An arrhythmia is a disorder of the heart rate (pulse) or heart rhythm, such as beating too fast (tachycardia), too slow (bradycardia), or irregularly.

Normally, the four chambers of the heart (two atria and two ventricles) contract in a very specific, coordinated way.

The electrical impulse that signals your heart to contract in a synchronized manner begins in the sinoatrial node (SA node). This is your heart's natural pacemaker.

The signal leaves the SA node and travels through the two upper chambers (atria). Then the signal passes through another node (the AV node). Finally, it passes through the lower chambers (ventricles). This path enables the chambers to contract in a coordinated fashion.

Problems can occur anywhere along this conduction system, causing various arrhythmias. Examples include:

• Bradycardia - a slow heart rate due to problems with the SA node's pacemaker ability, or an interruption in energy movement (conduction) through the natural electrical pathways of the heart.
• Supraventricular tachycardia - a fast heart rate that originates in the upper chambers (atria). The most common are atrial fibrillation or flutter and atrioventricular nodal reentry tachycardia (AVNRT).
• Ventricular tachycardia - a fast heart rate that originates in the lower chambers (ventricles).

The risk of getting a tachycardia or bradycardia varies greatly, depending on:

• Condition of your heart
• Blood chemistry imbalances
• Endocrine abnormalities
• Past heart attack

Arrhythmias may also be caused by some substances or drugs, including:

• Amphetamines
• Caffeine
• Cocaine
• Beta blockers
• Psychotropics
• Sympathomimetics

Sometimes anti-arrhythmic medications -- prescribed to treat one type of arrhythmia -- can actually cause another type of arrhythmia.

• Chest pain
• Fainting
• Fast or slow heartbeat (palpitations)
• Light-headedness, dizziness
• Paleness
• Shortness of breath
• Skipping beats - changes in the pattern of the pulse
• Sweating

You may not have symptoms.

The doctor will listen to your heart with a stethoscope and feel your pulse. Your blood pressure may be low or normal.

The following tests may be performed to identify arrhythmias:

• Ambulatory cardiac monitoring with a Holter monitor (used for 24 hours), event monitor, or loop recorder (worn for 2 weeks or longer)
• Coronary angiography
• ECG
• Echocardiogram
• Electrophysiology study (EPS)

If an arrhythmia is detected, various tests may be done to confirm or rule out suspected causes. EPS testing may be done to find the arrhythmia and determine the best treatment, especially if a pacemaker or catheter ablation procedure is being considered.

When an arrhythmia is serious, urgent treatment may be required to restore a normal rhythm. This may include:

• Electrical "shock" therapy (defibrillation or cardioversion)
• Implanting a temporary pacemaker to interrupt the arrhythmia
• Medications given through a vein (intravenous)

Supraventricular arrhythmias may be treated with:

• Medications that slow the pulse (beta blockers, calcium channel blockers)
• Medications that cause the heart rhythm to return to normal (anti-arrhythmic drugs)

Many supraventricular arrhythmias can be treated and cured with radiofrequency ablation. This avoids the need for lifelong drug therapy.

Increasingly, most ventricular tachycardias are treated with an implantable cardioverter-defibrillator (ICD). As soon as arrhythmia begins, the ICD sends a shock to stop it, or a burst of pacing activity to override it.

Bradycardias that cause symptoms can be treated by implanting a permanent pacemaker.

The outcome depends on several factors:

• The kind of arrhythmia -- whether it is supraventricular tachycardia, or a more dangerous arrhythmia such as ventricular tachycardia or ventricular fibrillation
• The overall pumping ability of the heart (ejection fraction)
• Whether you have heart disease (coronary artery disease, heart failure, valvular heart disease) and how well it can be treated

Some types of arrhythmias may be life-threatening if not promptly and properly treated.

With bradycardias treated with a permanent pacemaker, the outlook is usually good.

• Angina
• Heart attack
• Heart failure
• Stroke
• Sudden death

Call your health care provider if:

• You develop any of the symptoms of a possible arrhythmia
• You have been diagnosed with an arrhythmia and your symptoms worsen or do not improve with treatment

Taking steps to prevent coronary artery disease may reduce your chance of developing an arrhythmia. These steps include:

• Eating a well-balanced, low-fat diet
• Exercising regularly
• Not smoking