From the Guidelines
Atrial fibrillation (AF) caused by hyperthyroidism requires treatment of both conditions simultaneously, with a focus on controlling the rapid heart rate with beta-blockers and normalizing thyroid function with antithyroid medications. The relationship between atrial fibrillation and hyperthyroidism is well-established, with AF being the most common arrhythmia in patients with hyperthyroidism, affecting 5-15% of patients, especially those over 60 years old 1.
Key Considerations
- The primary goal is to restore a euthyroid state, which is usually associated with a spontaneous reversion of AF to sinus rhythm 1.
- Beta-blockers, such as metoprolol or propranolol, are effective in controlling the ventricular rate and should be initiated immediately 1.
- Antithyroid medications, such as methimazole or propylthiouracil, should be started to normalize thyroid function, which may take 2-8 weeks 1.
- Anticoagulation therapy should be considered based on the patient's CHA₂DS₂-VASc score to prevent stroke, regardless of whether the AF is thought to be temporary 1.
Treatment Approach
- Rate control should begin immediately with beta-blockers, while thyroid treatment is initiated to normalize thyroid function.
- Once hyperthyroidism is controlled, about 50-60% of patients will spontaneously convert to normal sinus rhythm within 2-3 months.
- If AF persists after achieving euthyroidism, standard AF management, including cardioversion or ablation, may be considered.
- Regular monitoring of thyroid function tests and heart rhythm is essential throughout treatment. The connection between these conditions occurs because excess thyroid hormone increases beta-adrenergic tone and affects atrial electrophysiology, creating the substrate for AF development 1.
From the Research
Relationship Between Atrial Fibrillation and Hyperthyroidism
- Atrial fibrillation (AF) is a common condition with a global estimated prevalence of 60 million cases, and it is the most common cardiac complication of hyperthyroidism, occurring in 5-15% of overtly hyperthyroid patients 2.
- Subclinical hyperthyroidism and high-normal free T4 have been associated with an increased risk in the development of AF 2.
- The presence of excess thyroid hormone alters adrenergic receptors in the heart and blood vessels, causing an increase in sympathetic function and AF as a sequela of this excess circulating hormone 3.
- Thyroid hormone contributes to arrythmogenic activity by altering the electrophysiological characteristics of atrial myocytes, shortening the action potential duration, enhancing automaticity, and triggered activity in the pulmonary vein cardio myocytes 4.
Management of Hyperthyroidism-Related Atrial Fibrillation
- Restoring thyroid function is an indispensable element in hyperthyroidism-related AF management, and the majority of patients spontaneously revert to sinus rhythm in 4-6 months during or after restoration of euthyroidism 2.
- Rate control with beta-blockers is a first-line therapy, reserving rhythm control in cases of persistent hyperthyroidism-related AF 2.
- Propranolol should be used over metoprolol in patients with hyperthyroidism-induced AF due to its effect on blocking the activity of T4 conversion to active T3, thereby blocking its effect on cardiac myocytes and terminating reentrant atrial excitation 3.
- Electrical cardioversion should be performed for patients with persistent AF and hyperthyroidism as soon as possible, with a recurrence rate similar to that of euthyroid patients 5.
Risk Factors and Complications
- Low serum thyrotropin concentration is an independent risk factor for AF 4.
- Hyperthyroidism results in excess mortality from increased incidence of circulatory diseases and dysrhythmias, with a higher incidence of cerebral embolism in hyperthyroid patients with AF, especially in the elderly 4.
- Anticoagulation is indicated in hyperthyroid patients with AF, especially in the elderly, and treatment with novel direct oral anticoagulants appears to be as beneficial and may be safer than warfarin in patients with hyperthyroidism-related AF 2.