Management of Hyperthyroidism with Tachycardia on Methimazole

Immediate Pharmacologic Management

The European Society of Cardiology recommends adding a beta-blocker immediately to control the tachycardia while continuing methimazole therapy, as beta-blockers are the first-line treatment for cardiovascular symptoms in hyperthyroidism and should be initiated promptly to reduce heart rate and prevent serious cardiac complications 1, 2
Initiate beta-blocker therapy (atenolol or propranolol) as necessary to control the ventricular rate, unless contraindicated, according to the European Heart Journal 1, 2
Beta-blockers provide rapid improvement in cardiac symptoms (tachycardia, palpitations) and neurological symptoms (tremors, anxiety) while methimazole takes effect, as stated by the European Society of Cardiology 2, 3

Look for signs of atrial fibrillation, which occurs in 10% to 25% of hyperthyroid patients, according to the European Heart Journal 1, 2
Evaluate for pulmonary artery hypertension, which can occur in hyperthyroidism and lead to right ventricular dilatation, as recommended by the European Society of Cardiology 2
If atrial fibrillation is present, oral anticoagulation (INR 2-3) is recommended to prevent thromboembolism, according to the European Heart Journal 1

Do not discontinue methimazole when adding beta-blockers—both medications serve different purposes and should be used together, as stated by the European Society of Cardiology 1, 2
Do not use beta-blockers, digitalis, diltiazem, or verapamil if the patient has Wolff-Parkinson-White syndrome with preexcited ventricular activation in atrial fibrillation (Class III contraindication), according to the European Heart Journal 1
Recognize that antiarrhythmic drugs and electrical cardioversion are generally unsuccessful while the thyrotoxic condition persists, as stated by the European Society of Cardiology 1
Be aware that cardiovascular complications are the chief cause of death after treatment of hyperthyroidism, especially in patients over 50 years, according to the European Society of Cardiology 2, 3