What is atrial fibrillation (AF)?
Atrial fibrillation (AF) is an electrical rhythm disturbance of the heart affecting the atria. Abnormal electrical impulses in the atria cause the muscle to contract erratically and pump blood inefficiently. The atrial chambers are thus not able to completely empty blood into the ventricles.
Pooling of blood in the atria can cause red blood cells to stick together and form a clot. Most clots within the heart form in a portion of the left atrium known as the left atrial appendage. The most worrysome complication of atrial fibrillation is dislodgement of a clot and embolism of the clot material to one of the major organs of the body (e.g., the brain).
A clot that embolizes to the brain can interrupt blood flow to a portion of the brain, resulting in a cerebrovascular accident, more commonly known as a stroke. Most individuals with atrial fibrillation are advised by their doctors to take one of a number of medications to prevent clot formation within the heart (and therefore reduce the risk of stroke secondary to clot embolism from the heart). The most commonly used medications are warfarin and aspirin. Atrial fibrillation is the most common form of irregular heartbeat (arrhythmia). Normally, your heart's electrical system controls the rhythm at which your heart beats. See illustrations of the heart and its electrical system .
During a normal heartbeat, the electrical impulses that cause the atria to contract come from the sinus node, a small area of the right atrium. During atrial fibrillation, however, these impulses come from all over the atria, triggering 300 to 500 contractions per minute within the heart's upper chambers. Under normal circumstances, the atrioventricular node would receive these impulses and conduct them to the ventricles (the lower two chambers of the heart that do the pumping). During atrial fibrillation, however, the atrioventricular node becomes overwhelmed by all of the impulses it receives from the atria, and the result is an irregular and rapid heartbeat — 80 to 160 beats per minute versus a normal range of 60 to 100 beats per minute.
The rapid and irregular heartbeat produced by atrial fibrillation cannot pump blood out of the heart efficiently. As a result, blood tends to pool in the heart chambers, increasing the risk of a blood clot formaing inside the heart. Blood clots can travel from the heart into the bloodstream and circulate through the body. Ultimately, they may become lodged in an artery, causing pulmonary embolism, stroke and other disorders. In atrial fibrillation, abnormal electrical impulses cause the upper chambers of the heart (atria) to fibrillate, or quiver, resulting in irregular and rapid beating of the ventricles, the heart's main pump. As a result, the heart pumps less efficiently, reducing blood flow to the body and to the heart muscle itself. For most people, this aspect of atrial fibrillation in itself is usually not life-threatening.
However, people with atrial fibrillation are at increased risk for life-threatening strokes, especially if they are not taking anticoagulant medications. Inefficient pumping of the atria allows blood to pool and clot there. If these clots are pumped out of the heart and into the bloodstream, they can lodge in the brain's blood vessels, resulting in stroke. In addition, if the heart rate is fast and uncontrolled over a long period, atrial fibrillation can damage the heart and lead to heart attack and heart failure.