In a patient with normal left‑ventricular ejection fraction and atrial fibrillation with a ventricular rate of about 140 bpm who is already on oral diltiazem 60 mg three times daily and metoprolol 25 mg once daily, what is the next step in management?

Management of Inadequate Rate Control in Atrial Fibrillation with Normal EF

Uptitrate the beta-blocker (metoprolol) to a higher dose and consider adding digoxin as combination therapy, because the current regimen uses subtherapeutic doses of both agents and beta-blockers remain first-line for rate control in patients with preserved ejection fraction. 1, 2

Current Medication Assessment

Your patient is receiving:

• Diltiazem 60 mg three times daily (180 mg/day total) – this is below the guideline-recommended maintenance dose of 120–360 mg daily of extended-release formulation 1
• Metoprolol 25 mg once daily – this is at the lower end of the therapeutic range (25–100 mg twice daily for metoprolol tartrate, or 50–400 mg daily for extended-release) 1

The ventricular rate of 140 bpm indicates inadequate rate control, as the target is <100 bpm at rest (ideally 60–80 bpm) 2, 1.

Recommended Next Steps

Step 1: Optimize Beta-Blocker Dosing

• Increase metoprolol dose incrementally – if using metoprolol tartrate, increase to 50 mg twice daily initially, with further titration up to 100 mg twice daily as tolerated 1
• Alternatively, switch to metoprolol succinate (extended-release) 100–200 mg once daily for improved compliance and more consistent rate control 1
• Beta-blockers are superior to calcium-channel blockers for rate control – the AFFIRM trial demonstrated 70% achievement of rate-control endpoints with beta-blockers versus only 54% with calcium-channel blockers 2
• Beta-blockers provide better exercise heart rate control than digoxin or calcium-channel blockers, which is essential since resting rate control does not guarantee adequate control during activity 2

Step 2: Add Digoxin as Second-Line Combination Therapy

• When beta-blocker monotherapy fails to achieve target heart rate, adding digoxin is guideline-recommended (Class IIa) 2, 1
• Start digoxin 0.125–0.25 mg once daily without loading dose in the outpatient setting 1
• The combination of digoxin plus beta-blocker controls heart rate both at rest and during exercise more effectively than either agent alone 2
• Digoxin onset is delayed (≥60 minutes, peak effect up to 6 hours), so do not expect immediate rate reduction 2

Step 3: Consider Reducing or Discontinuing Diltiazem

• Diltiazem can be continued at current dose or gradually reduced once beta-blocker is optimized, as the combination may increase risk of bradycardia or AV block 3
• If diltiazem is continued, uptitrate to 120–360 mg daily of extended-release formulation for adequate dosing 1
• However, beta-blocker plus digoxin is the preferred combination over beta-blocker plus calcium-channel blocker in patients with normal EF 2

Monitoring During Uptitration

• Assess heart rate both at rest and during moderate exertion – satisfactory resting control does not guarantee adequate control during activity 2, 1
• Monitor for hypotension, bradycardia, high-grade AV block, and symptoms of heart failure during beta-blocker dose escalation 2
• Target resting heart rate <100 bpm (ideally 60–80 bpm) and 90–115 bpm during moderate exercise 2, 3

Alternative Strategies if Combination Therapy Fails

Oral Amiodarone (Third-Line)

• If beta-blocker plus digoxin fails to achieve adequate rate control, consider oral amiodarone 100–200 mg daily (Class IIb) 2, 1
• Amiodarone provides effective rate control and is the most effective antiarrhythmic with low pro-arrhythmic risk, but reserve for refractory cases due to long-term toxicity concerns 2

AV Node Ablation (Last Resort)

• AV node ablation with permanent pacing is reasonable when pharmacologic management is inadequate (Class IIa), but it is contraindicated as first-line therapy (Class III Harm) until adequate pharmacologic rate control has been attempted 1, 2

Critical Pitfalls to Avoid

• Do not assume adequate resting heart rate equals adequate overall rate control – always assess during activity 2
• Do not give IV diltiazem if the patient has decompensated heart failure (Class III Harm), though this patient has normal EF 1, 3
• Do not combine multiple AV nodal blockers initially without careful monitoring due to risk of excessive bradycardia or heart block 3
• Do not delay beta-blocker optimization out of excessive concern for negative inotropy in stable patients with normal EF 2

Anticoagulation Consideration

• Ensure appropriate anticoagulation based on CHA₂DS₂-VASc score – patients with atrial fibrillation typically meet criteria for oral anticoagulation to reduce stroke risk (Class I) 2