart pumps

Heart can be

modeled as a

rotating dipole

Depolarisation begins at the SA node

The wave of depolarisation spreads across the atria

It reaches the AV node and the accessory bundle

Conduction is delayed as usual by the in-built delay in the AV node

However the accessory bundle has no such delay and depolarisation begins

early in the part of the ventricle served by the bundle

As the depolarisation in this part of the ventricle does not travel in the high

speed conduction pathway the spread of depolarisation across the ventricle is

slow causing a slow rising delta wave

Until rapid depolarisation resumes via the normal pathway and a more

normal complex follows

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection

Essentially the action

potentials from different

nodes in the heart are

what make up

electrocardiograph (ECG)

signals

ECG signals are

comprised of the

superposition of the

different action potentials

from the heart beating as

shown in Figure

ECG machines use

electrodes to convert the

ionic signals from the

body into electrical

signals to be displayed

and used for data analysis

However due to the size of the signals and outside noise ECG requires amplification and

filtering to produce high quality signals

Leads and what

they tell you

Each lead can be thought of as

lsquolooking atrsquo an area

of myocardium

Chest leads

V1 to V6 lsquolook rsquo at the heart on

the transverse plain

1048707

V1 and V2 look at the anterior

of the heart and R ventricle

1048707

V3 and V4 = anterior and septal

1048707

V5 and V6 = lateral and left

ventricle

Electrode label (in the USA) Electrode placement

RA On the right arm avoiding thick muscle

LA In the same location where RA was placed but on the left arm

RL On the right leg lateral calf muscle

LL In the same location where RL was placed but on the left leg

V1 In the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum

V2 In the fourth intercostal space (between ribs 4 and 5) just to the left of the sternum

V3 Between leads V2 and V4

V4 In the fifth intercostal space (between ribs 5 and 6) in the mid-clavicular line

V5 Horizontally even with V4 in the left anterior axillary line

V6 Horizontally even with V4 and V5 in the mid axillary line

The ECG measures

differences in the

electric potential V

VE

The Electric Potential is the Potential ability to do

work

Alternatively Work = Q V

Where V = 21 VV

For uniform electric fields dEVd

VE ||||

Electric Potential

bull Interior of Heart muscle cells are negatively

charged at rest

bull Called ldquopolarisationrdquo

bull K+ ions leak out leaving interior ndashve

bull Depolarisation occurs just proir to

contraction

Na+ ions enter cells

Occurs in waves across the heart

Re-polarisation restores ndashve charge in

interior

+ + + + - - - - -+ +

+ +

- -

- -

Polarisation Depolarisation

ECG

Works by

measuring changes

in electric field as

heart pumps

Heart can be

modeled as a

rotating dipole

Depolarisation begins at the SA node

The wave of depolarisation spreads across the atria

It reaches the AV node and the accessory bundle

Conduction is delayed as usual by the in-built delay in the AV node

However the accessory bundle has no such delay and depolarisation begins

early in the part of the ventricle served by the bundle

As the depolarisation in this part of the ventricle does not travel in the high

speed conduction pathway the spread of depolarisation across the ventricle is

slow causing a slow rising delta wave

Until rapid depolarisation resumes via the normal pathway and a more

normal complex follows

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection

Leads and what

they tell you

Each lead can be thought of as

lsquolooking atrsquo an area

of myocardium

Chest leads

V1 to V6 lsquolook rsquo at the heart on

the transverse plain

1048707

V1 and V2 look at the anterior

of the heart and R ventricle

1048707

V3 and V4 = anterior and septal

1048707

V5 and V6 = lateral and left

ventricle

Electrode label (in the USA) Electrode placement

RA On the right arm avoiding thick muscle

LA In the same location where RA was placed but on the left arm

RL On the right leg lateral calf muscle

LL In the same location where RL was placed but on the left leg

V1 In the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum

V2 In the fourth intercostal space (between ribs 4 and 5) just to the left of the sternum

V3 Between leads V2 and V4

V4 In the fifth intercostal space (between ribs 5 and 6) in the mid-clavicular line

V5 Horizontally even with V4 in the left anterior axillary line

V6 Horizontally even with V4 and V5 in the mid axillary line

The ECG measures

differences in the

electric potential V

VE

The Electric Potential is the Potential ability to do

work

Alternatively Work = Q V

Where V = 21 VV

For uniform electric fields dEVd

VE ||||

Electric Potential

bull Interior of Heart muscle cells are negatively

charged at rest

bull Called ldquopolarisationrdquo

bull K+ ions leak out leaving interior ndashve

bull Depolarisation occurs just proir to

contraction

Na+ ions enter cells

Occurs in waves across the heart

Re-polarisation restores ndashve charge in

interior

+ + + + - - - - -+ +

+ +

- -

- -

Polarisation Depolarisation

ECG

Works by

measuring changes

in electric field as

heart pumps

Heart can be

modeled as a

rotating dipole

Depolarisation begins at the SA node

The wave of depolarisation spreads across the atria

It reaches the AV node and the accessory bundle

Conduction is delayed as usual by the in-built delay in the AV node

However the accessory bundle has no such delay and depolarisation begins

early in the part of the ventricle served by the bundle

As the depolarisation in this part of the ventricle does not travel in the high

speed conduction pathway the spread of depolarisation across the ventricle is

slow causing a slow rising delta wave

Until rapid depolarisation resumes via the normal pathway and a more

normal complex follows

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection

Electrode label (in the USA) Electrode placement

RA On the right arm avoiding thick muscle

LA In the same location where RA was placed but on the left arm

RL On the right leg lateral calf muscle

LL In the same location where RL was placed but on the left leg

V1 In the fourth intercostal space (between ribs 4 and 5) just to the right of the sternum

