Section 3. Heart and Blood Vessel Disorders

Chapter 27. Abnormal Heart Rhythms

Topics: Introduction | Atrial Premature Beats | Atrial Fibrillation and Atrial Flutter | Paroxysmal Supraventricular Tachycardia | Wolff-Parkinson-White Syndrome | Ventricular Premature Beats | Ventricular Tachycardia | Ventricular Fibrillation | Pacemaker Dysfunction | Heart Block | Bundle Branch Block

Atrial Fibrillation and Atrial Flutter

Atrial fibrillation and atrial flutter are very fast electrical discharge patterns that make the atria contract very rapidly, with some of the electrical impulses reaching the ventricles and causing them to contract faster and less efficiently than normal.

Atrial fibrillation and atrial flutter are more common among older people.

Atrial fibrillation and atrial flutter may be intermittent or sustained. During atrial fibrillation or flutter, the contractions of the atria are so fast that the atrial walls quiver. As a result, blood is not pumped effectively to the ventricles. During atrial fibrillation, the atrial rhythm is irregular, so the ventricular rhythm is also irregular. During atrial flutter, the atrial rhythm is regular, and the ventricular rhythm may be regular or irregular. In both cases, the ventricles beat more slowly than the atria because the atrioventricular node cannot conduct electrical impulses at such a fast rate. As a result, only some impulses get through. Even though the ventricles beat more slowly than the atria, the ventricles often still beat too fast to fill completely. Therefore, the heart pumps inefficiently, blood pressure may fall, and heart failure may occur.

In atrial fibrillation or flutter, the atria do not empty completely into the ventricles with each beat. Over time, some blood inside the atria may stagnate, and clots may form. Pieces of the clot may break off, often shortly after atrial fibrillation converts back to normal rhythm--whether spontaneously or because of treatment. These pieces may pass into the left ventricle, travel through the bloodstream (becoming emboli), and block a smaller artery. If pieces of a clot block an artery in the brain, a stroke results. Rarely, a stroke is the first sign of atrial fibrillation or flutter.

Atrial fibrillation or flutter may occur even when there is no other sign of heart disease. However, more often, these arrhythmias are caused by such conditions as rheumatic fever, high blood pressure, coronary artery disease, alcohol abuse, an overactive thyroid gland (hyperthyroidism), or a birth defect of the heart. Rheumatic fever (which leads to heart valve disorders) and high blood pressure cause the atria to enlarge, making atrial fibrillation or flutter more likely.

Symptoms and Diagnosis

Symptoms of atrial fibrillation or flutter depend largely on how fast the ventricles beat. A modest increase in the ventricular rate--to less than about 120 beats per minute--may produce no symptoms. Higher rates cause unpleasant palpitations or chest discomfort.

In people with atrial fibrillation, the pulse is irregular and usually fast. In people with atrial flutter, the pulse is more likely to be regular and fast.

The reduced pumping ability of the heart may cause weakness, faintness, and shortness of breath. Some people, especially older people, develop heart failure or chest pain. Very rarely, shock (very low blood pressure) (see Section 3, Chapter 24) occurs in people who have atrial fibrillation or flutter and very severe heart disease.

Symptoms suggest the diagnosis of atrial fibrillation or flutter, and electrocardiography (ECG) confirms it.

Treatment

Treatment of atrial fibrillation or flutter is designed to control the rate at which the ventricles contract, to restore the normal rhythm of the heart, and to treat the disorder causing the arrhythmia. Drugs to prevent the formation of clots and emboli (anticoagulants) may also be given.

Usually, the first step in treating atrial fibrillation or flutter is to slow the beating of the ventricles so that the heart pumps blood more efficiently. Often, the first drug tried is digoxin, which may slow the conduction of impulses to the ventricles. However, digoxin is often insufficient and another drug may be required. A beta-blocker, such as propranolol or atenolol, or a calcium channel blocker, such as verapamil or diltiazem, may be used.

Atrial fibrillation or flutter may spontaneously convert to a normal rhythm. However, these arrhythmias must often be actively converted to normal. Certain antiarrhythmic drugs (most commonly, amiodarone, propafenone, or sotalol) may be effective, but cardioversion, or defibrillation (delivery of an electrical shock to the heart), is the most effective approach. Conversion to a normal rhythm by any means becomes less likely the longer the arrhythmia has been present (especially after 6 months or more), the larger the atria become, and the more severe the underlying heart disease becomes. When conversion is successful, the risk of recurrence is high, even if people are taking a drug to prevent recurrence (that is, one of the drugs used to convert the arrhythmia to a normal rhythm).

Rarely, when all other treatments of atrial fibrillation are ineffective, parts of the atrioventricular node can be destroyed by radiofrequency ablation (delivery of energy of a specific frequency through an electrode catheter inserted in the heart). This procedure slows the ventricular rate in some people who have atrial fibrillation or flutter. If this procedure is not successful, radiofrequency ablation is used to destroy the entire atrioventricular node, completely stopping conduction from the atria to the ventricles. In such cases, a permanent artificial pacemaker is required to activate the ventricles afterward. For people who have atrial flutter, radiofrequency ablation may be used to interrupt the flutter circuit and permanently re-establish normal rhythm. This procedure is successful in about 85% of people.

Usually, treatment of the underlying disorder does not alleviate atrial arrhythmias. However, treatment of an overactive thyroid gland or surgery to correct a heart valve disorder or a birth defect of the heart may help.

When atrial fibrillation or flutter is converted back to normal rhythm, the risk that a clot will be dislodged and cause a stroke is particularly high. Most people with atrial fibrillation or flutter and one or more risk factors for developing clots are given an anticoagulant to prevent clots, because they are at risk of a stroke. (Risk factors for developing blood clots include advancing age, high blood pressure, diabetes, an enlarged left atrium, and structural heart disease, especially mitral valve disorders (see Section 3, Chapter 28).) Unless conversion to a normal rhythm is needed immediately, doctors recommend that most people take an anticoagulant for 4 weeks before cardioversion of established atrial fibrillation or flutter is attempted. However, sometimes there is a specific reason not to use an anticoagulant. For example, people who have uncontrolled high blood pressure or a bleeding disorder should not be given anticoagulants. Anticoagulant therapy can cause bleeding, which can lead to hemorrhagic stroke and other bleeding complications, such as excessive bleeding after surgery. Therefore, doctors balance the potential benefits and risks for each person.