Page 201 - The Miracle of the Blood and Heart

AV node

SA node Purkinje
fibers

Atrial Ventricular Atrial/ventricular
systole systole diastole
Millivolts

Milliseconds
a)
Normal
ECG

b)

Sinus tachycardia Ventricular fibrillation Mitral stenosis
Abnormal ECGs

a) The sinus node (SA node) sends out a signal that causes the atria to
contract. When this signal reaches the AV node, it sends a signal to the
ventricles to contract by way of the Purkinje fibers.
b) A normal ECG shows the heart is working properly. The P wave
forms when the atria contract, the QRS wave when the ventricles con-
tract, and the T wave when the ventricles are recovering from contrac-
tion.
c) Abnormal ECGs: Sinus tachycardia is a rapid heartbeat due to
a fast pacemaker. An irregular heartbeat occurs because of the
ventricles' irregular stimulation (ventricular fibrillation).
Mitral stenosis occurs because the mitral valve is obstructed.
Adnan
Oktar

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