Atrial fibrillation, ventricular tachycardia and ventricular fibrillation are common arrhythmias.
Atrial fibrillation. About one in four people age 40 and older develop atrial fibrillation, a form of tachycardia in which the atria quiver (fibrillate) chaotically instead of contracting normally. This causes the ventricles to contract irregularly and often rapidly, and blood is not circulated efficiently throughout the body.
The risk of atrial fibrillation increases with age. People with CHD, heart valve abnormalities or an overactive thyroid (hyperthyroidism) are also at higher risk than the general population.
Common symptoms of atrial fibrillation include weakness, shortness of breath, lightheadedness, palpitations and chest pain, although some people have no symptoms. Atrial fibrillation can lead to blood clots in the atria that can loosen and travel through the circulatory system. If one of these clots blocks an artery supplying blood to the brain, a stroke can occur. People with atrial fibrillation have a five-fold increased risk of suffering a stroke.
Ventricular tachycardia and ventricular fibrillation. Both of these arrhythmias, which are caused by abnormal electrical signals that originate within the ventricles, are much more serious than atrial fibrillation. They can develop during a heart attack or in the weeks or months afterward, as damaged heart muscle releases substances that interfere with the normal conduction of electrical impulses in the heart.
In ventricular tachycardia, the heart beats at a rate of more than 100 beats a minute. This rapid heartbeat can cause palpitations, lightheadedness, dizziness, weakness and fainting, as well as a dangerous drop in blood pressure because too little blood is pumped with each beat.
Depending on how fast the heart rate is, individuals with ventricular tachycardia can survive for hours without treatment. But ventricular tachycardia can progress to ventricular fibrillation, which is fatal if not treated promptly.
During ventricular fibrillation the ventricles twitch rapidly and chaotically, rendering them unable to pump blood throughout the body. As a result, ventricular fibrillation leads to unconsciousness within seconds. Collapse and cardiac arrest can occur quickly and lead to death within a few minutes without treatment. More than 240,000 Americans die each year of cardiac arrest associated with ventricular fibrillation.