From the Guidelines
The primary treatment for new-onset atrial fibrillation (AF) due to hyperthyroidism should focus on addressing the underlying thyroid dysfunction and controlling the ventricular rate, with beta-blockers being the preferred initial treatment for rate control, as recommended by the 2014 AHA/ACC/HRS guideline 1.
Treatment Approach
To manage new AF due to hyperthyroidism, the following steps should be taken:
- Control the hyperthyroidism with antithyroid medications such as methimazole or propylthiouracil.
- For rate control of AF, use beta-blockers like metoprolol or propranolol, which have the added benefit of reducing hyperthyroid symptoms, as they are effective in controlling the ventricular rate in this situation 1.
- Non-dihydropyridine calcium channel blockers like diltiazem can be alternatives if beta-blockers are contraindicated, as recommended by the guideline 1.
- Anticoagulation therapy should be considered based on CHA₂DS₂-VASc score, regardless of whether the AF is thought to be temporary.
Rationale
The approach of treating the underlying hyperthyroidism and controlling the ventricular rate is supported by the fact that definitive treatment of hyperthyroidism often leads to spontaneous cardioversion to normal sinus rhythm within 8-12 weeks, making long-term antiarrhythmic drugs unnecessary in many cases. Hyperthyroidism causes AF through increased adrenergic tone and direct effects on atrial tissue, so treating the root cause often resolves the arrhythmia without need for specific antiarrhythmic therapy. If AF persists after achieving euthyroidism for 3-4 months, standard AF management approaches including cardioversion or ablation may be considered.
From the FDA Drug Label
The FDA drug label does not answer the question.
From the Research
Treatment of New-Onset Atrial Fibrillation due to Hyperthyroidism
- The initial treatment for new-onset atrial fibrillation (AF) due to hyperthyroidism is to control the heart rate with routine pharmacologic therapy and to start antithyroid therapy as quickly as possible 2.
- Attempted cardioversion should be deferred until approximately the fourth month of maintaining a euthyroid state, as more than 56% of atrial fibrillation spontaneously reverts to sinus rhythm when the thyroid hormone levels start to decline 2.
- Elective cardioversion for those whose atrial fibrillation persists is highly effective, with sinus rhythm maintenance rates of 56.7% and 47.6% at the 10th and 14th year, respectively 2.
Medications for Rate and Rhythm Control
- Propranolol should be used over metoprolol in patients with hyperthyroidism-induced atrial fibrillation due to its effect on blocking the activity of T4 conversion to active T3, which terminates reentrant atrial excitation 3.
- Anticoagulation therapy, such as warfarin, should be used early in hyperthyroid patients with AF to reduce the risk of ischemic stroke 4.
Risk of Ischemic Stroke
- Hyperthyroidism is a predictor of ischemic stroke in patients with new-onset AF, with a hazard ratio of 3.5 4.
- Persistent AF also predicts the occurrence of ischemic stroke, with a hazard ratio of 13.0 4.
- The majority of ischemic strokes (>70%) in patients with AF occur within the first 30 days of presentation, while AF is still present 4.
Subclinical Hyperthyroidism
- Subclinical hyperthyroidism is associated with an increased risk of atrial fibrillation, and treatment should be considered in patients older than 65 years with TSH < 0.4 mlU/L, or in younger patients with TSH < 0.1 mlU/L 5.
- Guidelines recommend screening for AF in patients with known hyperthyroidism, and wearable devices that measure heart electrical activity continuously may be a novel strategy to detect AF in patients at risk 5.