Defibrillation Settings for Ventricular Tachycardia
For pulseless VT, use unsynchronized high-energy shocks at 120-200 J (biphasic) or 200 J (monophasic) for the first shock, treating it identically to ventricular fibrillation; for stable VT with a pulse, use synchronized cardioversion starting at 100 J. 1
Critical Decision Point: Pulse Check First
The management of VT depends entirely on whether the patient has a pulse, as this determines both the energy level and synchronization mode 1, 2:
- Pulseless VT = Cardiac arrest rhythm → Treat as VF with unsynchronized defibrillation
- VT with pulse = Perfusing rhythm → Use synchronized cardioversion (if unstable) or medications (if stable)
Pulseless Ventricular Tachycardia (Cardiac Arrest)
Use unsynchronized high-energy shocks—never synchronized cardioversion—as synchronization may fail to deliver a shock or cause dangerous delays. 1
Initial Energy Settings
Biphasic defibrillators (preferred): 3
- Use manufacturer's recommended dose (typically 120-200 J)
- If unknown, use maximum dose available
- First-shock success rate: 85-98% at ≤200 J 3, 1
Monophasic defibrillators: 3, 1
- Initial shock: 200 J
- Biphasic waveforms are superior and preferred over monophasic 3
Subsequent Shocks for Refractory VT/VF
Follow manufacturer's instructions for fixed versus escalating energy. 3 If the defibrillator is capable of escalating energy, higher doses may be considered for second and subsequent shocks 3. One study showed higher VF termination rates with escalating energy (200-300-360 J) versus fixed energy (150 J) in patients requiring multiple shocks (82.5% vs 71.2%), though survival outcomes were similar 4.
Shock Delivery Protocol
Deliver single shocks followed by 2 minutes of CPR between rhythm checks—not stacked shocks. 1 The rationale is threefold: modern biphasic defibrillators achieve >90% first-shock efficacy, a brief period of asystole/PEA typically follows successful termination making immediate CPR more valuable than additional shocks, and the old 3-shock sequence creates 29-37 second delays that cannot be justified 1.
Ventricular Tachycardia With a Pulse
Unstable VT (Hypotension, Pulmonary Edema, Chest Pain, Altered Mental Status)
Use synchronized cardioversion starting at 100 J (biphasic or monophasic). 1, 2 If the initial 100 J shock fails, increase energy in a stepwise fashion for subsequent attempts 1. Never delay cardioversion for sedation in unstable patients 1.
Stable Monomorphic VT
Consider pharmacologic therapy first 1:
- Amiodarone: 150 mg IV over 10 minutes, then 1 mg/min for 6 hours 1
- Procainamide or lidocaine as alternatives 1
- If medications fail, proceed to synchronized cardioversion at 100 J 1
Polymorphic VT
Treat as VF with unsynchronized high-energy shocks, even if the patient has a pulse. 1 Synchronization is usually not possible with irregular polymorphic VT, and attempting it wastes critical time 1.
Common Pitfalls to Avoid
Never use synchronized cardioversion for: 1
- Ventricular fibrillation (device may not sense QRS, resulting in no shock delivery)
- Pulseless VT (delays treatment of cardiac arrest)
- Polymorphic VT (synchronization not possible)
Minimize interruptions in chest compressions to <10 seconds for rhythm checks and shock delivery in pulseless VT 1. Continue high-quality CPR immediately after each shock without checking pulse unless rhythm changes to one compatible with cardiac output 3, 1.
Ensure proper pad placement: anterolateral or anteroposterior positions are equally effective 3. Place pads at least 8 cm away from implanted devices if present 3.
Integration with Medications
For refractory VF/pulseless VT, administer epinephrine 1 mg IV/IO every 3-5 minutes throughout resuscitation 1. Consider amiodarone (300 mg IV bolus) or lidocaine (1-1.5 mg/kg IV/IO) after failed defibrillation attempts, though optimal timing remains unknown 1, 5.