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.

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-threateaning, 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 ventricular fibrillation; ventricular tachycardia that is rapid and sustained, or pulseless; and sustained episodes of other arrhythmias.

Other arrhythmias include 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, and ectopic heartbeat.

People who have a history of coronary artery disease, heart valve disorders, or other cardiac conditions and people with imbalances of blood chemistries are at higher risk for arrhythmias and complications from arrhythmias.

Arrhythmias can also be caused by some substances or drugs. These include antiarrhythmics, beta blockers, psychotropics, sympathomimetics, caffeine, amphetamines, and cocaine.

• 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

Note: The person may not have symptoms. The first symptom may be sudden cardiac arrest (loss of heart beat) requiring CPR.

Additional symptoms that may be associated with this disease:

• Paleness
• Temporarily absent breathing

Listening to the heart with a stethoscope (auscultation) or feeling the pulse may indicate an arrhythmia. Blood pressure may be low or normal.

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

• ECG
• 24 hour cardiac monitoring (Holter monitoring)
• Echocardiogram
• Coronary angiography

Various tests may be appropriate to confirm or rule out suspected causes of the arrhythmia.

When an arrhythmia is serious and not well-tolerated by the person, there may not be enough blood flow from the heart to vital organs, such as the brain, the kidneys, and 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 arrhyhmias have been increasingly treated with a procedure consisting of implanting 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.

The outcome is dependent on several factors:

1. The kind of arrhythmia -- whether it is simply an atrial arrhythmia (originating from the atrium) or a more potentially lethal arrhythmia, such as ventricular tachycardia or ventricular fibrillation.
2. The "ejection fraction" of the heart, or the overall pumping ability of the heart.
3. A person's differing response to the same arrhythmia.

Unfortunately, arrhythmias can sometimes cause sudden death.

• Angina (the arteries supplying the heart itself are not getting enough blood)
• Heart attack
• Heart failure
• Stroke
• Sudden death

Call your health care provider if symptoms indicating an arrhythmia may be present.

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