Arrhythmia, or heart rhythm disorder, is a general term for an irregular heartbeat. Most arrhythmias are not dangerous, but some may indicate serious underlying heart disease and some can lead to serious problems such as loss of consciousness, stroke and sudden cardiac death.  In this episode of Second Opinion, you'll learn about the causes and treatment of arrhythmia, and what to do if someone suddenly collapses next to you. Your early intervention can save lives!

The heart has four chambers. The upper two are the atria (the right and the left atrium) and the lower two chambers are the right and left ventricles. These chambers contract in a regular sequence, or rhythm (the heartbeat); the contractions enable the heart to pump blood to all parts of the body.  The normal rhythm of contractions is controlled by the heart's "pacemaker," a group of cells (called the sinoatrial node, SA node, or sinus node) in the right atrium that generate electrical impulses.  These impulses travel across the heart's chambers, making them contract. This is the "normal" rhythm, generated at a certain rate, usually 60 to 100 times a minute.  When that rate is abnormal or the cadence irregular, the heart may have an arrhythmia, also referred to as dysrhythmia by some experts.

There are several kinds of arrhythmia.  A heartbeat can be too fast (technical name: tachycardia ), too slow (technical name: bradycardia), or simply irregular. Arrhythmias can also be classified by where they happen, i.e., there are atrial arrhythmias and ventricular arrhythmias, and there are several kinds of each.

For example, one frequent type of atrial arrhythmia is atrial fibrillation , in which the atria quiver instead of contracting normally. Therefore, the heartbeat does not pump blood through the heart effectively.  Untreated atrial fibrillation can lead to heart failure or stroke - but atrial fibrillation may be successfully treated.

Ventricular fibrillation  is an especially dangerous form of arrhythmia in which the contractions of the ventricles are rapid, unsynchronized, and uncoordinated, so that the heart pumps very little or no blood.  Untreated ventricular fibrillation can cause collapse and sudden death - but again, it may be successfully treated. 

For information about defibrillation (treating fibrillation by using electric shocks to restore the heart's correct rhythm) refer to heart rhythm disorder points #2 and #3.

The symptoms of arrhythmia can vary, depending on the type of arrhythmia, but in general they include:

• Feeling like the heart "skipped a beat"
• Palpitations
• Throbbing and/or fluttering in the chest

In more serious cases, a person might feel dizzy or faint, have chest pain, and/or shortness of breath.