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Ventricular Fibrillation


L. Brent Mitchell

, MD, Libin Cardiovascular Institute of Alberta, University of Calgary

Reviewed/Revised Jan 2023
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Ventricular fibrillation is a potentially fatal, uncoordinated series of very rapid, ineffective contractions of the ventricles (lower chambers of the heart) 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 if the cause of cardiac arrest is ventricular fibrillation.

  • 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 Cardiac Arrest and CPR Cardiac arrest is when the heart stops pumping blood and oxygen to the brain and other organs and tissues. Sometimes a person can be revived after cardiac arrest, particularly if treatment is... read more Cardiac Arrest and CPR . It is fatal unless treated immediately.

The Conduction System

Idiopathic ventricular fibrillation

Some of these people likely have an unrecognized or unknown genetic disorder. Because of the possibility that the disorder is genetic, doctors recommend that family members be examined for possible cardiac events (for example, fainting or Fainting Light-headedness (near syncope) is a sense that one is about to faint. Fainting (syncope) is a sudden, brief loss of consciousness during which the person falls to the ground or slumps in a... read more palpitations Palpitations Palpitations are the awareness of heartbeats. The sensation may feel like pounding, fluttering, racing, or skipping beats. Other symptoms—for example, chest discomfort or shortness of breath—may... read more ) and that they undergo some testing, including electrocardiography, exercise stress testing, and echocardiography. It is unclear whether genetic testing is helpful.

Symptoms of Ventricular Fibrillation

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.

Diagnosis of Ventricular Fibrillation

  • Electrocardiography

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 Electrocardiography Electrocardiography (ECG) is a quick, simple, painless medical test that measures the heart’s electrical impulses. During an ECG, the heart's electrical impulses are measured, amplified, and... read more Electrocardiography (ECG).

ECG: Reading the Waves

ECG: Reading the Waves

An electrocardiogram (ECG) represents the electrical current moving through the heart during a heartbeat. The current's movement is divided into parts, and each part is given an alphabetic designation in the ECG.

Each heartbeat begins with an impulse from the heart's pacemaker (sinus or sinoatrial node). This impulse activates the upper chambers of the heart (atria). The P wave represents activation of the atria.

Next, the electrical current flows down to the lower chambers of the heart (ventricles). The QRS complex represents activation of the ventricles.

The electrical current then spreads back over the ventricles in the opposite direction. This activity is called the recovery wave, which is represented by the T wave.

Many kinds of abnormalities can often be seen on an ECG. They include a previous heart attack (myocardial infarction), an abnormal heart rhythm (arrhythmia), an inadequate supply of blood and oxygen to the heart (ischemia), and excessive thickening (hypertrophy) of the heart's muscular walls.

Certain abnormalities seen on an ECG can also suggest bulges (aneurysms) that develop in weak areas of the heart's walls. Aneurysms may result from a heart attack. If the rhythm is abnormal (too fast, too slow, or irregular), the ECG may also indicate where in the heart the abnormal rhythm starts. Such information helps doctors begin to determine the cause.

Treatment of Ventricular Fibrillation

  • Cardiopulmonary resuscitation

  • Preventing further episodes

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 defibrillation restores normal rhythm in 95% of people, and the prognosis is good. Shock Shock Shock is a life-threatening condition in which blood flow to the organs is low, decreasing delivery of oxygen and thus causing organ damage and sometimes death. Blood pressure is usually low... read more and heart failure Heart Failure (HF) Heart failure is a disorder in which the heart is unable to keep up with the demands of the body, leading to reduced blood flow, back-up (congestion) of blood in the veins and lungs, and/or... read more Heart Failure (HF) suggest severe damage to the ventricles. If the ventricles are severely damaged, 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 Implantable Cardioverter-Defibrillator (ICD) There are many causes of abnormal heart rhythms (arrhythmias). Some arrhythmias are harmless and do not need treatment. Sometimes arrhythmias stop on their own or with changes in lifestyle,... read more (ICD) surgically implanted to give a shock to treat the fibrillation if it recurs. ICDs continually monitor the rate and rhythm of the heart, automatically detect ventricular fibrillation, and deliver a shock to convert the arrhythmia back to a normal rhythm. Such people are often also given drugs to prevent recurrences.

More Information

The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.

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