# Ventricular Fibrillation

Ventricular fibrillation requires immediate defibrillation, uninterrupted high-quality CPR between shocks, protocolized epinephrine and antiarrhythmic therapy when shock-refractory, and rapid reassessment for recurrent versus persistent VF. Refractory cases require center-specific escalation decisions, including alternative pad vectors and selected extracorporeal CPR pathways.

**Clinical question:** How should physicians manage initial and shock-refractory ventricular fibrillation during cardiac arrest and after return of spontaneous circulation?

Updated: 2026-09-15T17:39:18.430498+00:00

## What matters in practice
- Treat confirmed VF or pulseless VT with immediate unsynchronized defibrillation; use the manufacturer-recommended biphasic energy (commonly 120-200 J) or 360 J for monophasic defibrillation, with subsequent shocks at the same or greater energy. [13][14]
- Resume chest compressions immediately after every shock and minimize interruptions; early defibrillation remains the definitive therapy for VF/pulseless VT. [3][14][17]
- For persistent shockable rhythm, give epinephrine 1 mg IV/IO every 3-5 minutes and consider amiodarone 300 mg IV/IO after continued VF/pulseless VT, with a 150-mg additional dose if needed; lidocaine is an alternative antiarrhythmic. [13][14][15]
- Persistent VF after at least three failed standard shocks is a practical definition of refractory VF; distinguish it from recurrent VF, which terminates transiently and then reappears. [12][17]
- In refractory VF, correct pad and energy problems, continue standard resuscitation, and use local protocols for vector-change or double sequential external defibrillation; randomized data associate both strategies with higher survival to discharge, while neurologic benefit was reported for DSED but not vector change. [22]
- For selected refractory VF/pulseless VT without prehospital ROSC, activate an established ECPR pathway early when available rather than treating ECMO cannulation as a routine rescue intervention. [4][12]

## Treat VF as a defibrillation emergency

Do not delay shock delivery for intravenous access, drug preparation, or waveform interpretation.

When rhythm analysis identifies VF or pulseless VT, deliver an immediate unsynchronized shock and immediately resume high-quality CPR. For biphasic defibrillators, use the manufacturer-recommended initial energy, commonly 120-200 J; use 360 J with a monophasic device. For subsequent shocks, use the same or a higher energy, escalating according to the defibrillator manufacturer until the maximum available energy is reached. [13][14]

Perform rhythm checks only at scheduled pulse/rhythm assessments and resume compressions immediately after each shock rather than waiting to assess electrical conversion. Early defibrillation and high-quality chest compressions with minimal interruption are the primary treatments for shockable cardiac arrest. [3][14]

Ensure that the rhythm is truly VF or pulseless VT before shocking. VF has fibrillatory waves without identifiable P waves, QRS complexes, or T waves; pulseless VT is also shockable. A nonshockable organized rhythm without a pulse requires the nonshockable-arrest pathway rather than repeated defibrillation. [13][21]
- Apply pads and use the defibrillator's recommended energy sequence before labeling a patient refractory. [14]
- Continue CPR during charging when equipment and workflow permit, then limit the shock pause. [3][14]
- If VF develops during thoracotomy or cardiac surgery, internal defibrillation uses a lower initial energy of 20 J to reduce myocardial burn-like injury. [14]

*Shockable-rhythm actions during initial VF/pulseless VT resuscitation. [13][14]*

| Resuscitation point | Required action | Decision implication |
| --- | --- | --- |
| Initial rhythm check | Confirm VF or pulseless VT and defibrillate immediately. [13] | Do not defer shock for medications or vascular access. [13][14] |
| Initial shock | Biphasic: manufacturer-recommended energy, commonly 120-200 J; monophasic: 360 J. [13][14] | Use unsynchronized defibrillation. [13][14] |
| After each shock | Immediately resume CPR. [14] | Avoid prolonged post-shock rhythm or pulse checks. [3][14] |
| Persistent VF/pulseless VT | Use equal or greater subsequent energy, up to the device maximum. [14] | Add protocolized vasopressor and antiarrhythmic therapy while continuing shocks and CPR. [14] |

## Use drugs as adjuncts, not substitutes for defibrillation

Medication administration should occur during CPR without extending pauses before or after a shock.

