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