Introduction

An abnormal heart rhythm may be too rapid, too slow, or irregular. The heart may beat abnormally in response to an emotion or event. The heart may seem to skip a beat when a person is excited. It may race when a person is nervous or afraid. These sensations are called palpitations. In such cases, palpitations are usually of no consequence. However, they can be symptoms of a disorder involving abnormal heart rhythm called an arrhythmia.

Normally in older people who are resting, the heart rate (heartbeats per minute) is 60 to 80. It may be slower if the heart is well-conditioned by regular physical activity. The heart rate may be faster in people who are physically inactive. The heart beats in a regular rhythm, changing its rate in response to different activities. That is, the heart speeds up or slows down to adjust the amount of blood it pumps in response to the body's needs.

Heartbeats are controlled by the heart's electrical system. Electrical currents are produced and coordinated by the heart's natural pacemaker (sinus or sinoatrial node), located in the upper right heart chamber (right atrium). The electrical currents flow through the heart along specific pathways in the heart and at a controlled speed. They stimulate the heart to contract, producing each heartbeat. Certain hormones and nerve impulses from other parts of the body signal the heart when a change in heart rate is needed.

Arrhythmias are more likely to develop as people age, particularly in those who have other heart disorders. In a few people, an arrhythmia occurs only once. In many other people, arrhythmias occur from time to time (intermittently). Some arrhythmias gradually occur more and more often and may become constant.

For most people, arrhythmias are harmless, although they can cause considerable anxiety if people become aware of them. However, some arrhythmias have serious consequences, such as falls, motor vehicle accidents, heart failure and, occasionally, death without any warning (sudden death). Most arrhythmias can be treated effectively.

Types

Arrhythmias are categorized partly by their speed. Slow arrhythmias are called bradycardias. Fast arrhythmias are called tachycardias. Arrhythmias are also categorized by what type of problem started the arrhythmia. A problem may involve the upper chambers (atria), the lower chambers (ventricles), or the initiation or conduction of electrical currents in the heart. Arrhythmias that result from problems in the atria include premature atrial beats, supraventricular tachycardia, atrial flutter, and atrial fibrillation. Arrhythmias that result from problems in the ventricles include premature ventricular beats, ventricular tachycardia, and ventricular fibrillation. Arrhythmias that result from problems initiating and conducting electrical currents include malfunction of the heart's pacemaker (some cases of sinus bradycardia and sick sinus syndrome) and heart block.

Causes

Arrhythmias are most commonly caused by other heart disorders, particularly coronary artery disease, heart valve disorders, and heart failure.

Many drugs, prescription and nonprescription, can cause or worsen arrhythmias. For example, taking certain drugs used to treat heart disorders (such as beta-blockers, calcium channel blockers, and digoxin) can cause slow arrhythmias. Taking theophylline (used to treat chronic obstructive pulmonary disease, or COPD) and decongestants (such as phenylephrine, pseudo-ephedrine, and oxymetazoline) can cause fast arrhythmias.

An overactive thyroid gland (hyperthyroidism) may cause fast arrhythmias. An underactive thyroid gland (hypothyroidism) may cause slow arrhythmias. Sometimes no cause for an arrhythmia can be identified.

Certain circumstances may trigger arrhythmias. Fast arrhythmias may be triggered by exercise, emotional stress, excessive alcohol consumption, or smoking. Slow arrhythmias may be triggered by pain, straining to urinate or to have a bowel movement, vomiting, or even swallowing. These circumstances can trigger slow arrhythmias because they may overstimulate the nerve that slows the heart rate (vagus nerve). Most arrhythmias triggered by these circumstances are not serious and resolve on their own.

Symptoms

Often, arrhythmias do not cause any symptoms. Sometimes an arrhythmia causes palpitations. That is, a person may sense that the heart is beating too rapidly, too forcefully, or irregularly.

Arrhythmias may make people feel weak and unable to do their normal activities. They may feel dizzy or faint and lose consciousness because the heart is not pumping enough blood to the brain. If these symptoms occur, people should see a doctor promptly. Arrhythmias that cause such symptoms may have serious consequences. Occasionally, in some people (usually those who have a heart disorder), certain arrhythmias cause death without any warning.

