ventricular fibrillation

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Ventricular Fibrillation



Ventricular fibrillation is a very rapid, uncoordinated, ineffective series of contractions throughout the lower chambers of the heart. Unless stopped, these chaotic impulses are fatal.


When the ventricles begin to quiver and do not employ coordinated contractions, the heart is said to be fibrillating. In this condition the ventricles cannot pump blood from the heart. Ventricular fibrillation (V-fib) is the worst kind of abnormal heart rhythm, and is a form of cardiac arrest. It involves the pumping of the lower chambers of the heart, while atrial fibrillation involves the upper chambers.

Causes and symptoms

Ventricular fibrillation often is associated with acute ischemic events (ischemia involves the deprivation of oxygenated blood to an area of tissue), and with chronic ischemic heart disease. It is frequently seen immediately following a heart attack. It also may develop during hypoxia, atrial fibrillation, or improper grounding of electrical devices. An extremely low level of potassium in the blood also can cause ventricular fibrillation.
The first, and usually the only, symptom of V-fib is sudden unconsciousness.


When an individual suddenly collapses, the possibility of ventricular fibrillation should be considered immediately. A quick assessment usually shows no pulse or heartbeat. The diagnosis of ventricular fibrillation is confirmed with an electrocardiogram.


Basic life support with standard cardiopulmonary resuscitation (CPR) must be started within a few minutes, followed as soon as possible with cardioversion. Cardioversion is an electric shock delivered to the heart to stop the fibrillating. Early defibrillation is the key to survival. If left untreated, irreversible brain damage, due to lack of oxygen to the brain, occurs after about five minutes. After the heart resumes its normal rhythm, medications are given to help maintain the rhythm.
Research continues into methods to deliver defibrillation as soon as possible to those experiencing ventricular fibrillation. One of the studies addressed in 2003 researched various clinical trials that implanted defibrillators into patients to prevent sudden cardiac death. The devices worked in many instances but more proof of their success was needed for widespread use.


Early and effective CPR may provide the time necessary for medical personnel to arrive with a defibrillator. If a defibrillator is able to promptly restore a normal rhythm, up to 25% of victims are able to leave the hospital without evidence of brain damage.
If ventricular fibrillation occurs in the hospital in conjunction with a heart attack, defibrillation has a 95% success rate. If shock and heart failure are present at the time, even with immediate defibrillation, only about 30% of those stricken are successfully restored to a normal heart rate.


A healthy lifestyle to reduce the risk of heart diseases which lead to ventricular fibrillation is the best prevention. For people who have experienced an episode of V-fib, an internal cardioverter-defibrillator may prevent further episodes.

Key terms

Atrial fibrillation — A condition in which the upper chambers of the heart quiver instead of contracting effectively
Cardiopulmonary resuscitation (CPR) — Using rescue breathing and chest compressions to help a person whose breathing and heartbeat have stopped
Cardioversion — An electrical shock delivered to the heart to restore a normal rhythm
Electrocardiogram — A visual representation of the heart beat
Heart failure — A term used when the heart is unable to pump enough blood to supply the needs of the body
Hypoxia — Insufficient oxygen in the cells of the body
Ischemic — Insufficient blood reaching the tissues



Ezekowitz, Justin A., et al. "Implantable Cardioverter Defibrillators in Primary and Secondary Prevention: A Systematic Review of Randomized, Controlled Trials." Annals of Internal Medicine January 2002: 445.


American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.


1. a small, local, involuntary, muscular contraction, due to spontaneous activation of single muscle cells or muscle fibers.
2. the quality of being made up of fibrils.
3. the initial degenerative changes in osteoarthritis, marked by softening of the articular cartilage and development of vertical clefts between groups of cartilage cells.
Fibrillation on an electrocardiographic tracing. From Fenstermacher and Hudson, 1995.
atrial fibrillation a reentrant cardiac arrhythmia marked by rapid randomized contractions of the atrial myocardium, causing a totally irregular rapid atrial rate. It is recognizable on an electrocardiogram by the absence of P waves and an irregular ventricular response. It may be controlled by drug therapy or cardioversion.
ventricular fibrillation a cardiac arrhythmia marked by fibrillary contractions of the ventricular muscle due to rapid repetitive excitation of myocardial fibers with ineffectual ventricular contraction; on the surface electrocardiogram it is characterized by lack of identifiable QRS complexes. This is a frequent cause of cardiac arrest. An apparatus called a defibrillator is used to alleviate it by delivering an electric shock to the heart muscle; this depolarizes the myocardium and ends the irregular contractions so that the heart can resume normal, regular contractions.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.

ven·tric·u·lar fi·bril·la·tion

coarse or fine, rapid, fibrillary movements of the ventricular muscle that replace the normal contraction.
Farlex Partner Medical Dictionary © Farlex 2012

ventricular fibrillation

An often fatal form of arrhythmia characterized by rapid, irregular fibrillar twitching of the ventricles of the heart in place of normal contractions, resulting in a loss of pulse.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.

ventricular fibrillation

V fib Cardiology An abnormal, life-threatening irregular heart rhythm characterized by rapid uncoordinated fluttering contractions of the ventricles of the heart; VF is often are life threatening and occur 2º to an acute MI or a healed infarction Physical examination Loss of synchrony between the heartbeat and pulse beat. Cf Ventricular tachycardia.
McGraw-Hill Concise Dictionary of Modern Medicine. © 2002 by The McGraw-Hill Companies, Inc.

ven·tric·u·lar fib·ril·la·tion

(ven-trik'yū-lăr fib'ri-lā'shŭn)
Coarse or fine, rapid, fibrillary movements of the ventricular muscle that replace the normal contraction. This causes a failure to eject blood from the ventricle efficiently.
Medical Dictionary for the Health Professions and Nursing © Farlex 2012

ventricular fibrillation

A rapid fluttering, or twitching motion of the heart muscle which has replaced the normal forceful contraction and which is ineffective in moving blood. Ventricular fibrillation is a form of cardiac arrest and causes irremediable brain damage within a matter of minutes and unless reversed by DEFIBRILLATION is soon fatal. The drug bretylium tosylate (Bretylate) can be used when electrical defibrillation fails.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005

ventricular fibrillation

Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005

ven·tric·u·lar fib·ril·la·tion

(ven-trik'yū-lăr fib'ri-lā'shŭn)
Coarse or fine, rapid, fibrillary movements of the ventricular muscle that replace the normal contraction.
Medical Dictionary for the Dental Professions © Farlex 2012