For persistent VF/pulseless VT after unsuccessful defibrillation, administer epinephrine 1 mg IV or IO every 3-5 minutes. In the shockable-rhythm sequence summarized in current ACLS references, epinephrine is given after an unsuccessful shock and continued while VF/pulseless VT persists. [13][14]

If VF/pulseless VT persists at the next rhythm check after ongoing shocks and CPR, administer amiodarone 300 mg IV/IO bolus. A further 150-mg dose may be used if an additional dose is needed. Amiodarone and lidocaine are both reasonable antiarrhythmic options for VF/pulseless VT unresponsive to defibrillation; comparative international guidance suggests any benefit is similar. [2][3][14][15]

When selecting lidocaine instead of amiodarone, use 1-1.5 mg/kg IV/IO initially, followed by 0.5-0.75 mg/kg for a second dose if needed. Avoid serially layering antiarrhythmics without a protocolized rationale; continue defibrillation, CPR, and search for a reversible trigger because antiarrhythmics do not replace electrical termination of VF. [14][15][17]
- Epinephrine: 1 mg IV/IO every 3-5 minutes during persistent VF/pulseless VT. [13][14]
- Amiodarone: 300 mg IV/IO bolus, then 150 mg if needed. [14]
- Lidocaine alternative: 1-1.5 mg/kg IV/IO, then 0.5-0.75 mg/kg if needed. [14]
- Pediatric shock-refractory VF/pulseless VT requires use of the pediatric cardiac arrest algorithm; the 2018 PALS update specifically addressed antiarrhythmic therapy while retaining the established treatment sequence. [2]

## Recognize refractory VF and change the resuscitation strategy

Persistent VF after repeated standard shocks requires a structured technical and systems-level reassessment.

Use a practical refractory-VF designation when VF/pulseless VT remains present after at least three failed standard defibrillation attempts. Separate true refractory VF from recurrent VF: recurrent VF terminates after a shock but returns later, whereas refractory VF remains present through sequential analyses and shocks. This distinction matters because recurrent VF has better reported survival than persistent refractory VF. [12][17][20]

Before changing defibrillation technique, verify pad contact and placement, ensure shocks are delivered at an appropriate escalating energy, and maintain short CPR interruptions. Persistent VF is not proof that a waveform-derived device metric should override standard care: ECG waveform analysis and machine-learning models can predict refractory VF in retrospective cohorts, but their clinical role remains decision support under investigation rather than a replacement for rhythm-based ACLS. [1][9][10][11]

For refractory VF in systems with an established protocol, consider vector-change defibrillation by moving pads to an anterior-posterior configuration or double sequential external defibrillation (DSED), which delivers rapid sequential transthoracic shocks from two defibrillators. In a cluster-randomized trial of 405 refractory-VF patients, both DSED and vector-change defibrillation were associated with higher survival to discharge; DSED, but not vector change, was associated with better neurologic outcome. [22]
- Continue standard single-shock defibrillation as the default for VF/pulseless VT; AHA and ERC guidance cited in recent reviews does not provide specific routine recommendations for DSED or vector-change defibrillation. [12]
- Use a preplanned local protocol when deploying DSED or vector change to avoid prolonged CPR pauses and uncoordinated placement of multiple pad sets. [12][20]
- Consider early ECPR activation for carefully selected refractory VF/pulseless VT when a mature ECMO-capable system can provide it; observational data associate an ECPR-based bundle with improved neurologic outcome in initial VF/VT without prehospital ROSC. [4]

### What not to infer from persistent VF

Do not equate the number of shocks alone with irreversible arrest. In retrospective ECG-based prediction studies, a threshold of three or more shocks has been used operationally for refractory VF, but the probability of refractory VF and response to rescue techniques require prospective validation before waveform algorithms can direct individual treatment. [9][10][11]

*Operational distinction between recurrent and refractory VF and associated next actions. [12][17][20][22]*

| Pattern | Operational finding | Next action |
| --- | --- | --- |
| Standard shockable arrest | VF/pulseless VT identified before three failed standard shocks. [12][17] | Defibrillate, resume CPR immediately, give epinephrine and antiarrhythmic therapy as indicated. [13][14] |
| Recurrent VF | VF terminates after a shock but later reappears. [17] | Continue shockable-rhythm ACLS and identify a reversible ischemic, metabolic, toxicologic, structural, or channelopathic cause after ROSC. [17][22] |
| True refractory VF | VF/pulseless VT persists after at least three standard shocks. [12][17] | Recheck technical factors; continue standard resuscitation; apply local vector-change, DSED, or ECPR escalation pathway when available. [12][22][4] |

## Target reversible causes during arrest and define substrate after ROSC

Use the arrest context to prioritize causes that immediately alter intervention or disposition.

