What is the dose of amiodarone for a patient with intraoperative atrial fibrillation and left ventricular dysfunction?

Amiodarone Dosing for Intraoperative Atrial Fibrillation with Left Ventricular Dysfunction

For a patient with intraoperative atrial fibrillation and left ventricular dysfunction, administer amiodarone as a 150 mg IV bolus over 10 minutes, followed by 1 mg/min infusion for 6 hours (360 mg), then 0.5 mg/min for 18 hours (540 mg), with a maximum total dose of 2.2 grams over 24 hours. 1, 2, 3

Why Amiodarone is the Preferred Agent in This Clinical Context

• Amiodarone is specifically indicated for patients with left ventricular dysfunction because it is relatively safe in structural heart disease, unlike Class IC agents (flecainide, propafenone) which are contraindicated. 4, 2
• The drug provides dual benefits: immediate ventricular rate control (typically after the first 300-400 mg) and potential cardioversion to sinus rhythm, though conversion may take 6-8 hours and often requires ≥1000 mg total dose. 4, 5

Standard IV Loading Protocol

Initial Bolus

• Administer 150 mg IV over 10 minutes as the loading dose. 1, 2, 3
• This initial bolus provides rapid rate control, which is critical in the intraoperative setting. 5

Maintenance Infusion - First 6 Hours

• Follow with 1 mg/min continuous infusion for 6 hours (total 360 mg). 1, 2, 3
• This early maintenance phase continues therapeutic loading while minimizing hypotension risk. 2

Maintenance Infusion - Next 18 Hours

• Continue at 0.5 mg/min for 18 hours (total 540 mg). 1, 2, 3
• The total 24-hour dose should not exceed 2.2 grams. 2, 3

Critical Administration Requirements

• Use a central venous catheter for concentrations >2 mg/mL to avoid peripheral vein phlebitis. 3
• Administer through a volumetric infusion pump (not drop counters, which can underdose by up to 30%). 3
• Use an in-line filter during administration. 3
• Administer in glass or polyolefin bottles containing D5W for infusions exceeding 2 hours. 3

Expected Clinical Response Timeline

• Ventricular rate control typically occurs after the first 300-400 mg (within 1-2 hours of starting therapy). 5, 6
• Cardioversion to sinus rhythm, if it occurs, usually takes 6-8 hours and often requires ≥1000 mg total dose. 4, 1
• In one study of critically ill patients with severe LV dysfunction (EF <15%), 7 of 8 patients reverted to sinus rhythm within 1 hour using 300 mg over 1 hour. 7

Mandatory Monitoring During Infusion

• Continuous ECG monitoring for bradycardia, heart block, and QT prolongation throughout the infusion. 1, 2
• Blood pressure monitoring for hypotension (occurs in 16% of patients receiving IV amiodarone). 2
• Watch for bradycardia (4.9% with IV therapy) and AV block. 2

Special Considerations for Left Ventricular Dysfunction

• Amiodarone is the preferred antiarrhythmic in patients with heart failure or reduced ejection fraction. 2
• Unlike other antiarrhythmics, slow IV amiodarone infusion is hemodynamically well-tolerated even in patients with marked LV dysfunction. 7
• Before cardioversion occurs, expect beneficial heart rate slowing (mean 28%) resulting in improved stroke volume index (mean 49%) and left ventricular stroke work index (mean 61%). 7
• Use with caution as it may cause negative inotropic effects, though this is less pronounced than with other agents. 2

Supplemental Dosing for Breakthrough Arrhythmias

• For breakthrough VF or hemodynamically unstable VT, administer 150 mg supplemental bolus (mixed in 100 mL D5W, infused over 10 minutes). 3
• Do not exceed an initial infusion rate of 30 mg/min. 3

Common Pitfalls to Avoid

• Do not use Class IC agents (flecainide, propafenone) in patients with structural heart disease or LV dysfunction - they are contraindicated. 4, 2
• Avoid rapid bolus administration, which increases hypotension risk; the 10-minute infusion time is critical. 1, 3
• Do not administer through peripheral IV at concentrations >2 mg/mL due to high phlebitis risk. 3
• Recognize that full antiarrhythmic effect takes days to weeks despite adequate serum levels, so patience is required. 1, 2

Contraindications to Verify Before Administration

• Severe bradycardia, second- or third-degree heart block without pacemaker. 1
• Severe hepatic dysfunction. 1
• Baseline QT prolongation with history of torsades de pointes. 1
• Significant lung disease (relative contraindication - use lowest effective dose if no alternative). 2

Drug Interactions Requiring Immediate Attention

• Reduce digoxin dose by 50% immediately, as amiodarone doubles digoxin levels. 1, 2
• Reduce warfarin dose by 30-50% and check INR within 3-5 days. 1, 2
• Reduce doses of other rate-controlling medications (beta-blockers, calcium channel blockers) as amiodarone's rate-control effect develops. 2