Atrial fibrillation (AF or AFib), the most common form of arrhythmia, is characterized by a fast and irregular heartbeat. It results from a disturbance of the electrical signals that normally make the heart contract in a controlled rhythm. Instead, chaotic and rapid impulses cause uncoordinated atrial filling and ventricle pumping action. This leads to a decrease in overall cardiac output, which can affect one's exercise capacity or even result in unconsciousness. In addition, AF causes blood to pool in the atria, which promotes the formation of blood clots that may break loose and enter the circulatory system; if this occurs, it may result in a stroke. Recent U.S. studies have shown a rising incidence of AF overall as well as significant racial differences in its prevalence. The lifetime risk of AF (at 80 years of age) was recently found to be 21 percent in white men and 17 percent in white women but only 11 percent in African-Americans of both sexes. By 2050, it is estimated that AF will affect between 5.6 million and 12 million Americans. These figures are significant, because AF is associated with a fourfold to fivefold higher risk of ischemic stroke. Individuals with AF, after adjustment for other risk factors, also have a twofold higher risk of dementia. The most common causes of AF are hypertension and coronary artery disease. Additional causes include a history of valvular disorders, hypertrophic cardiomyopathy (a thickening of the heart's muscle), deep vein thrombosis (DVT), pulmonary embolism, obesity, hyperthyroidism (also called "overactive thyroid"), heavy alcohol consumption, an imbalance of electrolytes in the blood, cardiac surgery and heart failure. Some people with AF experience no symptoms and are unaware they have the condition until it's discovered during a physical examination. Others may experience symptoms such as the following: - Palpitations (a racing, uncomfortable, irregular heartbeat or a flip-flopping sensation in the chest) - Weakness - Reduced ability to exercise - Fatigue - Lightheadedness - Dizziness - Confusion - Shortness of breath - Chest pain \nThe occurrence and duration of atrial fibrillation usually falls into one of three patterns: - *Occasional (or "paroxysmal"):* The rhythm disturbance and its symptoms come and go, lasting for a few minutes to a few hours, and then stop on their own. Such events may occur a couple of times a year, and their frequency typically increases over time. - *Persistent:* The heart's rhythm doesn't go back to normal on its own, and treatment — such as an electrical shock or medication — is required to restore a normal rhythm. - *Permanent:* The heart's rhythm can't be restored to normal. Treatment may be required to control the heart rate, and medication may be prescribed to prevent the formation of blood clots. Any new case of AF should be investigated and its cause determined. An investigation may include a physical exam; an electrocardiogram; a measurement of electrolyte levels, including magnesium; a thyroid-hormone test; an echocardiogram; a complete blood count; and/or a chest X-ray. Treating the underlying cause of AF can help control the fibrillation. Various medications, including beta blockers, may help regulate the heart rate. A procedure known as cardioversion — which can be performed with either a mild electrical shock or medication — may prompt the heart to revert to a normal rhythm; before cardioversion is attempted, it is essential to ensure that a clot has not formed in the atrium. Cardiac ablation, which is described in the "Extrasystole" section, may also be used to treat AF. In addition, anticoagulant drugs are often prescribed for individuals with AF to prevent the formation clots and thus reduce their risk of stroke. It is also of note that the neurological effects of an embolic stroke associated with AF can sometimes be confused with the symptoms of decompression sickness.