Some arrhythmias, particularly atrial fibrillation, can cause a stroke or sudden pain in an arm or a leg. These problems occur when part of a blood clot in the heart breaks off, travels through the bloodstream, and blocks an artery that carries blood to the brain or to an arm or a leg. A clot that travels through the bloodstream is called an embolus.

Arrhythmias may worsen symptoms of coronary artery disease, heart valve disorders, or heart failure (such as chest pain and shortness of breath).

Diagnosis

Doctors may suspect an arrhythmia on the basis of symptoms. So doctors may ask the following questions:

• Are the palpitations fast or slow?
• Are they regular or irregular?
• Are they brief or prolonged?
• Do they occur at rest or only during strenuous or unusual activity?
• Do they start and stop suddenly or gradually?
• Does the arrhythmia causes any other symptoms?

Doctors also check the person's pulse and blood pressure. All of this information helps doctors determine whether an arrhythmia is present and, if so, what type and how severe it is. However, additional tests are usually needed to be certain.

Electrocardiography (ECG) can often confirm the diagnosis. Usually, ECG is done in the doctor's office, and heart rhythm is recorded for less than a minute. Thus, an intermittent arrhythmia is often missed. So doctors sometimes ask a person to wear a portable ECG (Holter) monitor so that the heart rhythm can be recorded continuously, usually for 24 hours. A person can wear a Holter monitor for days if necessary. Another monitor, called an event recorder, can be worn for a longer period of time. It is similar to a Holter monitor, but it records heart rhythm only when the user or someone with the user activates it by pushing a button. The user is instructed to activate the monitor when symptoms occur. When wearing either type of monitor, a person may be asked to keep a diary of symptoms and activities. This information helps doctors determine whether the symptoms are caused by an arrhythmia and whether an arrhythmia is more likely to occur during certain circumstances.

See the figure Holter Monitor: Continuous ECG Readings.

If exercise is thought to trigger an arrhythmia, doctors may ask a person to walk on a treadmill while heart rhythm is recorded by ECG (a procedure called exercise stress testing).

If doctors think an arrhythmia could be life threatening, hospitalization is usually necessary. In the hospital, heart rhythm can be continuously recorded and displayed on a television-type monitor by the bedside or nursing station. Thus, any problems can be identified and managed promptly.

Occasionally, when a serious arrhythmia is suspected, electrophysiologic testing is done to confirm its presence and, if it is present, to determine its characteristics. For this test, a person is given a sedative but is conscious. Then a flexible tube (catheter) is inserted through a vein and threaded into the heart. The catheter contains many small wires with tiny electrodes at their tips. The electrodes stimulate the heart to determine whether a serious arrhythmia can be triggered. Doctors can stimulate specific parts of the heart and thus determine which part is causing the arrhythmia. This test can also help doctors determine the most effective treatment for the arrhythmia.

Treatment

Many arrhythmias do not require specific treatment. Sometimes arrhythmias occur less often or even stop when doctors change a person's drugs or adjust the doses. Limiting or eliminating alcohol and beverages that contain caffeine and stopping smoking may also help. If arrhythmias occur during exercise, a person can talk to a doctor about possible precautions to take during exercise.

Drugs: If an arrhythmia is thought to be serious or causes significant symptoms, antiarrhythmic drugs may be used. These drugs can prevent or control most intermittent arrhythmias. Often, antiarrhythmic drugs must be taken indefinitely. If the cause of the arrhythmia can be eliminated, the drugs may be discontinued. The type of antiarrhythmic drug used depends on which arrhythmia is present.

In older people, the dose of many antiarrhythmic drugs must be reduced because as people age, the body does not eliminate these drugs as quickly. One antiarrhythmic drug, disopyramide, is not usually given to older people. It can cause blurred vision, constipation, or retention of urine. It also tends to make the heart contract more weakly.

