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Atrial Fibrillation and Atrial Flutter
(See also Overview of Abnormal Heart Rhythms.)
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 irregularly, faster, and less efficiently than normal.
These disorders often result from conditions that cause the atria to enlarge.
Symptoms depend on how fast the ventricles contract and may include palpitations, weakness, dizziness or light-headedness, shortness of breath, and chest pain.
Electrocardiography (ECG) confirms the diagnosis.
Treatment includes drugs to slow the ventricles’ contractions and sometimes drugs or electrical shocks (cardioversion) to restore normal heart rhythm.
Atrial fibrillation and atrial flutter are more common among older people and people who have a heart disorder. Atrial fibrillation is much more common than atrial flutter. Many people with atrial flutter also have episodes of atrial fibrillation. Atrial fibrillation and atrial flutter may come and go or be sustained.
During atrial fibrillation, electrical impulses are triggered from many areas in and around the atria rather than just one area (the sinoatrial node—see Figure: Normal electrical pathway). The resulting electrical activity is chaotic rather than organized and thus, the atrial walls quiver rather than contract. Because the atria do not contract normally, they do not help pump blood into the ventricles. When the atria do not help pump blood to the ventricles, the maximum amount of blood that the heart pumps is reduced by about 10%. This slightly lower maximum output is usually not a problem except in people who have heart disease, particularly when they exert themselves.
Only some of the chaotic electrical impulses are conducted through the atrioventricular node to the ventricles. Thus, the ventricles beat irregularly. For most people who are not being treated for atrial fibrillation, the impulses are conducted to the ventricles at a faster-than-normal rate (often 140 to 160 times per minute, compared to the normal heart rate of about 70 to 80 beats per minute). Even faster rates occur during exercise.
During atrial flutter, unlike in atrial fibrillation, electrical activity in the atria is coordinated. Thus, the atria do contract, but at a very rapid rate (250 to 350 times per minute). This rate is too fast to allow every impulse to be conducted through the atrioventricular node to the ventricles. For most people who are not being treated, every second atrial impulse gets to the ventricules, resulting in a ventricular rate of about 150 beats per minute.
ECG: Reading the waves
Atrial fibrillation or atrial flutter may occur even when there is no other heart disorder. More often, these arrhythmias are caused by such conditions as high blood pressure, coronary artery disease, heart valve disorders affecting the mitral and/or tricuspid valves, alcohol abuse, an overactive thyroid gland (hyperthyroidism), or a birth defect of the heart. Heart valve disorders and high blood pressure cause the atria to enlarge, making atrial fibrillation or atrial flutter more likely.
The main complications include the following:
In atrial fibrillation or atrial flutter, the atria do not empty completely into the ventricles with each beat. Over time, some blood inside the atria may stagnate, and blood 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 of clot 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 atrial flutter.
When atrial fibrillation or atrial flutter causes the heart to beat too rapidly, the ventricles do not have enough time to fill completely with blood. Because they do not fill completely, the amount of blood pumped by the heart decreases. This decrease may cause the blood pressure to fall, and heart failure may occur.
Symptoms of atrial fibrillation or atrial flutter depend largely on how fast the ventricles beat. When the ventricular rate is normal or only slightly increased (less than about 120 beats per minute), people usually have no symptoms. Higher rates cause unpleasant awareness of heart beats (palpitations) or chest discomfort.
In people with atrial fibrillation, the pulse is usually rapid and is always irregular. In people with atrial flutter, the pulse is usually rapid and can be regular or irregular.
The reduced pumping ability of the heart may cause weakness, faintness, and shortness of breath. When the ventricular rate is very fast, some people, especially older people and those with heart disorders, develop heart failure or chest pain. Very rarely, such people may develop shock (very low blood pressure).
Symptoms suggest the diagnosis of atrial fibrillation or atrial flutter, and electrocardiography (ECG) confirms it.
Ultrasonography of the heart (echocardiography) is done. It enables doctors to evaluate the heart valves and look for blood clots in the atria.
Doctors usually also do blood tests to look for an overactive thyroid gland.
Treatment of atrial fibrillation or atrial 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 blood clots and emboli (anticoagulants or aspirin) are usually given.
Treatment of the underlying disorder is important but does not always 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.
