Arrhythmias are caused by a disruption of the normal electrical conduction system of the heart. Normally, the four chambers of the heart (two atria and two ventricles) contract in a very specific, coordinated manner.

The signal for the heart to contract in a synchronized manner is an electrical impulse that begins in the sinoatrial node (also called the SA node), which is the body's natural pacemaker.

The signal leaves the sinoatrial node and travels through the two atria, stimulating them to contract. Then the signal passes through another node (the AV node), and finally travels through the ventricles and stimulates them to contract in synchrony.

Problems can occur anywhere along the conduction system, causing various arrhythmias. There can 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.

Arrhythmias include tachycardias (the heartbeat is too fast), bradycardias (the heartbeat is too slow), and "true" arrhythmias (a disturbed rhythm).

Arrhythmias can be life-threatening if they cause a severe decrease in the pumping function of the heart. When the pumping function is severely decreased for more than a few seconds, blood circulation is essentially stopped, and organ damage (such as brain damage) may occur within a few minutes.

Life-threateaning arrhythmias include the following:

• Ventricular fibrillation
• Ventricular tachycardia that is rapid and sustained or pulseless
• Sustained episodes of other arrhythmias

Other arrhythmias include the following:

• Atrial fibrillation/flutter
• Multifocal atrial tachycardia
• Paroxysmal supraventricular tachycardia
• Wolff-Parkinson-White syndrome
• Sinus tachycardia
• Sinus bradycardia
• Bradycardia associated with heart block
• Sick sinus syndrome
• Ectopic heartbeat.

People at higher risk for arrhythmias and complications from arrhythmias include the following:

• Those who have a history of cardiac conditions such as coronary artery disease or heart valve disorders
• Those with imbalances of blood chemistries

Arrhythmias can also be caused by some substances or drugs. These include beta blockers, psychotropics, sympathomimetics, caffeine, amphetamines, and cocaine. Sometimes antiarrhythmic medications -- prescribed to treat one type of arrhythmia -- can actually cause another type of arrhythmia.

• Sensation of feeling the heart beat (palpitations)
• Fainting
• Light-headedness, dizziness
• Chest pain
• Shortness of breath
• Changes in the rate, rhythm, or pattern of the pulse
• Paleness
• Temporarily absent breathing

Note: The person may not have symptoms. The first symptom may be sudden cardiac arrest (loss of heartbeat), which requires CPR.

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

Tests that reveal arrhythmias and identify the type of arrhythmia include:

• ECG
• Ambulatory cardiac monitoring (for example, a Holter monitor is used for 24 hours; other monitors may be worn for two weeks or longer)
• Echocardiogram
• Electrophysiology study (EPS)
• Coronary angiography

Various tests are appropriate to confirm or rule out suspected causes of the arrhythmia. EPS testing may be performed to determine from where in the heart the arrhythmia originates and what is the best treatment, especially if a pacemaker or catheter ablation might be necessary.

When an arrhythmia is serious and not well-tolerated, there may not be enough blood flow from the heart to vital organs, such as the brain or kidneys or to the heart itself.

In such cases, treatment is urgent and may include electrical "shock" (defibrillation or cardioversion), the implantation of a temporary pacemaker to interrupt the arrhythmia by fast pacing (overdrive supression), or the administration of intravenous medications.

For long-term treatment of arrhythmias, daily medications may be necessary. These include antiarrhythmic medications, medications to speed up or slow down the heart rate, and others.

Over the past decade, life-threatening arrhythmias have been increasingly treated with an implantable cardioverter-defibrillator (ICD). As soon as an arrhythmia begins, the ICD can detect it and send an automatic electrical shock to terminate it, or it can activate a pacemaker function to overdrive the arrhythmia.

Some patients may be better candidates to have a procedure called radiofrequency catheter ablation. Radiofrequency catheter ablation can cure many paroxysmal supraventricular arrhythmias as well as some ventricular arrhythmias. This is performed at the time of EPS.

The outcome is dependent on several factors:

1. The kind of arrhythmia -- whether it is an atrial arrhythmia (originating from the atrium) or a more dangerous arrhythmia such as ventricular tachycardia or ventricular fibrillation, which are potentially fatal.
2. The ejection fraction of the heart, or the overall pumping ability of the heart. In other words, the percentage of blood that the heart pumps from the ventricles to the body with each beat.
3. A person's differing response to the same arrhythmia.

Unfortunately, certain arrhythmias can sometimes cause sudden death.

• Ischemia (the arteries supplying the heart itself are not getting enough blood), which may cause angina (chest pain)
• Heart attack
• Heart failure
• Stroke
• Sudden death

Call your health care provider if you develop symptoms indicating a possible arrhythmia.

Call your health care provider if an arrhythmia has been diagnosed and symptoms worsen or do not improve with treatment.