Background: what is shock-refractory VF?
Ventricular fibrillation (VF) and pulseless ventricular tachycardia (pVT) are the shockable rhythms in cardiac arrest. Early defibrillation and high-quality chest compressions with minimal interruptions form the basis of treatment. Drugs supplement these measures but do not replace them.
Shock-refractory VF refers to a rhythm that persists despite repeated defibrillation. It is distinct from recurrent VF, in which ventricular fibrillation recurs after successful termination. For the administration of antiarrhythmic drugs, the ERC Guidelines 2025 treat both situations in the same way. The deciding factor is the total number of shocks delivered.
Indication and timing according to ERC 2025
Shock count as the pacemaker
The timing of antiarrhythmic drug administration is determined solely by the number of shocks:
- After the 3rd shock: first dose of the antiarrhythmic drug, together with the first dose of adrenaline.
- After the 5th shock: second, reduced dose of the antiarrhythmic drug.
All shocks for persistent or recurrent VF/pVT are counted. A special rule applies to witnessed, monitored cardiac arrest: three stacked shocks count as one shock (ERC 2025). The shock count should be clearly communicated and documented within the team, for example by one person calling out the time and number of shocks aloud.
Adrenaline in shockable rhythms
In a shockable rhythm, ERC 2025 recommends adrenaline after the 3rd shock: 1 mg i.v./i.o., then every 3–5 min. It is commonly diluted to 0.1 mg/ml (1 ml adrenaline 1 mg/ml + 9 ml sodium chloride 0.9%, i.e. 1 mg = 10 ml) and followed by a flush. Because the antiarrhythmic drug and adrenaline are due at the same time, both syringes should be prepared during the cycles before the 3rd shock.
Amiodarone: the standard in the algorithm
Dosing in adults (VF/pVT)
For amiodarone in resuscitation in adults, ERC 2025 recommends:
| Timing | Dose | Volume (50 mg/ml) |
|---|---|---|
| after the 3rd shock | 300 mg i.v./i.o. | 6 ml |
| after the 5th shock | 150 mg i.v./i.o. | 3 ml |
The commercially available preparation contains 50 mg/ml (3 ml = 150 mg). Two ampoules are therefore required for the first dose.
Practical notes
- Contraindications: none in cardiac arrest. Outside resuscitation, the summary of product characteristics lists, among others, sinus bradycardia, high-grade AV block without a pacemaker, thyroid dysfunction and QT prolongation.
- Dilution: for infusion, amiodarone may only be diluted with glucose 5%.
- Adverse effects outside resuscitation: rapid administration may cause hypotension and bradycardia. This is relevant mainly in the post-resuscitation phase and in arrhythmias with a preserved circulation. Dose and rate of administration should then follow the current summary of product characteristics.
Children
According to the ERC Guidelines 2025 Paediatric Life Support, the dose is 5 mg/kg i.v./i.o. (max. 300 mg) after the 3rd shock. A second dose of 5 mg/kg follows after the 5th shock, then with a maximum of 150 mg. In children with a shockable rhythm, adrenaline is given after the 3rd and 5th shocks and then every 4 min.
Important for the choice of product: according to the product information, preparations containing benzyl alcohol as an excipient are contraindicated in neonates, infants and children up to 3 years of age. The product stocked should be checked in advance, not during a call-out. This article does not give a dose for lidocaine in children. The current ERC guideline Paediatric Life Support or the summary of product characteristics applies.
Lidocaine: the defined alternative
When to use lidocaine?
According to ERC 2025, lidocaine in ventricular fibrillation is an alternative to amiodarone. It is used in only two situations:
- amiodarone is not available, or
- lidocaine has been locally designated instead of amiodarone.
The two drugs are not combined. The decision should therefore ideally be made before the call-out, through standard operating procedures, drug stocking and team training, not at the bedside.
Dosing in adults (VF/pVT)
| Timing | Dose | Volume 2% (20 mg/ml) | Volume 1% (10 mg/ml) |
|---|---|---|---|
| after the 3rd shock | 100 mg i.v./i.o. | 5 ml | 10 ml |
| after the 5th shock | 50 mg i.v./i.o. | 2.5 ml | 5 ml |
These figures are taken from the German-language summary of the ERC Guidelines 2025. They apply to both refractory and recurrent VF/pVT.
