Ventricular fibrillationVentricular fibrillation is a condition in which disordered electrical activity causes the chambers of your heart, ("ventricles"), to contract chaotically. When this occurs, little or no blood is pumped from the heart. Ventricular fibrillation (VF) is an abnormal heart rhythm that causes death. It is responsible for 75% to 85% of sudden deaths due to heart problems. Normally, heart muscle cells squeeze (contract) in rhythm at the same time to pump blood. These groups of cells are located in the bottom
two pumping chambers of the heart (ventricles). In someone with ventricular fibrillation, some heart cells contract while others are relaxing, and blood stops flowing.
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. 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.
Ventricular fibrillation is almost invariably fatal because the uncoordinated contractions of ventricular myocardium result in ineffective pumping and little or no blood flow to the body. There is lack of a pulse and pulse pressure and the patients lose unconsciousness rapidly. When the patient has no pulse and respiration the patient is said to be in cardiac arrest. A person in cardiac arrest must receive CPR immediately. Electrical defibrillation, by passage of current at high voltage, may be successful in restoration of a normal regular rhythm. The electrical current stimulates each myocardial cell to depolarize simultaneously. Following synchronous repolarization of all ventricular cells, the SA node assumes the role of pacemaker and the ventricular myocardial cells can resume the essentially simultaneous depolarization of normal sinus rhythm. Ventricular fibrillation is associated with drug toxicity, electrocution, drowning and myocardial infarction.
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.
Drug treatment aimed at suppressing premature ventricular contractions to prevent serious ventricular arrhythmias often fails to reduce the risk of sudden death. Prospects for effective treatment have brightened, however, with the development of electrophysiology studies and treatment programs that combine drug therapy with surgery and antiarrhythmic devices, such as implantable defibrillators. Individuals who have ventricular fibrillation or ventricular tachycardia (especially combined with fainting) should probably undergo full evaluation to determine the best treatment.
Prevention of the potentially dangerous contractions is crucial because few victims of sudden cardiac arrest survive without immediate first aid. Vigorous citizen training in CPR has, however, improved survival rates for victims of ventricular fibrillation. Long-term prevention of ventricular fibrillation remains difficult. Unlike atrial arrhythmias that have no symptoms, ventricular arrhythmias or premature ventricular contractions that cause no discomfort can indicate an increased risk of life-threatening ventricular tachycardia or fibrillation, especially in patients with heart disease or a family history of sudden death - although most of the time, these individual contractions are not serious. A physician may need to perform tests to aid in the assessment of the risk of these extra beats.