heart and blood vessel disorders
Atrial Fibrillation and Atrial Flutter
Atrial fibrillation
During atrial fibrillation, electrical impulses are triggered from many areas in and around the atria rather than just one area (the sinoatrial node—see figure). The resulting electrical activity is chaotic rather than organized and thus, the atrial walls quiver rather than contract. Because the atria do not contract normally, they do not help pump blood into the ventricles. When the atria do not help pump blood to the ventricles, the maximum amount of blood that the heart pumps is reduced by about 10%. This slightly lower maximum output is usually not a problem except in people who have heart disease, particularly when they exert themselves. Only some of the chaotic electrical impulses are conducted through the atrioventricular node to the ventricles. Thus, the ventricles beat irregularly. For most people who are not being treated for atrial fibrillation, the impulses are conducted to the ventricles at a faster-than-normal rate (often 140 to 160 times per minute, compared to the normal heart rate of about 60 to 100 beats per minute). Even faster rates occur during exercise. 