What are the recommended drug dosages and electrical shock settings for cardioversion of atrial fibrillation, atrial flutter, ventricular tachycardia, and ventricular fibrillation?

Cardioversion Dosages for Atrial Fibrillation, Atrial Flutter, Ventricular Tachycardia, and Ventricular Fibrillation

For electrical cardioversion of atrial fibrillation, start with 150-200 joules using a biphasic waveform device; for atrial flutter, start with 50 joules; for unstable monomorphic VT, start with 100 joules synchronized; and for VF or pulseless VT, use unsynchronized 200 joules initially. 1, 2, 3

Atrial Fibrillation

Electrical Cardioversion

• Initial energy: 150-200 joules biphasic waveform 1
• Monophasic alternative: 200 joules initially, then 200-300 joules, then 360 joules if needed 2
• Pad positioning: Anterior-posterior placement is more effective than anterior-lateral 1
• Sedation: Use rapid-acting agents (fentanyl, propofol, midazolam) 1

The 2011 Canadian guidelines specifically recommend starting higher (150-200J biphasic) to increase first-shock success and minimize cumulative energy exposure 1. This represents a shift from older stepwise protocols.

Pharmacological Cardioversion

First-line agents for recent-onset AF:

• Procainamide: 15-17 mg/kg IV over 60 minutes 1
  • Alternative dosing: 20-50 mg/min until arrhythmia suppressed, hypotension occurs, QRS widens by 50%, or maximum 17 mg/kg reached 4
• Propafenone: 450-600 mg PO 1
• Flecainide: 300-400 mg PO 1
• Ibutilide: 1-2 mg IV over 10-20 minutes 1
  • Critical caveat: Pretreat with magnesium sulfate 1-2 g IV to reduce 2-3% risk of torsades de pointes 1

Second-line agents:

• Amiodarone: 150 mg IV over 10 minutes, may repeat if necessary, followed by 1 mg/min infusion for 6 hours, then 0.5 mg/min (maximum 2.2 g/24 hours) 4
  • Note: Not effective in first 6-8 hours for recent-onset AF 1

Rate control (not cardioversion):

• Metoprolol: 5 mg IV over 1-2 minutes, repeat every 5 minutes to maximum 15 mg 4
• Diltiazem: 15-20 mg (0.25 mg/kg) IV over 2 minutes; additional 20-25 mg (0.35 mg/kg) in 15 minutes if needed 4

Atrial Flutter

Electrical Cardioversion

• Initial energy: 50 joules synchronized 2
• Atrial flutter cardioverts at much lower energies than AF
• Success rates approach 97.9-100% with electrical cardioversion 5

Pharmacological Cardioversion

Most effective agents (compared to placebo):

• Ibutilide: 1-2 mg IV over 10-20 minutes (efficacy 38-76%) 1, 6
  • Superior to other agents for flutter specifically
• Propafenone: 450-600 mg PO 1
• Dofetilide: Effective but dosing requires careful titration 5
• Sotalol: 1.5 mg/kg IV (less effective than ibutilide: 19% vs 70%) 6

Ventricular Tachycardia

Hemodynamically Unstable Monomorphic VT

• Synchronized cardioversion: 100 joules initially, increase stepwise if no response 3
• If cardioversion fails or VT recurs, proceed to pharmacological therapy

Hemodynamically Stable Monomorphic VT

First-line pharmacological options:

• Procainamide: 20-50 mg/min until arrhythmia suppressed, hypotension occurs, QRS widens by 50%, or maximum 17 mg/kg; OR 100 mg every 5 minutes 4, 7
• Amiodarone: 150 mg IV over 10 minutes, may repeat, then 1 mg/min × 6 hours, then 0.5 mg/min 4, 7

Second-line options:

• Lidocaine: 1-1.5 mg/kg IV bolus (or simplified 100 mg IV push), may repeat 0.5-0.75 mg/kg every 5-10 minutes to maximum 3 mg/kg, then 2-4 mg/min infusion 4, 8, 7
• Sotalol: 1.5 mg/kg infused over 5 minutes 4

Polymorphic VT

With normal QT interval:

• Amiodarone: 150 mg IV over 10 minutes, may repeat 4, 7
• Lidocaine: 100 mg IV push 7
• Treat underlying ischemia aggressively

With prolonged QT (Torsades de Pointes):

• Magnesium sulfate: 1-2 g IV over 15 minutes (even if magnesium levels normal) 4, 7
• Remove/correct precipitants (QT-prolonging drugs, electrolytes)
• Overdrive pacing (atrial preferred)
• Beta-blocker (non-selective preferred, e.g., propranolol)
• Lidocaine if refractory 7

Ventricular Fibrillation / Pulseless VT

Electrical Defibrillation

• Unsynchronized shock: 200 joules initially
• If unsuccessful: 200-300 joules
• If still unsuccessful: 360 joules 8
• Resume CPR immediately after each shock

Pharmacological Therapy for Shock-Refractory VF/VT

After 1-2 failed defibrillation attempts:

• Amiodarone: 300 mg IV push (150 mg if <45 kg), may give additional 150 mg if VF/VT recurs 4, 7

  • This is the first-choice antiarrhythmic for refractory VF/VT 9

• Lidocaine (alternative if amiodarone unavailable): 100 mg IV push (50 mg if <45 kg), may give additional 50 mg 7

Do not give lidocaine in addition to amiodarone 9

Adjunctive therapy:

• Epinephrine: 1 mg IV every 3-5 minutes 9
• Magnesium: 8 mmol (1-2 g) IV if suspected hypomagnesemia or refractory VF 4, 9

Electrical Storm (≥3 VT/VF episodes in 24 hours)

Immediate management:

• Non-selective beta-blocker (propranolol preferred over metoprolol) 7
• IV Amiodarone: 300 mg bolus, then infusion 7
• Consider sedation/general anesthesia
• Involve electrophysiology specialist early
• Treat acute heart failure if present

Critical Caveats

Pre-excited Atrial Fibrillation (Wolff-Parkinson-White)

• Urgent electrical cardioversion if hemodynamically unstable 1
• If stable: Procainamide or Ibutilide 1
• Contraindicated: AV nodal blockers (digoxin, calcium channel blockers, beta-blockers, adenosine) - these can precipitate VF 1
• Use amiodarone with extreme caution (case reports of VF) 1

Drug-Specific Warnings

• Procainamide: Avoid in QT prolongation and CHF 4
• Ibutilide: 2-3% risk of torsades - always pretreat with magnesium 1
• Class IC agents (flecainide, propafenone): Risk of 1:1 atrial flutter with rapid conduction; avoid in structural heart disease 1
• Beta-blockers/calcium channel blockers: Avoid in decompensated heart failure, asthma, pre-excited AF 4

Anticoagulation

All patients undergoing cardioversion for AF/flutter require appropriate anticoagulation strategy - either 3 weeks pre-procedure or TEE-guided approach, plus 4 weeks post-cardioversion 1