What are arrhythmias?

Arrhythmias (or dysrhythmias) are problems that affect the electrical system of the heart muscle, producing abnormal heart rhythms. They can cause the heart to pump less effectively.

The heart has four chambers. The top two are the atria, and the lower two are the ventricles. Normally the heartbeat starts in the right atrium when a special group of cells sends an electrical signal. (These cells are called the sinoatrial or SA node, the sinus node or the heart's "pacemaker.") This signal spreads throughout the atria and to the atrioventricular (A-V) node. The A-V node connects to a group of fibers in the ventricles that conduct the electrical signal. The impulse travels down these specialized fibers (the His-Purkinje system) to all parts of the ventricles. The electrical signal must follow this exact route for the heart to pump properly.

Under some conditions almost all heart tissue can start a heartbeat. In other words, another part of the heart can become the pacemaker. An arrhythmia occurs...

• when the heart's natural pacemaker develops an abnormal rate or rhythm.
• when the normal conduction pathway is interrupted.
• when another part of the heart takes over as pacemaker. 

What is a normal heart rate or pulse?

The heart contracts (beats) as the electrical impulse moves through it. This normally occurs 60 to 80 times a minute when a person is at rest. The atria contract a split-second before the ventricles. This lets the atria empty their blood into the ventricles before the ventricles contract.

What causes arrhythmias?

Many arrhythmias have no known cause. However, a number of factors can contribute to arrhythmias. They include coronary artery disease, high blood pressure, diabetes, smoking, excessive use of alcohol or caffeine, drug abuse and stress. Certain substances, including some over-the-counter and prescription medications, dietary supplements and herbal remedies are known to cause arrhythmias in some people.

What are the symptoms and treatments for a slow heartbeat?

A heart rate of less than 60 beats per minute is called bradycardia. Physically active people often have a resting heart rate slower than 60 beats per minute. For them, this isn't abnormally slow. Bradycardia doesn't usually require treatment unless there are prolonged or repeated symptoms such as fatigue, dizziness, lightheadedness, fainting or near-fainting spells. These symptoms are usually due to insufficient blood flow to the brain. Elderly people are more prone to problems with a slow heart rate. These symptoms can be treated and, in certain cases, can be corrected by implanting an electronic pacemaker under the skin to speed up the heart rhythm, when the heart rate becomes too slow.

What are the symptoms and treatments for rapid heart beating?

Rapid heart beating, called tachycardia or tachyarrhythmia, can produce palpitations, rapid heart action, chest pain, dizziness, lightheadedness, fainting or near fainting if the heart beats too fast to circulate blood effectively. Heartbeats may be either regular or irregular in rhythm.

When rapid heart beating starts in the ventricles — called ventricular tachycardia — it can interfere with the heart's ability to pump enough blood to the brain and other vital organs. This dangerous arrhythmia can change without warning into the most serious heart rhythm disturbance — ventricular fibrillation. In this, the lower chambers quiver and the heart can't pump any blood. Collapse and sudden cardiac death follow unless medical help is provided immediately.

If treated in time, ventricular tachycardia and ventricular fibrillation can be converted into normal rhythm with electrical shock. Rapid heart beating can be controlled with medications or by identifying and destroying the focus of rhythm disturbances. One effective way to correct these life-threatening rhythms is by using an electronic device called an implantable cardioverter / defibrillator.

Blood clots can form during atrial fibrillation, a disorder found in 2.2 million Americans. In atrial fibrillation the atria quiver instead of beating effectively. Blood isn't pumped completely out of them when the heart beats, so the blood pools and clots.

If part of a blood clot in the atria leaves the heart and lodges in an artery in the brain (or leading to it), a stroke results. About 15 percent of strokes occur in people with atrial fibrillation.

See the Related Items box above for link to the Cardiology Patient Page in Circulation, Journal of the American Heart Association:

• Atrial Fibrillation
• Cardioversion
• Catheter Ablation of Arrhythmias
• Fainting
• The Implantable Cardioverter-Defibrillator
• Supraventricular Tachycardia

Arrhythmia News 

Related AHA publications:

• Heart and Stroke Facts
• "What Is an Arrhythmia?" printable sheet in Answers By Heart kit
• Heart Disease and Stroke Statistics 
• Living With Atrial Fibrillation brochure
• Your Child's Abnormal Heart Rhythm brochure

Related AHA Scientific Statements
Arrhythmias
Pacemakers