Ventricular fibrillation is a potentially fatal, uncoordinated series of very rapid, ineffective contractions of the ventricles caused by many chaotic electrical impulses.

• Ventricular fibrillation causes unconsciousness in seconds, and if the disorder is not rapidly treated, death follows.
• Electrocardiography (ECG) helps determine the cause of cardiac arrest.
• Cardiopulmonary resuscitation (CPR) must be started within a few minutes, and it must be followed by defibrillation (an electrical shock delivered to the chest) to restore normal heart rhythm.

ECG: Ventricular Fibrillation

In ventricular fibrillation, the ventricles merely quiver and do not contract in a coordinated way. No blood is pumped from the heart, so ventricular fibrillation is a form of cardiac arrest. It is fatal unless treated immediately.

The most common cause of ventricular fibrillation is inadequate blood flow to the heart muscle due to coronary artery disease, as occurs during a heart attack. Other causes include the following:

• Shock (very low blood pressure—see Shock), which can result from coronary artery disease and other disorders
• Electrical shock
• Drowning
• Very low levels of potassium in the blood (hypokalemia)
• Drugs that affect electrical currents in the heart (such as sodium or potassium channel blockers—see Some Drugs Used to Treat Arrhythmias)

Symptoms and Diagnosis

Ventricular fibrillation causes unconsciousness in seconds. If untreated, the person usually has seizures and develops irreversible brain damage after about 5 minutes because oxygen no longer reaches the brain. Death soon follows.

Cardiac arrest is diagnosed when a person suddenly collapses, turns deadly white, has very dilated pupils, and has no detectable pulse, heartbeat, or blood pressure. Ventricular fibrillation is diagnosed as the cause of the cardiac arrest by electrocardiography (ECG).

Treatment

Ventricular fibrillation must be treated as an extreme emergency. Cardiopulmonary resuscitation (CPR) must be started as soon as possible—within a few minutes. It must be followed by defibrillation (an electrical shock delivered to the chest), as soon as the defibrillator is available. Antiarrhythmic drugs may then be given to help maintain the normal heart rhythm.

When ventricular fibrillation occurs within a few hours of a heart attack in people who are not in shock and who do not have heart failure, prompt cardioversion restores normal rhythm in 95% of people, and the prognosis is good. Shock and heart failure suggest major damage to the ventricles. If they are present, even prompt cardioversion has only a 30% success rate, and 70% of resuscitated survivors die without regaining normal function.

People who are successfully resuscitated from ventricular fibrillation and survive are at high risk of another episode. If ventricular fibrillation is caused by a reversible disorder, that disorder is treated. Otherwise, most people have an automatic defibrillator surgically implanted to correct the problem, if it recurs, by delivering a shock. Such people are often also given drugs to prevent recurrences.

Last full review/revision January 2008 by L. Brent Mitchell, MD