Thyrotoxicosis is caused by hyperthyroidism. The thyroid glands produces excessive amounts of thyroxine with resultant stimulation of the heart and tachycardia. Atrial fibrillation is a well-known complication and bothersome palpitations with tachycardia of 120–180 beats per minute may occur. The tachycardia is controlled with beta-blocking drugs such as propranolol, and the thyroid gland is treated with medications or radioactive iodine.
G. Idiopathic Atrial Fibrillation
It is not uncommon for atrial fibrillation to occur in the absence of an abnormal structural or functioning heart. This condition is called lone atrial fibrillation. Data from various countries are not available, but in the United States approximately 15% of patients are found to have lone atrial fibrillation. In some of these patients, and particu¬larly in those with paroxysmal atrial fibrillation, recent investigations have revealed foci located in the proximal pulmonary veins that may cause ectopic atrial activation.

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