How is atrial fibrillation (AFib) different from a normal heartbeat?

In atrial fibrillation (also called Afib), your heart beats rapidly or unevenly. Here's a comparison of how the heart beats normally and what happens with Afib:

  • In a normal heart: Electrical impulses are generated by the sinoatrial node (SA node), a small area in the hearts right upper chamber (atrium). As the electrical impulses travel smoothly through the heart, the two upper chambers (the atria) squeeze at the same time to pump blood down to the lower chambers (the ventricles). Then the two ventricles squeeze at the same time, pumping blood to your lungs to pick up oxygen and to the rest of your body. The heart beats regularly and evenly, about 60 to 100 times a minute.
  • With Afib, electrical impulses come too rapidly and don't travel smoothly. Instead, many of the impulses cycle around within the atria. This can cause the atria to quiver, and in turn the ventricles can beat rapidly. The atria and ventricles don't coordinate in a normal rhythm, and the heart can beat rapidly, up to 300 times per minute.

Afib can come and go—returning to normal after a few minutes or hour—or it can persist.

In atrial fibrillation (AFib) the rhythm of contractions and blood movements among the chambers of the heart doesn't function correctly.

The atria are the two chambers of the heart that receive blood back to the heart, either from the circulation throughout the body on the right side or blood returning from the lungs on the left side. Normally, these two chambers contract, sending blood to the other to chambers, the ventricles, which then contract to pump the blood out to the lungs (systemic circulation). In a normal heartbeat, the atria beat together followed by a relaxation period while the ventricles contract, allowing blood to be collected before the cycle repeats itself. In atrial fibrillation, however, this rhythm is lost, and the atria continually contract at a fast rate, with little time to properly collect blood and with no connection to when the ventricles are contracting.

The heart itself has four chambers. Electrical impulses start at the top, move through the middle (AV node) and reach the bottom. When you experience atrial fibrillation, the mechanism at the top of the heart stops working properly. The fibrillation in the top chambers bombards the AV node of the heart and results in a varying number of electrical impulses getting to the bottom chambers. This results in fast and irregular heartbeat.

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