Atrial fibrillation (AF) describes the rapid, irregular beating of the left atrium (upper chamber) of the heart. These rapid contractions of the heart are weaker than normal contractions, resulting in slow flow of blood in the atrium. The blood pools and becomes sluggish and can result in the formation of blood clots. If a clot leaves the heart and travels to the brain, it can cause a stroke by blocking the flow of blood through cerebral arteries. Some people with AF have no symptoms, but others will experience a fluttering feeling in the area of the chest above the heart, chest pain, lightheadness or fainting, shortness of breath, and fatigue. AF is diagnosed via an electrocardiogram (ECG), a device that records the heart’s electrical activity. Other tests are often performed to rule out contributing causes, such as high blood pressure, an overactive thyroid gland, heart failure, faulty heart valves, lung disease, and stimulant or alcohol abuse. Some people will have no identifiable cause for their AF.

To prevent the possibility of clotting and stroke, doctors often prescribe the drug warfarin to thin the blood in AF patients determined to have a high risk of stroke. Individuals on warfarin therapy must be monitored with periodic blood tests to make sure their blood is thin enough to prevent clots, but not so thin as to promote bleeding. Some AF patients have a lower risk of stroke and are treated with aspirin, which reduces clotting but is not as strong as warfarin. Other treatments for AF include medications such as beta blockers or calcium channel blockers to slow the heartbeat, and anti-arrhythmic drugs or electrical cardioversion (which delivers an electrical shock to the heart) to normalize the heartbeat.

AF, which affects as many as 2.2 million Americans, increases an individual’s risk of stroke by 4 to 6 times on average. The risk increases with age. In people over 80 years old, AF is the direct cause of 1 in 4 strokes. Treating individuals with warfarin reduces the rate of stroke for those who have AF by approximately one-half to two- thirds.

Prepared by the National Institutes of Health