thaler chapter 1

P Waves, QRS Complexes, T Waves, and Some Straight Lines

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The EKG records a small deflection, the P wave.

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.

Right atrial component

Left atrial component

The components of the P wave.

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.