What is the recommended IV dose of amiodarone for a patient with a pacemaker (artificial cardiac pacemaker) for tachy-brady syndrome who develops fast atrial fibrillation (AF) with hemodynamic instability?

IV Amiodarone Dosing for Hemodynamically Unstable Atrial Fibrillation in Pacemaker Patient

For a patient with a pacemaker who develops fast atrial fibrillation with hemodynamic instability, administer IV amiodarone with an initial loading dose of 150 mg over 10 minutes, followed by a continuous infusion of 1 mg/min for 6 hours, then 0.5 mg/min thereafter. 1, 2

Initial Loading Regimen

The FDA-approved dosing protocol for hemodynamically unstable atrial fibrillation consists of: 2

• Loading dose: 150 mg IV in 100 mL D5W infused over 10 minutes
• Maintenance infusion: 1 mg/min for 6 hours (360 mg total)
• Continued maintenance: 0.5 mg/min (720 mg per 24 hours) thereafter

The total recommended dose over the first 24 hours is approximately 1000 mg. 2

Supplemental Dosing for Breakthrough Episodes

If breakthrough episodes of hemodynamically unstable atrial fibrillation recur during the infusion, administer supplemental 150 mg boluses mixed in 100 mL D5W and infused over 10 minutes. 2 The initial infusion rate should not exceed 30 mg/min to minimize hypotension risk. 2

Why Amiodarone is Preferred in This Clinical Scenario

Amiodarone is specifically recommended by the American Heart Association for hemodynamically unstable patients because it has a superior hemodynamic profile compared to beta-blockers or calcium channel blockers. 1, 3 The 2014 AHA/ACC/HRS guidelines give IV amiodarone a Class I, Level B recommendation for acute heart rate control in patients with heart failure and atrial fibrillation, which commonly presents with hemodynamic instability. 4

Standard AV nodal blockers (beta-blockers, nondihydropyridine calcium channel blockers) are contraindicated in hemodynamically unstable patients as they can worsen hypotension and further compromise cardiac output. 1, 3 In contrast, amiodarone can be used safely even in critically ill patients with depressed left ventricular function. 5

Critical Safety Considerations

Pacemaker-Specific Concerns

The presence of a pacemaker for tachy-brady syndrome is actually protective in this scenario, as amiodarone can cause bradycardia requiring permanent pacing. 4 Since the patient already has pacing capability, this common adverse effect is mitigated.

Pre-excitation Exclusion

Verify the patient does NOT have Wolff-Parkinson-White syndrome or other pre-excitation pathways before administering amiodarone. 4 IV amiodarone is potentially harmful (Class III: Harm recommendation) in patients with WPW and pre-excited atrial fibrillation, as it may increase ventricular response and precipitate ventricular fibrillation. 4

Administration Requirements

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

Expected Clinical Response

The most immediate and predictable response is reduction of ventricular rate, typically noted after the first 300-400 mg. 6 In critically ill patients, amiodarone infusion (mean 242 mg over 1 hour) decreased heart rate by 37 beats/min while increasing systolic blood pressure by 24 mm Hg. 5

Restoration of sinus rhythm may occur but often takes 24 hours and a total dose of 1000 mg or more. 6 The mean time to conversion ranges from 1-6 hours depending on the arrhythmia type. 7

Monitoring During Infusion

Monitor continuously for: 2

• Hypotension: The most common adverse effect (16% incidence). Slow the infusion rate and add vasopressors, positive inotropes, or volume expansion as needed. 2
• Bradycardia/AV block: Slow or discontinue the infusion if excessive. 2
• QT prolongation: Although amiodarone prolongs QT, it has low proarrhythmic potential compared to other antiarrhythmics. 2

Duration of Therapy

Maintenance infusion at 0.5 mg/min can be continued for 2-3 weeks regardless of age, renal function, or left ventricular function. 2 However, transition to oral amiodarone or alternative rhythm/rate control strategies should be planned once hemodynamic stability is achieved. 1

Alternative if Amiodarone Fails

If amiodarone is unsuccessful or contraindicated, urgent electrical cardioversion is indicated for hemodynamically unstable atrial fibrillation. 4 The 2014 AHA/ACC/HRS guidelines give cardioversion a Class I, Level C recommendation for patients who become hemodynamically unstable with new-onset atrial fibrillation. 4