The heartbeat is controlled by the electrical system of the heart. This system is made up of several parts that tell the muscle of the heart when to contract. The SA node starts the heartbeat, causing the atria, or upper chambers of the heart, to contract. The signal then travels through the AV node, bundle of His, bundle branches, and Purkinje fibers. This causes the ventricles, the lower chambers of the heart, to contract. This flow of electrical signals produces a normal heartbeat. Normal heartbeats can be seen in an Electrocardiogram or ECG.
Ventricular fibrillation is a very fast, irregular heartbeat that is caused by abnormal firing of electrical signals in the ventricles of the heart. In ventricular fibrillation, disorganized electrical impulses in the heart’s lower chambers cause the heart to stop beating (cardiac arrest). The ventricles quiver uselessly instead of pumping blood. This irregular heartbeat can be seen on an electrocardiogram.
Ventricular fibrillation usually causes a loss of consciousness and is a medical emergency because the brain and body are no longer receiving blood from the heart. CPR may be performed until an external defibrillator can be used to deliver a quick shock that will restore the normal heartbeat. If ventricular fibrillation is not treated, it may result in sudden cardiac arrest and death.
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