Download MBBS Physiology Presentations 36 Electrocardiography Part 1 Lecture Notes

Download MBBS (Bachelor of Medicine, Bachelor of Surgery) 1st Year, 2nd Year, 3rd Year and Final year Physiology 36 Electrocardiography Part 1 PPT-Powerpoint Presentations and lecture notes


Electrocardiography

Department of Physiology

Specific learning objectives

? Introduction
? History
? Normal ECG
? Procedure
? Limb Leads


ECG, EKG

It is the procedure of recording the electrical activity of the heart. The

electrode combination records the difference of potential difference at two

sites on the body. The potential differences are produced due to the electrical

activity of the heart.

Electrocardiograph is the machine

Electrocardiogram is the record

The characteristic shape and timing of the ECG waves are due to the spread

of wave of depolarization and repolarization associated with each heart beat.


? The ECG is not

only the oldest

but, in fact, over

100 years after

its introduction,

continues as the

most commonly

used

cardiovascular

laboratory

procedure.

What does the ECG look like?



Waves

R

T

P

Q

S

Electrocardiogram waves

? P-wave ? depolarization of atria

? Atria begin contracting about 25msec after the start of

the p-wave

? QRS-complex ? ventricular depolarization

? Ventricles begin contracting shortly after the peak of

the R wave

? T-wave ? ventricular repolarization


Electrocardiogram intervals/segments

? Segments ? extend from the end of one wave to

the start of another

? P-R interval: start of atrial depolarization to start

of QRS

? Q-T interval: time required for ventricles to

undergo a single cycle of depolarization and

repolarization; measured from end of P-R to end

of T

Instantaneous potentials developed

on the surface of a cardiac muscle mass


Recording depolarization

and repolarization waves

Flow of current in the chest around

partially depolarized ventricles
Generation of dipole over heart

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

-

- - + +

+ + + +

- + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

+
If the polarity is reversed?

+

- - + +

+ + + +

- + + +

+ + + +

+ + + +

+ + + +

+ + + +

+ + + +

-

-

- -

- - + + + +

-

- + + + + +

-

- - - +

+ + + +

- + + +

+ + + +

+
-

- -

- - - -

- -

-

- - - - -

+ +

-

- - - - - + +

- - - - - - + +

+

-

- -

- - - -

- -

-

- - - - -

- -

-

- - - - -

- -

- - - - - -

- -

+
Remember

The representation of the electrical activity of the

heart is critically dependent on the

position of the electrodes. The same electrical

activity will look different on different electrode

combinations

A combination of electrodes for recording is called a LEAD

Leads that are routinely used for standard 12 lead ECG

Standard Limb Leads

Wilhem Einthoven

Augmented Limb Leads

E Goldberger

Precordial Leads

Frank Wison


Standard Limb Leads

-

+

Limb lead I

Limb

- Lim

le

-

b

a

le

d

a

I I

d I

+

+

Einthoven's triangle

Einthoven's Law


Unipolar Limb Leads

-

+

VR

VL

VF

Augmented Limb Leads

aVR

+

Similarly, aVL and aVF
Augmented lead is 1.5 X unipolar lead

aVL = VL ? (VR + VF) /2

2 aVL = 2 VL ? (VR + VF)

VL + VR + VF = 0

VL = - ( VR + VF)

2 aVL = 2VL + VL

aVL = 3/2 VL
Thank You

This post was last modified on 08 April 2022