What is the appropriate workup and management for an adult with hyperthyroidism presenting with palpitations?

Management of Hyperthyroidism with Palpitations

Start a beta-blocker immediately for symptomatic control while initiating definitive antithyroid therapy with methimazole, and screen for atrial fibrillation with an ECG. 1

Immediate Workup

Essential Diagnostic Steps

• Obtain thyroid function tests (TSH, free T4, free T3) to confirm hyperthyroidism, though treatment should not be delayed if clinical hyperthyroidism is evident. 1
• Perform a 12-lead ECG to screen for atrial fibrillation, which occurs in 10-25% of hyperthyroid patients, with higher rates (up to 15%) in those over 60 years. 2
• Consider 24-hour Holter monitoring if paroxysmal arrhythmias are suspected, as supraventricular dysrhythmias are significantly more prevalent in hyperthyroid patients. 3

Additional Cardiovascular Assessment

• Check blood pressure as hyperthyroidism produces characteristic hemodynamic changes including elevated systolic pressure from increased cardiac output (up to 300% above euthyroid state). 4
• Assess for signs of heart failure, particularly in elderly patients or those with persistent tachycardia, as cardiovascular complications are the chief cause of death in patients over 50. 4

Immediate Pharmacologic Management

Beta-Blocker Therapy (First-Line)

• Administer a beta-blocker immediately to control ventricular rate and provide symptomatic relief of palpitations. 2, 1
• Nonselective beta-blockers are preferred (propranolol or atenolol) because they provide superior metabolic benefits beyond heart rate control. 1
• High doses may be required in severe cases or thyroid storm, with intravenous administration appropriate for hemodynamically unstable patients. 2

Alternative Rate Control (If Beta-Blockers Contraindicated)

• Use nondihydropyridine calcium channel blockers (diltiazem or verapamil) as second-line alternatives for rate control if beta-blockers are absolutely contraindicated. 2, 1
• Avoid calcium channel blockers and nitrates as monotherapy in most cases because they can cause reflex tachycardia in the hyperthyroid state. 1
• Digoxin is less effective when adrenergic tone is high, which is typical in hyperthyroidism. 2

Definitive Antithyroid Treatment

Initiation of Antithyroid Drugs

• Start methimazole immediately as the preferred antithyroid medication for definitive treatment. 1, 5
• Treatment is primarily directed toward restoring a euthyroid state, which is usually associated with spontaneous reversion to sinus rhythm in up to two-thirds of patients with atrial fibrillation. 2, 6
• Recheck thyroid function tests in 4-6 weeks after initiating methimazole to adjust dosing. 1, 7

Important Drug Monitoring

• Monitor for agranulocytosis by instructing patients to report sore throat, fever, or general malaise immediately, particularly in the first months of therapy. 7
• Check prothrombin time before surgical procedures as methimazole may cause hypoprothrombinemia. 7
• Counsel patients about vasculitis risk and instruct them to report new rash, hematuria, decreased urine output, dyspnea, or hemoptysis. 7

Management of Atrial Fibrillation (If Present)

Anticoagulation Decisions

• Use CHA₂DS₂-VASc score to guide anticoagulation, not simply the presence of hyperthyroidism, as the independent thromboembolic risk from thyrotoxicosis alone is controversial. 2, 1
• Anticoagulation with heparin or warfarin is appropriate when AF persists longer than 48 hours. 2
• Once euthyroid state is restored, anticoagulation recommendations are the same as for patients without hyperthyroidism. 2

Rhythm Control Strategy

• Do not attempt cardioversion or rhythm control until the patient is euthyroid, as antiarrhythmic drugs and electrical cardioversion typically fail while thyrotoxicosis persists. 2, 1
• Normalize thyroid function prior to cardioversion to reduce the risk of AF recurrence. 2
• Predictors for successful reversion to sinus rhythm include lower blood pressure at presentation and achieving an initial hypothyroid state with antithyroid therapy. 3

Critical Safety Considerations and Pitfalls

Common Pitfalls to Avoid

• Do not delay beta-blocker initiation while waiting for thyroid function test results if clinical hyperthyroidism is evident—symptomatic tachycardia requires immediate treatment. 1
• Be aware that bradyarrhythmias can rarely occur with hyperthyroidism (sick sinus syndrome, complete AV block), making aggressive beta-blocker or calcium channel blocker therapy potentially dangerous in these atypical presentations. 8, 9
• Reduce beta-blocker dosing as patient becomes euthyroid, as hyperthyroidism causes increased clearance of beta-blockers with high extraction ratios. 7, 10

Long-Term Monitoring

• Some cardiovascular abnormalities persist despite effective antithyroid therapy, including palpitations, dyspnea, and postural hypotension, requiring continued monitoring. 3
• Mortality remains higher in hyperthyroid patients compared to controls even after treatment, emphasizing the importance of prompt recognition and aggressive management. 3
• Monitor for left ventricular hypertrophy, which develops more commonly in women with hyperthyroidism, particularly those with concurrent hypertension. 4