What is the optimal initial voltage for cardioversion?

Optimal Voltage for Cardioversion

For cardioversion, the optimal initial energy is 200 J for monophasic waveforms and 100-150 J for biphasic waveforms, with higher initial energies (200 J) recommended for atrial fibrillation of longer duration. 1

Energy Requirements by Arrhythmia Type

Atrial Fibrillation

• Monophasic waveform:

  • Start with 200 J (not 100 J, which has only 14% success rate)
  • Increase in 100 J increments to maximum of 400 J
  • Evidence shows 95% success rate with 360 J initial energy compared to only 39% with 200 J 2

• Biphasic waveform:

  • Start with 100-150 J
  • Higher initial energy (200 J) for AF of long duration (>180 days) 1, 3
  • More effective than monophasic (99.1% vs 92.4% success) 2

Atrial Flutter

• Start with lower energy: 50-100 J (100 J has higher first-shock success rate of 85% vs 70% with 50 J) 4

Ventricular Tachycardia

• Monomorphic VT:

  • Start with synchronized shock at 50-100 J 2, 1
  • For hemodynamically unstable patients, use synchronized shock 2

• Polymorphic VT/Ventricular Fibrillation:

  • Use unsynchronized shock (defibrillation) at 200 J initially
  • If unsuccessful, increase to 200-300 J, then 360 J 2, 1

Technical Considerations

Paddle Position

• Anterior-posterior configuration is generally more effective than anterior-lateral (87% vs 76% success) 2, 1
• For patients with implanted devices, position paddles as far as possible from the device 1

Shock Delivery Technique

• Properly synchronize with QRS complex (except for VF/polymorphic VT)
• Select ECG lead that clearly displays both R waves and P waves 2
• Minimize resistance with electrolyte-impregnated pads
• Deliver shock during expiration when possible 2
• Maintain at least 1-minute intervals between shocks to prevent myocardial damage 2, 1

Factors Affecting Energy Requirements

• Duration of arrhythmia: Longer duration requires higher energy 3, 5

  • AF >180 days: Consider starting with 360 J (monophasic) to reduce total energy delivery 5
  • AF <30 days: Lower energy may be sufficient

• Patient factors:

  • Body mass index and chest diameter correlate with transthoracic impedance 6
  • Higher impedance may require higher energy

Practical Approach

1. Identify arrhythmia type and waveform technology available
2. Select initial energy:
   • AF with monophasic: 200 J
   • AF with biphasic: 100-150 J (200 J if long-standing)
   • Atrial flutter: 100 J
   • Monomorphic VT: 50-100 J (synchronized)
   • Polymorphic VT/VF: 200 J (unsynchronized)
3. If unsuccessful, increase energy in 100 J increments
4. Consider alternative paddle position if initial attempts fail

This approach maximizes first-shock success rates while minimizing the total energy delivered and procedure time, which is particularly important for patient safety and comfort.