Thyrotoxic Atrial Fibrillation

Malvinder S. Parmar, MD, FRCPC, FACP

In This Article

Atrial Fibrillation and Hyperthyroidism

What Is the Incidence of Atrial Fibrillation in Thyrotoxicosis?

Atrial fibrillation is the most common cardiac complication of hyperthyroidism. It occurs in up to 15% of hyperthyroid patients[1] compared with .4% in the general population[2] and is more common in men and in patients with triiodothyronine (T3) toxicosis,[3] and its incidence increases with advancing age. Although it is rare in patients under 40 years of age, 25% to 40% of hyperthyroid individuals over the age of 60 experience atrial fibrillation, possibly reflecting an age-related reduction in threshold for acquiring atrial fibrillation.[4] In addition, subclinical hyperthyroidism is a risk factor that is associated with a 3-fold increase in risk of developing atrial fibrillation,[5] and up to13% of patients with unexplained atrial fibrillation have biochemical evidence of hyperthyroidism.[6]

What Is the Frequency of Hyperthyroidism in Patients Presenting With Atrial Fibrillation?

In a large study[7] of patients with new-onset atrial fibrillation, less than 1% were caused by overt hyperthyroidism. Therefore, although serum TSH is measured in all patients with new-onset atrial fibrillation to rule out thyroid disease, this association is uncommon in the absence of additional symptoms and signs of hyperthyroidism.[7]


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