What is the recommended initial shock dose in joules for ventricular tachycardia using a biphasic defibrillator?

Recommended Shock Energy for Ventricular Tachycardia

For ventricular tachycardia with a pulse, use synchronized cardioversion starting at 100 joules (biphasic or monophasic); for pulseless ventricular tachycardia, use unsynchronized defibrillation at 200 joules or the manufacturer's recommended dose for biphasic devices. 1, 2

Critical First Step: Assess for Pulse

The presence or absence of a pulse fundamentally changes your approach:

• Pulseless VT = Cardiac Arrest: Treat identically to ventricular fibrillation with immediate unsynchronized high-energy shocks (defibrillation) 1, 2
• VT with Pulse = Perfusing Rhythm: Use synchronized cardioversion at lower initial energy 1, 2

Never use synchronized cardioversion for pulseless VT—this delays treatment of a cardiac arrest rhythm and worsens mortality. 1, 3

For Pulseless Ventricular Tachycardia (No Pulse)

Initial Energy Dose

• Biphasic defibrillators: Use manufacturer's recommended dose (typically 120-200 J); if unknown, use maximum dose 4
• Monophasic defibrillators: Start at 200 J 5
• Biphasic shocks achieve 85-98% effectiveness at ≤200 J 4

Subsequent Shocks

• Follow manufacturer's instructions for fixed versus escalating energy 4
• If using escalating energy protocol, higher energy for second and subsequent shocks may be considered 4
• Deliver shocks immediately without delay—do not synchronize 1

Key Technical Points

• Use unsynchronized shocks only—the device cannot reliably detect QRS complexes in VF/pulseless VT 1
• Deliver shock immediately after rhythm check without waiting for synchronization 1
• Continue high-quality CPR between shocks 4

For Ventricular Tachycardia with Pulse

Monomorphic VT (Regular, Wide Complex)

• Initial energy: 100 joules synchronized (applies to both biphasic and monophasic waveforms) 1, 2
• If first shock fails, escalate energy in stepwise fashion 1, 2
• Must use synchronized mode—shock delivered at peak of QRS complex, never on T wave 2

Polymorphic VT (Irregular, Wide Complex)

• Treat as ventricular fibrillation with unsynchronized high-energy shocks 1, 3
• Never attempt synchronized cardioversion—synchronization is not possible with irregular rhythm 1, 3
• Use ≥200 J (or manufacturer's recommended biphasic dose) 1

Critical Safety Considerations

Before Delivering Shock

• Hemodynamically unstable patients: Cardiovert immediately without delay for sedation 3, 2
• Hemodynamically stable patients: Provide adequate sedation or anesthesia before synchronized cardioversion 3, 2
• Establish IV access if time permits, but do not delay shock in extremely unstable patients 3

Synchronization Verification

• Turn on synchronization function and verify the device is detecting QRS complexes appropriately before proceeding 3
• Ensure visible artifact indicates shock timing in relation to QRS 4
• Common pitfall: Forgetting to reactivate synchronization mode after each shock—most devices default back to unsynchronized mode 2

Equipment Readiness

• Have defibrillation equipment immediately available when treating unstable VT, as patients may deteriorate to pulseless VT or VF at any moment 1, 3
• Be prepared for post-cardioversion arrhythmias including atrial or ventricular premature complexes that may trigger recurrent episodes 3

Electrode Positioning

• Anteroposterior configuration is preferred over anterolateral (87% vs 76% success rate, requires less energy) 2
• For patients with implanted cardiac devices, position electrodes as far as possible from pulse generator, preferably anteroposterior 2

Energy Escalation Protocol

If initial shock fails:

1. Increase energy in stepwise fashion for subsequent attempts 1, 2
2. Allow at least 1 minute between consecutive shocks to avoid myocardial damage 2
3. Consider antiarrhythmic medication (amiodarone) to prevent recurrence 3

Special Populations

Pediatric Patients

• VF or pulseless VT: 2 J/kg first shock, 4 J/kg second shock, 4-10 J/kg subsequent shocks 1
• These are unsynchronized defibrillation doses, not cardioversion doses 1

Common Pitfalls to Avoid

1. Never synchronize for pulseless VT—this is cardiac arrest requiring immediate unsynchronized defibrillation 1, 3
2. Never synchronize for polymorphic VT—even with a pulse, treat as VF 1, 3
3. Never use synchronized cardioversion for VF—device may not sense QRS and deliver no shock 1, 3
4. Never delay cardioversion in unstable patients to attempt pharmacological conversion 3
5. Never use calcium channel blockers in VT—they worsen hemodynamic status 3