Shock Synchronization in Ventricular Fibrillation and Tachycardia

Introduction to Ventricular Fibrillation and Tachycardia Management

The American College of Cardiology recommends delivering an immediate unsynchronized shock for witnessed ventricular fibrillation (VF), with an initial energy of 200J (monophasic) or manufacturer's recommended dose (biphasic) 1
VF requires immediate high-energy unsynchronized shocks (defibrillation) 2, 3
Synchronized cardioversion must never be used for VF as the device may not sense a QRS wave, potentially resulting in no shock delivery 2, 4, 1

Ventricular Tachycardia Management

Pulseless ventricular tachycardia (VT) is treated exactly like VF with unsynchronized high-energy shocks (defibrillation doses) 2, 5, 6
For monomorphic VT with a pulse, synchronized cardioversion is recommended 2, 5, 6
Initial energy for monomorphic VT with pulse: 100J for biphasic or monophasic waveforms 6, 7
Polymorphic VT should be treated as VF using unsynchronized high-energy shocks 2, 6

Special Considerations

Unsynchronized shocks should be delivered immediately for pulseless rhythms to avoid delays in treatment 1
Never use synchronized cardioversion for VF as it may result in no shock delivery 2, 1
Never use synchronized cardioversion for pulseless VT as it delays treatment of a cardiac arrest rhythm 2, 3
Never use synchronized cardioversion for polymorphic (irregular) VT even with a pulse, as synchronization is usually not possible 2, 6
For pediatric patients with VF or pulseless VT, use 2 J/kg for the first shock, 4 J/kg for the second shock, and 4-10 J/kg for subsequent shocks 1

Initial Energy Dose for Synchronized Cardioversion in Unstable Ventricular Tachycardia

Key Considerations for Synchronized Cardioversion

The American Heart Association recommends starting with 100 J using synchronized cardioversion with either monophasic or biphasic waveforms for unstable monomorphic ventricular tachycardia with a pulse 8
For unstable VTach WITH a pulse, synchronized cardioversion starting at 100 J is recommended, whereas pulseless VTach should be treated as ventricular fibrillation with unsynchronized high-energy shocks 8

Energy Escalation Protocol

If the initial 100 J shock fails to convert the rhythm, increase energy in a stepwise fashion for subsequent attempts, as recommended by expert consensus 8
The specific escalation increments represent expert consensus, as no studies have definitively addressed optimal dose escalation 8

Preparation and Management

The American Heart Association suggests having electrical cardioversion equipment immediately available when treating unstable VT, as the patient may deteriorate to pulseless VT or VF at any moment 9
Ensure adequate sedation or anesthesia before cardioversion in stable patients, though hemodynamically unstable patients require immediate cardioversion 9

Recommended Shock Energy for Ventricular Tachycardia

Critical Care Guidelines

The American Heart Association recommends using biphasic defibrillators at the manufacturer's recommended dose (typically 120-200 J) for pulseless ventricular tachycardia, with a success rate of 85-98% at ≤200 J 10, 11, 12
For subsequent shocks, the American Heart Association suggests following the manufacturer's instructions for fixed versus escalating energy, and considering higher energy for second and subsequent shocks 10, 11
The American Heart Association advises continuing high-quality CPR between shocks for pulseless ventricular tachycardia 10
The American College of Cardiology recommends ensuring visible artifact indicates shock timing in relation to QRS complexes when using synchronized cardioversion 13

Management of Ventricular Tachycardia

Initial Treatment

The American Heart Association recommends continuing defibrillation attempts as long as ventricular tachycardia/ventricular fibrillation persists and resuscitation efforts are ongoing, with no maximum limit on the number of shocks 14
For pulseless ventricular tachycardia, the American College of Cardiology recommends escalating energy if the defibrillator is capable of delivering higher energy doses, starting with an initial energy of 200J (monophasic) or manufacturer's recommended dose for biphasic (typically 120-200J) 14

Treatment of Hemodynamically Unstable VT

The American College of Cardiology recommends using synchronized cardioversion starting at 100J for hemodynamically unstable ventricular tachycardia with a pulse 15, 16
The American College of Cardiology suggests considering brief trials of antiarrhythmic medications (such as procainamide, amiodarone, or lidocaine) before cardioversion for hemodynamically stable ventricular tachycardia with a pulse 15, 16

