Final answer:
Hyperthyroidism, particularly due to Graves' disease, can cause atrial fibrillation because of the overproduction of thyroid hormones, which increases heart rate and contractility.
Step-by-step explanation:
Patients with hyperthyroidism, such as those with Graves' disease, often experience atrial fibrillation due to the effect of excessive thyroid hormone on the heart. Thyroid hormones are known to increase the cardiac rate and contractility. In particular T3 or triiodothyronine, the active form of thyroid hormone can direct enter cardiomyocytes and alter activity at the genomic level which also enhances the beta adrenergic response similar to epinephrine and norepinephrine.
This leads to an increased metabolic rate, body heat and heart rate. Graves' disease, which is characterized by the production of thyroid-stimulating immunoglobulin (TSI) that acts like thyroid-stimulating hormone (TSH),can lead to an overproduction of thyroid hormones. This, in turn, can cause symptoms like rapid and irregular heartbeat—a hallmark of atrial fibrillation.