Usually, the first step in treating atrial fibrillation or atrial flutter is to slow the beating of the ventricles so that the heart pumps blood more efficiently. Usually, drugs can slow the ventricle. Often, the first drug tried is a calcium channel blocker, such as diltiazem or verapamil, which may slow the conduction of impulses to the ventricles (see Table: Some Drugs Used to Treat Arrhythmias). A beta-blocker, such as propranolol or atenolol, may be used. For people who have heart failure, digoxin may be used.
Atrial fibrillation or atrial flutter may spontaneously convert to a normal rhythm. In some people, these arrhythmias must be actively converted to a normal rhythm (cardioversion). Such people include those in whom the atrial fibrillation or atrial flutter causes heart failure or other symptoms of low heart output.
Before restoring normal rhythm, because there is a risk that a blood clot will break off and cause a stroke during conversion, measures must be taken to prevent blood clots.
If the atrial fibrillation or atrial flutter has been present for more than 48 hours, doctors give an anticoagulant such as warfarin for 3 to 4 weeks before attempting conversion. Alternatively, doctors can give a short-acting anticoagulant, such as heparin, and do echocardiography. If echocardiography does not show a clot in the heart, the person can undergo conversion immediately. If the rhythm has clearly been present less than 48 hours, people do not need an anticoagulant before conversion. However, most people need an anticoagulant for at least 4 weeks after conversion.
Methods of conversion include
An electrical shock to the heart is the most effective approach. The electrical shock is synchronized to be given only at a certain point in the heart's electrical activity (synchronized cardioversion) so that it does not cause ventricular fibrillation. Cardioversion is effective in 75 to 90% of people.
Certain antiarrhythmic drugs (most commonly, amiodarone, flecainide, procainamide, propafenone, or sotalol—see Table: Some Drugs Used to Treat Arrhythmias) also may restore a normal rhythm. However, these drugs are effective in only about 50 to 60% of people and often cause side effects.
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 disorder becomes. When conversion is successful, the risk of recurrence is high, even if people are taking a drug to prevent recurrence (typically one of the same drugs used to convert the arrhythmia to a normal rhythm).
Rarely, when all other treatments of atrial fibrillation are ineffective, 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 completely stops conduction from the atria to the ventricles and slows the ventricular rate. However, a permanent artificial pacemaker is required to activate the ventricles afterward.
Another type of ablation procedure destroys atrial tissue near the pulmonary veins (pulmonary vein isolation). Pulmonary vein isolation spares the atrioventricular node but is less often successful (60 to 80%), and the risk of serious complications is significant (1 to 5%). Accordingly, this procedure is often reserved for people who are more likely to have a good response—young people who have atrial fibrillation that does not respond to drug treatment and who do not have other serious heart disorders.
For people who have atrial flutter, radiofrequency ablation may be used to interrupt the flutter circuit in the atrium and permanently re-establish normal rhythm. This procedure is successful in about 90% of people.
Measures to prevent blood clots (and thus prevent stroke) are necessary when atrial fibrillation or atrial flutter is converted back to normal rhythm. Most people also usually need such measures during long-term treatment. Doctors typically give an anticoagulant such as warfarin, dabigatran, or a clotting factor Xa inhibitor (rivaroxaban, apixaban, or edoxaban). People who cannot be given an anticoagulant may be given aspirin, but aspirin is not as effective as warfarin.
Otherwise healthy people who had only one episode of atrial fibrillation that converted to normal rhythm (spontaneously or with treatment) need anticoagulant treatment for only 4 weeks. People who had several episodes of atrial fibrillation or atrial flutter or who remain in such rhythms despite treatment should take a drug to prevent blood clots indefinitely. Doctors use warfarin or other anticoagulants for people who have one or more risk factors for developing stroke. Such risk factors include age 65 or older, high blood pressure, diabetes, heart failure, a previous stroke or transient ischemic attack, vascular disease, and being female. Some people without those risk factors are given aspirin, and some are not given any treatment to prevent strokes.
Even after atrial fibrillation or atrial flutter converts to normal rhythm, doctors usually continue anticoagulant treatment, often for the remainder of the person’s life. This anticoagulant treatment is needed because the arrhythmia may come back without the person being aware of it. Dangerous blood clots can form during these episodes.
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