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 is often 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 may also develop during hypoxia, atrial fibrillation, or improper grounding of electrical devices. An extremely low level of potassium in the blood can also 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.
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 restore 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.
McGoon, Michael D., ed. Mayo Clinic Heart Book: The Ultimate Guide to Heart Health. New York: William Morrow and Co., Inc., 1993.
American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. <http://www.americanheart.org>.
Dorothy Elinor Stonely
Atrial fibrillation—A condition in which the upper chambers of the heart quiver instead of contracting effectively
Cardioversion—A 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