What is the preferred initial rate control strategy between Cardizem (diltiazem) and digoxin for atrial fibrillation (AF) with a normal left ventricular ejection fraction (LVEF)?

Rate Control Strategy for Atrial Fibrillation with Normal LVEF

For patients with atrial fibrillation and normal left ventricular ejection fraction (LVEF >40%), diltiazem (Cardizem) is preferred over digoxin as the initial rate control agent due to superior effectiveness in controlling heart rate both at rest and during activity.

First-Line Options for Rate Control in AF with Normal LVEF

Diltiazem (Cardizem) Advantages:

• Recommended as a first-line agent by the 2024 ESC guidelines for patients with AF and LVEF >40% 1
• More effective at achieving rapid heart rate control compared to digoxin 2
• Provides better control during both rest and exercise 3
• Achieves quicker time to heart rate control (median 13 minutes vs. 27 minutes for beta-blockers) 4
• More frequently results in heart rate reduction of ≥20% at 30 minutes (63% vs. 27% for beta-blockers) 4

Digoxin Limitations:

• Only effective for rate control at rest, not during exercise 5
• Slower onset of action compared to diltiazem 2
• Should be used as a second-line agent rather than first-line therapy 5
• Has a narrower therapeutic window with risk of toxicity
• Requires monitoring of serum levels
• Multiple drug interactions, particularly with P-glycoprotein inhibitors 1

Clinical Decision Algorithm

1. Initial Assessment:

   • Confirm normal LVEF (>40%)
   • Assess hemodynamic stability
   • Check for contraindications to calcium channel blockers

2. First-Line Treatment:

   • Diltiazem (Cardizem):
     • IV administration: 15-25 mg IV bolus (consider low-dose 0.2 mg/kg to reduce hypotension risk) 6
     • Oral maintenance: 60-120 mg TID or 120-360 mg daily modified release 5

3. If Inadequate Response to Diltiazem:

   • Consider combination therapy with digoxin 1
   • Target heart rate: <110 bpm (lenient control) 1
   • Consider stricter control if symptoms persist

4. Alternative First-Line Options (if diltiazem contraindicated):

   • Beta-blockers (metoprolol, bisoprolol, carvedilol)
   • Verapamil (alternative calcium channel blocker)

Important Considerations

• Combination Therapy: If single-agent therapy is insufficient, consider adding digoxin to diltiazem for enhanced rate control both at rest and during exercise 3
• Heart Rate Target: Initial target should be a resting heart rate <110 bpm (lenient control), with stricter control reserved for those with continuing symptoms 1
• Monitoring: Assess heart rate both at rest and during physical activity to ensure adequate rate control
• Caution: Monitor for hypotension with diltiazem, especially with higher doses (risk increases with dose: 18% with low dose vs. 35-42% with standard/high doses) 6

Special Situations

• If patient develops reduced LVEF: Switch from diltiazem to beta-blocker and/or digoxin 1
• For highly symptomatic patients despite rate control: Consider rhythm control strategy
• For patients unresponsive to pharmacological rate control: Consider AV node ablation with pacemaker implantation 1

Diltiazem offers superior rate control compared to digoxin in patients with normal LVEF, with faster onset and better control during both rest and activity, making it the preferred initial agent for rate control in atrial fibrillation.