Are there any contraindications to initiating metoprolol 25 mg twice daily for rate control in a patient with paroxysmal atrial fibrillation and a ventricular rate of 139 beats per minute?

Contraindications to Metoprolol 25 mg BID in Paroxysmal Atrial Fibrillation with Heart Rate 139

Metoprolol 25 mg BID is appropriate for this patient with paroxysmal atrial fibrillation and heart rate of 139 bpm, provided you first exclude the absolute contraindications listed below. Beta-blockers are Class I, Level of Evidence B recommendations for rate control in atrial fibrillation, and metoprolol specifically is the preferred first-line agent 1, 2.

Absolute Contraindications That Must Be Ruled Out

Before initiating metoprolol, you must verify the patient does not have any of the following:

Cardiac Contraindications

• Decompensated heart failure – signs of pulmonary congestion (rales on auscultation), peripheral edema, or acute dyspnea indicate low output state and preclude beta-blocker initiation 1, 3
• Severe bradycardia – heart rate < 45-60 beats/min is an absolute contraindication 3, 4
• High-grade AV block – second- or third-degree heart block without a functioning pacemaker, or PR interval ≥ 0.24 seconds (significant first-degree block) 1, 3
• Severe hypotension – systolic blood pressure < 100 mmHg, particularly if symptomatic with dizziness or altered mental status 1, 3
• Cardiogenic shock – any signs of shock or severely reduced cardiac output 1, 3

Respiratory Contraindications

• Active asthma or severe reactive airway disease – current bronchospasm or active wheezing is an absolute contraindication 1, 3, 4
• Note: Mild COPD or history of bronchospasm without active symptoms is not an absolute contraindication, though caution is warranted 1, 4

Other Contraindications

• Pre-excitation syndromes (Wolff-Parkinson-White) – beta-blockers can paradoxically accelerate ventricular response in accessory pathway-mediated atrial fibrillation 1, 2
• Known hypersensitivity to metoprolol or other beta-blockers 3

Why Metoprolol Is Appropriate Here

The heart rate of 139 bpm is an indication FOR treatment, not a contraindication. This represents rapid ventricular response requiring rate control 2. The AFFIRM study demonstrated beta-blockers were the most effective drug class for rate control, achieving target heart rate in 70% of patients compared to 54% with calcium channel blockers 1.

Dosing Strategy

• Start with metoprolol tartrate 25 mg twice daily as you proposed, which is the standard initial dose 4, 5
• Target resting heart rate < 110 bpm (lenient control) or < 80 bpm (strict control) 5
• Can titrate up to 100 mg twice daily (maximum 200 mg twice daily) if needed for adequate rate control 1, 4

Monitoring Parameters

• Check heart rate and blood pressure at each visit during titration 4
• Assess for symptomatic bradycardia (HR < 60 bpm with dizziness or lightheadedness) 4
• Monitor for signs of worsening heart failure (increased dyspnea, edema, weight gain) 4
• Listen for new or worsening bronchospasm, particularly if any history of reactive airway disease 4

Common Pitfalls to Avoid

• Do not withhold beta-blockers in stable heart failure – metoprolol provides mortality benefit in heart failure with reduced ejection fraction and should be initiated cautiously once compensated 1
• Do not use digoxin as sole agent for paroxysmal atrial fibrillation – it is ineffective during high sympathetic tone and physical activity (Class III recommendation) 1
• Avoid abrupt discontinuation – sudden withdrawal can precipitate severe angina, myocardial infarction, and ventricular arrhythmias with 2.7-fold increased mortality risk 4