Ventricular Fibrillation

Definition

Ventricular fibrillation is a life-threatening abnormality in the electrical rhythm of the nerves of the ventricular portion of the heart. In this case, the rhythm is very fast and irregular causing the heart to stop effectively beating.

Description

Abnormally fast heart rates are classified into two types: supraventricular (meaning "above the ventricle") tachycardias - those that arise in the atria or the atrioventricular node - and ventricular tachycardias. In both instances, an extra or early beat may trigger the rapid rhythms.

Although the sinus node develops as the specialized site of impulse production, all cardiac muscle cells retain the capacity to become pacemaker cells. Normally the pace making activity of the sinus mode suppress impulse production by other cells, but if conductance to some part of the heart muscle is blocked, or if the heart is over-stimulated, islands of cells may express their latent impulse-production ability, resulting in extra beats. In other words, impulses are fired from one or more locations in addition to the normal pacemaker, the sinus node.

In contrast to supraventricular arrhythmias, ventricular arrhythmias are potentially more serious and are more often, but not always, associated with structural heart disease.

Premature ventricular contractions (PVCs) are the most common form. Like premature atrial contractions, premature ventricular contractions are early or extra beats that commonly occur and are innocuous in normal hearts, but can cause problems in unhealthy hearts. In rare circumstances, premature ventricular contractions can cause the ventricles to lapse into ventricular fibrillation; the heart quivers and ceases to pump blood effectively, and death can occur within 3 to 4 minutes.

Causes

Damaged heart muscle due to a heart attack or other acute diminution of oxygen supply to the heart can cause ventricular fibrillation.

Symptoms

Symptoms of occasional premature contractions can feel like heart palpitations. If ventricular fibrillation occurs, the heart stops effectively beating. This is diagnosed by monitoring the electrical activity of the heart with a heart monitor or EKG.

Treatment

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

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 however, has 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.