PASCO CI-6539A EKG SENSOR - Manual (Page 8)

EKG Sensor 012–06852A
4
The Electrocardiogram
One part of a typical EKG (electrocardiogram) is a ‘flat line’ or trace
indicating no detectable electrical activity. This line is called the
Isoelectric line. Deviation from this line indicates electrical activity
of the heart muscles.
The first deviation from the Isoelectric line in a typical EKG is an
upward pulse followed by a return to the Isoelectric line. This is called
the P wave and it lasts about 0.04 seconds. This wave is caused by the
depolarization of the atria and is associated with the contraction of the
atria.
After a return to the Isoelectric line there is a short delay while the
heart’s AV node depolarizes and sends a signal along the
atrioventricular bundle of conducting fibers (Bundle of His) to the
Purkinje fibers, which bring depolarization to all parts of the ventricles
almost simultaneously.
After the AV node depolarizes there is a downward pulse called the
Q wave. Shortly after the Q wave there is a rapid upswing of the line
called the R wave followed by a strong downswing of the line called
the S wave and then a return to the Isoelectric line. These three waves
together are called the QRS complex. This complex is caused by the
depolarization of the ventricles and is associated the with the
contraction of the ventricles.
After a short period of time the sodium and calcium ions that have
been involved in the contraction migrate back to their original
location in a process that involves potassium ions and the sodium-
potassium pump. The movement of these ions generates an upward
wave that then returns to the Isoelectric line. This upward pulse is
called the T wave and indicates repolarization of the ventricles. The
atria repolarize during the QRS complex and therefore this
repolarization is not separately detectable.