- Related Topics:
- human cardiovascular system
- arrhythmia
- atrium
- ventricular fibrillation
- On the Web:
- Johns Hopkins Medicine - Atrial Fibrillation: Prevention, Treatment and Research (Oct. 16, 2026)
atrial fibrillation
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What is atrial fibrillation?
Atrial fibrillation is an irregular rhythm of contraction of the muscles of the atrium, the upper chamber of the heart, and the most common type of cardiac arrhythmia. Patients may not notice the fibrillations, but the chaotic, rapid, and shallow beats are often felt as heart palpitations, frequently accompanied by shortness of breath, dizziness, and fatigue.
Atrial fibrillation arises when muscle cells in the wall of the atrium change in ways that interfere with the proper propagation of electrical nerve impulses. It occurs more frequently as fibrous tissue increases in the aging heart, but there is also a familial propensity to the condition. Other cardiac conditions, such as mitral valve disease and chronic congestive heart failure, can also bring on atrial fibrillation. Overstimulation (as in hyperthyroidism) or irritation (as in pericarditis) may also transiently cause atrial fibrillation.
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Which part of the heart does atrial fibrillation affect?
Atrial fibrillation primarily affects the atria, the upper chambers of the heart. This condition arises when changes to muscle cells in the atrial wall interfere with the normal propagation of electrical nerve impulses. Atrial fibrillation interrupts the sinoatrial node's function, disturbing both the atrial rhythm and the impulses activating the ventricles. The atrioventricular node protects the ventricles from the bombardment of impulses originating in the fibrillating atrium.
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What happens to the heart's rhythm during atrial fibrillation?
During atrial fibrillation, the heart's rhythm becomes irregular due to chaotic electrical impulses in the atria, the upper chambers of the heart. The normal function of the sinoatrial node, the heart's natural pacemaker, is disrupted, leading to rapid, disorganized atrial contractions. The atrioventricular node protects the ventricles from the bombardment of impulses, but the ventricular rhythm becomes irregularly irregular. This can lead to palpitations, shortness of breath, dizziness, and fatigue.
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What causes atrial fibrillation?
Atrial fibrillation, the most common cardiac arrhythmia, involves an irregular rhythm of the atrium, the upper chamber of the heart. This condition arises when changes to muscle cells in the atrium wall interfere with the proper propagation of electrical nerve impulses.
Several factors can cause atrial fibrillation. These include increased fibrous tissue in the aging heart, familial propensity, and other cardiac conditions that increase the load on the atrium, such as mitral valve disease and chronic congestive heart failure. Overstimulation (as in hyperthyroidism) or irritation (as in pericarditis) can also transiently bring on atrial fibrillation.
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How does atrial fibrillation change the way blood moves through the heart?
In atrial fibrillation, the atria, the heart's upper chambers, experience a rapid and chaotic rhythm due to disorganized electrical impulses. This irregular contraction impairs the atria's ability to efficiently pump blood into the ventricles, the heart's lower chambers. The atrioventricular node, which protects the ventricles from the bombardment of impulses, transmits a fraction of these impulses unpredictably, leading to an irregular heartbeat. Consequently, the normal flow of blood through the heart is disrupted, potentially causing palpitations, shortness of breath, dizziness, and fatigue. The lack of coordinated atrial contractions can also lead to the formation of blood clots, increasing the risk of stroke.
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Why can atrial fibrillation increase the risk of stroke or blood clots?
Atrial fibrillation can increase the risk of stroke and blood clots because the irregular contractions in the atria allow blood to pool and clot within the chamber, especially in the left auricle. These clots can break free and lodge in smaller vessels in the brain, causing tissue damage and stroke. Normally, the sinoatrial node regulates heart impulses, but atrial fibrillation disrupts this, leading to chaotic rhythm. Consequently, a common treatment involves anticoagulants to prevent clot formation and reduce the risk of embolism.
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atrial fibrillation, irregular rhythm of contraction of the muscles of the atrium, the upper chamber of the heart. In some cases the fibrillations are not noticed by the patient, but frequently the chaotic, rapid, and shallow beats are felt as significant palpitations of the heart, often accompanied by shortness of breath, dizziness, and fatigue. Atrial fibrillation is the most common type of cardiac arrhythmia, or disturbance in normal rhythm. It is not necessarily a serious condition in itself and need not result in significant restriction of activity; nevertheless, its presence may create problems for other cardiac functions, particularly in the ventricles, or lower chambers of the heart.
Atrial fibrillation arises when muscle cells in the wall of the atrium go through changes that interfere with the proper propagation of electrical nerve impulses. It is known to occur more frequently as the amount of fibrous tissue increases in the aging heart; there is also a significant familial propensity to the condition. Atrial fibrillation can also be brought on by other cardiac conditions that increase the load on the atrium, such as mitral valve disease and chronic congestive heart failure. Finally, atrial fibrillation may occur transiently as a result of overstimulation (as in hyperthyroidism) or irritation (as in pericarditis).
Atrial fibrillation interrupts the normal functioning of the sinoatrial node, a mass of specialized muscle tissue in the right atrium that is the primary source of the impulses which serve as the natural pacemaker of the heart. Thus, not only is atrial rhythm disturbed but also the impulses activating the ventricles, which pump blood to the lungs and body. The ventricles are protected by another node, known as the atrioventricular node, from the extraordinary bombardment of impulses originating in the fibrillating atrium; however, people with atrial fibrillation, upon exercise or stress, frequently experience excessive increases in heart rate that must be treated with beta-adrenergic blocking agents (beta-blockers), calcium channel blockers, or digitalis. In addition, atrial fibrillation can worsen the condition of cardiac patients whose ventricular functions are already impaired by heart failure or thickening of the ventricular walls (ventricular hypertrophy) by eliminating the secondary ventricular filling energy provided by a normally contracting left atrium. The most prevalent complication of atrial fibrillation results from the formation of blood clots in the wall of the fibrillating left atrium. These clots frequently break off into the circulation, where they may form emboli that can block arterial beds, thus causing substantial tissue damage. It is estimated that 25 percent of people with chronic atrial fibrillation ultimately will suffer a major embolism and stroke if they are not treated with anticoagulants such as warfarin (Coumadin©).
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The primary strategy for treating atrial fibrillation is to address the underlying abnormality. Fibrillations can be interrupted by administering electric shocks to the ventricles, though in most cases this treatment must be followed by drug therapy to maintain a normal rhythm. Recent progress in clinical electrophysiology has offered the promise of a technique in which aberrant pacemakers can be ablated by ultrasound delivered through a catheter in order to provide stable defibrillation in some patients. However, in many cases, atrial fibrillation persists or recurs, and patients with chronic atrial fibrillation require treatment with the anticoagulant and antiarrhythmic drugs mentioned above. See also ventricular fibrillation.