Ventricular Fibrillation
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Ventricular fibrillation causes unconsciousness in seconds, and if the disorder is not rapidly treated, death follows.
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Electrocardiography helps determine if the cause of cardiac arrest is ventricular fibrillation.
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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.
(See also Overview of Abnormal Heart Rhythms.)
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. Other causes include the following:
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Shock (very low blood pressure), which can result from coronary artery disease and other disorders
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Long QT syndrome (which may cause torsades de pointes ventricular tachycardia) including that due to very low levels of potassium in the blood (hypokalemia)
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Drugs that affect electrical currents in the heart (such as sodium channel blockers or potassium channel blockers—see table Some Drugs Used to Treat Arrhythmias)
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Brugada syndrome and other channelopathies
Symptoms
Diagnosis
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).
ECG: Reading the Waves
Treatment
Ventricular fibrillation must be treated as an extreme emergency. Cardiopulmonary resuscitation (CPR) must be started as soon as possible. It must be followed by defibrillation (an electrical shock delivered to the chest), as soon as the defibrillator is available. Drugs used to treat abnormal heart rhythms (see table Some Drugs Used to Treat Arrhythmias) 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 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 (ICD) surgically implanted to correct the problem 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.
