What dose of metoprolol should be used to reduce tachycardia and convert atrial fibrillation?

Metoprolol Dosing for Tachycardia and Atrial Fibrillation

Metoprolol will effectively reduce tachycardia in atrial fibrillation, but it does NOT convert atrial fibrillation to sinus rhythm in most patients—its primary role is rate control, not rhythm conversion. 1

Critical Distinction: Rate Control vs. Rhythm Conversion

Metoprolol is a rate-control agent, not a rhythm-control agent for atrial fibrillation. 1, 2 While isolated case series from the 1980s showed occasional conversion of supraventricular tachycardias including atrial fibrillation with IV metoprolol, the conversion rate was only 12.5% (1 out of 8 patients with atrial fibrillation). 3 The primary therapeutic goal is to slow the ventricular rate to <80-110 bpm, not to restore sinus rhythm. 1, 2

IV Metoprolol Dosing for Acute Rate Control

For hemodynamically stable patients with atrial fibrillation and rapid ventricular response requiring immediate rate control:

• Initial dose: 5 mg IV administered slowly over 1-2 minutes 1, 2
• Repeat dosing: Additional 5 mg boluses every 5 minutes as needed based on heart rate and blood pressure response 1, 2
• Maximum total dose: 15 mg (three 5 mg boluses) 1, 2
• Target heart rate: <100-110 bpm (lenient control) or <80 bpm (strict control) 1, 2

Absolute Contraindications Before IV Administration

Do not administer IV metoprolol if any of the following are present:

• Signs of heart failure, low output state, or decompensated heart failure 1, 2
• Systolic blood pressure <100-120 mmHg 1
• Heart rate <60 bpm or >110 bpm 1
• PR interval >0.24 seconds or second/third-degree AV block without pacemaker 1, 2
• Active asthma or severe reactive airway disease 1, 2
• Pre-excitation syndromes (Wolff-Parkinson-White) 1, 2

Required Monitoring During IV Administration

• Continuous ECG monitoring 1
• Frequent blood pressure checks after each bolus 1
• Auscultation for new pulmonary rales (heart failure) 1
• Auscultation for bronchospasm 1

Transition to Oral Therapy

After IV loading, begin oral metoprolol 15 minutes after the last IV dose:

• Initial oral regimen: Metoprolol tartrate 25-50 mg every 6 hours for 48 hours 1
• Maintenance dosing: Metoprolol tartrate 50-100 mg twice daily (maximum 200 mg twice daily) 1, 2, 4
• Alternative extended-release: Metoprolol succinate 50-200 mg once daily (maximum 400 mg daily) 1, 2

Oral Metoprolol for Chronic Rate Control

For non-acute management of atrial fibrillation:

• Starting dose: Metoprolol tartrate 25 mg twice daily 2, 4
• Titration: Increase to 50 mg twice daily, then 100 mg twice daily as needed 2, 4
• Target heart rate: Resting heart rate <80 bpm for symptomatic patients or <110 bpm for asymptomatic patients with preserved left ventricular function 2, 4

Evidence on Rhythm Conversion

The evidence for metoprolol converting atrial fibrillation to sinus rhythm is weak and inconsistent:

• One 1979 study showed only 1 out of 8 patients (12.5%) with atrial fibrillation converted to sinus rhythm with IV metoprolol 2-20 mg. 3
• A 2000 study using metoprolol CR/XL after successful cardioversion showed it reduced relapse into atrial fibrillation (48.7% vs 59.9% placebo, p=0.005), but this was for maintaining sinus rhythm after electrical or chemical cardioversion—not for converting atrial fibrillation. 5
• In multifocal atrial tachycardia (a different arrhythmia), metoprolol showed 68-100% conversion rates, but this does not apply to atrial fibrillation. 6, 7

Common Pitfalls to Avoid

• Never give the full 15 mg IV dose as a single rapid bolus—this dramatically increases the risk of severe hypotension and bradycardia. 1
• Do not use IV metoprolol in decompensated heart failure—the COMMIT trial showed this increases cardiogenic shock by 11 per 1,000 patients, particularly in the first 24 hours. 1
• Do not expect rhythm conversion—if the goal is to restore sinus rhythm, electrical cardioversion or antiarrhythmic drugs (amiodarone, flecainide, propafenone) are required, not metoprolol. 1, 2
• Never abruptly discontinue metoprolol—this can precipitate severe angina, myocardial infarction, ventricular arrhythmias, and a 2.7-fold increase in mortality. 1

Alternative for High-Risk Patients

For patients at high risk of hypotension or bradycardia, consider esmolol instead:

• Loading dose: 500 mcg/kg over 1 minute 1
• Maintenance infusion: 50-300 mcg/kg/min 1
• Advantage: Ultra-short half-life (10-30 minutes) allows rapid titration and immediate reversibility 1