Definition of Arrhythmias:

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

Causes, incidence, and risk factors:

Normally, your heart is able to pump blood out to your body without working any harder than is needed.

To help this happen, your heart has an electrical system that makes sure it contracts (squeezes) in an orderly way.

The electrical impulse that signals your heart to contract begins in the sinoatrial node (also called the sinus node or 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).
• Different nerve messages signal your heart to beat slower or faster.

Arrhythmias are caused by problems with the heart's electrical conduction system. Other areas of the electrical system may also send out signals. Other times, electrical signals are not able to move as easily or at all.

When an arrhythmia is present, your heartbeat may be:

• Too slow (bradycardia)
• Too quick (tachycardia)
• Irregular

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

• Atrial fibrillation or flutter
• Atrioventricular nodal reentry tachycardia (AVNRT)
• Heart block or atrioventricular block
• Multifocal atrial tachycardia
• Paroxysmal supraventricular tachycardia
• Sick sinus syndrome
• Ventricular fibrillation
• Ventricular tachycardia -- a fast heart rate that originates in the lower chambers (ventricles)
• Wolff-Parkinson-White syndrome

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

• Blood chemistry imbalances, such as abnormal potassium levels
• Cardiomyopathy -- a weakening of the heart muscle or a change in the heart muscle
• Heart failure
• Overactive thyroid gland
• 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.