Surgery: Two types of electronic devices that are implanted surgically are used to treat serious arrhythmias: artificial pacemakers and implanted cardioverter-defibrillators (ICDs). Sometimes one device that combines the two functions is used. The type of device a person needs depends on the arrhythmia. These devices are permanently implanted under the skin, usually below the left or right collarbone. They are connected to the heart by wires running inside a vein.

See the figure Keeping the Beat: Artificial Pacemakers.

Artificial pacemakers are most commonly used to treat slow arrhythmias. When the heart beats too slowly, a pacemaker stimulates the heart to make it beat more rapidly. Occasionally, pacemakers are used to treat fast arrhythmias. Implantable artificial pacemakers act in place of the heart's own pacemaker.

An implanted cardioverter-defibrillator is about the size of a deck of cards. It automatically senses life-threatening fast arrhythmias (ventricular tachycardia or ventricular fibrillation) and delivers an electrical shock to the heart. The shock almost always restores the normal heart rhythm. Most often, this device is used to treat people who might otherwise lose consciousness or die of the arrhythmia.

Sometimes destroying or removing an abnormal area in the heart's electrical system can control or eliminate an arrhythmia. Usually, a catheter with electrodes at its tip is inserted into the heart. Heat from the electrodes destroys the abnormal area. This procedure, called catheter ablation, is successful in most people. Less commonly, the area is destroyed or removed during open-heart surgery.

Occasionally, angioplasty or coronary artery bypass surgery may be done to control arrhythmias due to coronary artery disease.

Emergency treatment: If an arrhythmia develops rapidly and causes severe chest pain, heart failure, or loss of consciousness, emergency treatment is needed.

If the heart is beating too slowly, atropine or other drugs may be given intravenously to stimulate the heart to beat faster. A temporary external pacemaker may be needed. It is connected to the heart by wires inserted into a large vein in the neck or near the collarbone.

If the heart is beating too rapidly but the problem is not life threatening, doctors may ask a person to bear down as if having a bowel movement. Or, doctors may massage the carotid arteries in the neck. These maneuvers sometimes slow the heart rate or return the heart rhythm to normal.

If the heart is beating too rapidly, antiarrhythmic drugs given intravenously can usually restore the normal heart rhythm. However, if drugs do not work, an electrical shock may be applied to the person's chest. One of two procedures is used. Defibrillation is used to restore an irregular fast heart rhythm to normal. Cardioversion is used to restore a regular fast heart rhythm to normal. Devices that can do either, called cardioverter-defibrillators, are often used. For these procedures, a health care practitioner applies two small paddles to the chest. These procedures are safe but cause pain. If conscious, the person is given a small dose of a sedative intravenously to relieve pain and anxiety.

If ventricular fibrillation occurs, defibrillation, done promptly, can often prevent sudden death. A health care practitioner should apply the shock to the unconscious person as soon as possible, preferably within 5 minutes. A health care practitioner is not always needed. Trained lay people can use machines called automated external defibrillators (AEDs), another type of cardioverter-defibrillator. These machines automatically detect the arrhythmia, determine if a shock is advisable, and, if so, deliver the shock. Lay people can learn to use these machines at a first-aid course. AEDs are being put in public places, such as airplanes, stadiums, and shopping malls.

Outlook

In many people, arrhythmias do not have serious consequences and do not require treatment. Whether an arrhythmia has serious consequences depends on how fast the heart beats, which parts of the heart are affected, and how long the arrhythmia lasts. Generally, arrhythmias started by a problem in the ventricles are the most serious. Sometimes an arrhythmia started by a problem in the atria, such as atrial fibrillation, also has serious consequences. The seriousness of an arrhythmia also depends partly on the cause. The outlook tends to be the worst with arrhythmias due to severe, long-standing (chronic) heart disorders. In contrast, in people who do not have a heart disorder, arrhythmias are often harmless.

Symptoms do not reliably indicate how serious an arrhythmia is. Some potentially life-threatening arrhythmias may cause no symptoms, and some otherwise inconsequential arrhythmias cause significant symptoms.

See the table Some Drugs Used for Arrhythmias.