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.
(See also Overview of Abnormal Heart Rhythms Overview of Abnormal Heart Rhythms Abnormal heart rhythms (arrhythmias) are sequences of heartbeats that are irregular, too fast, too slow, or conducted via an abnormal electrical pathway through the heart. Heart disorders are... read more .)
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 . 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 Overview of Coronary Artery Disease (CAD) Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more , as occurs during a heart attack Acute Coronary Syndromes (Heart Attack; Myocardial Infarction; Unstable Angina) Acute coronary syndromes result from a sudden blockage in a coronary artery. This blockage causes unstable angina or a heart attack (myocardial infarction), depending on the location and amount... read more . Other causes include the following:
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 (very low blood pressure), which can result from coronary artery disease and other disorders
Long QT syndrome Long QT Interval Syndromes The long QT interval syndromes are disorders of the heart's electrical activity that predispose people to dangerous heart rhythms and sudden death. People may be born with an abnormality that... read more (which may cause torsades de pointes ventricular tachycardia Torsades de Pointes Ventricular Tachycardia Torsades de pointes ventricular tachycardia is a specific type of ventricular tachycardia that occurs in people who have a particular disorder of the heart's electrical activity called a long... read more ) including that due to very low levels of potassium in the blood (hypokalemia Hypokalemia (Low Level of Potassium in the Blood) In hypokalemia, the level of potassium in blood is too low. A low potassium level has many causes but usually results from vomiting, diarrhea, adrenal gland disorders, or use of diuretics. A... read more )
Drugs that affect electrical currents in the heart (such as sodium channel blockers or potassium channel blockers—see table )
Idiopathic ventricular fibrillation
People who have been resuscitated from cardiac arrest caused by ventricular fibrillation typically are evaluated for heart disease, particularly coronary artery disease Overview of Coronary Artery Disease (CAD) Coronary artery disease is a condition in which the blood supply to the heart muscle is partially or completely blocked. The heart muscle needs a constant supply of oxygen-rich blood. The coronary... read more , cardiomyopathies Overview of Cardiomyopathy Cardiomyopathy refers to progressive impairment of the structure and function of the muscular walls of the heart chambers. There are 3 main types of cardiomyopathy: Dilated cardiomyopathy, in... read more , and channelopathies Cardiac Channelopathies Cardiac channelopathies are abnormalities in heart cell proteins that control heart electrical activity and thus can cause heart rhythm disturbances. (See also Overview of Abnormal Heart Rhythms... read more . If testing does not identify any causative disorder, the person is considered to have idiopathic ventricular fibrillation. Idiopathic means the cause is unknown.
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.
People with idiopathic ventricular fibrillation are treated with 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 .
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
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 (ECG).
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
Preventing further episodes
Ventricular fibrillation must be treated as an extreme emergency. Cardiopulmonary resuscitation First-Aid Treatment for Cardiac Arrest 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 (CPR) must be started as soon as possible. It must be followed by defibrillation Cardioversion-Defibrillation 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 (an electrical shock delivered to the chest), as soon as the defibrillator is available. Drugs used to treat abnormal heart rhythms (see table ) 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 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 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.
The following English-language resource may be useful. Please note that THE MANUAL is not responsible for the content of this resource.
American Heart Association: Arrhythmia: Information to help people understand their risks of arrhythmias as well as information on diagnosis and treatment