What is the first medication for ventricular fibrillation refractory to a second shock?

First Medication for Ventricular Fibrillation Refractory to Second Shock

Amiodarone is the preferred first medication for ventricular fibrillation that remains refractory after a second shock, with an initial dose of 300 mg IV/IO. 1

Medication Selection Algorithm

First-Line Treatment

• Amiodarone: 300 mg IV/IO bolus
  • Formulations: Available in polysorbate-containing or captisol-based formulations
  • The captisol-based formulation has fewer hemodynamic side effects 2, 1
  • Consider pre-treatment with vasopressor if using polysorbate formulation to prevent hypotension 1

Second-Line Treatment (if amiodarone unavailable or contraindicated)

• Lidocaine: 1-1.5 mg/kg IV/IO
  • Additional doses of 0.5-0.75 mg/kg IV push at 5-10 minute intervals
  • Maximum total dose: 3 mg/kg 1

Evidence Supporting Amiodarone as First Choice

The 2018 American Heart Association guidelines indicate that amiodarone has demonstrated superior rates of survival to hospital admission compared to placebo in shock-resistant VF 2. The ALIVE trial specifically showed that amiodarone improved survival to hospital admission compared with lidocaine in patients with shock-resistant VF 2, 3.

Multiple studies support amiodarone as the first-line antiarrhythmic agent:

• Amiodarone leads to substantially higher rates of survival to hospital admission compared to lidocaine in patients with shock-resistant out-of-hospital ventricular fibrillation (22.8% vs 12.0%, P=0.009) 3
• Current guidelines from Praxis Medical Insights recommend amiodarone as the preferred medication over lidocaine 1

Important Clinical Considerations

Timing of Administration

• Administer after CPR, defibrillation attempts, and vasopressor therapy have failed 1
• Do not delay defibrillation or CPR to administer antiarrhythmic medications 1

Dosing Specifics

• Initial dose: 300 mg IV/IO bolus over 10 minutes
• For breakthrough episodes: Consider additional 150 mg IV/IO 1, 4
• Maintenance: Follow with 1 mg/min infusion for 6 hours, then 0.5 mg/min 1, 4

Monitoring and Side Effects

• Monitor for hypotension and bradycardia during administration 1
• Be prepared to treat hypotension with vasopressors if needed
• Watch for QT prolongation with continued administration

Special Situations

• For torsades de pointes (polymorphic VT with prolonged QT): Consider magnesium sulfate (1-2g IV/IO) instead of amiodarone 1
• For patients with severe heart failure or cardiogenic shock (secondary VF): Be especially vigilant for hypotension with amiodarone administration 2

Limitations of Evidence

While amiodarone improves rates of ROSC and survival to hospital admission, it's important to note that neither amiodarone nor lidocaine has definitively demonstrated improved long-term survival or neurological outcomes 2, 1. The primary goal of antiarrhythmic therapy in shock-refractory VF/pVT is to facilitate successful defibrillation and reduce the risk of recurrent arrhythmias, not necessarily to convert the rhythm directly 2.