Cardiology Teaching Package
A Beginners Guide to Normal Heart Function, Sinus Rhythm & Common Cardiac Arrhythmias
The P Wave
Now look again at the sinus complex.
The first wave (p wave) represents atrial depolarisation. When the valves between the atria and ventricles open, 70% of the blood in the atria falls through with the aid of gravity, but mainly due to suction caused by the ventricles as they expand.
Atrial contraction is required only for the final 30% and therefore a relatively small muscle mass is required and only a relatively small amount of voltage is needed to contract the atria.
Image: The P Wave
