What is atrial fibrillation (AF)?

Atrial fibrillation (AF) is characterized as a heart rhythm disorder where the heart's upper chambers, or atria, experience chaotic electrical signals that lead to an irregular and often rapid heart rate. In AF, the atria may contract out of sync with the heart's lower chambers, or ventricles, which can disrupt the normal flow of blood through the heart. This irregularity can lead to various symptoms, including palpitations, fatigue, and a higher risk for stroke due to the potential for blood clots forming in the atria.

While the other options touch on related cardiovascular issues, they do not accurately define AF. For instance, option B refers to a general heart condition affecting blood flow, which can be associated with atrial fibrillation, but it is not specific to the disorder itself. Option C, which describes a type of heart valve disease, and option D, mentioning sudden heart failure, are also separate conditions that do not describe the unique characteristics of atrial fibrillation. Thus, the defining qualities of AF align best with the description of a heart rhythm disorder marked by irregularity and speed in heart rate.