Arrhythmias (general)

Ventricular tachycardia

Atrial fibrillation

Sudden cardiac arrest

Arrhythmias

An arrhythmia is a problem with the speed or rhythm of the heartbeat. During an arrhythmia, the heart can beat too fast, too slow, or with an irregular rhythm. A heartbeat that is too fast is called tachycardia. A heartbeat that is too slow is called bradycardia. Most arrhythmias are harmless, but some can be serious or even life threatening. When the heart rate is too slow, too fast, or irregular, the heart may not be able to pump enough blood to the body. Lack of blood flow can damage the brain, heart, and other organs.

Many arrhythmias cause no signs or symptoms. When signs or symptoms are present, the most common ones are:

• Palpitations (a feeling that your heart has skipped a beat or is beating too hard)
• A slow heartbeat
• An irregular heartbeat
• Feeling of pauses between heartbeats

More serious signs and symptoms include:

• Anxiety
• Weakness
• Dizziness and light-headedness
• Fainting or nearly fainting
• Sweating
• Shortness of breath
• Chest pain

Outlook

Usually the first test used to diagnose an arrhythmia is an EKG (electrocardiogram). Arrhythmias can be treated with medicines, medical procedures (for example, electrical energy delivered to the heart), and surgery. Serious arrhythmias can often be successfully treated. Most people with arrhythmias are able to live normal lives.

Ventricular tachycardia

Ventricular tachycardia is a fast, regular beating of the ventricles that may last for only a few seconds or for much longer. A few beats of ventricular tachycardia often don’t cause problems, but ventricular tachycardia episodes that last for more than just a few seconds can be dangerous. Ventricular tachycardia can turn into other, more dangerous arrhythmias, such as ventricular fibrillation (v-fib).

V-fib occurs when disorganized electrical signals make the ventricles quiver instead of pump normally. Without the ventricles pumping blood out to the body, a person will lose consciousness within seconds and will die within minutes if not treated. To prevent death, the condition must be treated immediately with defibrillation, an electric shock to the heart. V-fib may happen during or after a heart attack, or in a heart that is already weak because of another condition. Health experts think that most of the sudden cardiac deaths that occur every year are due to v-fib.

Atrial fibrillation

Atrial fibrillation (AF) is the most common type of serious arrhythmia. It’s a very fast and irregular contraction of the atria. It occurs when the heart’s electrical signal begins in a different part of the atrium than the sinoatrial (SA) node or when the signal is conducted abnormally. When this happens, the electrical signal doesn’t travel through the normal pathways in the atria, but instead may spread throughout the atria in a fast and disorganized manner. This causes the walls of the atria to quiver very fast (fibrillate) instead of beating normally. As a result, the atria aren’t able to pump blood into the ventricles the way they should. It is not usually life threatening, although it can be dangerous when it causes the ventricles to beat very fast.

The two most serious complications of chronic (long-term) atrial fibrillation are stroke and heart failure. Stroke can happen when a blood clot travels to an artery in the brain, blocking off blood flow. In AF, blood clots can form in the atria because some of the blood “pools” in the fibrillating atria instead of flowing into the ventricles. If a piece of a blood clot in the left atrium breaks off, it can travel to the brain, causing a stroke. People with AF are often treated with blood-thinning medicines to reduce the chances of developing blood clots.

Heart failure is when the heart can’t pump enough blood to meet the needs of the body. AF can cause heart failure when the ventricles beat too fast and don’t have enough time to fill with blood to pump out to the body. Heart failure causes tiredness, leg swelling, and shortness of breath.

AF and other supraventricular arrhythmias can occur for no apparent reason. Most of the time, however, they are caused by an underlying condition that damages the heart muscle and its ability to conduct electrical impulses. These conditions include high blood pressure (hypertension), coronary artery disease, heart failure, or rheumatic heart disease. Other conditions also can lead to AF, including overactive thyroid gland (too much thyroid hormone produced) and heavy alcohol use. AF also becomes more common as people get older.

Sudden cardiac arrest

Sudden cardiac arrest (SCA), also known as sudden cardiac death, is when the heart suddenly and unexpectedly stops beating as a result of an arrhythmia. When this occurs, blood stops flowing to the brain and other vital organs. SCA usually causes death if not treated in minutes.

SCA is not the same thing as a heart attack. A heart attack is a problem with blocked blood flow to a part of the heart muscle. In a heart attack, the heart usually does not suddenly stop beating. SCA, however, may happen during recovery from a heart attack.

People with heart disease have a higher chance of having SCA. But most SCAs happen in people who appear healthy and have no known heart disease or other risk factors for SCA.

Signs & Symptoms

Usually, the first sign of sudden cardiac arrest is loss of consciousness, which is similar to fainting. At the same time, breathing often stops and no heartbeat (or pulse) can be felt. Some people may first notice that they have a racing heartbeat or feel dizzy or lightheaded just before they faint.

Outlook

Ninety-five percent of people who have SCA die from it, most within minutes. SCA requires immediate treatment with a device called a defibrillator, which delivers an electrical shock to the heart. Successful defibrillation restores normal rhythm to the heart. Defibrillation must be provided within minutes after SCA to avoid permanent damage to the body and brain and to prevent death. With every minute of delay in providing defibrillation, the chances of surviving SCA drop rapidly.

People experiencing SCA should be given cardiopulmonary resuscitation (CPR) until they can be treated with a defibrillator.

Special defibrillators called automated external defibrillators (AEDs) can be used by untrained bystanders in an emergency. AEDs are becoming increasingly available at public places, such as airports, office building, and shopping centers.

People who survive SCA may need an implantable cardioverter defibrillator to help prevent death if another SCA happens.

Beta blocker drugs also help reduce the chance of death from SCA in people with known heart disease. Heart healthy lifestyle choices may lower people's chances for SCA.

Source: "Heart and Vascular Diseases." Diseases and Conditions Index. The National Heart, Lung, and Blood Institute.  The National Institutes of Health.