Ventricular fibrillation is a very fast, irregular heartbeat that is caused by abnormal firing of electrical signals in the ventricles of the heart.
The electrical system of the heart is made up of several parts that communicate with one another to signal the heart muscle fibers when to contract (see fig 1). The SA node starts the signal causing the atria to contract. This signal travels through the AV node and on to the bundle of His, bundle branches, and Purkinje fibers causing the ventricles to contract. The flow of electrical signals is what produces a normal heartbeat (see fig. 2).
In ventricular fibrillation, disorganized electrical impulses in the heart’s lower chambers (see fig. 3 and 4) cause the heart to stop beating (cardiac arrest). The ventricles quiver uselessly, instead of pumping blood.
Figure 1: Parts of the electrical system of the heart.
Figure 2: Flow of electrical signals in a normal heartbeat.
Figure 3: Ventricular fibrillation with abnormal signals originating in the ventricles.
Figure 4: Normal ECG compared with ventricular fibrillation ECG.
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