During ongoing VF/pulseless VT, pursue correctable causes in parallel with defibrillation rather than pausing to complete a broad diagnostic evaluation. In refractory out-of-hospital VF, coronary artery disease is frequently present in observational reports; VF waveform analysis has also been studied as an early indicator of acute myocardial infarction, but coronary diagnosis is generally established after ROSC with formal evaluation. [19][20]

After ROSC, obtain a 12-lead ECG and determine whether the patient has evidence of myocardial ischemia, structural heart disease, conduction disease, bradycardia or pauses, valve disease, pulmonary embolism, aortic dissection, acute heart failure, tamponade, or cardiomyopathy. These findings should direct urgent coronary, echocardiographic, electrophysiologic, or disease-specific evaluation rather than assigning an idiopathic VF label prematurely. [8][22]

Reserve idiopathic VF for patients in whom structural, channelopathic, metabolic, and toxicologic etiologies have been excluded. This exclusion is clinically important because patients with apparently idiopathic VF may have subtle microstructural abnormalities or premature ventricular complex triggers identified by invasive mapping studies. [22]
- Acute ischemic pattern after ROSC: prioritize coronary assessment because acute MI is a potentially treatable VF substrate. [19][20]
- Structural or hemodynamic pattern: use echocardiography to assess ventricular function, tamponade, critical valvular disease, and pulmonary arterial pressure when right-heart failure is suspected. [8]
- No structural, metabolic, toxicologic, or channelopathic explanation: do not label idiopathic VF until these etiologies have been excluded. [22]

*Post-ROSC findings that redirect VF evaluation. [8][19][22]*

| Finding or clinical context | Targeted next test or assessment | Interpretation and action |
| --- | --- | --- |
| Concern for acute myocardial infarction | 12-lead ECG and coronary evaluation after ROSC. [19] | Treat acute MI as a potentially reversible VF substrate. [19] |
| Hypotension, acute heart failure, suspected tamponade, valvular disease, or right-heart failure | Bedside echocardiography. [8] | Assess ventricular function, pulmonary pressures, and structural/hemodynamic causes requiring disease-specific intervention. [8] |
| No immediately apparent substrate | Evaluate for structural, channelopathic, metabolic, and toxicologic etiologies. [22] | Only after exclusion should idiopathic VF be considered. [22] |

## Stabilize, investigate recurrence risk, and plan secondary prevention

Survival from VF does not end the emergency pathway; recurrence and post-arrest instability require active management.

After ROSC, monitor for hemodynamic instability, recurrent ventricular arrhythmia, and neurologic injury while expediting evaluation of the precipitating cause. Post-arrest patients with VF/VT have historically shown variation in access to coronary catheterization, electrophysiologic study, and implantable cardioverter-defibrillator therapy; ensure that candidacy for these potentially lifesaving interventions is assessed without inequitable exclusion. [16]

For patients with recurrent VF or clustered ventricular arrhythmias, evaluate ischemic, structural, inherited channelopathy, metabolic, and toxicologic drivers. The electrical-storm consensus statement emphasizes that idiopathic VF requires exclusion of these etiologic categories and that invasive mapping can identify arrhythmogenic substrate in selected patients. [22]

Refer survivors for electrophysiology-based recurrence-risk assessment and consideration of ICD therapy when appropriate to the underlying substrate and post-arrest evaluation. The immediate resuscitation decision remains defibrillation; definitive prevention is cause-directed and should follow stabilization and diagnostic clarification. [16][22]
- Monitor for recurrent VF/VT and hemodynamic deterioration after ROSC. [13][16]
- Use coronary, echocardiographic, and electrophysiologic assessment according to post-ROSC findings. [8][16][22]
- Consider ICD and electrophysiology evaluation as part of secondary prevention after a VF/VT arrest survivor's substrate has been assessed. [16]

## References
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9. Prediction of Shock-refractory Ventricular Fibrillation in Patients with Out-of-Hospital Cardiac Arrest: External Validation of an ECG-based Approach - PMC — pmc.ncbi.nlm.nih.gov — https://pmc.ncbi.nlm.nih.gov/articles/PMC13218281
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## Editorial note

Prepared from cited clinical literature using Astra's research workflow. Verify recommendations against current guidance and patient-specific factors.