What percentage of patients with hyperthyroidism (an overactive thyroid) develop atrial fibrillation (Afib)?

From the Guidelines

Approximately 5% to 15% of patients with hyperthyroidism develop atrial fibrillation (Afib). This condition is more frequent among those over 60 years of age 1. The development of Afib in hyperthyroidism is attributed to the elevated thyroid hormone levels, which directly affect cardiac tissue, increasing heart rate, contractility, and cardiac output.

Key Factors Influencing Afib Development

• The duration and severity of hyperthyroidism influence Afib risk, with longer and more severe cases having higher rates.
• Treating the underlying hyperthyroidism often resolves Afib, particularly in younger individuals without pre-existing heart disease.
• Beta-blockers are frequently used alongside antithyroid medications to control symptoms while the thyroid function normalizes 1.

Management and Treatment

• Treatment is directed primarily toward restoring a euthyroid state, which is usually associated with a spontaneous reversion of Afib to sinus rhythm.
• Antiarrhythmic drugs and cardioversion often fail to achieve sustained sinus rhythm while thyrotoxicosis persists 1.
• Beta blockers are effective in controlling the ventricular rate in this situation, and treatment with beta blockers is particularly important in cases of thyroid storm; nondihydropyridine calcium channel antagonists are recommended for rate control 1.

From the Research

Prevalence of Atrial Fibrillation in Hyperthyroidism Patients

• The prevalence of atrial fibrillation (Afib) in patients with hyperthyroidism varies across studies, with reported ranges including:
  • 5-15% of overtly hyperthyroid patients 2
  • 10-15% of patients with hyperthyroidism 3
  • 1.7% of new hyperthyroid patients 4
  • 3.6% of patients with hyperthyroidism or subclinical hyperthyroidism 5
• A study analyzing data from the National Inpatient Sample database found that 0.9% of Afib patients had hyperthyroidism, with a higher prevalence of hyperthyroidism in patients with Afib compared to those without Afib 6

Factors Influencing the Development of Atrial Fibrillation

• Low serum thyrotropin concentration is an independent risk factor for atrial fibrillation 3
• Thyroid hormone contributes to arrhythmogenic activity by altering the electrophysiological characteristics of atrial myocytes 3
• Age and sex may also influence the development of atrial fibrillation, with higher rates observed in older males 4 and a higher prevalence of hyperthyroidism in female Afib patients 6

Clinical Outcomes of Atrial Fibrillation with Hyperthyroidism

• Patients with Afib and hyperthyroidism may have better clinical outcomes compared to those with Afib without hyperthyroidism, including lower hospitalization costs, shorter lengths of stay, and lower in-hospital mortality 6
• Treatment of hyperthyroidism can lead to conversion to sinus rhythm in up to two-thirds of patients 3