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P Waves, QRS Complexes, T Waves, and Some Straight Lines
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Because the sinus node is located in the right atrium, the right
atrium begins to depolarize before the left atrium and finishes
earlier as well. Therefore, the first part of the P wave predominantly
represents right atrial depolarization, and the second part left atrial
depolarization.
Once atrial depolarization is complete, the EKG again becomes
electrically silent.
A Pause Separates Conduction From the Atria to the Ventricles
In healthy hearts, there is an electrical gate at the junction of the atria
and the ventricles. The wave of depolarization, having completed its
journey through the atria, is prevented from communicating with
the ventricles by the heart valves that separate the atria and ventricles.
Electrical conduction must be funneled along the interventricular
septum, the wall that separates the right and left ventricles. Here, a
structure called the
atrioventricular
(
AV
)
node
slows conduction to a
crawl. This pause lasts only a fraction of a second.
The EKG records a small deflection, the P wave.
Right atrial component
Left atrial component
The components of the P wave.