Ventricular fibrillation is caused by either:
- A problem in the heart's electrical properties
- A disruption of the blood supply to the heart muscle
Sometimes, the cause of ventricular fibrillation is unknown.
To understand more about how ventricular fibrillation occurs, it may be helpful to know how the heart typically beats.
The heartbeat
The typical heart has four chambers — two upper chambers (atria) and two lower chambers (ventricles). Within the upper right chamber of the heart (right atrium) is a group of cells called the sinus node. The sinus node is the heart's natural pacemaker. It produces the signals that start each heartbeat.
These electrical signals move across the atria, causing the heart muscles to squeeze (contract) and pump blood into the ventricles.
Next, the signals arrive at a cluster of cells called the AV node, where they slow down. This slight delay allows the ventricles to fill with blood. When the signals reach the ventricles, the lower heart chambers contract and pump blood to the lungs or to the rest of the body.
In a typical heart, this heart signaling process usually goes smoothly, resulting in a typical resting heart rate of 60 to 100 beats a minute. But in ventricular fibrillation, rapid, irregular electrical signals cause the lower heart chambers to quiver uselessly instead of pumping blood.