Atrial fibrillation, or AFib, is the most common type abnormal heart rhythm (arrhythmia). Normally, a specific group of cells begins the signal to start your heartbeat. These cells are in the sinoatrial (SA) node. This node is in the right atrium, the upper right chamber of the heart. The signal quickly travels down the heart’s conducting system. It travels to the upper-left filling chamber of the heart (left atrium) and to the left and right ventricle, the 2 lower pumping chambers of the heart. As it travels, the signal triggers the chambers of the heart to contract. The atria contract with each heartbeat to move blood into the ventricles.
During AFib, the signal to start the heartbeat is disorganized. This causes the atria to quiver (fibrillate). The disorganized signals are then transmitted to the ventricles. It causes them to contract irregularly and sometimes quickly. The contraction of the atria and the ventricles is no longer coordinated. The amount of blood pumped out to the body will vary with each heartbeat. The ventricles may not be able to pump blood efficiently to the body.
The quivering atria can lead to blood pooling. This pooling can cause blood clots to form inside the heart. Most clots form inside the left atrium. That’s because the left atrium has a pouch (left atrial appendage) in the muscle wall. This pouch is often large with several lobes. Blood can pool and form clots inside the lobes. This increases the risk of forming blood clots. These clots can then be pumped out of the heart and travel to the brain, causing a stroke. This is why AFib greatly increases the risk for stroke.