What happens during ventricular fibrillation?

Atrial fibrillation occurs in the heart’s upper two chambers, also known as the atria. Ventricular fibrillation occurs in the heart’s lower two chambers, known as the ventricles . If an irregular heartbeat (arrhythmia) occurs in the atria, the word “atrial” will precede the type of arrhythmia.

Previous studies of patients with an out-of-hospital cardiac arrest with ventricular fibrillation have reported survival rates after hospital discharge ranging from 3 to 33 percent in a variety of settings . In communities without access to early defibrillation, mortality rates exceed 90 to 95 percent.

External electrical defibrillation remains the most successful treatment for ventricular fibrillation (VF). A shock is delivered to the heart to uniformly and simultaneously depolarize a critical mass of the excitable myocardium.

An arrhythmia that starts in your ventricle is called ventricular fibrillation. This occurs when the electrical signals that tell your heart muscle to pump cause your ventricles to quiver (fibrillate) instead . The quivering means that your heart is not pumping blood out to your body.