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Ventricular Fibrillation

by L. Brent Mitchell, MD

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 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.

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 a heart disorder, particularly inadequate blood flow to the heart muscle due to coronary artery disease, as occurs during a heart attack, cardiomyopathies, and Brugada syndrome. 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

  • Long QT syndrome (which may cause torsades de pointes ventricular tachycardia) including that due to 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 a brief seizure and then becomes limp and unresponsive. People develop 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 deathly pale, stops breathing, and has no detectable pulse, heartbeat, or blood pressure. Ventricular fibrillation is diagnosed as the cause of the cardiac arrest by electrocardiography (ECG).


Ventricular fibrillation must be treated as an extreme emergency. Cardiopulmonary resuscitation (CPR—see Cardiac Arrest : First-Aid Treatment) 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 severe damage to the ventricles. If they are present, even prompt cardioversion has only a 30% success rate, and 70% of people who are resuscitated 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 implantable cardioverter-defibrillator (ICD—see Abnormal Heart Rhythms:Restoring normal rhythm) surgically implanted to correct the problem, if it recurs, by delivering a shock. Such people are often also given drugs to prevent recurrences.

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