(See also Overview of Arrhythmias Overview of Arrhythmias The normal heart beats in a regular, coordinated way because electrical impulses generated and spread by myocytes with unique electrical properties trigger a sequence of organized myocardial... read more 
.)
Ventricular fibrillation (VF) is due to multiple wavelet reentrant electrical activity and is manifested on electrocardiogram (ECG) by ultrarapid baseline undulations that are irregular in timing and morphology.
VF is the presenting rhythm for about 70% of patients in cardiac arrest Cardiac Arrest Cardiac arrest is the cessation of cardiac mechanical activity resulting in the absence of circulating blood flow. Cardiac arrest stops blood from flowing to vital organs, depriving them of... read more and is thus the terminal event in many disorders. Overall, most patients with VF have an underlying heart disorder (typically ischemic cardiomyopathy Overview of Cardiomyopathies A cardiomyopathy is a primary disorder of the heart muscle. It is distinct from structural cardiac disorders such as coronary artery disease, valvular disorders, and congenital heart disorders... read more , but also hypertrophic cardiomyopathy Hypertrophic Cardiomyopathy Hypertrophic cardiomyopathy is a congenital or acquired disorder characterized by marked ventricular hypertrophy with diastolic dysfunction (eg, due to valvular aortic stenosis, coarctation... read more 
or dilated cardiomyopathy Dilated Cardiomyopathy Dilated cardiomyopathy is myocardial dysfunction causing heart failure in which ventricular dilation and systolic dysfunction predominate. Symptoms include dyspnea, fatigue, and peripheral edema... read more 
, arrhythmogenic right ventricular cardiomyopathy Arrhythmogenic Right Ventricular Cardiomyopathy Arrhythmogenic right ventricular cardiomyopathy (ARVC), also called arrhythmogenic right ventricular dysplasia (ARVD), is a genetic cardiac disorder affecting mainly the right ventricle and... read more , or Brugada syndrome Brugada Syndrome Brugada syndrome is an inherited channelopathy causing an increased risk of ventricular tachycardia (VT) and ventricular fibrillation (VF) leading to syncope and sudden death. (See also Overview... read more ). Patients in whom no underlying disorder is detected are considered to have idiopathic VF. Idiopathic ventricular fibrillation Ventricular fibrillation causes uncoordinated quivering of the ventricle with no useful contractions. It causes immediate syncope and death within minutes. Treatment is with cardiopulmonary... read more 
Risk of VF in any disorder is increased by electrolyte abnormalities, acidosis, hypoxemia, or ischemia.
Ventricular fibrillation is much less common among infants and children, in whom asystole is the more common presentation of cardiac arrest.
Idiopathic ventricular fibrillation
Patients who have been resuscitated from VF cardiac arrest typically are evaluated for cardiac disease, particularly coronary artery disease Overview of Coronary Artery Disease Coronary artery disease (CAD) involves impairment of blood flow through the coronary arteries, most commonly by atheromas. Clinical presentations include silent ischemia, angina pectoris, acute... read more 
, cardiomyopathies Overview of Cardiomyopathies A cardiomyopathy is a primary disorder of the heart muscle. It is distinct from structural cardiac disorders such as coronary artery disease, valvular disorders, and congenital heart disorders... read more , and channelopathies Overview of Channelopathies Channelopathies are a group of genetic, autoimmune, or inflammatory conditions that alter cardiomyocyte ion channel function in a manner that predisposes to bradyarrhythmias or tachyarrhythmias... read more . If comprehensive electrocardiographic, imaging, and provocative testing do not identify any such causative disorder, the patient is considered to have idiopathic ventricular fibrillation. It is thought that some of these patients likely have an unrecognized or unknown genetic disorder. Because of the possibility that the disorder is familial, it is recommended that family members have clinical evaluation for possible cardiac events (eg, syncope, palpitations) and limited testing, including ECG, exercise stress testing, and echocardiography. The role of genetic testing is undefined. Treatment is an implantable cardioverter-defibrillator Implantable Cardioverter-Defibrillators (ICD) The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more 
.
Treatment of Ventricular Fibrillation
Defibrillation
Implantable cardioverter-defibrillator
Treatment of ventricular fibrillation is with cardiopulmonary resuscitation Cardiopulmonary Resuscitation (CPR) in Adults Cardiopulmonary resuscitation (CPR) is an organized, sequential response to cardiac arrest, including Recognition of absent breathing and circulation Basic life support with chest compressions... read more , including defibrillation Defibrillation Cardiopulmonary resuscitation (CPR) is an organized, sequential response to cardiac arrest, including Recognition of absent breathing and circulation Basic life support with chest compressions... read more . The success rate for immediate (within 3 minutes) defibrillation is about 95%, provided that overwhelming pump failure does not preexist. When it does, even immediate defibrillation is only 30% successful, and most resuscitated patients die of pump failure before hospital discharge.
Patients who have VF without a reversible or transient cause are at high risk of future VF events and of sudden death. Most of these patients require an implantable cardioverter-defibrillator Implantable Cardioverter-Defibrillators (ICD) The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more ; many require concomitant antiarrhythmic drugs Medications for Arrhythmias The need for treatment of arrhythmias depends on the symptoms and the seriousness of the arrhythmia. Treatment is directed at causes. If necessary, direct antiarrhythmic therapy, including antiarrhythmic... read more to reduce the frequency of subsequent episodes of ventricular tachycardia and VF.
