Where are signals that cause atrial fibrillation primarily generated?

Atrial fibrillation is primarily characterized by disorganized electrical activity in the atria, leading to an irregular and often rapid heart rhythm. The signals that initiate this irregularity typically arise from the atria themselves rather than from the structures associated with the ventricles or the conduction system.

The sinoatrial (SA) node, located in the right atrium, is the natural pacemaker of the heart, and while it normally regulates heart rhythm by generating regular electrical impulses, its role in atrial fibrillation shifts when abnormal impulses, often due to ectopic foci, begin to dominate. In many cases, these ectopic foci are often located in the pulmonary veins adjacent to the left atrium. When these abnormal signals overwhelm the normal conduction pathway, it leads to the chaotic electrical activity characteristic of atrial fibrillation.

Therefore, the correct choice reflects the primary source of the disorganized electrical signals that result in atrial fibrillation, highlighting the significance of the atrial structures, particularly the SA node and the surrounding atrial tissue, in contributing to this arrhythmia.