Energy Escalation Protocol

The International Consensus recommends escalating shock energy if initial attempts fail and the defibrillator is capable of delivering higher energy, for refractory ventricular fibrillation/pulseless ventricular tachycardia and recurrent ventricular fibrillation after initial successful termination 14

Management of Ventricular Tachycardia with a Pulse

Immediate Assessment and Treatment

The American Heart Association recommends that the initial management of VT with a pulse depends entirely on whether the patient is hemodynamically stable or unstable 17, 18
Hemodynamic instability is defined as: hypotension (low blood pressure), pulmonary edema, ongoing chest pain/ischemia, or altered mental status, according to the American College of Cardiology 19
For unstable monomorphic VT with a pulse, the American Heart Association recommends immediate synchronized cardioversion starting at 100 J (biphasic or monophasic) 17, 18
If the initial 100 J shock fails, the American Heart Association recommends increasing energy in a stepwise fashion for subsequent attempts 17, 18

Pharmacologic Therapy

The American College of Cardiology recommends first-line pharmacologic options for stable monomorphic VT, including amiodarone, procainamide, and lidocaine 19
Amiodarone can be administered as 150 mg IV over 10 minutes, followed by 1 mg/min infusion for 6 hours, then 0.5 mg/min maintenance, according to the American College of Cardiology 19

Key Safety Considerations

The American Heart Association recommends never using synchronized cardioversion for pulseless VT, polymorphic VT, or ventricular fibrillation, as it may waste critical time or fail to deliver a shock 17, 18
The American Heart Association recommends never delaying cardioversion for sedation in unstable patients, as it can worsen outcomes 20, 21
The American College of Cardiology recommends being cautious when using amiodarone in already hypotensive patients, as it can worsen hypotension 19

Refractory Ventricular Tachycardia Shock Management

Core Defibrillation Strategy

The American Heart Association guidelines recommend delivering single shocks followed by 2 minutes of CPR between rhythm checks, rather than stacked shock sequences, for patients with refractory ventricular arrhythmias 22, 23
Biphasic waveforms should be used at manufacturer-recommended doses, typically 120-200 J initially, with equivalent or higher energy for subsequent shocks, for patients with refractory ventricular arrhythmias 23

The Shift from Stacked Shocks

Modern biphasic defibrillators achieve >90% first-shock efficacy for VF termination, making multiple immediate shocks less necessary, in patients with ventricular fibrillation 22
A brief period of asystole or PEA typically follows successful VF termination, making immediate CPR more valuable than additional shocks, in patients with ventricular fibrillation 22
The 3-shock sequence creates 29-37 second delays before resuming compressions, which cannot be justified given high first-shock success rates, in patients with ventricular fibrillation 24
No difference in 1-year survival was found when comparing single-shock protocols with 2 minutes of CPR versus 3 stacked shocks, in a randomized trial of 845 patients with ventricular fibrillation 22

Integration with Antiarrhythmic Therapy

The American Heart Association recommends administering amiodarone or lidocaine, with a dose of 1-1.5 mg/kg IV/IO, if available, for patients with refractory VF/pVT, although the optimal timing remains unknown 23
Epinephrine should be given 1 mg IV/IO every 3-5 minutes throughout the resuscitation, for patients with refractory ventricular arrhythmias 23

Critical Pitfalls to Avoid

The American Heart Association guidelines emphasize that CPR should not be delayed to deliver additional shocks, and the 2-minute CPR cycle between shocks is essential for myocardial perfusion, in patients with ventricular fibrillation 22, 23
Minimizing interruptions in chest compressions to <10 seconds for rhythm checks and shock delivery is crucial, for patients with ventricular fibrillation 23

Energy Escalation Protocol

The American Heart Association recommends starting with 120-200 J for biphasic or 360 J for monophasic waveforms, and using equivalent or higher energy doses for subsequent shocks, if the defibrillator is capable, for patients with refractory ventricular arrhythmias 23