Final answer:
The most common arrhythmia in patients with Graves' disease is atrial fibrillation, characterized by a rapid and irregular heartbeat.
Step-by-step explanation:
The most common arrhythmia in patients with Graves' disease is atrial fibrillation. Graves' disease, which is the most prevalent cause of hyperthyroidism in the United States, leads to an overproduction of thyroid hormones. These hormones can elevate the basal metabolic rate (BMR) significantly, causing symptoms like weight loss, increased heart rate, and heat intolerance. As a manifestation of hyperthyroidism, the increased heart rate can lead to various heart rhythm disorders, with atrial fibrillation being the most common. This arrhythmia is characterized by a rapid and irregular heartbeat, which can increase the risk of stroke and heart failure.