Should I remove metoprolol (beta blocker) and replace it with digoxin (digitalis glycoside) in a patient with atrial fibrillation (AF) and an ejection fraction (EF) of 35%?

No, Do Not Remove Metoprolol and Replace with Digoxin

In a patient with atrial fibrillation and an ejection fraction of 35%, you should maintain the beta-blocker (metoprolol) as the primary rate control agent, and consider adding digoxin if rate control remains inadequate, rather than replacing the beta-blocker with digoxin alone. 1

Rationale for Beta-Blocker Superiority

Beta-Blockers Are First-Line for Rate Control in Heart Failure with Reduced Ejection Fraction

• Beta-blockers provide mortality benefit in patients with heart failure and reduced ejection fraction (EF <40%), which digoxin does not offer 1
• In the AFFIRM study, beta-blockers achieved rate control targets in 70% of patients compared to 54% with calcium channel blockers, demonstrating superior efficacy 1
• Beta-blockers are more effective than digoxin for controlling ventricular rate during exercise, which is critical for active patients 1
• Beta-blockers should be initiated cautiously but are recommended in patients with AF and heart failure with reduced ejection fraction 1

Digoxin Has Significant Limitations as Monotherapy

• Digoxin should not be used as the sole agent to control ventricular rate in patients with paroxysmal AF 1
• Digoxin is no longer considered first-line therapy for rapid management of AF, except in patients with heart failure or LV dysfunction who are sedentary 1
• Digoxin efficacy is reduced in states of high sympathetic tone, which commonly precipitates AF 1
• Digoxin provides delayed onset of action (60 minutes minimum, peak effect at 6 hours) for acute rate control 1
• Digoxin does not improve survival in heart failure patients, though it may reduce hospitalizations 1

Appropriate Use of Digoxin in This Clinical Scenario

When to Add (Not Replace) Digoxin

• Digoxin may be used in addition to, or prior to, a beta-blocker in patients with AF and LVEF <40% 1
• In the longer term, a beta-blocker, either alone or in combination with digoxin, is the preferred treatment for rate control in patients with LVEF <40% 1
• Consider adding digoxin when rate control cannot be adequately controlled with beta-blocker alone, both at rest and during exercise 1
• Digoxin may be useful in the presence of hypotension or absolute contraindication to beta-blocker treatment 2

Digoxin Dosing in Heart Failure

• Starting dose: 0.25 mg daily in adults with normal renal function 1
• Reduced dose of 0.125 or 0.0625 mg daily should be used in elderly patients and those with renal impairment 1
• Target therapeutic serum concentration: 0.6 to 1.2 ng/mL, lower than previously recommended 1
• Monitor serum electrolytes (especially potassium and magnesium) and renal function regularly, as hypokalemia or hypomagnesemia sensitizes the myocardium to digoxin toxicity 3

Critical Safety Considerations

Beta-Blocker Precautions in Heart Failure

• Initiate beta-blockers cautiously in patients with AF and heart failure with reduced ejection fraction, starting at low doses and titrating slowly 1
• The mortality benefit of beta-blockers may be somewhat lower in heart failure patients when AF is present, but they remain beneficial 2

Digoxin Toxicity Risks

• Digoxin can cause atrial and ventricular arrhythmias, particularly with hypokalemia 1
• Toxicity may occur despite serum digoxin concentrations below 2.0 ng/mL in patients with electrolyte abnormalities 3
• Certain drugs increase plasma digoxin levels: amiodarone, diltiazem, verapamil, certain antibiotics, and quinidine 1, 3
• Signs of toxicity include: confusion, nausea, anorexia, visual disturbances, and cardiac arrhythmias 1

Clinical Algorithm

1. Continue metoprolol as the foundation of rate control therapy
2. Optimize beta-blocker dosing to achieve resting heart rate <100 bpm (or <80 bpm if symptomatic) 1
3. If rate control remains inadequate despite optimized beta-blocker therapy, add digoxin rather than replacing the beta-blocker 1
4. Monitor for adequate rate control both at rest and during activity 1
5. Ensure appropriate anticoagulation based on CHA2DS2-VASc score (this patient with EF 35% has ≥1 point and requires anticoagulation) 1

Common Pitfall to Avoid

The most critical error would be discontinuing the beta-blocker entirely, as this removes the only rate control agent that provides mortality benefit in heart failure with reduced ejection fraction while simultaneously losing superior exercise rate control 1. Digoxin alone is inadequate for comprehensive rate control in active patients and provides no survival advantage 1.