Arrhythmias are deviations from the normal rhythm or pattern of heartbeats which cause the heart to pump improperly. The heartbeat can be too slow, too fast, have extra beats, skip a beat, or otherwise beat irregularly.

The heart has four chambers or sections. Blood from the body enters the rightauricle. It flows to the right ventricle. From there it is pumped out to thelungs where it picks up oxygen. The blood returns to the heart where it enters the left auricle, flows into the left ventricle, and is pumped out to thebody where it gives up its oxygen to the cells. The blood then returns to theright auricle where it starts its travels over again. The sequence of contractions of the four chambers (the heartbeat) must be exact, otherwise the effectiveness of the pumping mechanism is decreased.

A normal heartbeat starts in the right auricle. Here the heart's natural pacemaker, the sinus node, sends an electrical signal to the center of the heart.This signal causes the main pumping chambers, the ventricles, to contract. Arrhythmias occur when the heartbeat starts in a part of the heart other thanthe sinus node, an abnormal rate or rhythm develops in the sinus node, or a heart conduction "block" prevents the electrical signal from traveling down the normal pathway.

More than four million Americans have arrhythmias, most of which are harmless. Middle-aged adults who do not have heart disease commonly experience harmless arrhythmias. As people age, the probability of experiencing an arrhythmiaincreases. In people with heart disease, it is usually the heart disease thatis dangerous, not the arrhythmia.

Arrhythmias often occur during and after heart attacks. Some types of arrhythmias, such as ventricular tachycardia, are serious and even life threatening.In the United States, arrhythmias are the primary cause of sudden cardiac death, accounting for more than 350,000 deaths each year. Ventricular fibrillation is the most serious arrhythmia and is fatal unless medical help is immediate.

Slow heart rates (less than 60 beats per minute) are called bradycardias, while fast heart rates (more than 100 beats per minute) are called tachycardias.Bradycardia can result in poor circulation of blood, leading to a lack of oxygen throughout the body, especially the brain. Tachycardias also can compromise the heart's ability to pump effectively because the ventricles do not have enough time to completely fill.

In many cases, the cause of an arrhythmia is unknown. Known causes of arrhythmias include heart disease, stress, caffeine, tobacco, alcohol, diet pills, and decongestants in cough and cold medicines.

Symptoms of an arrhythmia include a fast heartbeat, pounding or fluttering chest sensations, skipping a heartbeat, "flip-flops," dizziness, faintness, shortness of breath, and chest pains.

Examination with a stethoscope, electrocardiograms, and electrophysiologic studies are all used to diagnose arrhythmias. Sometimes arrhythmias can be identified simply by listening to the patient's heart through a stethoscope. Moreoften, an electrocardiogram (ECG) that shows the heart's activity will reveal an arrythmia. In other cases, cardiac catheterization for electrophysiologic studies is performed in a hospital to identify the origin of serious arrhythmias and determine the heart's response to various treatments.

Many arrhythmias do not require any treatment. For serious arrhythmias, treating the underlying heart disease sometimes controls the arrhythmia. In some cases the arrhythmia itself is treated with drugs, electrical shock, automaticimplantable defibrillators, artificial pacemakers, or surgery.

Drug therapy can manage many arrhythmias, but finding the right drug and doserequires care and can take time. Common drugs for suppressing arrhythmias include beta-blockers, calcium channel blockers, quinidine, digitalis preparations, and procainamide. All of the drugs used to treat arrhythmias have possible side effects ranging from mild to serious.

In emergency situations, cardioversion or defibrillation (the application ofan electrical shock to the chest wall) is used. Cardioversion restores the heart to its normal rhythm. It is followed by drug therapy to prevent recurrence of the arrhythmia.

Artificial pacemakers that send electrical signals to make the heart beat properly can be implanted under the skin during a simple operation. Leads from the pacemaker are anchored to the right side of the heart. Pacemakers are usedto correct bradycardia and are sometimes used after surgical or catheter ablation.

Automatic implantable defibrillators correct life-threatening ventricular arrhythmias by recognizing them and then restoring a normal heart rhythm by pacing the heart or giving it an electric shock. They are implanted within the chest wall without major surgery and store information for future evaluation byphysicians. Automatic implantable defibrillators have proven to be more effective in saving lives than drugs alone, although they often are used in conjunction with drug therapy.

Ablation, a procedure to alter or remove the heart tissue causing the arrhythmia in order to prevent a recurrence, can be performed through a catheter orsurgery. Supraventricular tachycardia can be treated successfully with ablation. Ablation treatments are used when medications fail.

Maze surgery treats atrial fibrillation by making multiple incisions throughthe atrium to allow electrical impulses to move effectively. This often is recommended for patients who have not responded to drugs or cardioversion.

Advances in diagnostic techniques, new drugs, and medical technology have extended the lives of many patients with serious arrhythmias. Diagnostic techniques enable physicians to accurately identify arrhythmias, while new drugs, advances in pacemaker technology, the development of implantable defibrillators, and progress in ablative techniques offer effective treatments.

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