The normal heart rhythm can be disrupted in different ways:
Bradycardia, or a slow heartbeat, may be due to problems with the heart's electrical system. It can be caused by aging, electrolyte abnormalities, medications, and abnormal thyroid function. Bradycardia can be normal in athletic individuals or those taking medications that slow the heart rate.
A slow heart rate can cause fatigue, dizziness, and fainting. It should be evaluated by a doctor, especially if it is associated with symptoms. Bradycardia can be treated with implantation of a pacemaker.
Tachycardia, or a fast heartbeat, can have many different causes. The heart normally beats faster with physical activity or emotional stress, but if the heart races at other times or for a prolonged period of time it should be evaluated. Tachycardias are grouped by the chamber from which they originate:
Atrial fibrillation is the most common form of arrhythmia. It occurs when the upper chambers beat erratically, causing an irregular heartbeat. People with atrial fibrillation often experience palpitations, fatigue, chest discomfort or shortness of breath. However, some people may not feel anything and it is discovered only on a routine doctor's visit.
Atrial fibrillation is a leading cause of stroke. If left untreated, the rapid heartbeat can also weaken the heart and cause heart failure. Treatments are available to control atrial fibrillation and reduce the risk of stroke.
Atrial flutter is similar to atrial fibrillation, though the heartbeat can be more regular with this arrhythmia. It also increases the risk of stroke and heart failure. Many people with atrial flutter will go on to develop atrial fibrillation.
Supraventricular tachycardia is usually caused by either an abnormal electrical circuit or rapidly-firing cells in the upper chambers of the heart. Symptoms can include palpitations, lightheadedness and shortness of breath. Episodes generally are not life threatening but can be bothersome and debilitating. SVT can often be cured with an ablation procedure.
Some people can be born with an extra electrical pathway between the top and bottom chambers of the heart. This is the cause of WPW syndrome. The extra pathway can cause abnormal circuits to form and lead to a fast heart rhythm. WPW usually can be noted on a routine EKG and can be dangerous even if there are no symptoms, thus it should be evaluated by a doctor.
Ventricular arrhythmias are abnormal heartbeats in the lower chambers of the heart (ventricles).
Premature beats are early, extra heartbeats. They are often called "skipped beats". Premature beats can arise from the upper or the lower chambers of the heart. While normally not dangerous, they can be associated with other heart diseases or predict future cardiac problems or arrhythmias. Premature beats can be aggravated by smoking or excess caffeine. Treatment may be necessary if they occur frequently or cause symptoms.
You should consult a doctor if you experience a prolonged or recurrent arrhythmia. Abnormal heartbeats can be clues to an underlying medical condition and should be evaluated