V2 In the fourth intercostal space (between ribs 4 and 5) just to the left of the sternum

V3 Between leads V2 and V4

V4 In the fifth intercostal space (between ribs 5 and 6) in the mid-clavicular line

V5 Horizontally even with V4 in the left anterior axillary line

V6 Horizontally even with V4 and V5 in the mid axillary line

The ECG measures

differences in the

electric potential V

VE

The Electric Potential is the Potential ability to do

work

Alternatively Work = Q V

Where V = 21 VV

For uniform electric fields dEVd

VE ||||

Electric Potential

bull Interior of Heart muscle cells are negatively

charged at rest

bull Called ldquopolarisationrdquo

bull K+ ions leak out leaving interior ndashve

bull Depolarisation occurs just proir to

contraction

Na+ ions enter cells

Occurs in waves across the heart

Re-polarisation restores ndashve charge in

interior

+ + + + - - - - -+ +

+ +

- -

- -

Polarisation Depolarisation

ECG

Works by

measuring changes

in electric field as

heart pumps

Heart can be

modeled as a

rotating dipole

Depolarisation begins at the SA node

The wave of depolarisation spreads across the atria

It reaches the AV node and the accessory bundle

Conduction is delayed as usual by the in-built delay in the AV node

However the accessory bundle has no such delay and depolarisation begins

early in the part of the ventricle served by the bundle

As the depolarisation in this part of the ventricle does not travel in the high

speed conduction pathway the spread of depolarisation across the ventricle is

slow causing a slow rising delta wave

Until rapid depolarisation resumes via the normal pathway and a more

normal complex follows

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection

The ECG measures

differences in the

electric potential V

VE

The Electric Potential is the Potential ability to do

work

Alternatively Work = Q V

Where V = 21 VV

For uniform electric fields dEVd

VE ||||

Electric Potential

bull Interior of Heart muscle cells are negatively

charged at rest

bull Called ldquopolarisationrdquo

bull K+ ions leak out leaving interior ndashve

bull Depolarisation occurs just proir to

contraction

Na+ ions enter cells

Occurs in waves across the heart

Re-polarisation restores ndashve charge in

interior

+ + + + - - - - -+ +

+ +

- -

- -

Polarisation Depolarisation

ECG

Works by

measuring changes

in electric field as

heart pumps

Heart can be

modeled as a

rotating dipole

Depolarisation begins at the SA node

The wave of depolarisation spreads across the atria

It reaches the AV node and the accessory bundle

Conduction is delayed as usual by the in-built delay in the AV node

However the accessory bundle has no such delay and depolarisation begins

early in the part of the ventricle served by the bundle

As the depolarisation in this part of the ventricle does not travel in the high

speed conduction pathway the spread of depolarisation across the ventricle is

slow causing a slow rising delta wave

Until rapid depolarisation resumes via the normal pathway and a more

normal complex follows

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection

bull Interior of Heart muscle cells are negatively

charged at rest

bull Called ldquopolarisationrdquo

bull K+ ions leak out leaving interior ndashve

bull Depolarisation occurs just proir to

contraction

Na+ ions enter cells

Occurs in waves across the heart

Re-polarisation restores ndashve charge in

interior

+ + + + - - - - -+ +

+ +

- -

- -

Polarisation Depolarisation

ECG

Works by

measuring changes

in electric field as

heart pumps

Heart can be

modeled as a

rotating dipole

Depolarisation begins at the SA node

The wave of depolarisation spreads across the atria

It reaches the AV node and the accessory bundle

Conduction is delayed as usual by the in-built delay in the AV node

However the accessory bundle has no such delay and depolarisation begins

early in the part of the ventricle served by the bundle

As the depolarisation in this part of the ventricle does not travel in the high

speed conduction pathway the spread of depolarisation across the ventricle is

slow causing a slow rising delta wave

Until rapid depolarisation resumes via the normal pathway and a more

normal complex follows

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection

Depolarisation begins at the SA node

The wave of depolarisation spreads across the atria

It reaches the AV node and the accessory bundle

Conduction is delayed as usual by the in-built delay in the AV node

However the accessory bundle has no such delay and depolarisation begins

early in the part of the ventricle served by the bundle

As the depolarisation in this part of the ventricle does not travel in the high

speed conduction pathway the spread of depolarisation across the ventricle is

slow causing a slow rising delta wave

Until rapid depolarisation resumes via the normal pathway and a more

normal complex follows

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection

How does the ECG work

1048707

Electrical impulse (wave of depolarisation) picked

up by placing electrodes on patient

1048707

The voltage change is sensed by measuring the

current change across 2 electrodes ndash a positive

electrode and a negative electrode

1048707If the electrical impulse travels towards the

positive electrode this results in a positive

deflection

1048707

If the impulse travels away from the positive

electrode this results in a negative deflection