From the Guidelines
Methimazole should be given immediately to hyperthyroid patients presenting with supraventricular tachycardia (SVT) and atrial flutter, as these arrhythmias are often triggered by excess thyroid hormone. The goal of treatment is to restore a euthyroid state, which is usually associated with a spontaneous reversion of AF to sinus rhythm 1.
Key Considerations
- Methimazole works by inhibiting thyroid hormone synthesis, with clinical improvement typically beginning within 2-3 weeks.
- The typical starting dose is 10-30 mg daily (divided into 2-3 doses), with higher doses (30-40 mg) appropriate for severe hyperthyroidism.
- While treating the arrhythmias with rate control medications like beta-blockers, concurrent methimazole therapy addresses the underlying cause.
- Patients should be monitored with thyroid function tests every 4-6 weeks initially, with dose adjustments made to achieve euthyroidism.
Important Side Effects and Monitoring
- Common side effects include rash, nausea, and rarely agranulocytosis.
- Baseline complete blood count and liver function tests should be obtained before starting therapy.
Rationale for Immediate Treatment
- Treating the hyperthyroidism is essential as rate control medications alone may be ineffective while the thyrotoxic state persists 1.
- Efforts to restore normal sinus rhythm may be deferred until the patient is euthyroid, as antiarrhythmic drugs and cardioversion often fail to achieve sustained sinus rhythm while thyrotoxicosis persists.
From the Research
Hyperthyroidism Treatment with Methimazole
- Methimazole is an antithyroid medication used to treat hyperthyroidism caused by overproduction of thyroid hormones 2.
- The choice of treatment for hyperthyroidism depends on the underlying diagnosis, presence of contraindications, severity of hyperthyroidism, and patient preference 2.
- Methimazole can be used temporarily to treat thyrotoxicosis in preparation for more definitive treatment with radioactive iodine or surgery, or in select cases, patients can remain on antithyroid medications long-term 3.
Cardiovascular Manifestations of Hyperthyroidism
- Hyperthyroidism can lead to cardiovascular manifestations such as hypertension, tachycardia, atrial fibrillation, and sinus tachycardia 3, 4.
- Early treatment of cardiovascular manifestations along with treatment of hyperthyroidism can prevent significant cardiovascular events 3.
- Beta blockers can be used to treat cardiovascular manifestations such as tachycardia and hypertension 3, 5.
Supraventricular Tachycardia (SVT) and Atrial Flutter in Hyperthyroidism
- SVT and atrial flutter are common arrhythmias associated with hyperthyroidism 4, 5.
- Treatment of SVT and atrial flutter in hyperthyroidism involves addressing the underlying hyperthyroidism with antithyroid medications, radioactive iodine, or surgery, as well as managing the arrhythmia with beta blockers, calcium channel blockers, or cardioversion 3, 5.
- Catheter ablation can be considered for long-term management of recurrent, symptomatic SVT 5.
Treatment Approach
- Patients with hyperthyroidism and SVT or atrial flutter should be treated with a patient-centered approach, taking into account the underlying cause of hyperthyroidism, presence of contraindications, and severity of symptoms 2, 3, 6.
- Methimazole can be initiated to control hyperthyroidism, along with beta blockers to manage cardiovascular manifestations such as tachycardia and hypertension 2, 3.