Which condition is characterized by a rapid heartbeat that is irregular?

• A. Sick sinus syndrome
• B. Atrial flutter
• C. Arrhythmia
• D. Atrial fibrillation

Answer: (D)

Atrial fibrillation is characterized by a rapid and irregular heartbeat due to disorganized electrical signals in the atria. In this condition, the heart's two upper chambers (the atria) do not contract in a coordinated manner, leading to an irregular and often rapid heart rhythm. This can sometimes result in the heart beating as fast as 100 to 175 beats per minute or more, making it a significant clinical concern due to its association with stroke and heart failure.

In the context of this question, atrial fibrillation specifically stands out because the irregularity of the heartbeat is a defining feature. While other conditions, such as arrhythmia, may involve an irregular heartbeat, arrhythmia is a broader term that encompasses various types of irregular heartbeats, both rapid and slow, while the distinct rapid irregularity of atrial fibrillation makes it a more precise answer here.