Which dysrhythmia is characterized by multiple rapid impulses depolarizing the atria in a disorganized manner?

Atrial fibrillation is characterized by multiple rapid impulses that depolarize the atria in a disorganized manner. This results in an irregular and often rapid heart rhythm that can lead to various complications, including stroke and heart rate variability. In atrial fibrillation, the electrical signals in the atria become chaotic, preventing the atria from contracting effectively. Instead of a coordinated contraction, the atria quiver, leading to ineffective pumping of blood into the ventricles.

This condition contrasts sharply with the other options. Sinus bradycardia involves a slower than normal heart rate originating from the sinoatrial node, maintaining organized atrial depolarization. Supraventricular tachycardia (SVT) refers to a fast heart rate originating above the ventricles, often characterized by a regular rhythm rather than the chaotic electrical activity seen in atrial fibrillation. A paced rhythm indicates that an artificial pacemaker is controlling heartbeats, which brings regularity to the heart's rhythm rather than disorganization.

Thus, the defining feature of atrial fibrillation is its rapid and disorganized depolarization of the atria, making it the correct choice for this question.