PASCO CI-6539A EKG SENSOR User Manual

Page 7

012–06852A

EKG Sensor

simultaneously. This process causes a small time delay and so there

is a short pause after the atria contract before the ventricles contract.

Because the cells of the heart muscle are interconnected, this wave of

depolarization, contraction and repolarization spreads across all the

connected muscle of the heart. See Figure 2.

Bundle of His
(Atrioventricular Bundle)

Purkinje Fibers
(Conduction Myofibers)

Right Ventricle

Right Atrium

Atrioventricular (AV)
Node

Sinoatrial (SA)
Node

Figure 2

Cross section of human heart

When a portion of the heart is polarized and the adjacent portion is

depolarized this creates an electrical current that moves through the

body. This current is greatest when one half of the connected portion

of the heart is polarized and the adjacent half is not polarized. The

current decreases when the ratio of polarized tissue to non-polarized

tissue is less than one-to-one. The changes in these currents can be

measured, amplified, and plotted over time. The EKG represents the

summation of all the actions potentials from the heart as detected on

the surface of the body and does not measure the mechanical

contractions of the heart directly.

The two atria contract due to the pacemaker and force blood into the

two ventricles. Shortly after this contraction the two ventricles

contract due to the signal conducted to them from the atria. The blood

leaves the two ventricles through pulmonary and aortic arteries. The

heart muscle cells recover their polarity and in another second the

cycle starts again.

➤

➤ Note: An excellent text about the

electrocardiogram and other

phenomena of bioelectricity is Physics

with Health Science Applications by

& Sons, Inc., New York.