thaler chapter 1

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

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branch. The right and left ventricles then depolarize at about the same time, but most of what we see on the EKG represents left ventricular activation because the muscle mass of the left ventricle is about three times that of the right ventricle.

Repolarization After myocardial cells depolarize, they pass through a brief refractory period during which they are resistant to further stimulation. They then repolarize ; that is, they restore the electronegativity of their interiors so that they can be restimulated. Just as there is a wave of depolarization, there is also a wave of repolarization. This, too, can be seen on the EKG. Ventricular repolarization inscribes a third wave on the EKG, the T wave . Depolarization of the septum The initial part of the QRS complex represents septal depolarization. Sometimes, this septal depolarization may appear as a small, discrete, negative deflection, a Q wave.

Note: There is a wave of atrial repolarization as well, but it coincides with ventricular depolarization and is hidden by the much more prominent QRS complex.