Sources of error
- Check the concentration: 1% and 2% solutions are both commercially available. Confusing them doubles or halves the dose.
- Only solutions without added adrenaline: as an antiarrhythmic, only solutions without a vasoconstrictor may be used. Lidocaine is also stocked as a local anaesthetic, so there is a risk of mix-ups in emergency kits with mixed contents.
- Contraindications: none in cardiac arrest. Outside cardiac arrest, the summary of product characteristics lists, among others, second-/third-degree AV block, sick sinus syndrome or severe bradycardia, cardiogenic shock (benefit–risk assessment) and allergy to amide local anaesthetics.
After ROSC: watch for toxicity
Lidocaine is an amide-type local anaesthetic. After return of spontaneous circulation, signs of overdose or systemic toxicity must therefore be monitored:
- PR prolongation or QRS widening on the ECG
- perioral paraesthesia, metallic taste, agitation, seizures
- arrhythmias up to and including asystole
Treatment of local anaesthetic toxicity includes, among other measures, lipid emulsion 20%. Older patients require lower doses. Accumulation is to be expected in impaired liver function or reduced cardiac output. For further treatment after ROSC, for example with a continuous infusion, the current summary of product characteristics and close clinical and ECG monitoring are decisive.
Evidence: what do we know and what don't we know?
The recommendations on antiarrhythmic drugs in shock-refractory VF are based on an overall limited body of evidence. A definite benefit in survival with good neurological outcome has not been clearly demonstrated for either drug. The ERC Guidelines 2025 include amiodarone as the standard in the algorithm and name lidocaine as an alternative that can be used equivalently when amiodarone is unavailable or a different local standard applies. Superiority of either drug cannot be inferred from this.
Three practical conclusions follow:
- Basic measures take priority: defibrillation, high-quality chest compressions and the search for reversible causes take precedence over any drug therapy.
- Consistency rather than switching: a clearly defined local standard, i.e. amiodarone or lidocaine, reduces errors. An improvised switch of drug during resuscitation is not intended.
- Adhere to timing: administration after the 3rd and 5th shocks is tied to the shock count. Early or significantly delayed administration deviates from the algorithm.
Team checklist
- Assign shock counting and communicate it aloud. Stacked shocks in witnessed arrest count as one shock.
- Prepare adrenaline 1 mg and the antiarrhythmic drug before the 3rd shock.
- Amiodarone: 300 mg (6 ml) after the 3rd shock, 150 mg (3 ml) after the 5th shock.
- Lidocaine only as an alternative: 100 mg after the 3rd shock, 50 mg after the 5th shock. Check the concentration and that the solution is free of adrenaline.
- Do not combine amiodarone and lidocaine.
- In children, use the weight-based regimen according to ERC 2025 and, for amiodarone, check the product for benzyl alcohol.
- After ROSC, monitor circulation, ECG and signs of toxicity. Further treatment according to the summary of product characteristics.
Conclusion
In shock-refractory or recurrent VF/pVT, amiodarone is the first-line antiarrhythmic drug in the algorithm according to ERC 2025. Lidocaine is a defined alternative if amiodarone is unavailable or has been locally designated. Both drugs follow the same logic: first dose after the 3rd shock, second dose after the 5th shock. The evidence for a survival benefit is limited. This makes high-quality resuscitation, accurate shock counting and a clear local standard all the more important.
References
- Soar J, Böttiger BW et al. European Resuscitation Council Guidelines 2025 Adult Advanced Life Support. Resuscitation 2025;215 Suppl 1:110769 (Korrigendum 2026).
- Djakow J, Turner NM, Skellett S et al. European Resuscitation Council Guidelines 2025 Paediatric Life Support. Resuscitation 2025;215 Suppl 1:110767.
- Kurzfassung der Leitlinien des European Resuscitation Council 2025. Notfall Rettungsmed 2025.
This article does not replace clinical judgement in the individual case or the current summary of product characteristics and guidelines.
