What is better for atrial fibrillation (AFib) with rapid ventricular response (RVR), amiodarone (amiodarone) drip or diltiazem (diltiazem) drip?

Diltiazem is Superior to Amiodarone for AFib with RVR in Patients with Normal Left Ventricular Function

For patients with atrial fibrillation with rapid ventricular response (AFib RVR) and preserved left ventricular function (LVEF >40%), diltiazem drip is superior to amiodarone drip due to its faster onset of action, better rate control efficacy, and more favorable side effect profile.

Patient Assessment and Treatment Algorithm

Step 1: Assess Hemodynamic Stability

• If patient is unstable (hypotension, angina, acute heart failure, altered mental status) → immediate electrical cardioversion
• If stable → proceed with pharmacologic rate control

Step 2: Determine Left Ventricular Function

1. LVEF >40% (Normal or Mildly Reduced Function)

   • First-line: Diltiazem drip
     • Dosing: 0.25 mg/kg IV over 2 min, then 5-15 mg/h IV 1
     • Higher weight-based dosing (≥0.13 mg/kg) achieves faster rate control 2
     • Alternative: Beta-blockers (esmolol, metoprolol)

2. LVEF ≤40% (Moderate to Severe LV Dysfunction)

   • First-line: Amiodarone drip
     • Dosing: 150 mg IV over 10 min, then 0.5-1 mg/min IV 1
     • Alternative: Digoxin (0.25 mg IV each 2h, up to 1.5 mg)
   • Avoid diltiazem and verapamil due to negative inotropic effects 3

Step 3: Monitor Response

• Target heart rate: <110 bpm at rest 1
• Monitor blood pressure, heart rate, and symptoms
• If inadequate response, consider combination therapy or alternative agent

Evidence Supporting Diltiazem for AFib RVR

Efficacy

• Diltiazem provides rapid and effective rate control in AFib RVR 3
• Weight-based dosing ≥0.13 mg/kg achieves heart rate <100 bpm significantly faster (169 vs 318 minutes) compared to lower doses 2
• Even low-dose diltiazem (≤0.2 mg/kg) shows similar efficacy to standard doses with fewer side effects 4
• Prehospital studies show 57% of patients have clinical improvement with diltiazem, defined as heart rate decrease by 20% or to <100 bpm 5

Safety

• The primary concern with diltiazem is hypotension, which occurs in approximately 18-42% of patients depending on dosing 4
• Lower doses (≤0.2 mg/kg) are associated with significantly less hypotension compared to standard doses (18% vs 35%) 4
• No patients discontinued diltiazem for hypotension or bradycardia in recent studies 2

When Amiodarone is Preferred

Amiodarone should be used as first-line therapy in specific situations:

1. Patients with heart failure or LV dysfunction (LVEF ≤40%) 3
2. When beta-blockers and calcium channel blockers are contraindicated 3
3. When other rate control measures are ineffective 3

Important Caveats and Special Considerations

1. Wolff-Parkinson-White (WPW) Syndrome

   • AVOID diltiazem, beta-blockers, and digoxin in patients with pre-excited AFib 3, 1
   • These agents can enhance conduction over accessory pathway and increase risk of ventricular fibrillation 3
   • Use procainamide or ibutilide instead, or proceed to immediate cardioversion 3

2. Hypotension

   • Consider lower initial doses of diltiazem (0.15-0.2 mg/kg) in elderly or patients at risk for hypotension 4
   • Amiodarone may be preferred if baseline blood pressure is borderline

3. Chronic Obstructive Pulmonary Disease (COPD)

   • Diltiazem is preferred over beta-blockers 1

4. Combination Therapy

   • If single-agent therapy is insufficient, consider adding digoxin to diltiazem or beta-blocker 3
   • The combination of digoxin and beta-blocker is generally more effective than digoxin with calcium channel blocker 3

By following this algorithm and considering the patient's specific cardiac function, diltiazem provides superior rate control for most patients with AFib RVR who have preserved left ventricular function, while amiodarone remains the preferred agent for those with heart failure or significant LV dysfunction.