ECG Flashcards
electrocardiography
electrodes are placed on the body surface.
The electrodes are therefore moved from the heart in varying degrees depending upon their placement.
But since the heart is in electrical contact with the body surface via blood and ECF, potential changes due
to the heart’s electrical activity can be recorded at the body surface.
there are three approaches to the recording of the electrical potential of the heart.
The 3 approaches can be characterized by the site of electrode placement.
In the first, one electrode is placed
inside the cell; the other is placed opposite the first one, the outside of the cell. The trans membrane potential changes associated with each contraction are recorded by this method
In the second, one electrode is placed on the surface of the heart; the other is placed on the body at as great distance as possible from the first electrode. The potential changes associated with each beat are recorded.
Electrodes are placed ON:
on the right arm, left arm, left leg, and right leg.
The right leg electrode
is a ground connection which prevents unwanted external potential fields from distortion
The other 3 are used in
pairs:
to pick up the cardiac potentials
Lead 1
potential difference (P.D.) between the left arm and right arm
Lead 11
records the P.D
between the left leg and right arm.
Lead 111
records the P.D. between the left leg and left arm
initiates the excitation wave
The sinus node
It then spreads at a ratio of about one meter per second across the atria.
P Wave duration
0.08 seconds
delay at the A-V node
0.10 sec
P-R interval
represents the time taken for the excitation wave to spread from its origin to the beginning of its spread through the ventricular muscular
measured from the beginning of the P wave to the onset of the first component of the QRS complex.
