Diagnosis of atrial fibrillation is based on history, clinical examination, and confirmation with an ECG. The patient may experience rapid and irregular heartbeats usually from one to several hours. Associated symptoms include mild shortness of breath that can become severe if serious underlying heart disease is present. During atrial fibrilla¬tion the atrium does not contract normally and blood is therefore not delivered rapidly into the left ventricle. Poor filling of the ventricle and the fast ventricular rate may cause a fall in blood pressure resulting in lightheadedness and dizziness. Because the atrium is fibrillating and notcontracting, there is stasis of blood in the atrial appendage. Stasis predisposes the patient to clot formation and these thrombi may be dislodged and fly into the circulation and travel to other organs (embolize). The embolus can block an artery in the brain and cause a stroke.
Atrial fibrillation may last several hours to a couple of days and then disappear for several days to weeks; this condition is referred to as paroxysmal atrial fibrillation. These patients may have no symptoms from 6 months up to 2 years and then fibrillation may recur. Atrial fibrillation, therefore, does not always cause symptoms and the disease can be misdiagnosed. In the Cardiovascular Health study, 12% of new cases of atrial fibrillation were diagnosed on the basis of ECG screening alone and these individuals presumably had no symptoms.

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