Definition
An arrhythmia is any disorder of heart rate or rhythm.

Causes, incidence, and risk factors
Arrhythmias are caused by a disruption of the normal electrical conduction system of the heart. Normally, the 4 chambers of the heart (2 atria and 2 ventricles) contract in a very specific, coordinated manner. When the heart beats faster than normal, it is called tachycardia. Bradycardia is a slower-than-normal rhythm.

Problems can occur anywhere along the conduction system, causing various arrhythmias. Electrical impulses signal the heart to contract in a synchronized manner. There may be a problem in the heart muscle itself, causing it to respond differently to the signal, or causing the ventricles to contract independently of the normal conduction system.

Tachycardia that originates in the atria is called supraventricular tachycardia, and ventricular tachycardia when it originates in the ventricles. The most common supraventricular tachycardias are atrial fibrillation, atrial flutter, and atrioventricular nodal reentry tachycardia.

Bradycardia is due either to altered pacemaker function of the sinoatrial node or an interrupted impulse conduction through the natural electrical pathways of the heart.

Arrhythmias may also be caused by some substances or drugs, including beta blockers, psychotropics, sympathomimetics, caffeine, amphetamines, and cocaine.

Symptoms

• Fast or slow heart beat (palpitations)
• Skipping beats
• Fainting
• Light-headedness, dizziness
• Chest pain
• Shortness of breath
• Changes in the rate, rhythm, or pattern of the pulse
• Paleness
• Sweating

Treatment
When an arrhythmia is serious and not well-tolerated, urgent intervention may be required to restore normal rhythm. Electrical "shock" (defibrillation or cardioversion), the implantation of a temporary pacemaker to interrupt the arrhythmia, or antiarrythmic drugs may be used.

Most supraventricular arrythmias can be treated and cured with radiofrequency ablation, eliminating 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 detects it, and sends either an automatic electrical shock to terminate it, or a burst of pacing activity to overdrive it.

Symptomatic bradycardias and heart blocks are treated with the implantation of a pacemaker.

Expectations (prognosis)
The outcome is dependent on several factors:

• The kind of arrhythmia -- whether it is supraventricular tachycardia, or a more dangerous arrhythmia such as ventricular tachycardia or ventricular fibrillation, which are potentially fatal
• The overall pumping ability of the heart
• The underlying disease and its treatability

With bradycardias that are treated with a permanent pacemaker, there is usually good outcome.

Complications

• Angina (chest pain caused by imbalance of supply and demand for oxygen in the heart muscle)
• Heart attack
• Heart failure
• Stroke
• Sudden death

Prevention
Using methods of preventing coronary artery disease may in turn decrease the likelihood of developing an arrhythmia. These methods include not smoking, eating a well-balanced, low-fat diet, and exercising regularly.